By Jack P. t·loeh 1e and A. Sozen

174
UILU-ENG-78-2014 EARTHQUAKE-SH1ULATION TESTS OF A TEN-STORY REINFORCED CONCRETE FRAr-1E WITH A DISCONTINUED FIRST-LEVEL BEAM By Jack P. t·loeh 1e and t4ete A. Sozen University of Illinois Urbana, Illinois August, 1978 1\

Transcript of By Jack P. t·loeh 1e and A. Sozen

Page 1: By Jack P. t·loeh 1e and A. Sozen

UILU-ENG-78-2014

EARTHQUAKE-SH1ULATION TESTS OF A TEN-STORY REINFORCEDCONCRETE FRAr-1E WITH A DISCONTINUED FIRST-LEVEL BEAM

By

Jack P. t·loeh1eand

t4ete A. Sozen

University of IllinoisUrbana, Illinois

August, 1978

1\

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BIBLIOGRAPHIC DATA 11. Reporr No.SHEET UILU-ENG-78-20l44. Title and Subtitle

EARTHQUAKE-SmULATIOtI TESTS OF A TEN-STORY REINFORCEDCONCRETE FRAt1E WITH A DISCorlTINUED FIRST-LEVEL BEAr~

7. Author(s) Jack P. Moehle and t1ete A. Sozen

9. Performing Organization Name and Address

University of Illinois at Urbana-ChanpaignUrbana, Illinois 61801

12. Sponsoring Organization Name and Address

National Science FoundationWashington, D.C. 20013

15. Supplementary Notes

5. Re·port IJatew< ~ ~

August 19786.

8. Performin~Organization Rept.No. SR::> No. 451

10. Project/Task/Work Unit No.

11. Contract/Grant No.

NSF EliV-7422962

13. Type of Report & PeriodCovered

14.

16. Abstracts

A small-scale, ten-story, reinforced concrete frame structure withrelatively flexible lower stories was subjected successively to simulatedearthquakes of increasing intensity on the University of Illinois EarthquakeSimulator. The test structure comprised two fra~es situated opposite oneanother with strong axes parallel to a horizontal base motion and with story­masses spanning betv.Jeen. The franes had relatively "tall" first and laststories and a discontinued first floor-level, exterior,span beam. Earthquakesimulation tests were complemented by free-vibration tests and steady-statesinusoidal tests at a series of frequencies bounding the apparent funda~ental

frequency. This report documents the experimental work, presents data(including time-response histories), and discusses the observed dynamic responsein relation to stiffness, strength, and energy-dissipative capacity.

17. Key Words and Document Analysis. 170. Descriptors

Damping, dyna~ics, earthquake-simulation response, free-vibration, framedstructure, multistory structure, spectral-modal analysis, steady-statesinusoidal tests, stiffness, strength

17b~ Identifiers/Open-Ended Terms

17c. COSATI Field/Group

18. Availability Statement

Release Unlimited

FOR.... NTI5-3!l (REI/. 10'731 ENDORSED BY ANSI AND UNESCO.,

19•. Security Class (ThisReport)

t1NrIA"SI~lF:J)20. Securiry Class (This

PageUNCI.ASSI F IEJ)

THIS FORM MAY BE REPRODUCED

21. No. of Pages

(71-

useo......• De 8Z05·P74

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TABLE OF CONTENTS

1

11

3

347

15

15161718

19

191922

28

28283132

42

42424344

48

Page

. . .

. . . . . . . . . .., . . .

. '. .

• • • • • • • • • • • • 0 •

Introductory Remarks • • • •Apparent Natural FrequenciesMeasures of Damping••• 0 ••••

Response to Simulated Earthquakes.

Test Structure • • • • • • . • . • •Instrumentation and Recording of DataTest Motions ••Testing Sequence

SUr~~1ARY • • • • • • • •

6. 1 Object and Scope ••6.2 Experimental Work6.3 Data and Studies •••••••••6.4 Observed Response Characteristics.

2.1 General Criteria •••••2.2 Design Method•.•••.•••2.3 Determination of Design Forces.

4.1 Introductory Remarks •••••••4.2 Nature of Data Presented.4.3 Test Results ••...

1.1 Object and Scope.1.2 Acknowledgments ••••

INTRODUCTION.

5. DISCUSSION OF TEST RESULTS.••

5. 15.25.35.4

6.

3. DESCRIPTION OF EXPERIMENTAL PROCEDURE .

3. 13.23.33.4

4. OBSERVED RESPONSE • •

2. DESIGN OF THE TEST STRUCTURE.

1.

LIST OF REFERENCES

APPENDIX

A DESCRIPTION OF EXPERIMENTAL WORK. • • • • . • . • . • • • • 135

Chapter

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COt1PLEMENTARY DATA • •

Introductory Remarks•••••••Horizontal Response Measurements.Torsional Motions ••••••••Vertical Motions ••••••••

. .

APPENDIX

B

A.1A.2A.3A.4A.5

B.1B.2B.3B.4

iv

Concrete. • • • • •Reinforcing Steel •••Specimen DetailsDynamic Tests ••Data Reduction •••••

. . .

. . .

. . .

. .. . .. . . . . . .

Page

135136136140145

158

158158159159

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2.3 Frame Reinforcing Schedule .••••••.••

TABLE

2. 1

2.2

4. 1

v

LIST OF TABLES

Mode Shapes and Characteristic Values Usedin Design. . . . . • . . .- . . . .....

Design Peak Acceleration, Modal Frequencies,Spectral Amplification, Substitute DampingFactor, and Design Spectral AccelerationUsed in Design. • • • • . .••

Response Maxima Observed During the FirstSimulated Earthquake ••••..••••

Page

49

50

51

52

4.2 Response Maxima Observed During the SecondSimulated Earthquake · · · · · · · · · · · · · · · · · · · · 53

4.3 Response Maxima Observed During the ThirdSimulated Earthquake · · · · · · 54

4.4 First Steady-State Test. · · · · 55

4.5 Second Steady-State Test • · · · · 56

4.6 Third Steady-State Test · · · · · · · · · · · · · · · 57

5. 1 Spectrum Intensities 58· ·5. 1 Comparison of Calculated and Measured Response

for the Design Earthquake. · · · · · · · · · · · · · · · · · 58

A.1 Measured Gross Cross-sectional Beam DimensionsNorth Frame · · · · · · · · · · · · · · · · · · · · · · · · 148

A.2 t~easured Gross Cross-sectional Beam DimensionsSouth Frame · · · · · · · · · · · · · · · · · · · · · · · · 149

A.3 Measured Gross Cross-sectional Column DimensionsNorth Frame · · · · · · · · · · · · · · · · · · · · · · · · 150

A.4 ~leasured Gross Cross-sectional Column DimensionsSouth Frame · · · · · · · · · · · · · · · · · · · · · · · · 151

A.5 Summary of Measured Gross Cross-sectional MemberDimensions • • • • • • 0 ••••••

A.6 Measured Story Masses••••.•••.•.•••.

152

153

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vi

LIST OF FIGURES

Figure Page

2.2 Test Structure •••••••••

2.3 Smoothed Design Spectrum for a DampingFactor of 0.02 Compared with EstimatedTest Structure Frequencies ••••••

Calculated Modal Shapes for the FirstThree Modes •• • • • • • • • • • • · . . .. . . . .

2. 1

2.4

2.5

2.6

Configuration and Positioning ofTest Frames.

Interpretation of Damage Ratio ••

Test Frame and Idealized Models ••

. . . . . .

. . ... . . .. .

. . . . .

59

60

61

62

63

64

2.7

2.8

Lateral Forces, Story Shears, OverturningMoments, and Displacements Used in Design(First Mode) •••••••••••••••

Lateral Forces, Story Shears, OverturningMoments, and Displacements Used in Design(Second Mode) ••••••••••••••

· . . . . . . .

· . . . . . . .

65

66

2.9 Lateral Forces, Story Shears, OverturningMoments, and Displacements Used in Design(Third Mode) • • • • • • • • 67

Column Axial Forces Including Gravity Loadfor First Mode. • .••••••

2.10

2. 11

Column End Moments for First Mode••• . . . . .. . . 68

69

2.12

2.13

Column End Moments for RSS of First ThreeModes ... . . . • • . . • • . . .. . •

Column Axial Forces Including Gravity Loadfor RSS of First Three Modes

. . . . . . . . . 70

71

Beam End Moments • •2.14

2.15 Laterally Displaced, One-Bay,One-Story Frame. • • • • • • . . . . . . . . . . . . . . .

72

73

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vii

Figure

2.16 Nominal Member Cross Sections~ •

Page

• • • • 74

2.17 Column Interaction Diagram.

2.18 Representative Frame Details.

· .. . . .

75

• 76

. . . . . . . . . . . .

• • 80

Free-Vibration Test Setup • ;, •••••••••

Crack Patterns Observed Before Test Run One.

Location and Orientation of Instrumentation.

• 79

• 81

.77

78

. .• • •

· . . . . .· . .

. . .· . .

Crack Patterns Observed After FirstSimulated Earthquake ••••••

2.19 Location of Reinforcement Throughout aFrame. . . . • . • . . . . . • • • •

3. 1

3.2

4. 1

4.2

4.3 Crack Patterns Observed After SecondSimulated Earthquake • • • • • • • . • • • ••••••••• 82

4.4 Crack Patterns Observed After ThirdSimulated Earthquake • • • • • • • • •••••••••• 83

4.5 Free-Vibration Waveforms of Tenth-levelAccelerations, Observed (Broken) andFiltered (Solid) ••••••••••• . . . . . . . . . . · 84

4.6 Fourier Amplitude Spectra of Tenth-LevelAccelerations During Free Vibration•• . . . . . . . . . . • 85

4.7

4.8

First Simulated Earthquake. LinearResponse Spectra • • • • • • • • • •

First Simulated Earthquake. ObservedResponse (Broken) and ComponentsBelow 3.0 Hz (Solid) ••••••••

· . . . . . . . . . .

· . . . . . . .

• 86

• 88

4.9 First Simulated Earthquake..of Displacements •••••

Fourier Amplitude Spectra· . . . . . . . . . . . . • • • • 94

· . . . . . . . . . . . . . . .Fourier Amplitude4.10

4.11

First Simulated Earthquake.Spectra of Accelerations •

Second Simulated Earthquake.Response Spectra • • • • •

Linear· . . . . . . . . .• 95

· . . • . . . 96

4012 Second Simulated Earthquake. Observed Response(Broken) and Components Below 3.0 Hz (Solid) •••••••• 98

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· . . . . . . . . . .

· . . . . . . . . . .

Figure

4.13

4. 14

4.15

4.16

viii

Second Simulated Earthquake. FourierAmplitude Spectra of Displacements.

Second Simulated Earthquake. FourierAmplitude Spectra of Accelerations.

Third Simulated Earthquake. LinearResponse Spectra •••••••••

Third Simulated Earthquake. ObservedResponse (Broken) and Components Below3.0 Hz (Solid) ••••••••••••• . . . . . . . . .

Page

104

105

106

108

4.17

4.18

Third Simulated Earthquake. FourierAmplitude Spectra of Displacements.

Third Simulated Earthquake. FourierAmplitude Spectra of Accelerations.

· . . . . . . . . . .

· . . . . . . .

114

115

4.19 First-Mode Resonance Shapes Observed DuringSteady-State Tests. • • . • • • • • • • • • • • • • • • • 116

5.1 Comparison of Apparent Modal Frequencieswith Maximum Tenth-Level DisplacementPreviously Experienced by Test Structure. • • • • • • • • 117

5.2 Comparison of Apparent First-Mode Frequencywith Maximum Tenth-Level DisplacementPreviously Experienced by Test Structure. · . . . . . . . 118

5.3 Comparison of Observed High Frequencieswith First-Mode Frequency •••••••••• 0 ••••• 119

5.4

5.5

5.6

"t·1oda1 11 Amplification Compared withExciting Frequency in Steady-StateTests . . . • • . . .. . • • . . • . .

r~easured Simu1 ated Earthquake Waveforms

Fourier Amplitude Spectra of SimulatedEarthquake Base Accelerations ••••

· . 120

121

• 122

5.7

5.8

Displacements, Lateral Forces, Story Shearsand Story-Level Moments Measured DuringSimulated Earthquakes • • • • • • 0 • • •

Comparison of Measured Displacement Shapes andShapes Calculated for the Substitute StructureMode1 •••••••••••••••• 0 • • •

• • • • • 123

126

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ix

Figure Page

5.9 Comparison of Maximum Tenth-Level Displacementand Spectrum Intensity at a Damping Factorof 0.20...............•......... 127

· . . . . . . .130· . . . . . . .

5.10

5.11

5.12

Measured Response Through a Half-CycleIncluding the Maximum Displacement Duringthe First Simulated Earthquake •••••

Comparison of Base Shear and Tenth-LevelDisplacement ••••••••••••

Comparison of Measured Base Shear andCalculated Collapse Base Shears forMechanism Acting Through Various StoryHeights••••.••..•••••••

128

130. . . . . .

. . . . . . .

5.13

5.14

Calculated Collapse Mechanisms and Base Shearsfor a Triangular Load Distributipn •••••

Cumulative Number and Value of DisplacementPeaks During Simulated Earthquakes.

131• • • • • !I'

132

5.15 Comparison of Design Response Spectrumand Spectrum Calculated from FirstSimul ated Earthquake • • • • • • • • 133· . . . . . . .

5.16

A. 1

Comparison of Design Response and MeasuredResponse for Identical Base Motions••••

Envelope of Measured Concrete Stress-StrainRelations and Design Relation•••••

134

154

. . . .

• • • 157

• '160

•• 156

154

155. . .. . .. .

First Simulated Earthquake. Comparison ofLateral Response as Measured on Northand South Test Frames••••••••••

Overall Configuration of Test Setup••

Detail of Mass-to-Frame Connection ••

Measured Mean Stress-Strain Relation andDesign Relation for No. 13 Gage Wire.

Detail of Base-Girder Reinforcement

A.2

A.3

A.4

A.5

B. 1

B.2 First Simulated Earthquake.Vertical Accelerations ••

Transverse and. . . . . . . . • 162

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1. INTRODUCTION

1.1 Object and Scope

The overall objective of this work was to observe the effect of strong

simulated earthquake motions on a small-scale, ten-story, reinforced

concrete frame structure with relatively flexible lower stories. The

structure was designed according to the substitute structure method [5]*

which is a design method using linear modal spectral analysis. A secondary

objective, then, was to observe the applicability of the method and, hence,

the applicability of modal spectral analysis.

The experimental work included the building and testing of the small-

scale structure. The test structure comprised two reinforced concrete

frames situated opposite one another with strong axes parallel to base

motions and with story-masses spanning between the frames to increase

inertial forces (Fig. 2.2). The test structure was subjected successively

to three simulated earthquake motions of increasing intensity. Free-

vibration and steady-state sinusoidal tests were complementary tests used

to observe effects of the earthquake simulations.

1.2 Acknowledgments

This work is part of a continuing investigation of reinforced concrete

structure response to earthquakes being carried out at the Structural

Research Laboratory of the University of Illinois Civil Engineering Department.

This work was sponsored by the National Science Foundation under grant

ENV-74-22962.

*References are listed alphabetically at the end of the text. Numbersin brackets [ ] are the number of the reference in the reference list.

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2

The writers wish to thank project staff members D. Abrams, B. Algan,

H. Cecen and T. Healey for valuable discussion and assistance with data

reduction. Appreciation is due project staff member M. Saiidi for use of

his modal analysis program and to Professor L. Lopez for assistance in the

use of the IIFinite ll structural analysis system.

Professor V. Jo McDonald provided direction for instrumentation and

data reduction facilities. Mr. G. Lafenhagen provided invaluable assistance

in the instrumentation setup and experimental conduct. Mr. O. H. Ray and

his staff helped in fabricating the specimens and hardware used in the test.

The writers are indebted to the members of the panel of consultants

for their advice and criticism. The panel 'included t·t H. Eligator,

Weiskopf and Pickworth; A. E. Fiorato, Portland Cement Association; W. D.

Holmes, Rutherford and Chekene; R. G. Johnston, Brandow and Johnston;

J. Lefter, Veterans Administration; W. P. ~1oore, Jr., Walter P. t100re

and Associates; and A. Walser, Sargent and Lundy.

The IBM-360/75 computer system of the Department of Computer Science

was used for data reduction. The Burroughs 6700 at the Civil Engineering

Systems Laboratory was used for structural analysis computation.

This experimental work and report were undertaken as a special project

toward the Master of Science Degree ln Civil Engineering by Jack P. Moehle,

Research Assistant in Civil Engineering, under the direction of M. A. Sozen,

Professor of Civil Engineering.

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3

2. DESIGN OF THE TEST STRUCTURE

2.1 General Criteria

The overall configuration of the test structure was governed by

modeling and equipment limitations and by the objective of the test.

As ideally conceived, the test structure consisted of two ten-story,

three-bay, reinforced concrete frames (Fig. 2.1). Bay widths were

305 mm while story heights varied, being 279 mm for the first and tenth

stories and 229 mm for intermediate stories. In addition, one beam was

omitted at one side of each frame as shown in Fig. 2.1. The gross

cross-sectional dimensions of beams were 38 by 38 mm and of columns

were 51 by 38 mm. Situated opposite one another, the frames would be

subjected to a unidirectional simulated earthquake with motion parallel

to the strong axis of the frames. Supported by and spanning between

the two frames were ten story masses, one at each of ten story levels

(Fig. 2.2). The mass at level one, the level with the lIr.Jissing ll beam,

was nomi na11y 302 kg. Masses at all other 1eve1s were 454 kg.

The configuration described in the foregoing was selected for the

purpose of studying experimentally the effect of strong base motion on a

multistory reinforced concrete structure, in particular, a nonsymmetric

structure with increased top and bottom story heights. Nonstructural

masses are used to increase the inertia forces during the test. The use

of ten such masses allows for the convenient determination of response

variation with height. Particular dimensions of the structure were

based on equipment limitations. The humble nature of the structure, being

nearly a stick structure with a single plane of loading, is advantageous

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4

from the analytical viewpoint. The structure becomes a simple physical

model of an ana1~tical concept without the embellishments (architectural

or otherwise) found in a full-scale, multistory building. Indeed, the

test structure is meant in no way to be a prototype or model for any

full-scale structure.

The base motion to which the test structure was subjected was modeled

after the El Centro-NS, 1940 earthquake. The time· scale of the prototype

earthquake was compressed by a factor of 2.5 and accelerations were

amplified in order to excHe the test structure into the inelastic range.

The reproduced motion at this time compression and for small amplifications

is relatively undistorted from the original motion. A smoothed design

spectrum of the assumed model earthquake [5 J is shown in Fig. 2.3. Also

shown are the estimated modal frequencies of the test structure for the

first three modes (see Sec. 2.3, for determination of modal frequencies).

As seen in Fig. 2.3, the second and third modes are in the range of

high amplification. Thus, the motion chosen would be expected to excite

the higher modes of vibration.

2.2 Design Method

The design method used in determining design forces was the substitute

structure method [5 J. This method features a linear dynamic analysis

whiCh recognizes nonlinear energy dissipation in a reinforced concrete

structure. Minimum structural strength requirements are set so that a

tolerable set of designer-specified lateral displacements is not likely to

be exceeded in the event of a base motion corresponding to the design

spectrum.

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5

Design via the substitute structure ~ethod can be described under

three basic steps.

(1) Given an expected class of earthquake motion, define a smoothed

acceleration response spectrum for a linear, single-degree-of-freedom

system. This design spectrum should be chosen so as to approximate the

calculated response spectrum at a damping factor of 0.10 since this value

is typical of values derived from the substitute structure model. An

acceptable expression [5] relating response at any damping to response

at damping of 0.02 is

Response at damping factor of 6Response at damping factor of 0.02

8= -="6-+--=--::-'10::-::0'-6 (2.1)

Approximate response accelerations can then be determined for any damping.

(2) Define the· substitute structure. Flexural stiffness of

substitute structure members is defined as

(El) ai(E1)s; =---'-

].liwhere

(El) . = substitute cross-sectional stiffness of member iS1

(El)ai = actual cross-sectional stiffness of member i

based on the cracked section

].1. = selected damage ratio of member i1

The damage ratio is seen in Fig. 2.4 to be the ratio of initial cracked

section stiffness to the minimum effective stiffness obtained for a

reinforced concrete member. The damage ratio becomes a measure of

inelastic energy dissipation. It is comparable with ductility only in

that a large damage ratio requires a large ductility. The damage assigned

toa member is largely a matter of choice. However, since practical

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6

experience emphasizes the desirability of maintaining a stiff spine

throughout the height of the structure, a damage ratio of one is normally

assigned to columns. Damage ratios assigned to beams depend on the amount

of inelastic action considered to be acceptable.

(3) Determine modal frequencies, shapes, and forces from a linear

analysis of the substitute structure. Member forces can be determined at

at damping factor of 0.02 from which, using an assumed damping factor in

Eq. 2.1, modified member forces can be calculated. These modified member

forces permit calculation of the substitute structure damping factor as

P. * SsiS = L

1m i L: P.

i 1

where~

1 + 10 (1 - (1/ 11 ;) )Ssi = 50

L. 2 2 t1bi )P. = 6(EI) . (Mai + t'1bi M .1 a1Sl

where

S = substitute structure damping for mode mmP. = strain energy of member i1

Ssi = substitute damping of member i

L. = length of member i1M. and t-1bi = end moments of member i for mode ma1

(2.3)

(2.4)

(2.5)

Equation 2.4 is an expression based on dynamic tests and provides an

estimate of the viscous damping required to simulate observed hysteretic

behavior in reinforced concrete [ 1]. Equation 2.3 assumes that each

member contributes to the overall structural damping in accordance with

its strain energy.

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7

Having obtained the substitute structure damping factor, new modal

forces can be obtained, again using Eq. 2.1. One iteration is normally

sufficient given the approximate nature of Eq. 2.4.

Having determined member forces for distinct modes, design forces

are based on the root-sum-square (RSS) combination modified by a base

shear factor as

(2.6)

where

F. = design force in member i1

Firss = root-sum-square force in member i

v = root-sum-square base shearrssVabs = absolute sum of the base shear for any two modes.

It is then suggested that design column moments be additionally factored

by 1.2 in order to further reduce the risk of inelastic action.

2.3 Determination of Design Forces

Design of the test structure followed rather closely the substitute

structure method. However, owing to the experimental nature of this work

and to previous experience with similar structures, certain exceptions

to the method were made. As made, these exceptions will be noted and

the reasoning behind the deviations will be presented. Substitute

structure modeling and design calculations are described below.

(a) Model for Analysis

The model used for static analysis of the structure is depicted

in Fig. 2.5b. The structure was considered a stick structure with

lateral forces concentrated at floor levels and gravity forces distributed

equally to beam-column joints at a given level. Columns were assumed to

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8

be rigidly fixed at the base. Rigid zones were assumed at member ends,

the zones being the size of beam-column joints in the actual structure.

Axial deformations were considered only for columns. Member flexural

stiffnesses were based on cracked sections modified by a chosen damage

ratio.

The assigned damage ratios were one for columns and four for beams.

This distribution of damage ratios was selected with the intent that

energy be dissipated in the beams and that columns remain in the elastic

range. The specific value of four for beams was based upon the satis­

factory upper bound of displacements that resulted in the analysis.

Member cross-sectional stiffnesses for the model were based on

material properties, either known or assumed, and on assumed cross­

sectional member dimensions. No strength reduction factors were used. As

determined from coupon tests, Youngs' modulus and yield stress for steel

were 200,000 MPa and 358 MPa, respectively. Assumed concrete modulus was

21,000 MPa. Concrete strength was taken as 35 MPa at a strain of 0.003.

Nominal cross-sectional dimensions for columns and beams were as shown in

Fi g. 2.16.

(b) Method of Dynamic Analysis

Modal analysis of the model was performed using a computer program

developed by M. Saiidi at the University of Illinois. As used for this

analysis, the structural stiffness matrix was constructed by considering

only beam and column flexural deformations and column axial deformations.

The matrix was then condensed to a ten-degree-of-freedom system with

masses lumped at story levels (Fig. 2.5c). After condensation, the ten

freedoms were lateral motions at each of ten floor levels parallel to the

strong axis of the frames. No vertical or rotational inertias were considered.

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9

Modal vectors, frequencies, and participation factors obtained from

the analysis are listed in Table 2.1. Modal shapes are plotted in Fig.

2.6.

Lateral forces were determined using the above modal quantities

and a smoothed design spectrum [5]. A design peak acceleration of 0.4 g

was chosen. A design acceleration amplification spectrum for the model

earthquake (El Centro-NS, 1940, time-scale compressed by 2.5) is shown in

Fig. 2.3. Design spectral accelerations for each mode and for a damping

factor of S are calculated asm

where

am = design spectral acceleration for mode m at damping of Sm

ad = design peak acceleration (=0.4 g)

(SA) = spectral amplification for mode mat damping of 0.02.m

(2.7)

Design lateral forces are then calculated as

F. = ¢. * t1. * P * a (2.8)Jm Jm J m m

where

F. = lateral force at level j for mode mJrn¢jm = modal vector at level j for mode m

Mj = mass at level j

Pm = participation factor for mode m

Page 22: By Jack P. t·loeh 1e and A. Sozen

for beams,

10

(c) Member Design Forces

computations to determine member forces were carried out on FINITE

at the University of Illinois [3 J. The structure was modelled as shown

in Fig. 2.5b. As a first trial, lateral forces F. were applied to theJmmodel with 8m assumed at 10% for all modes. With member end moments

determined for these externally applied forces, new damping factors were

calculated. Using Eq. 2.3

1 + 10 (1 - (l)~Q - _--;:-::--_--:.4 = o. 12jJsi - 50

for columns, 8 . = 0.02.Sl

The "smeared" substitute structure damping, 8 , was then determinedm

using Eq. 2.4 and 2.5. Numerical values of design peak acceleration,

modal frequency, spectral amplification, substitute damping factor, and

design spectral acceleration for the first three modes and for first and

second trial calculations are shown in Table 2.2.

Using the new damping factors, the model was again analysed. New

Values for lateral forces, story shears, overturning moments (not including

resisting moment from gravity load), and displacements were obtained for

each of two frames in the test structure. These are plotted for the first

three modes in Fig. 2.7, 2.8, and 2.9.

Column end moments and axial forces for the first mode and for the

root-sum-square of the first three modes are plotted for each story and

each column in Fig. 2.10 to Fig. 2.13.

Beam end moments for the substitute structure were essentially

constant at a given floor level despite the frame irregularity. ~1ean

beam end moments are plotted for the first mode and for the root-sum­

square of the first three modes in Fig. 2.14.

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11

Having determined member forces for distinct modes, the substitute

structure method stipulates that design forces will be root-sum-square

(RSS) forces modified by a base shear factor (Eq. 2.6) and that column

end moments be additionally factored by 1.2. However, the experimental

nature of this design work was better satisfied by deleting the base

shear factor and working solely with RSS forces and factored column end

moments. In so doing, the design became less conservative, with increased

likelihood that design moments would be realized or surpassed in the

actual test. Such unconservative proportioning is, of course, undesirable

for an actual structure but is desirable for an experimental structure

through which the limits of a design method are being tested. Unfactored

RSS column end moments, column axial forces, and beam end moments are

shown in Fig. 2.10, 2.12, and 2.14.

Use of the column end moment factor as prescribed by the substitute

structure method was modified without misconstruing the intent of the

requirement. The intent of the column end moment factor is best illus­

trated by a one-story, one-bay frame as shown in Fig. 2.15a. If the frame

is a laterally displaced as shown in Fig. 2.15b, equal end moments will

exist in both the column and beam at the top level (Fig. 2.15c). If

both are designed for the same moment, yielding may occur at either section.

However, if the column design end moment is increased by a factor of 1.2,

yielding will occur in the beam only. The situation at the base of the

frame in Fig. 2.15a is somewhat different. If yielding occurs, it will

necessarily occur in the column. Factoring of this base end moment

becomes the equivalent of applying a general load factor or strength

reduction factor.

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12

Application of the column end moment factor of 1.2 to the test

structure is analogous to its application to the simple structure of

Fig. 2.15a. The factor was applied throughout the height of the structure

with the exception of base column end moments. In keeping with the

convention that no strength reduction or general load factors be employed,

these column base moments were left unfactored. Final design column

end moments are those of Fig. 2.12 factored at every level, except the

base, by 1.2.

(d) Reinforcement

Longitudinal reinforcement requirements for members were based on

design forces as presented in Sec. 2.3(c). Proportioning for these

requirements was aimed at avoiding frequent or extreme changes in member

stiffness and at providing a system that could be readily constructed.

The most convenient arrangement of longitudinal reinforcement from

the analytical and constructional viewpoint is one that has equal steel

throughout the structure. As can be seen from member end moment distri­

butions (Fig. 2.12 and 2.14), such an arrangement results in either

overdesign or underdesign of the structure. Gross underdesign is undesir­

able because the structure will be unlikely to withstand the design base

motion satisfactorily. Overdesign is undesirable in that it is uneconomical

and results in a structure significantly different from the substitute­

structure model. For these reasons, longitudinal reinforcement was varied

to conform to the distribution of design moments.

Figure 2.14b is a plot of design beam end moments. Provided yield

moment with two and three bars per face is plotted in that figure to the

same scale as beam end moments. Nominal cross-sections of beams are

shown in Fig. 2.16a and 2.16b.

Page 25: By Jack P. t·loeh 1e and A. Sozen

13

Column design end forces are plotted versus provided strength in

the interaction diagram of Fig. 2.17. Nominal cross sections of columns

are shown in Fig. 2.16c and 2.16d.

The tension condition controls the design of the column section.

The design forces for one exterior column in tension falls considerably

outside the interaction diagram (Fig. 2.17). This was accepted on the

basis that base shear not carried by the yielding column would be carried

by other columns of the first story-level. The trend in redistribution of

moments after this column yielded was investigated by assigning a damage

ratio of two to the column. The changes in moment for column base end

moments are indicated in Fig. 2.17 where arrows indicate the extent of

redistribution for each column. Under actual conditions, column B

(Fig. 2.17) is already near yield and would be expected to maintain its

yield capacity as columns C and 0 would be expected to pick up more moment.

A failure mechanism is not expected to result from the design forces.

A typical beam-column detail is shown in Fig. 2.18. Shown in addition

to the longitudinal steel is helical transverse reinforcement. This

reinforcement was the same throughout the structure and was designed with

a factor of safety of three to resist the worst possible shear assuming

that shear strength of concrete was zero. A spiral beam-column joint

reinforcement can also be seen in Fig. 2.18. This reinforcement was used

with the intent of confining the joint core. Tubing in beam-column joint

centers was used to prevent deterioration of the joint caused by support

of the story masses at these joints. No special calculations were made

for either of the joint core reinforcements.

Page 26: By Jack P. t·loeh 1e and A. Sozen

14

The location throughout the frame of all types of steel is shown

schematically in Fig. 2.19. A frame reinforcing schedule for longitudinal

steel is presented in Table 2.3.

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15

3. DESCRIPTION OF EXPERIMENTAL PROCEDURE

3.1 Test Structure

The overall configuration of the test structure is shown in Fig. 2.2.

Distinctive characteristics, the effects of which were being tested,

included increased first and last story heights as compared with inter­

mediate stories and the omission of one first level beam in each of the

two reinforced concrete frames which composed the structure. Ten story

masses were supported between the two frames, one mass centered at each

floor level. In keeping with the omission of a beam in each frame, the

first story mass was close to two thirds the mass at other floors

(Table A.6).

Construction of the test structure was begun with the two reinforced

concrete frames. The frames were cast monolithically with base girders

and in a horizontal position. The concrete was a small aggregate type.

All longitudinal steel for columns and beams (No. 13 gage wire) was

continuous with the exception of cutoffs in longitudinal column steel as

allowed in design (see Chapter 2 for reinforcement details). Anchorage

and development of steel was provided where necessary. Following a

curing period, the frames were fixed to the test platform of the earthquake

simulator in a vertical position and with the strong axis of the frames

parallel to the line of motion of the test platform. The ten story masses

were then connected between the frames (Fig. 2.2 and A.4). No gravity load

from the story masses was transferred to the frames until the day of the

test.

Page 28: By Jack P. t·loeh 1e and A. Sozen

16

Connections between story masses and frames were designed to

minimize transfer of moments. Each mass was supported by two cross

beams which were in turn supported at each end by a pair of perforated

channels (Fig. A.5). These perforated channels were connected to the

frame by bolts through the center of beam-column joints. This mass­

supporting mechanism was such that gravity load was transmitted approxi­

mately equally to all columns at a given story level for levels two through

ten. The supporting mechanism was indeterminate at level one (Fig. 2.2).

A bellows system connecting the masses at each level provided increased

stiffness in the transverse direction, thereby restricting out of plane

motion of the test structure (Fig. 2.2).

3.2 Instrumentation and Recording of Data

Two basic types of test data were obtained: (1) displacements

and accelerations of the test structure and (2) visible structural

damage.

Data from the response of the structure included both absolute

accelerations and relative displacements. Accelerations were measured

with accelerometers while displacements were measured with differential

transformers (LVDT's). The location and orientation of these instruments

are shown in Fig. 3.1. Response as' measured was recorded on magnetic

tape. All instruments were calibrated and amplified to maintain suffici­

ent sensitivity but to avoid saturating the recorded recores. Both

mechanical and electrical calibrations were made before the test.

Electrical calibrations were again made throughout the test as a check

of temperature effects on the instruments.

Page 29: By Jack P. t·loeh 1e and A. Sozen

17

Information concerning structural damage consisted of the location

of cracks and of crushing or spalling in the concrete. Location of

cracks was facilitated through the use of a fluorescent fluid. The fluid

collected in cracks and reflected IIblack light ll to shovi crack patterns.

These were marked on the frames and recorded on data sheets. Crack sizes

and crushing and spalling information were also recorded.

3.3 Test Motions

Response to three types of motion were measured during the test.

These are described briefly below.

(1) Simulated Earthquake. During a simulated earthquake, the

test structure was subjected to a predetermined base motion (El Centro­

1940, North-South component, time scale compressed by a factor of 2.5).

The first earthquake input had an expected peak acceleration of 0.4 g

and was the design earthquake. TVIO subsequent inputs had peak acceler­

ations approximately two and three times that of the design earthquake.

All instruments were active during the simulated earthquakes.

(2) Steady-State. The structure was given a sinusoidal base motion

that varied in steps from a frequency below the apparent resonance

frequency of the structure to a frequency above the observed apparent

resonance frequency of the structure. The amplitude of motion was

chosen so as to avoid damaging the structure (approximately 5 mm). All

instruments were in operation during a steady-state test.

(3) Free Vibration. The structure was given a small lateral

displacement (approximately 1 mm) at level ten and then released. The

setup for a free vibration test is shown schematically in Fig. 3.2. A

tenth level accelerometer was the only instrument recording data. The

Page 30: By Jack P. t·loeh 1e and A. Sozen

18

voltage from that accelerometer was amplified so as to be sensitive to

the small accelerations produced.

3.4 Testing Sequence

The test was begun by locating and marking all shrinkage cracks.

This was done both before and after the story ma~ses had been connected

to the frames~ but before any testing had begun. The structure was

then subjected to the motions described in Sec. 3.3 in the following

sequence:

1. Free Vibration

2. Simulated Earthquake

3. Free Vibration

4. Steady~State

Following each simulated earthquake~ structural damage was observed and

recorded. This sequence, together with the observation of structural

damage, formed one test run. Three such test runs were performed. The

only variable from test run to test run was the intensity of the simulated

earthquake.

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19

4. OBSERVED RESPONSE

4.1 Introductory Remarks

The test structure was tested according to the procedure described

in Chapter 3. Observations of response consist of or were derived from

relative-displacement and absolute-acceleration waveforms recorded during

the test. These waveforms and corresponding Fourier amplitude spectra

are presented for free vibrations and simulated earthquakes. Spectrum

intensities and response spectra were determined for earthquake base

accelerations, and shear and moment waveforms were derived from earthquake

response records. Displacement amplitudes at several frequencies are

presented for steady-state tests. Crack patterns which developed during

simulated earthquake~ are also presented.

Data presented in this chapter refer to the north frame of the test

structure. Recorded waveforms for both frames were almost identical.

(See Appendix B for a comparison).

4.2 Nature of Data Presented

(a) Frequency Content

Fourier analysis was used to determine frequency content of recorded

waveforms. Using the Fourier Transform, a responsewaveformwas repre­

sented in terms of its harmonic components. The relative amplitude of

each component is plotted versus the frequency of that component in a

Fourier amplitude spectrum (e.g. Fig. 4.9).

The Fourier Transform is also suitable for filtering certain

frequencies from the original waveform. In this chapter, all waveforms

are plotted for the original and filtered response. A typical waveform

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20

is plotted in Fig. 4.8 where the broken curve represents measured response

and the solid curve represents filtered response. All filtered response

waveforms contain only those harmonic components below 3.0 Hz.

A definition is appropriate at this time as to terms used to designate

those frequencies (or narrow ranges of frequencies) at which peaks on the

Fourier amplitude spectra occur. The lowest of these frequencies is defined

as the first-mode frequency, the next as the second-mode frequency, and

so on. These modal frequencies can be associated tentatively with phase

relationships among the floor level motions. As can be observed generally

on acceleration waveforms (Fig. 4.8) at any instant this first mode can be

associated with a condition that all levels are in phase, the second mode

has one node, and so on. It cannot be assumed that the phase relations

are constant with time for any mode.

(b) Free Vibrations

Free vibrations were imparted to the test structure by laterally

displacing and then releasing the tenth level (Fig. 3.2). Acceleration

waveforms measured at the tenth level and Fourier amplitude spectra

determined for the first three seconds of free vibration are plotted

(Fig. 4.5 and Fig. 4.6).

(c) Simulated Earthquakes

Base motions were modelled after El Centro-NS, 1940. Time scales

were compressed by a factor of 2.5 and acceleration amplitudes were

magnified to achieve the desired motion. Spectrum intensity [ 2 ] at

a damping factor of 0.20 is used to represent the intensity of the base

motion. To be consistent with time-scaling of the base motion, spectrum

intensities were calculated between 0.04 and 1.0 Hz. Response spectra at

various damping factors were also determined for the base motion (e.g.

Fig. 4.7).

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21

As noted earlier, response waveforms are reported only for the north

frame. Typical acceleration and displacement waveforms are plotted in

Fig. 4.8. Shear and moment waveforms were derived from the acceleration

and displacement waveforms and structural configuration. The P-delta

moment, typically less than two percent of the total base moment, was

included. Typical story shears are also plotted in Fig. 4.8. Base level

moment is plotted with displacement waveforms in that figure. Maxima

and minima of all waveforms were determined automatically during the data

reduction process.

Fourier amplitude spectra were determined for relative displacement

and absolute acceleration response waveforms (e.g. Fig. 4.9 and 4.10).

(d) Steady-State Tests

Base motion for steady-state tests consisted of an approximately

sinusoidal displacement at nearly constant amplitude. The frequency of

input motion varied in steps and ranged from below to above the observed

apparent first-mode resonance frequency of the test structure. This

frequency is defined as that for which the ratio of tenth-level relative

displacement amplitude to base displacement amplitude was a maximum. All

displacement amplitudes were measured when the test structure was in an

apparent steady-state condition.

Observations reported consist of base motion frequency, base displace­

ment amplitude, and the relative displacement amplitude at a level for

each frequency step. In addition, relative displacement amplitude at each

story level is reported for the apparent resonance frequency. In order to

automate frequency and amplitude measurements and to insure that vibration

frequencies higher than the base motion frequency be excluded from the

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22

measurements, the waveforms were filtered. Data obtained, then, refer to

the filtered waveforms. Filtered and original waveforms appeared identical

at all but the lowest input frequencies. For those input frequencies at

which higher frequencies interfered substantially with the principal

input frequency, no data are presented.

(e) Crack Patterns

Crack patterns were observed before the test'and after each of three

simulated earthquakes. These are reported typically as in Fig. 4.3.

In crack pattern figures, frame-member depths are drawn to a larger scale

than are lengths.

It is important to note that crack patterns could not be observed in

beam spans in external bays because of the mass connections (Fig. A.5).

Therefore. only shrinkage cracks are presented for these spans.

4.3 Test Results

(a) Test Run One

Crack patterns before the first test run are presented in Fig. 4.1.

All crack widths were small (less than 0.05 mm).

A free-vibration waveform determined before the first simulated

earthquake is included in Fig. 4.5. The Fourier amplitude spectrum of

that waveform is plotted in Fig. 4.6'. The three lowest modal frequencies

were estimated to be 4.5, 14, and 25 Hz. Because of the higher initial

first-mode frequency, the filtered waveform (Fig. 4.5) includes all

component frequencies below 5.0 Hz as opposed to the upper limit of 3.0 Hz

used in all other waveforms.

Two negative peaks of high magnitude can be seen at 0.5 sec. of the

first free vibration (Fig. 4.5). Peaks are to be expected because the

way by which free vibration is imparted (Fig. 3.2) excites the second mode.

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23

However, the large magnitude of these peaks as compared with those of

other free vibrations suggests an error in the recording system.

Characteristics of the first simulated earthquake are summarized

below.

1. Base Motion

(a) Peak acceleration was 0.36 g at 0.88 sec. with majority

of large acceleration peaks occurring during the first

2.5 sec. (Fig. 4.8).

(b) Spectrum intensity for a damping factor of 0.20 was 185 mm.

(c) Response spectra (Fig. 4.7).

2. Response Motion

(a) Displacement and acceleration waveforms (Fig. 4.8) and

response maxima (Table 4.1).

(b) Fourier amplitude spectra (Fig. 4.9 and 4.10).

(c) Base moment waveform and story shear waveforms (Fig. 4.8)

and maxima (Table 4.1).

3. Crack Patterns (Fig. 4.2).

Simulated earthquake response waveforms reveal three intervals of

relatively high-level response. These occurred during 0.5 to 3.0, 5.0

to 7.5, and 10.5 to 12.5 sec. intervals. Response (especially during

these intervals) was dominated by the first mode as is particularly

evident in displacement waveforms (Fig. 4.8) and Fourier amplitude

spectra for displacements (Fig. 4.9). Contributions of higher frequencies

are more evident in acceleration waveforms (Fig. 4.8) and acceleration

Fourier amplitude spectra (Fig. 4.10). In the latter it is also evident a

gradual change from high frequency dominance in the lower floors levels to

first-mode dominance in the upper floor levels.

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24

The three lowest modal frequencies of response to the first simulated

earthquake could be estimated from acceleration Fourier amplitude spectra

(Fig. 4.10) to be 2.1, 7.8, and 16 Hz. Nodal points can be located

approximately by these spectra as the floor level where a particular modal

frequency has less influence in the total response. For the second mode,

the node is near the seventh floor level, while for the third, nodes

appear at floor levels four and nine. The modal 'frequencies cited refer

only to peaks on the amplitude Fourier spectra and thus refer to dominant

frequencies rather than to invariant properties of the structure.

Crack patterns were as shown in Fig. 4.2. All column cracks were

very fine (less than 0.05 mm in width) as were beam cracks above floor

level four. Beam crack sizes in the lower floor levels ranged from 0.05

to 0.15 mm, the largest cracks appearing in the two floor levels immediately

above the long column. No crushing or spalling was observed.

After the first simulated earthquake, a free vibration waveform

(Fig. 4.5) was obtained. Estimated modal frequencies were 2.8, 9 and 17

Hz (Fig. 4.6).

The first steady-state test followed with frequencies, base displace­

ment amplitudes, and tenth-level displacement amplitudes as tabulated in

]able 4.4. The apparent first-mode resonance frequency was between 1.75

and 1.85 Hz with maximum recorded tenth-level amplification of the base

displacement of 5.87. The normalized mode shape at 1.75 Hz is presented

in Fi g. 4. 19.

(b) Test Run Two

Before the second simulated earthquake, a free vibration test

resulted in the waveform and Fourier amplitude spectrum plotted in Fig.

4.5 and 4.6. The modal frequencies are estimated from Fig. 4.6 to be

2.7, 8.8, and 16 Hz. These frequencies are lower than the respective

Page 37: By Jack P. t·loeh 1e and A. Sozen

25

frequencies measured before the first steady-state test, indicating that

minor damage to the structure may have resulted during the steady-state

test.

The second simulated earthquake had the characteristics summarized

below.

1. Base motion

(a) Peak acceleration of 0.83 9 at 0.88 sec. and waveform

(Fig. 4.12) almost identical in shape and frequency content

to that of test run one.

(b) Spectrum intensity at a damping factor of 0.20 was 336 mm.

(c) Response spectra (Fig. 4.11).

2. Response motion

(a) Displacement and acceleration waveforms (Fig. 4.12) and

response maxima (Table 4.2).

(b) Fourier amplitude spectra (Fig. 4.13 and 4.14).

(c) Base moment waveform and story shear waveforms (Fig. 4.12)

and maxima (Table 4.2).

3. Crack patterns (Fig. 4.3).

The general shapes of response waveforms were different from those

determined during the first simulated earthquake. t1aximum response

occurred during two intervals with relatively low-level response occurring

approximately seven seconds into the earthquake duration (Fig. 4.12).

Displacements were again dominated by the first mode. However, acceleration

waveforms reveal a greater dominance by higher frequencies than was

apparent in the first simulated earthquake. Acceleration Fourier amplitude

spectra (Fig. 4.14) also reveal the dominance of the higher frequencies.

Page 38: By Jack P. t·loeh 1e and A. Sozen

26

The lowest apparent frequencies were 1.4,5.5, and 12 Hz (Fig. 4.14).

Nodal points were indicated to be in approximately the same locations as

in the first simulated earthquake.

Crack patterns apparent after the second simulated earthquake are

shown in Fig. 4.3. Cracks wider than 0.05 mm were limited to beams at

column interfaces in the lower five floor levels. Cracks were largest

(up to 0.30 mm) in exterior beam column joints. Minor spalling was

observed (Fig. 4.3).

Response in free vibration after the second simulated earthquake is

plotted in Fig. 4.5 with the Fourier amplitude spectrum in Fig. 4.6.

The first and second mode frequencies were,2.4 and 7.3 Hz. The third-mode

frequency was not apparent (Fig. 4.6).

Test results of the second steady-state test are presented in Table

4.5. The apparent first-mode resonance frequency was near 1.48 Hz with a

maximum measured base displacement amplification of 4.24 at floor level ten.

The displacement shape determined at 1.48 Hz is presented in Fig. 4.19.

(c) Test Run Three

Results from the free-vibration test before the third simulated

earthquake are presented in Fig. 4.5 and 4.6. The two lowest dominant

frequencies were 2.3 and 7.1 Hz.

Characteristics of the third simulated earthquake are summarized

below.

1. Base motion

(a) Peak acceleration of 1.28 g at 0.88 sec. with waveform

shape (Fig. 4.16) and frequency components similar to the

first two simulations.

Page 39: By Jack P. t·loeh 1e and A. Sozen

27

(b) Spectrum intensity at damping factor of 0.20 was 411 mm.

(c) Response spectra (Fig. 4.15)

2. Response motion

(a) Displacement and acceleration waveforms (Fig. 4.16) and

maxima (Table 4.3).

(b) Fourier amplitude spectra (Fig. 4.17 and 4.18).

(c) Base moment waveform and story shear waveforms (Fig. 4.16)

and maxima (Table 4.3).

3. Crack patterns (Fig. 4.4).

Response to the third simulated earthquake indicated a softer

structure. The estimated first three modal frequencies were 1.3, 5.4,

and 10 Hz. Nodal points appeared ~ be at about the same levels as in

earlier simulated earthquakes.

Crack patterns after the third simulated earthquake are sketched in

Fig. 4.4. The worst damage occurred in lower level beams where the

largest crack widths approached 0.40 mm. Measureable cracks (wider than

0.05 mm) extended the height of the structure. More spalling was observed

in the locations indicated in Fig. 4.4.

The waveform of the free vibration after the third simulated earthquake

(Fig. 4.5) was analysed to reveal a first mode frequency of 2. 1 Hz

(Fig. 4.6).

Results of the third steady-state test are tabulated in Table 4.6.

Difficulties with calibrations precluded determination of the tenth level

response and of the deflected shape at resonance. For this reason, relative

displacements are presented in Table 4.6 for level six (rather than level

ten). No resonance shape is presented. The approximate resonance frequency

was 1.30 Hz.

Page 40: By Jack P. t·loeh 1e and A. Sozen

28

5. DISCUSSION OF TEST RESULTS

5.1 Introductory Remarks

Apparent characteristics of response of the test structure are summarized

and discussed in this chapter. The effects of damage and of response ampli­

tude on dominant frequencies and apparent damping are noted. Response to

simulated earthquakes is compared and response maxima in the "design"

earthquake are then compared with those calculated for the linear substi-

tute model.

5.2 Apparent Natural Freguencies

Apparent natural frequencies of the test structure were determined

from free vibration, simulated earthquake, and steady-state tests. Values

of measured frequencies averaged over the duration of each test are plotted

versus response history in Fig. 5.1 and 5.2. Maximum double-amplitude

displacement (absolute sum of adjacent positive and negative displacement

peaks) incurred during or prior to the indicated test is used to represent

response history. Characteristics of measured frequencies are described

below.

(a) Initial Freguencies

The three lowest frequencies were determined from a free vibration of

the test structure before the first simulated earthquake. Values of these

frequencies are plotted in Fig. 5.1 at the zero displacement ordinate.

Also plotted are frequencies calculated for the uncracked structure (based

on gross section of members and concrete modulus of 21,000 MPa). The

measured first, second and third apparent modal frequencies were 94, 97,

and 94 percent of the respective calculated values.

Page 41: By Jack P. t·loeh 1e and A. Sozen

29

Possible sources of discrepancy between measured and calculated

frequency values are basically inadequate modelling and unintentional

damage sustained by the test structure during construction. However,

because the discrepancy is small, it is reasonable to assume that the

"uncracked" model was adequate and that only a small amount of damage

occurred during construction. It should also be noted that the initial

"Uncracked ll frequency of the test structure is an insignificant charac­

teristic concerning response to simulated earthquakes.

(b) Variation of Apparent Freguencies

An important characteristic of the test structure was reduction of

apparent frequencies observed during or after simulated earthquakes.

Reduction of frequency values with increasing double-amplitude displacement

can be seen in Fig. 5.1 and 5.2.

Study of change in free-vibration frequencies (Fig. 5.1 and 5.2)

reveals that the largest reduction in frequency occurred during the first

simulated earthquake (70 percent of the total observed reduction). The

large reduction is an expected result since the test structure is trans­

formed duri ng the fi rs t tes t run from an II uncracked" to a cracked con­

dition. Damage in subsequent simulated earthquakes had a much less profound

effect in reducing frequencies than was observed in the first simulation

(Fig. 5.1 and 5.2).

Response frequencies averaged over simulated earthquake durations

also decreased with increasing double-amplitude displacement (Fig. 5.1

and 5.2). It is impoy·tant to note that the apparent frequency for any

given response history was significantly lower than that for free vibrations

and also that the rate of frequency reduction from test to test was

approximately 20 percent greater. Both of the above points indicate the

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30

effect of inelastic "softening" caused by the large displacements that

occur during simulated earthquakes and which cannot be accounted for by

low-amplitude free vibration tests.

Simulated earthquake response waveforms (Fig. 4.8,4.12, and 4.16)

indicate that most of the frequency reduction occurring during a simula­

tion occurred during the first two seconds. This is seen not as a

characteristic of the test structure but of the base motion because it is

most intense during the first few seconds. More characteristic of the test

structure is the increasing uncertainty in determining response frequencies

as testing proceeded because of the less harmonic character of response

waveforms. This is especially evident by comparing the first and last

test runs (Figs. 4.8 and 4.16).

The rate of reducti.on in the steady-state apparent first mode resonance

frequency (Fig. 5.2) was about the same as that in simulated earthquakes.

The observed values of apparent first-mode frequency also was close to

those observed in simulated earthquakes despite differences in displacement

amplitudes. The mean displacement amplitude in the simulation test was

at least twice that in the steady-state test. No apparent trend related

the values of frequencies in the two test types (Fig. 5.2).

Some interesting observations can be made by comparing the ratios

of higher frequency values to the fundamental value (Fig. 5.3). For

free vibrations the ratios were about the same as those calculated for

the "uncracked" and the substitute-structure models, which indicates that

damage affected the three lowest frequencies approximately equally.

However, for simulated earthquakes the ratios of higher to fundamental

frequencies increased with increasing base-motion intensity (Fig. 5.3).

Page 43: By Jack P. t·loeh 1e and A. Sozen

31

5.3 Measures of Damping

Damping in the test structure was investigated by assuming that

measured response was that of a linearly-elastic system. By making this

assumption damping could be estimated from free vibration and steady-state

tests using well-known methods. Quantitative estimates of damping for

each test type is described below.

Damping apparent in free vibration tests was determined by applying

the logarithmic-decrement method to the filtered components of tenth-level

acceleration response waveforms (Fig. 4.5). Care was exercised so as not

to include any transients apparent immediately after the test structure

was released. The value determined for the first free-vibration test

(uncracked structure) was 0.02. The corresponding value increased to 0.07

after test run one. Free-vibration tests after runs two and three indicated

values of 0.08 and 0.09. It is apparent from the above results that

damping capacity at small amplitudes (approximately one mm) increased

substantially as a result of damage incurred during the first simulated

earthquake, but only slightly after subsequent simulations.

Damping apparent during steady-state tests was determined by first

constructing frequency response curves (Fig. 5.4). Modal displacement

relative to the base was determined by reducing the relative story-level

response (Table 4.4 to 4.6) to a single-degree-of-freedom response by

normalizing with respect to observed resonance shapes (Fig. 4·.19). Modal

amplification (vertical axis, Fig. 5.4) was then the ratio of normalized

relative displacement amplitude to base displacement amplitude. Although

normalization as described here is not a correct procedure for a nonlinear

system, the extent of nonlinear behavior during steady-state tests can be

Page 44: By Jack P. t·loeh 1e and A. Sozen

32

assumed to be small enough that a reasonable responseampl itude results.

Response in the third steady-state test was normalized with respect to

the resonance shape of the second test because no resonance shape was

determined in the third test.

Given the frequency response curves (Fig. 5.4) equivalent viscous

damping could be estimated by the bandwidth method, or by observing the

resonance amplification. Values of damping determined by either method

were on the order of 0.10 to 0.15 for all steady-state tests. r40re precise

estimates need not be given because apparent damping can be attributed

more to hysteretic response than to viscous-type damping. Indeed t the

frequency response curves (Fig. 5.4) only remotely resemble those ,of a

linearly-elastic t viscously-damped system.

Damping apparent in steady-state tests was different from that

observed for free-vibration tests. One difference was that calculated

values were on the order of twice those observed in free vibrations t

possibly because amplitudes of steady-state tests were about five times

those of free vibrations. Another difference was that response amplification

in steady-state tests decreased after the second simulated earthquake

but remained unchanged after the third t indicating that apparent damping

capacity first increased and then remained relatively constant for these

tests. Free vibrations, on the other hand, indicated that damping increased

slowly and steadily after subsequent simulations.

5.4 Response to Simulated Earthquakes

Response characteristics of the test structure subjected to three

simulated earthquakes are discussed and compared. Characteristics for

comparison were base motions, observed damage, displacements, accelerations,

forces, and moments. These are discussed below.

Page 45: By Jack P. t·loeh 1e and A. Sozen

33

(a) Base Motions

Base motions for simulated earthquakes were modelled after the

North-South component of El Centro, 1940, with a time scale compression

of 2.5. Response spectra are plotted in Chapter 4 (Fig. 4.7, 4.11, and

4.15). Peak accelerations and spectrum intensities at various damping factors

are presented for successive earthquake simulations in Table 5.1

Base accelerations and displacements are plotted for comparison in

Fig. 5.5. The three motions were nearly identical with the exception of

magnitude. Fourier amplitude spectra of the base accelerations (Fig. 5.6)

indicate that frequency content was similar for each base motion.

(b) Observed Damage

Cracks observed in the test frames before testing began were all smaller

than 0.05 mm. in width (Fig. 4.1). During the first simulated earthquake,

measurable cracks (wider than 0.05 mm) developed only below the fifth level,

the most severe being immediately above the "long" column (Fig. 4.2).

Measurable cracks were observed through level five after the second simulated

earthquake (Fig. 4.3), and by the third they were measurable throughout the

height of the test structure. Minor spalling developed during the last

two simulations (Fig. 4.3 and 4.4) It was noted that the widest cracks

were in the beams at the column faces.

Permanent deformation parallel to the strong axis of the frames was

apparent after the first and third simulations. The permanent deformation

resulting from these two test runs was 1.5 and 1.0 mm, respectively,

measured at the tenth level. Permanent deformation transverse to the frames

Page 46: By Jack P. t·loeh 1e and A. Sozen

34

was 0.5 mm at level ten after the first simulation. The tenth story

returned to its original position (in the transverse direction) after test

run two and remained there after test run three.

(c) Characteristics of Response Waveforms

Displacement waveforms (Fig. 4.8,4.12 and 4.16) indicate that, as

would be expected, displacements of the test structure were dominated by

first mode response. Higher mode influence was so slight as to be immeasur­

able at displacement maxima. Displacement maxima at all story levels

appeared to occur simultaneously.

Acceleration waveforms (Fig. 4.8, 4.12 and 4.16) reveal that higher

modes had a large influence on accelerations. The high frequencies apparent

in base motions (Fig. 5.6) were evident in response waveforms for lower

levels but were less apparent at higher levels, having been "filtered"

by the structure. Response waveforms also indicate that, overall, higher

frequencies had more influence on acceleration response as the earthquake

intensity increased, even though base accelerations did not indicate the

same increase in higher frequencies (Fig. 5.6).

Although mode shapes were not directly measured, nodal points of

apparent second and third modes were readily visible on acceleration

waveforms (Fig. 4.8, 4.12 and 4.16) a.nd Fourier amplitude spectra (Fig.

4.10,4.14 and 4.18). For the second mode, a nodal point was located near

the seventh level. Nodal points for the third mode were located approxi­

mately at levels four and nine. The nodal points calculated for the

substitute model were near level seven for the second mode and near levels

five and nine for the third (Fig. 2.6). An interesting point is that loca­

tions of nodal points did not appear to change during earthquake simulations.

Page 47: By Jack P. t·loeh 1e and A. Sozen

35

Base-level moment waveforms are plotted at the top of Fig. 4.8, 4.12

and 4.16. As is apparent in the figures, base moment was dominated by

first-mode response. It can also be noted that the base moment was quite

similar in appearance to the tenth level displacement.

Story shear waveforms (Fig. 4.8, 4.12 and 4.16) indicate that higher

frequency shears had a large influence on total story shear at the upper

levels of the test structure. At the lower levels, story shear was

dominated by the fundamental mode. The maxima of story shears (Tables 4.1,

4.2 and 4.3) occurred at approximately the same time in lower story levels.

The maximum base shear was almost totally first-mode in the first simulated

earthquake. However, other peaks in shear waveforms during that simulation

and during the maxima of subsequent simulations indicate that the first mode

contribution to the total shear could be as low as 80 percent (Fig. 4.8,

4.12 and 4.16).

In general, all response waveforms revealed changes as testing

proceeded. In the first simulated earthquake (Fig. 4.8) response appeared

to be nearly harmonic. However, by the third test when the structure was

most heavily damaged, response had lost its harmonic character (Fig. 4.16).

The latter waveforms indicate a softened structure and one with less

clearly defined modal frequencies as compared with that of the first

simulated earthquake.

(d) Response Maxima

Maximum deflections, accelerations, and story-shears are tabulated

for each simulated earthquake in Tables 4.1, 4.2, and 4.3. Deflections,

lateral forces, story shears, and story-level moments occurring at the

instant of maximum base-level moment are plotted in Fig. 5.7.

Page 48: By Jack P. t·loeh 1e and A. Sozen

36

Maximum or nearly-maximum deflections occurred at approximately

the same instant as the maximum base-level moment (Fig. 5.7). Comparison

is made in Fig. 5.8 among maximum double-amplitude shapes observed during

simulated earthquakes, steady-state resonance shapes, and calculated linear

substitute model shape. The measured shapes are all quite similar,

indicating that the fundamental-mode shape was relatively insensitive to

either the amount of damage or amplitude of displacement. Co~paring

measured with calculated shapes, it is apparent that the substitute model

assumed the lower levels of the structure to be more stiff relative to

upper levels than they actually were. This result is consistent with the

observed cracking which was concentrated in the lower stories of the. .

structure. The design model was based on uniformly damaged elements over

the height of the structure and columns fixed at the base.

Another feature of tenth-level displacement maxima is their relation

with spectrum intensity (Fig. 5.9). That figure indicates that the rate of

change in displacement between runs three and two exceeds that between

runs two and one. It is possible that this result indicates that damping

capacity in the third simulation did not increase to the extent that it

increased during the second simulation. It should be noted that this

conclusion is consistent with results obtained in the steady-state tests

(Fig. 5.4).

A characteristic of forces measured at the instant of maximum base

moment is the influence of higher modes (Fig. 5.7). Figure 5.10 depicts

response through a half-cycle of oscillation including the maximum dis­

placement during the first simulated earthquake. Higher-mode components

in lateral forces are obvious in that figure. It is esti~ated that higher­

mode components could constitute up to 20 percent of the maximum base shear

Page 49: By Jack P. t·loeh 1e and A. Sozen

37

in any test run.

The centroid of lateral forces acting on the test structure at the

instant of maximum base-level moment in the first test run was found to be

at a height of 0.67 H, where H is the height of the structure. This height

increased to approximately 0.8 Hand 0.9 H during subsequent runs.

An important characteristic of the response of a structure to earthquake

motions is the ratio of the maximum base shear to the total weight of the

structure. For the first (or design) earthquake this base shear coefficient

was approximately 0.29. The ratio of the base-shear coefficient to the

maximum base acceleration (in units of g), was 0.76. It can be observed

in Fig. 5.11 that the base-shear coefficient determined from the design

earthquake approached the upper-bound base-shear strength of the test model.

The maximum base shears in the second and third earthquake simulations

increased only slightly as member yi~ld apparently spread throughout the

structure.

The measured magnitude of the maximum base shear can be checked

approximately by calculating a first-mode shear as the sum of the products

at each level of three quantities: (1) displacement, (2) the square of

the apparent first-mode frequency, and (3) the mass. The calculation for

the maximum displacement during each test run is plotted in Fig. 5.11.

The calculated base-shear does not correlate well with the measured maxima

except for run one in which the measured shear was primarily first mode.

This calculation indicates that displacement, frequency, and lateral force

measurements are consistent.

Page 50: By Jack P. t·loeh 1e and A. Sozen

38

Static limits to the strength of the test structure under dynamic

1oadi ng conditi ons can be determined for va ri ous 1oadi ng conditi ons.

Figure 5.13 shows three collapse mechanisms of interest. Ultimate flexural

capacity was assigned to yielding members at member faces as indicated in

the figure. Axial dead load was assumed uniformly distributed among

columns at a level. A triangular loading distributi'on was used to determine

the base shear to cause collapse (Fig. 5.13). The minimum base shear so

required was 12 kN for the mechanism of Fig. 5.l3b. The base shear

required to constitute collapse by mechanisms acting through various

story heights is plotted with the maximum measured base-shear in Fig. 5.12.

As may be concluded from the latter figure, calculated collapse base

shears to not correspond well with the maximum measured base shear. Indeed,

residual crack widths and interstory displacements incurred during test

run three suggest that yielding occurred in upper story levels and that

the test structure was approaching the collapse mechanism of Fig. 5.l3c

rather than the minimum (Fig. 5.l3b). By the mechanism of Fig. 5.l3c, the

calculated collapse base shear was within five percent of the maximum base

shear measured.

Two likely sources of discrepancy between measured and calculated

base shears to form collapse are strain rate and loading distribution.

Strain rate effects are not included in calculated collapse base shears.

The effect, especially in the third test run, could be substantial. The

effect of lateral load distribution could be expected to have an even

greater effect on the collapse strength of the test structure, especially

during test runs two and three when higher modes had a substantial effect

on lateral loads. It should be noted that the first-mode component of

Page 51: By Jack P. t·loeh 1e and A. Sozen

39

base shear is apparently between 12 and 13 kN for all test runs, a range

of values comparable with the minimum collapse base shear of 12 kN

calculated for a triangular distribution.

The magnitude and quantity of displacement excursions of the test

structure is of interest because behavior of reinforced concrete is

dependent on response history. For convenience, tenth level displacement

peaks were divided into intervals of five mm magnitude for all displacements

larger than five mm. The number at such displacement peaks is summarized

cumulatively in the bar chart of Fig. 5.14. Referring to Fig. 5.11, the

threshold of overall nonlinear response can be said to occur at a tenth­

level displacement of approximately ten mm. The bar chart (~ig. 5.14)

reveals that for the first simulated earthquake and for this test structure,

approximately 60 percent of the peaks greater than five mm extended into the

nonlinear range of response. In subsequent simulations for this test

structure, it is important to note that most of the displacement response

was less than three times that which was taken to indicate general nonlinear

behavior. However, the maxima were observed to extend approximately five

to six times that value.

(e) Comparison of Measured and Design Response

Design forces and displacements for each of two frames in the test

structure were presented in Chapter 2. Design was based on a linear model,

with substitute member stiffnesses and damping factors, subjected to forces

determined from modal spectral analysis with a design response spectrum

(Fig. 2.3). The design spectrum is compared with that obtained during the

first simulated earthquake in Fig. 5.15. The design spectrum is seen to

have been conservative for frequencies higher than 7 Hz but unconservative

for lower frequencies. Because of the difference between the design and

Page 52: By Jack P. t·loeh 1e and A. Sozen

40

measured base motions, response of the substitute model based upon the

measured spectrum was determined for comparison with measured response.

Calculated and measured displacements, story shears, and story-level

moments are compared in Fig. 5.16.

Displacements calculated for the substitute model compare fairly

well with the maxima measured during the first (or design) simulated

earthquake (Fig. 5.16). Only near the base of the'test structure are

calculated displacements exceeded. The discrepancy at the base can be

attributed to the fact that the design model assumed absolute fixity at

the base and that columns at the base did not yield. Release of either

of these restraints would likely have increased the values of displace­

ments calculated for lower story-levels.

Forces calculated for the substitute model were substantially less

than the measured maxima (Fig. 5.16). A likely reason for the discrepancy

is that the test structure was not so severely damaged as had been assumed

in the linear model (measured fundamental frequency was 2.1 Hz versus

1.74 Hz assumed). The stiffer structure would be expected to attract

more forces than the softer structure assumed.

During the design earthquake simulation the maximum tenth-level

displacement was approximately one percent of the total height of the

test structure. The maximum interstory displacement was about two percent

of the inters tory height.

A superficial comparison between measured response and response

calculated for a linear model based on gross member sections is of some

value. A spectral analysis of the model used to calculate "uncracked"

modal frequencies resulted in the response values tabulated in Table 5.2

Also tabulated for comparison are measured response and response calculated

Page 53: By Jack P. t·loeh 1e and A. Sozen

41

for the substitute design model. All values in the table were determined

for the same base motion (the design simulated earthquake). As determined

from values in that table, the gross-section model underestimates deflec­

tions by a factor of about 2 and overestimates the base shear by a factor

of about 2.

Page 54: By Jack P. t·loeh 1e and A. Sozen

42

6. SW4MARY

60 1 Object and ScoRe

The primary objective of the experiment was to observe the behavior

during simulated earthquake motions of a ten-story, reinforced concrete

frame structure with relatively flexible lower stories. The small-scale

structure (Fig. 2.1 and 2.2) had IItall ll top and first stories. An

exterior-span beam omitted at the first story-level further reduced lower

story-stiffnesses.

The test structure was subjected successively to three base motions

of increasing intensity. The base motions were scaled versions of one

horizontal component of the record obtained at El Centro (1940).

Observations included response of the test structure (1) to earthquake

simulations, (2) in free vibration, and (3) to steady-state sinusoidal

motion at a series of frequencies bounding the estimated fundamental

frequency.

The object of this report is to document the experimental work,

present data, and discuss the observed dynamic response in relation to

stiffness, strength, and energy-dissipative capacity.

6.2 Experimental Work

One test structure, comprising two reinforced concrete frames, was

built and tested. The frames were situated opposite one another with

strong axes parallel to base motions. Ten story-masses spanned between

the test structure to increase inertial forces (Fig. 2.2). The mass at

each level was proportional to the total length of beams at the level

(nominally 302 kg at level one and 454 kg at other levels).

Page 55: By Jack P. t·loeh 1e and A. Sozen

43

Concrete used in the test frames was a small-aggregate type with a

compressive strength of 38 MPa. Longitudinal steel was No. 13 gage

(diameter = 2.3 mm) wire with a yield stress of 358 MPa. Transverse steel

was No. 16 gage (diameter = 2.0 mm) wire bent in a helical shape.

Reinforcement was selected principally according to the substitute

structure method [J. The method features a linear modal spectral analysis

but accounts for nonlinear response of reinforced concrete structures.

Flexural steel ratios ranged between 0.74 to 1.11 percent for beams and

0.88 to 1.75 percent for columns (Fig. 2.16). Transverse reinforcement was

provided to minimize the likelihood of shear failure in the frame elements

and joints.

The test structure was subjected to simulated earthquakes with target

peak accelerations of 0.4, 0.8, and 1.2 g, the first of which was the

design earthquake. The simulations were modelled after El Centro-NS,

1940 with time scales compressed by a factor of 2.5. In addition to

simulation tests, low-amplitude free-vibration and steady-state tests

were conducted. Steady-state tests were sinusoidal base motions at

various frequencies bounding the apparent fundamental resonance frequency.

Data obtained during tests included displacements and accelerations

at each story level as well as visible structural damage. Displacements

and accelerations were recorded in analog form and were later manipulated

through the use of computers for presentation and analysis.

6.3 Data and Studies

Earthquake response data were organized in a series of time histories.

Shear and moment histories were determined from acceleration and displace­

ment histories and structural configuration. Time histories are presented

Page 56: By Jack P. t·loeh 1e and A. Sozen

44

in original form and in a form which excludes components with frequencies

higher than the fundamental frequency. Frequency contents were determined

and are presented in Fourier amplitude spectra. Response maxima are

discussed in comparison with design response and strength of the structure. '

Development of crack patterns and spalling are presented in a series

of figures.

The character of base mati ons is descri bed i'n terms of waveforms,

frequency contents, response spectra, and spectrum intensities.

Response in free-vibration and steady-state tests is presented and

discussed. Estimates of damping were made for each test.

Variation in apparent response frequencies is presented for each

test. The effects on apparent frequencies' of damage and response amplitude

is discussed.

6.4 Observed Response Characteristics

It is important before summarizing the test results to stress that the

test structure was subjected to simulated earthquakes of large intensity

to obtain overall nonlinear behavior. During the simulations, the struc­

ture underwent numerous cycles at or beyond displacements where overall

nonlinear behavior occurred. In the last simulation, displacements were

observed at approximately six times that which was assumed to be the

threshold of overall nonlinear behavior. The observations and conclusions

which follow should be interpreted considering the extent of nonlinear

behavior obtained. Furthermore, the "damage" was limited to softening of

various elements resulting from axial, flexural, and bond stresses.

Despite nonlinear behavior, clearly identifiable natural response

frequencies were observed during all tests. At any stage of testing, the

Page 57: By Jack P. t·loeh 1e and A. Sozen

45

apparent frequency varied with the displacement amplitude used in the

determination of that frequency. The higher the displacement, the lower

was the frequency. Nodal points could generally be observed for the

apparent second and third modes.

An important characteristic of apparent frequencies was the decrease

in frequency values with increasing displacement previously experienced.

Frequency values decreased by approximately 50 percent of their initial

values during the first (or design) simulated earthquake. Rate of decrease

was lower in subsequent simulations. It was observed that, for the base

motion used, approximately 70 percent of the frequency reduction in a

test run occurred during the first few seconds when response was maximum.

The amount of damage did not extensively change mode shapes although some

change in shape was observed (Fig. 5.8). The amount of damage also did

not have much effect on the ratios of first-to higher-mode frequencies at

low-amplitude response. However, for response amplitudes on the order of

those occurring during simulations, the first-mode frequency appeared to

decrease more compared with the decrease in high frequencies.

The initial "uncracked" frequencies of the test structure were within

approximately five percent of calculated uncracked frequencies. The

frequencies observed during the design earthquake did not correlate well

with those assumed for the design model because of the differences between

the assumed stiffness distribution and that in the test structure. However,

nodal points matched approximately those of the design model. The frequency

ratios calculated for the design model compared well with those observed

for all low-amplitude tests but not for higher-amplitude simulated earth­

quakes.

Page 58: By Jack P. t·loeh 1e and A. Sozen

46

The relative influence of different frequencies on response was as

would be inferred from modal spectral analysis. Displacements were

dominated by the fundamental mode while accelerations (and thus lateral

story forces) were influenced by higher-mode frequencies. Base-level

moment was predominantly first mode and in phase with the tenth-level

displacement. The contributions of higher modes were larger in the third

test run than in the first.

As inferred from residual crack widths, flexural yielding during

the design earthquake was limited to the lower four stories. By the third

simulation, measurable cracks spread through the height of the structure

and spalling was noted. Permanent deformation was small during all tests.

An equivalent viscous damping factor for the Ifuncrackedll structure was

found from the amplitude "decrement of free vibration to be approximately

0.02. This value increased substantially during the first simulation to

0.07 and then increased gradually after other simulations. Damping factors

inferred from maximum response amplifications in the higher amplitude

steady-state tests were higher than those in the free-vibration tests.

Maximum amplification in steady-state tests decreased from the first to

second tests but remained relatively constant between the second and third

tests.

Maximum displacements during earthquake simulations increased with

increasing spectrum intensity, apparently at an increasing rate. The

maximum interstory displacement during the first simulation was nearly

two percent of the story height, a condition which would be likely to

lend to serious nonstructural damage in a real building. Interstory

displacements by the end of the third simulation were large enough to

Page 59: By Jack P. t·loeh 1e and A. Sozen

47

suggest yield in all beams of the test structure, an observation which

was confirmed by the residual crack widths.

Maximum base shear during simulations was dominated by the fundamental

mode (the first-mode component accounted for at least 80% of the measured

maxima). The maximum base shear during the design simulation was 29 percent

of the structure weight. Maxima during subsequent simulations were not

much larger in magnitude than that of the first earthquake simulation.

Various calculated collapse mechanisms for a triangular lateral­

load distribution were investigated. The mechanism resulting in the

minimum base shear for the assumed load distribtuion indicated a yielding

pattern different from that apparent during the tests. A calculated base

shear for the apparent collapse mechanism was five percent less than the

observed maximum.

Response obtained during the design earthquake simulation was compared

with that determined for the design model using the measured response

spectrum. The design was intended specifically to achieve an upper-bound

set of displacements. Measured displacements were within the upper bounds

except in the lower levels. The shortcoming in the design method could be

attributed to yielding in the first-story columns which was expected from

design forces but which was not considered during the design.

Overall, apparent effects of the relatively flexible lower stories

were excessive interstory displacements in lower levels and greater-than­

expected damage in beam-column joints near the top of the IItall ll column

(Fig. 2.1). Overall behavior appeared no more unsymmetric than that which

would be expected for a symmetric structure subjected to the same base

motions.

Page 60: By Jack P. t·loeh 1e and A. Sozen

48

LIST OF REFERENCES

1. Gulkan, P. and M. A. Sozen, "Inelastic Response of Reinforced ConcreteStructures to Earthquake Motions," Journal of the American ConcreteInstitute, V. 71, No. 12, November 1974, pp. 601-609.

2. Housner, G. W., "Behavior of Structures During Earthquakes," Journalof the Engineering Mechanics Division, AS_E, Vol. 85, No. EM4, October1959, pp. 108-129.

3. Lopez, L. A., "FINITE: An approach to Structural Mechanics Systems,"International Journal for Numerical Methods in Engineering, Vol. 11,No.5, 1977, pp. 851-866.

4. Otani, S. and M. A. Sozen, "Behavior of Hultistory Reinforced ConcreteFrames During Earthquakes," Civil Engineering Studies, StructuralResearch Series No. 392, University of Illinois, Urbana, November1972.

5. Shibata, A. and M. A. Sozen, "Substitute Structure Method for SeismicDesign in RIC," Journal of the Structural Division, ASCE, Vol. 102,No. ST1, January 1976, pp. 1-18.

6. Sozen, M. A. and S. Otani, "Performance of the University of IllinoisEarthquake Simulator in Reproducing Scaled Earthquake r~otions,"

Proceedings, U.S.-Japan Seminar on Earthquake Engineering withEmphasis on the Safety of School Buildings, Sendai, September 1970,pp. 278-302.

Page 61: By Jack P. t·loeh 1e and A. Sozen

49

TABLE 2.1

Mode Shapes and Characteristic Values Used in Design

Level First Second ThirdMode Mode ~1ode

10 1.000 1.000 1.000

9 0.941 0.583 0.027

8 0.874 0.176 -0.642

7 0.793 -0.220 -0.900

6 0.699 -0.537 -0.656

5 0.591 -0.740 -0.069

4 0.469 -0.796 0.557

3 0.337 -0.699 0.905

2 0.203 -,0.474 0.803

1 0.079 -0.196 0.374

r10da1Frequency 1. 74 5.24 9.49(Hz)

ModalDamping Factor 0.099 0.094 0.080

t·1oda1 Parti ci-pat; on Factor 1. 33 0.51 0.28

Page 62: By Jack P. t·loeh 1e and A. Sozen

TABL

E2.

2

Des

ign

Peak

Acc

eler

atio

n,M

odal

Fre

quen

cies

,S

pect

ral

Am

plif

icat

ion,

Sub

stit

ute

Dam

ping

Fac

tor,

and

Des

ign

Spe

ctra

lA

ccel

erat

ion

Use

din

Des

ign

Des

ign

Peak

Mod

alS

pect

ral

Sub

stit

ute

Des

ign

Spe

ctra

lT

rial

No.

Mod

eN

o.A

ccel

erat

ion

Freq

uenc

yA

mpl

ific

atio

nDa

mpi

ngA

ccel

erat

ion

(g)

(Hz)

Fac

tor

(g) -

1

11

.74

1.05

0.10

0.21

12

5.24

3.14

0.10

0.63

39.

493.

750.

100.

750

1

0.4

a

1

I1

.74

1.05

0.09

9O~

212

25.

243.

140.

094

0.65

39.

493,

.75

0.08

00.

86

Page 63: By Jack P. t·loeh 1e and A. Sozen

TABL

E2.

3

Fram

eR

einf

orci

ngSc

hedu

le

Num

ber

ofN

o.13

g.W

ires

Per

Face

Sto

ryor

Leve

l 10 9 8 7 6 5 4 3 2 1

Beam

s

2 2 2 3 3

lnte

rio

rC

olum

ns

2 2 4

Ext

erio

rC

olum

ns

2 2 4 4

(J'l

--'

Page 64: By Jack P. t·loeh 1e and A. Sozen

52

TABLE 4.1

Response r1axima Observed Duringthe First Simulated Earthquake

Level Acceleration Displacement Shearor Story (g) (mm) ( KN)

(+) (-) (+) (- ) DA* (+ ) (- )

10 0.59 0.42 16.8 24.4 41.2 1.9 2.7

9 0.48 0.38 16.4 23.4 39.8 3.6 .4.8

8 0.43 0.36 16.0 22.8 38.8 5.2 6.5

7 0.39 0.35 15.2 21.6 36.8 6.7 8.0

6 0.38 0.32 13.4 19.7 33.1 8.0 9.4

5 0.35 0.30 12. 1 17.3 29.4 9.3 10.5

4 0.39 0.28 10.2 14.3 24.5 10.2 11.3

3 0.43 0.26 7.3 12. 1 19.4 10.7 12.2

2 0.40 0.26 4.9 7.4 12.3 10.9 12.6

1 0.34 0.29 2.4 3.8 6.2 11.0 12.8

Base 0.38 0.31

*Maximum absolute sum of any two adjacent positive and negative displacementpeaks.

Page 65: By Jack P. t·loeh 1e and A. Sozen

53

TABLE 4.2

Response Maxima Observed Duringthe Second Simulated Earthquake

Level Acceleration Displacement Shearor Story (g) (mm)

(+) (- ) (+ ) (-) DA* (+ ) (-)

10 0.99 0.89 33.0 43.5 72.8 4.0 4.5

9 0.71 0.69 31. 7 41.6 69.4 7.2 7.5

8 0.58 0.52 31.1 40.6 68.0 9.1 9.5

7 0.51 0.45 28.8 38.3 63.0 9.8 10.8

6 0.63 0.43 26. 1 35.0 57.6 10.9 11.8

5 0.71 . 0.41 22.8 30.5 50.0 11.7 12.7

4 0.77 0.46 18.8 25.2 41.2 12.8 13.5

3 0.74 0.55 14.0 20.4 32.4 13. 1 13.7

2 00 57 0.57 9.0 13.3 20.6 12.5 13.2

1 0.60 0.52 4.3 7.3 10.6 12.7 14.0

Base 0.83 0.54

*Maximum absolute sum of any two adjacent positive and negative displacementpeaks.

Page 66: By Jack P. t·loeh 1e and A. Sozen

54

TABLE 4.3

Response Maxima Observed Duringthe Third Simulated Earthquake

Level Acce1era ti on Displacement Shearor Story (g) (mm) (Kn)

(+) (- ) (+ ) (- ) DA* (+ ) (-)

10 1.25 1.20 49.9 57.6 106.8 5.4 5.7

9 0.85 0.81 47.0 55.2 101.8 8.6 9. 1

8 0.68 0.62 44.5 52.0 96.2 10.6 11. 1

7 0.60 0.58 41. 3 48.6 88.6 11. 5 12.4

6 0.61 0.59 36.5 43.5 79.2 12.4 12.9

5 0.59 0;60 31.6 37.5 67.2 1308 13.2

4 0.59 0.58 24.8 30.7 54.2 13.8 13.5

3 0.78 0.69 18.7 24.7 41.8 12 0 5 13.4

2 1.04 0.70 11 .9 16.0 27.0 12.0 13.4

1 1.07 0.74 5.9 9.0 14.6 11.8 14.3

Base 1.28 0.74

*Maximum absolute sum of any two adjacent positive and negative displacementpeaks.

Page 67: By Jack P. t·loeh 1e and A. Sozen

55

TABLE 4.4

First Steady-State Test

Input Base Tenth Level AmplificationFrequency Displacement Displi'lcement at Tenth Level(Hz) (rom) (rrrn)

1.07 1.00 0.27 0.27

1.28 1.02 0.39 0.39

1.44 1.00 0.83 0.83

1. 52 0.96 1.32 1. 38

1.64 1.01 3.20 3~ 13

1.75 1. 01 50 74 5.71

1.85 0.98 5.73 5.87

1. 90 0.97 5.14 5.28

2.11 0.98 3.52 3.60

2.30 0.97 2.98 3.06

2.48 0.98 2.66 2.73

2.68 0.96 2.39 2.50

Page 68: By Jack P. t·loeh 1e and A. Sozen

56

TABLE 4.5

Second Steady-State Test

Input Base Tenth Level AmplificationFrequency Displacement Displacement at Tenth Level

(Hz) (mm) (mm)

1.02 1. 00 0.43 0.43

1. 27 1.02 1.22 1. 19

1.43 0.97 3.96 4.10

1.48 0.99 4.18 4.24

1.53 0.99 3.88 3.93

1.64 1.03 3.48 3.38

1.83 0;99 2.97 3.01

2.01 0.96 2.61 2.73

2.21 0.95 2.33 2.44

2.41 0.98 2.13 2.18

Page 69: By Jack P. t·loeh 1e and A. Sozen

57

TABLE 4.6

Third Steady-State Test

Input Base Sixth Level Ampl ification.Frequency Displacement Displacement at Sixth Level

(Hz) (mm) (mm)

0.85 0.94 0.39 0.41

1.05 0.94 0.67 0.71

1.19 0.94 2.79 3.0

1.26 0.94 3.24 3.4

1.30 0.93 3.20 3.4

1.36 .0.93 2.99 3.2

1.47 0.94 2.88 3. 1

1.67 0.90 2.38 2.6

1. 79 0.89 2.15 2.4

2.03 0.90 1.84 2.0

Page 70: By Jack P. t·loeh 1e and A. Sozen

58

Table 5.1

Spectrum Intensities

Test Run Peak Spectrum Intensity forAcceleration, Damping Factor of

g 0.00 0.02 0.05 0.10 0.20

1 0.38 545 349 276 223 185

2 0.83 983 627 497 403 336

3 1.28 1170 752 597 487 411

TABLE 5.2

Comparison of Calculated and Measured Responsefor the Design Earthquake

"Gross-Section" Substitute-Structure t-1easured~1odel * Model*

Tenth-Leve1Deflection, mm 10.5 27.8 20.6**

Base Shear,kN 28.0 9.64 12.8

Base-Levelr~oment, kN-m 44.7 14.5 22

*Root-sum-square of first three modes

**Double-amplitude displacement divided by two

Page 71: By Jack P. t·loeh 1e and A. Sozen

59

(All Dimensions In mm)

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m N

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Page 75: By Jack P. t·loeh 1e and A. Sozen

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Page 76: By Jack P. t·loeh 1e and A. Sozen

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Page 78: By Jack P. t·loeh 1e and A. Sozen

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Page 81: By Jack P. t·loeh 1e and A. Sozen

Leve

l 10

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Page 82: By Jack P. t·loeh 1e and A. Sozen

'-J

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Page 84: By Jack P. t·loeh 1e and A. Sozen

......

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ents

Page 85: By Jack P. t·loeh 1e and A. Sozen

<t..

(a)

On

e-B

oy,

On

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Fra

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eral

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Page 86: By Jack P. t·loeh 1e and A. Sozen

74

(All Dimensions In Mill imefers)

19

, (\

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No. 16 Gage

No. 13 Gage

__t7.75

19

~=~" .... ,· ').·,."q:~+t-"':-=-:-:'"""'I' r--ir--- <t

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(a) Beam With Two BarsPer Face

(b) Beam With Three BarsPer Face

19

ct

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No. 16 Gage

r;;::::;;;;~~;::;~ ...",' ...o.· .': .

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25.5

(c) Column With Two BarsPer Face

(d) Column With Four BarsPer Face

Fig. 2.16 Nominal Member Cross Sections

Page 87: By Jack P. t·loeh 1e and A. Sozen

30

1-

ttfi

"1"",9

.,,,,C

i,,,,,L

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Col

umn

Inte

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on

Dia

gram

Page 88: By Jack P. t·loeh 1e and A. Sozen

76

Spirals

12.70.0. x .56 ThickTubing76

Cutoff Point For AdditionalReinforcement

Typical Top /Column Detai I

No. 16 g Wire Spirals

31,8 0.0. - Pitch =10

TypicalDetai I

,-......--,...,.:;-------_......_--'I\

1)EII

----:;\-+-H-t--tt--++-..L--=--=Begm""--~:--_+t__t+t_ttt_-_ff_II

+t:te:::1j::::U=====:::u:::~l:t~~~~~

No. 13g Wire - See Frome ReinforcingSchedule For Numberof Bars Per Face

38

:tJ :'... \

.. : . ,0 .. :

: .~

25.5

<l Column

25.5

5 CL

Section "~I.!.'A" Section l al_"8 11

(All Dimensions Are In Millimeters)

Fig. 2.18 Representative Frame Details

Page 89: By Jack P. t·loeh 1e and A. Sozen

77ItI

305 __ j 305 305

I

(1)NN

Cut Off For-+--~-­Interior 1./

Column· /~Steel -/'r<)

~r<)

~,ODO

:~~~OOOTypical JOintty °0°Reinforcement: I

No.16g Wire

Typical Shear : L V :0:Reinforcemen~ 0 r'r-T b"No. /6g Wire I il ,lO:~~

~I~~~~~~~t:~ood Typical ~U °0° N(X)-o

Typical Flexural ~ ____Reinforcement: / ~ I

No. 13g Wire ~"(5~~~~~~~=~

Cut Off For ~ °0°Exterior ColumnSteel ---.,.......-----11

I[£~~~~~ft~;;t=~o~--......,o

t ~~ Column Flexural\'

Reinforcement Welded '\To 102 x 51 x 3 It -

Fig. 2.19 Location of Reinforcement Throughout a Frame

Page 90: By Jack P. t·loeh 1e and A. Sozen

78

Tenth Level Mass

Typical AccelerometerMeasures Minor Direct ionHorizontal Acceleration

Typical AccelerometerMeasures Major DirectionHorizontal Accelerat ion ....._-

Typical LVDTMeasures Major Direct ionHorizontal Displacement

Typical AccelerometerMeasures Vert ical Accelerat ion

Fig. 3.1 Location and Orientation of Instrumentation

Page 91: By Jack P. t·loeh 1e and A. Sozen

Wir

e

Fre

eV

ibra

tio

nI.

Wei

ght

Hun

gF

rom

Wir

eTo

Dis

plac

eS

tru

ctu

re2

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ire

Cu

tT

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seS

tru

ctu

re

Fig.

3.2

Fre

e-V

ibra

tion

Tes

tSe

tup

45

kg

Pu

lley

'-l

\.0

Page 92: By Jack P. t·loeh 1e and A. Sozen

80

Fig. 4.1 Crack Patterns Observed Before Test Run One

Page 93: By Jack P. t·loeh 1e and A. Sozen

81

Fig. 4.2 Crack Patterns Observed After First Simulated Earthquake

Page 94: By Jack P. t·loeh 1e and A. Sozen

82

"IndicatesSpoiling

t-

( \

Fig. 4.3 Crack Patterns Observed After Second Simulated Earthquake

Page 95: By Jack P. t·loeh 1e and A. Sozen

83

Fig. 4.4 Crack Patterns Observed After Third Simulated Earthquake

Page 96: By Jack P. t·loeh 1e and A. Sozen

84

0.0tl FREE VlBAATIl'lN 8EF~RE RUN ONE. UNl1 = G

0.00

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UNIT = GO. 0I.lI I'. • ffl'E VllmTlIlN AfTER IlJN THREE.

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"I,-O.OIl f1. SEC.O~ l+-iO 2_il-0 3

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Fig. 4.5 Free-Vibration Wavefor~s of Tenth-level Accelerations,Observed (Broken) and Filtered (Solid)

Page 97: By Jack P. t·loeh 1e and A. Sozen

DYN.

TEST

HF2

-SE

PT13

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11-

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Dur

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Page 98: By Jack P. t·loeh 1e and A. Sozen

1..6

0Iiii.iii

i

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ra

Page 99: By Jack P. t·loeh 1e and A. Sozen

87

2000. 0 J._--¥----I--~~-J._+_~___I--_¥__+--+_~_;

1000.0 ~--¥:"-n---+foJt~-+--~~-+---?~+---4c~--t

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1.0 2.0 5.0 10.0 20.0 50.0

FREQUENCY. HZ.

DYN TEST MF2 - SEPT. 1977 - RUN 1 - ABNDAMPING FACTOR = 0.00 0.02 0.05 0.10 0.20

Fig. 4.7 (contd.) First Simulated Earthquake. Linear Response Spectra

Page 100: By Jack P. t·loeh 1e and A. Sozen

II

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Page 101: By Jack P. t·loeh 1e and A. Sozen

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Page 102: By Jack P. t·loeh 1e and A. Sozen

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Page 103: By Jack P. t·loeh 1e and A. Sozen

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Page 104: By Jack P. t·loeh 1e and A. Sozen

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Page 105: By Jack P. t·loeh 1e and A. Sozen

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r,.

rwri'i"~

"9

11

7."\

Fvv

uv

""

""'"

...v~

'"."

.vV

w;;

10.0

0.00

0.00

0.00

0.00

0.00

0.00

-10

.0

10.0

-10

.0

10.0

-10

.0

10.0

-10

.0

0.50

-10

.0

10.0

-0.5

0T

SEC

0.0

1.0

2.0

3.0

11.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

12.0

13.0

14.0

15.0

••

II

II

II

II

II

II

II

II

Fig

.4.

8(c

ontd

.)F

irst

Sim

ulat

edE

arth

quak

e.O

bser

ved

Res

pons

e(B

roke

n)an

dC

ompo

nent

sB

elow

3.0

Hz(S

olid

)

Page 106: By Jack P. t·loeh 1e and A. Sozen

1.0'

1.0

llYN

TEST

HF2

-SE

PT.

1977

-RU

N1

-LI

NOY

NTE

STH

F2"

SEPT

.19

TI

-RU

N1

-Le

N

10.

15.

20.

25.

30.

35.

FREQ

.IH

Zl5.

10.

15.

20.

25.

30.

35

.FR

EQ.

(HlJ

llYN

TEST

HF2

-SE

PT.

1977

-RU

N1

-L2

NOY

NTE

STttF

2-

SEPT

.19

77-

RUN

1-

L7N

35

.FR

EQ.

(HZ!

30.

25.

20.

15.

10.

1.0'

35.

FREQ

.IH

Zl3

0.

25.

20.

15.

10.

1.

DTN

TEST

ttF2

-SE

PT.

1977

-RU

N1

-Lt

IN

OYN

TEST

""2

-SE

PT.

19T

I-

RUN

1-

L3N

\0 ~

35.

FREQ

.1H

Z!

35

.FR

EQ.

IHZl

30.

30.

25.

25.

20.

20.

15.

15.

OYN

TEST

1tF2

-SE

PT.

19T

I-

RUN

1-

L9N

OYN

TEST

1tF2

-SE

PT.

19T

I-

RUN

1-

LeN

10.

10.

5.

1.0

35.

FREQ

.(H

Z!

35.

FREQ

.IH

Zl

30

.

30

.

25.

25.

20.

20.

15.

15.

10.

10

.

5.

5.

1.

OYN

TEST

""2

-SE

PT.

19T

I-

RUN

1-

LSN

OYN

TEST

1tF2

-SE

PT.

19T

I-

RUN

1-

LIO

N

35.

FREQ

.(H

Z!30

.25

.20

.15

.10

.5

.

1.

35.

FREQ

.IH

lJ3

0.

25.

20.

15.

10.

5.

1.0

Fig

.4.

9F

irst

Sim

ulat

edE

arth

quak

e.F

ouri

erA

mpl

itude

Spe

ctra

of

Dis

plac

emen

ts

Page 107: By Jack P. t·loeh 1e and A. Sozen

OrN

TEST

HF2

-SE

PT.

1977

-lU

I1

-A

INO

rNTE

ST11

F2-

SEPT

.19

77-

RUN

1-

ASN

35.

FAEQ

.1H

Z!30

.25

.20

.15

.10

.5

.

1.0

35.

FAEQ

.1H

Z}30

.25

.20

.15

.10

.5.

1'1 1.1

.0

OYN

TEST

HF2

-.SE

PT.

1977

-lU

I1

-A2

NaY

NTE

STH

F2-

SEPT

.19

77-

lUI

1-

A7N

OYN

TEST

HF2

-SE

PT.

1977

-lU

I1

-A3

N

~ CJ"I

35.

FAEQ

.1H

Z!

35.

FAEQ

.1H

Z!

35

.fA

Ell.

1HZ!

30.

30.

30.

25.

25.

25.

20.

20.

20.

IS.

15.

15.

OrN

TEST

HF2

-SE

PT.

1977

-IU

l1

-R9

N

OYN

TEST

11F2

-SE

PT.

1977

-RO

O1

-RE

IN

10.

10.

10

.

5.5.

35.

FAEQ

.(H

Z!

35

.FA

EQ.

1HZ!

35.

FAEQ

.1H

Z!

30.

30

.

30.

25.

25

.

25.

20.

20.

20.

15

.

15

.

15.

OYN

TEST

HF2

-SE

PT.

1977

-lU

I1

-/¥

IN

10.

10

.

10.

5.

5.

5.

1.

OYN

TEST

HF2

-SE

PT.

1977

-lU

I1

-AS

NOY

NTE

STH

F2-

SEPT

.19

77-

ROO

1-

AI0

N

35.

FIlE

Q.

(HZ)

30.

25.

20.

15.

10.

s.35

.F

AE

ll.{H

Z!30

.25

.20

.15

.1

0.

5.

Fig

.4

.10

Fir

stS

imul

ated

Ear

thqu

ake.

Fo

uri

erA

mpl

itud

eS

pec

tra

of

Acc

eler

atio

ns

Page 108: By Jack P. t·loeh 1e and A. Sozen

~ m

1.0

0.6

0.8

PEA

lml.S

EC0.

1120

105 0.2

FREQ

UENC

YpHZ

30

/ 1//'

11//,

:if/' lv~

V-I

\.-

I.V

~y~

~V

.....=

-lI

110

100.

20..

120.

o.160.

11l0

.

110.

i a-:

80Ci

,.

~ a: ~60

...... c

1.0

0.6

0.8

PEAI

ODpS

EC0.

1120

105 0.2

FREQ

UENC

YpHZ

so

~1\

.)/t

1\~\~

h~;J~

,'"]~

-J

'"---

--...

~~

~~

,----

.---.

--------

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0

8..0

0

2..5

0

0.00

110

It.0

0

0..5

0

8.50

C) . is

2.0

0.... i i:i:l

1.5

0

~

OYN

TEST

HF2

-SE

PT.

1977

-RU

N2

-AB

N

OAl1P

ING

FACT

OR;::

0.02

0..0

50.

100.

20OY

NTE

STH

F2-

SEPT

,19

77-

RUN

2-

ABN

OAf1P

ING

FACT

OR=

0.02

0..0

50.

100.

.20

Fig.

4.11

Seco

ndSi

mul

ated

Ear

thqu

ake.

Lin

ear

Res

pons

eS

pect

ra

Page 109: By Jack P. t·loeh 1e and A. Sozen

97

.)0­r­....~id>

10. 0 L-.._~--J._----"::~_--L_----":::~--L.._~L-...J.-_~~---A

1.0 2.0 5.0 10.0 20.0 50.0

FREQUENCY.. HZ.

orN lEST HF2 - SEPT .. 1977 - RUN 2 - RBNDAMPING FACTOR = 0.00 0.02 0.05 0.10 0.20

Fig. 4.11 (contd.) Second Simulated Earthquake. Linear Response SpectraI

Page 110: By Jack P. t·loeh 1e and A. Sozen

II

II

II

II

II

II

II

II

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BA

SE

LEV

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EN

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NIT

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11

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15

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II

II

II

II

II

II

II

I

Fig

.4.

12Se

cond

Sim

ulat

edE

arth

quak

e.O

bser

ved

Res

pons

e(B

roke

n)an

dC

ompo

nent

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elow

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Hz(S

olid

)

Page 111: By Jack P. t·loeh 1e and A. Sozen

II

II

II

II

II

II

II

II

qO.OI

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II

II

II

II

II

II

II

II

Fig

.4.

12(c

ontd

.)Se

cond

Sim

ulat

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arth

quak

e.O

bser

ved

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pons

e(B

roke

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elow

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Hz(S

olid

)

\.0

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Page 112: By Jack P. t·loeh 1e and A. Sozen

II

II

II

II

II

II

II

II

TENT

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4.12

(con

td.)

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thqu

ake.

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erve

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nse

(Bro

ken)

and

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(Sol

id)

Page 113: By Jack P. t·loeh 1e and A. Sozen

1.0

0

II

II

II

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4.12

(con

td.)

Seco

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mul

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thqu

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erve

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(Bro

ken)

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id)

Page 114: By Jack P. t·loeh 1e and A. Sozen

II

II

II

II

II

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Fig.

4.12

(con

td.)

Seco

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id)

Page 115: By Jack P. t·loeh 1e and A. Sozen

II

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-..

1/V

V4

nf

"r

tnlr

ufIi,

V"l

ll\1

---

V"",.

.4

-1.0

0

TSE

C0.

01.

02.

03.

0ll.

O5.

06.

07.

08.

09.

010

.011

.012

.013

.014

.015

.0•

•I

II

II

II

II

II

II

II

I

Fig.

4.12

(con

td.)

Seco

ndSi

mul

ated

Ear

thqu

ake.

Obs

erve

dR

espo

nse

(Bro

ken)

and

Com

pone

nts

Bel

ow3

.0Hz

(Sol

id)

Page 116: By Jack P. t·loeh 1e and A. Sozen

1.

llll

ITE

STIl

f2-

SEPT

.19

77-

ftlJ

l2

-U

N

"1 I

llll

ITE

ST""

2-

SEPT

.19

77-

ftlJ

l2

-L6

Il

1.

5.

10.

IS.

20.

25.

30.

35.

FAE

ll.1H

Z!

I·or10

.15

.20

.25

.30

.35

.FA

Ell.

lHZl

llll

ITE

ST1F

2-

SEPT

.19

77-

ftlJ

l2

-L2

Nll

llI

TEST

""2

-SE

PT.

1977

-lU

I2

-L7

N

0.0

O.

5.

10.

IS.

20.

25.

30.

35.

FIlE

D.

1HZ!

---0

.5

.10

.15

.20

.25

.30

.35

.FA

Ell.

1HZ!

1.O

T•

1•

llll

ITE

STIF

2-

SEPT

.19

77-

ftlJ

l2

-L3

Il

~Jll

llI

TEST

""2

-SE

PT.

1977

-lU

I2

-Ll

lN

--0

0 ~0

.0"I'-~

II

II

II

I0

.0'",.~

II

II

II

IO

.5

.10

.IS

.20

.25

.30

.35

.FA

Ell.

lHZl

O.

5."

10.

IS.

20.

25.

30.

35.

FAE

ll.1H

Z!

I.O

T.

1•

llll

ITE

ST1F

2-

SEPT

.19

77-

ftlJ

l2

-LI

lNII

llll

ITE

STIl

f2-

SEPT

.19

77-

lUI

2-

L9N

1.

S.

10.

IS.

20.

25.

30.

35

.FA

Ell.

IHlJ

1.

s.10

.IS

.20

.25

.30

.35

.FA

Ell.

1HZ!

llll

ITE

ST1F

2-

SEPT

.19

77-

lUI

2-

L5N

llll

ITE

ST""

2-S

EP

T.

IBn

-lU

I2

-u

Oli

S.

10.

IS.

20.

25.

30.

0.0

'-'

1"'""

"""'"

II

I1

II

I35

.FA

Ell.

1HZ!

O.

S.

10.

15.

20.

25.

~O.

35.

fRED

.1H

Z!

Fig.

4.13

Seco

ndSi

mul

ated

Ear

thqu

ake.

Fou

rier

Am

plitu

deS

pect

rao

fD

ispl

acem

ents

Page 117: By Jack P. t·loeh 1e and A. Sozen

1.

1.

OTN

TEST

1F2

-SE

PT.

1977

-AU

N2

-A

I"OT

NTE

ST1F

2-

SEPT

.19

77-

AUN

2-

A6N

35.

FRED

.lH

Zl30

.25

.20

.15

.

OTN

TEST

1F2

-SE

PT.

1977

-lU

I2

-A7

N

10.

5.

1.0

35.

FAEQ

.(H

Zl30

.25

.20

.15

.

OTN

TEST

IF2

-SE

PT.

1977

-lU

I2

-A2

N

10.

5.

10.

15.

20

..2

5.30

.35

.FA

EQ.

lHZl

O.5

.10

.15

.20

.25

.30

.35

.FR

ED.

lHZl

I.,

I1.

ll.OT

NTE

STIF

2•

VT

.19

77-

lUI

2-

A3N

OTN

TEST

1F2

-SE

PT.

1977

-lU

I2

-Al

lN

..... 0 CJ1

O.OU

'"W'Irrq

_. ,

1st'

I1O.OUI'I·U~"

II

O.

5.

10.

15.

20

.25

.30

.35

.FR

Eg.

(HZ!

O.5

.10

.15

.20

.25

.30

.3

5.

FRE

g.(H

Zl

I.,

I1.

III

OTN

TEST

IF2

-SE

PT.

1977

-lU

I2

-_

OTN

TEST

1F2

-SE

PT.

1977

-lU

I2

-AS

H

OTN

TEST

1F2

-SE

PT.

1977

-lU

I2

-A

10N

O.oUI'I~'~·~r"l~~~_.1'

II

35.

FRED

.(H

Z)O

.5

.10

.15

.20

.25

.30

.35

.FA

Eg.

,HZ)

30.

25.

20

.15

.

OTN

TEST

IF2

-SE

PT.

1977

-lU

I2

-A5

N

10.

5.

1.o.o

lllr'iV

1lrIl"r~"'f"'_~"

IO.OV'··~'

TIl~"ee!.M¥""""·

fe.

I'mI

IO

.5

.10

.15

.2

0.

25.

30.

35.

FRE

g.(H

ZlO

.5

.10

.15

.2

0.

25.

30

.3

5.

FRE

g.IH

Zl

1.

Fig.

4.14

Seco

ndSi

mul

ated

Ear

thqu

ake.

Fou

rier

Am

plitu

deS

pect

raof

Acc

eler

atio

ns

Page 118: By Jack P. t·loeh 1e and A. Sozen

......

o O'l

1.0

0.6

0.8

PEA

leJO

"SEC

O.I!

2010

5 0.2

FREQ

UENC

Y.H

l

so

/ 1/ II,/N

il/

1/1

/1\

1/~~

/

lMi~

~,/

~/

~Y

~

110

o.20.

1l0.160.

11!0

.

120.

100.

i ~80

.w %

:.~ a: ~

60.

-c

1.0

0.6

0.8

PEAI

eJO

.SEC

O.q

2010

5 0.2

FREQ

UENC

Y.H

l

so

)\

L\

~\~

1\~

I~~~

\~

~f\

~,

r\~" "~--~

~---

--0

.00 11

0

0.5

0

2.5

0

3.00

I!.O

O

3.50

C) i

2.0

0

~ fOSO

1.00

DYN

TEST

MF2

-SE

PT.

19T

I-

RUN

S-

ABN

DAMP

ING

FACT

OR.

0.02

0.05

0.10

0.20

OYN

TEST

11F2

-SE

PT.

1977

-RU

N9

-AB

N

OA1P

ING

FACT

OR=

0.02

0.05

0.1

00.

20

Fig

.4.

15T

hird

Sim

ulat

edE

arth

quak

e.L

inea

rR

espo

nse

Spe

ctra

Page 119: By Jack P. t·loeh 1e and A. Sozen

500.0

ul£Jen.......•

:J::J:.>- 200.0)--UDIi:I>

100.0

10.0 '--_~:""--.L...-_~:""--_......L.-._~~......L.-._~~....L-_~~_--J

1.0 2.0 5.0 10.0 20.0 50.0

FAEWENCY p HZ.

OYN TEST MF2 - SEPT p 1977 - RUN 3 - ABNDAMPING FACTOR. 0.00 0.02 0.05 0.10 0.20

Fig. 4.15 (contd.) Third Simulated Earthquake. Linear Response Spectra

Page 120: By Jack P. t·loeh 1e and A. Sozen

II

II

II

II

II

II

II

II

NINT

HLE

VEL

DISP

LACE

MEN

T.UN

IT=

HM

TENT

HLE

VEL

DISP

LACE

MEN

T.UN

IT=H

M

BASE

LEVE

LM

OMEN

T.UN

IT=

KN-M

20

.0

0.0

0

-20

.0"' "

50

.0

0.0

0

-50

.0

50

.0

0.0

0

--'

-50

.0~

V';;

~

50

.0If

EIG

HTH

LEV

EL

OIS

PLAC

EHEN

T.U

NIT

•MM

Iti'

.

00

0-~

h!\

,../\~_

~/\

--6

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O>

·~V

\TV

V\7~~~'J=?

--5

0.0

50

.0I"

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VENT

HLE

VE

lO

ISP

LlI:E

HE

NT.

UN

IT•

MM

00

0_~

hf\

~1

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_r-

...

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.--

V\T~

~'7V

~\;=7

--5

0.0

"

50

.0If

SIX

THLE

VE

lO

lSPL

ACEM

ENT.

UN

IT•

HI'

o00_~

{\

h.

f\~

-/'

0..

..A

"r...

___·

-V

\7\T

V\J'C7~~~~

-50

.0T

SEC

0.0

1.0

2.0

3.0

(j.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

12.0

13.0

lll.

01

5.0

••

II

II

II

II

II

II

II

II

Fig

.4.

16T

hird

Sim

ulat

edE

arth

quak

e.O

bser

ved

Res

pons

e(B

roke

n)an

dC

ompo

nent

sB

elow

3.0

Hz(S

olid

)

Page 121: By Jack P. t·loeh 1e and A. Sozen

II

II

II

II

II

II

II

II

so.O

If.

FIFT

HLE

VEL

OIS

PLA

CE",N

T.U

NIl

•HH

a00

.f\.

.~

f\....

1\~

r--.

.../"

..~

·'Q~V~'V~~~-~

v--

---

-50

.0

so.o

IfFO

URTH

LEVE

LOI

SPLA

CEM

ENT.

UNIT

•MM

a00

f\.....

J"

jf\

_/\

.--.

.--

--f"

'..

~·~VV~~V~~~

~~-

-50

.0

50.01

lHIf

IlLE

VEL

OISP

LACE

HENT

.UN

.IT=

HM

A00

A..

....

/'\

C\

...r.

....--

·'4J~V

C7~~___.c-.

~--~

......

......

...»~

-50

.0 :~:If

-~'7-=v='~~~

'-~:O~:

OJSPLA

CEM:T~

UNIT

•MM

-50

.0

so.o1

FIRS

TLE

VEL

DISP

LACE

HENT

.U

NIl

=HH

O.0

0...

......

......

......

......

......

....~

-=---""

"'""

-50

.01.

00-

II3F

1SE

LEVE

LAC

CELE

PEll

Il)N

.UN

IT=

G

0.0

0

-1.0

0

TSE

C0

.01

.02

.03

.011

.05

.06

.07

.08

.09

.010

.01

1.0

12

.01

3.0

14

.015

.0•

•I

II

II

II

II

II

II

II

I

Fig

.4.

16(c

ontd

.)T

hird

Sim

ulat

edE

arth

quak

e.O

bser

ved

Res

pons

e(B

roke

n)an

dC

ompo

nent

sB

elow

3.0

Hz(S

olid

)

.......

a 1.0

Page 122: By Jack P. t·loeh 1e and A. Sozen

~_________

•I

IJ_

__I~

----

---.

l~~~

__

J~_____

L_

__

_I

I-.I

I

IA

'.J

YIL

tfj$

AI

GS

.~.

.-'

.,

.....

\Y.~....."",

~~

""""";i.f"~:

,,.'''''

OJ....

...-~

........

........

...tu

d*;,

.'.'.,

......

......

.....

,-~

..

1.00

0.00

-1.0

0

1.00

0.0

0

-1.0

0

1.00

0.0

0

-1.0

0

1.00

'f ~

1/ " •

TENT

HLE

VEL

ACCE

LERA

TION

.UN

IT=

G

•.~

I";.~

f,•.

\.

·'1

\f.,.,

" •

NINT

HLE

VEL

ACCE

LERA

TION

.UN

IT=

G

•t,

v

EIGH

THLE

VEL

ACCE

LERA

TION

.UN

IT=

G

SEVE

NTH

LEVE

LAC

CELE

RATI

ON.

UNIT

=G

..... ..... a

0.0

0

-1.0

0

1.0

0

0.0

0

-1.0

0

~.,

..

.....

..

~"

SIXT

HLE

VEL

ACCE

LERA

TION

.UN

IT=

G

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V

TSE

C0

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.07

.08

.09

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0.0

11

.01

2.0

13

.01

4.0

15

.0•

•I

II

II

II

II

II

II

II

I

Fig.

4.16

(con

td.)

Thi

rdSi

mul

ated

Ear

thqu

ake.

Obs

erve

dR

espo

nse

(Bro

ken)

and

Com

pone

nts

Bel

ow3.

0Hz

(Sol

id)

Page 123: By Jack P. t·loeh 1e and A. Sozen

II

II

II

II

II

II

II

II

......

......

......

1,•

Ii

...,,

','n

.-

1'.

".":.

.',

,...

\

~':

't."

''-".

...,..

."

1.;'.

"1

\_,

I>It

•'i

-.:-.;~

...

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~~

'.t

,....

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'.-"

"IU

".'..~",

/'

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URTH

LEVE

LAC

CELE

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ON.

UNIT

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THIR

DLE

VEL

ACCE

LERA

TION

,UN

IT=

G

BASE

LEVE

LAC

CELE

RATI

ON,

UNIT

=G

FIRS

TLE

VEL

ACCE

LERA

TION

,UN

IT=

G

SECO

ND~EVEL

ACCE

LERA

TION

,UN

IT=

G

,.----"

.

,I~

~

,''I

I,"

'~"';

,~,

~,~t.

"."-

'.'-

" ~

FIFT

HLE

VEL

ACCE

LERA

TION

,UN

IT=

G

. ""."

't'f

'J7\

T'~

'1-"

,;"'t

".!,!

'...

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1.0

0

0.0

0

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0

1.0

0

0.0

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•'I

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0

1.0

0

0.0

0

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0

1.0

0

0.0

0

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0

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~

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0

1.0

0

0.0

0

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0

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5.0

6.0

7.0

8.0

9.0

10.a

11.a

12

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3.0

14

.01

5.0

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II

II

II

II

II

II

II

II

Fig.

4.16

(con

td.)

Thi

rdSi

mul

ated

Ear

thqu

ake.

Obs

erve

dR

espo

nse

(Bro

ken)

and

Com

pone

nts

Belo

w3.

0Hz

(Sol

id)

Page 124: By Jack P. t·loeh 1e and A. Sozen

I',-

-,-'--«'.','

,.',

'rJ-

-'

)~

'J4,..~'

,"r,'.

0,

)~

",

,"

•\I

~-

~....

...~.~""t

~e.

"-4

,,~V~

'"'{

.t~

10.0

0.00

-10

.0

10.0

TEN

THST

ORY

SH

eAR

.U

NIT

=KN

NIN

THST

ORY

SHEA

R.

UN

IT=

KN

,.

EIG

HTH

ST~RY

SHEA

R.

UN

IT=

KN

SEVE

NTH

ST~RY

SHEA

R.

UNIT

=KN

0.00

-10

.0

10.0

0.00

-10

.0

10.0

0.00

-10

.0

"'--\1

1".-

""

--...~

..-,.

\'

...

_".,

,t\i

-II...

'7

".,

-,

..... ..... N

10.0

0.00

-10

.0

SIX

lHST

CJRY

SH

EFR

.U

NIT

=KN

"1\ "

TSE

C0

.01

.02

.03

.0Y

.O5

.06

.07

.08

.09

.010

.011

.012

.013

.0l~.O

15.0

••

II

II

II

II

II

II

II

II

Fig.

4.16

(con

td.)

Thi

rdSi

mul

ated

Ear

thqu

ake.

Obs

erve

dR

espo

nse

(Bro

ken)

and

Com

pone

nts

Belo

w3.

0Hz

(Sol

id)

Page 125: By Jack P. t·loeh 1e and A. Sozen

II

II

II

II

II

II

II

II

-'

-'

w

FIFT

HST~RY

SHEA

R.UN

IT=

KN

BASE

LEVE

LACCELERATI~N.

UNIT

=G

F~URTH

ST~RY

SHEA

R.UN

IT=

KN

THIR

DST~RY

SHER

R.UN

IT=

KN

SECO

NDST~RY

SHEA

R.UN

IT=

KN

FIRS

TST

ORY

SHEA

R.UN

IT=

KN

iO.O

U.O

O

-H

I.(J

10.0

0.00

-10

.0

10.0~

• II

0.00

-10

.0

10.0

0.00

-10

.0

10.0

0.00

-10

.0

1.00

0.00

-1.0

0

TSE

C0.

01.

02.

03.

04:

.05.

06.

07.

08

.09.

010

.011

.012

.013

.014

.015

.0•

•I

II

II

II

II

II

II

II

I

Fig.

4.16

(con

td.)

Thi

rdSi

mul

ated

Ear

thqu

ake.

Obs

erve

dR

espo

nse

(Bro

ken)

and

Com

pone

nts

Bel

ow3.

0Hz

(Sol

id)

Page 126: By Jack P. t·loeh 1e and A. Sozen

1.1

.0

DTN

TEST

HF2

-SE

PT.

1977

-lU

I3

-L

INO

THTE

STH

F2-

SEPT

.19

77-

lUI

3-

LaN

10

.1

5.

20

.2

5.

30.

35.

FAEQ

.(H

Zl5.

10

.1

5.

20

.25

.3

0.

35.

FAEQ

.IH

Zl

OTH

TEST

HF2

-SE

PT.

1977

-lU

I3

-L2

N

DYN

TEST

HF2

-SE

PT.

1977

-lU

I3

-L3

N.....

......

.~

35.

FAEQ

.IH

Zl3

0.

25

.20

.15

.

OTH

TEST

HF2

-SE

PT.1

97

7-

lUI

3-

LaN

DYN

TEST

HF2

-SE

PT.

1977

-lU

I3

-L7

N

HI.

5.

1.1. 0.0

'I

.....

"."

....

.I

tI

II

II

35.·

FAEQ

.IH

ZlO

.5

.1

0.

15.

20

.2

5.

30.

35.

FAEQ

.IH

Zl

1.

35.

FAEQ

.IH

Zl

30.

30.

25

.

25.

20

.

20

.

15

.

15

.

10

.

10

.5

.

5.

1.

DYN

TEST

HF2

-SE

PT.

1977

-lU

I3

-LI

IHDY

NTE

STH

F2-

SEPT

.19

77-

lUI

3-

L9N

o.O

rr'I"'~

II

II

II

IO

.5

.1

0.

15

.2

0.

25.

30

.35

.FA

EQ.

(HZl

5.

10

.1

5.

20

.2

5.

3D.

35.

FAEQ

.(H

Zl

1.

1.0

DYN

TEST

HF2

-SE

PT.

1977

-lU

I3

-LS

NOY

HTE

ST11

F2-

SEPT

.19

77-

lUI

3-

LIO

N

5.

10

.1

5.

20

.2

5.

30.

0.0

""

r''I''

''I

II

II

II

35.

FAEQ

.(H

lJO

.5

.1

0.

15.

20

.25

.30

.35

.FA

EQ.

(HlJ

Fig

.4.

17T

hird

Sim

ulat

edE

arth

quak

e.F

ouri

erA

mpl

itude

Spe

ctra

of

Dis

plac

emen

ts

Page 127: By Jack P. t·loeh 1e and A. Sozen

1.

1.

llYN

TEST

1f'2

-SE

PT.

1977

-lU

I3

-A

IMOT

NTE

ST1f

'2-

SEPT

.19

77-

lUI

3-

A6N

S.

10

.1

5.

20.

25.

30.

35

.FR

EQ.

IHZl

5.

10.

15.

20

.25

.3

0.

35

.FR

EQ.

(Hll

OTN

TEST

111'2

-SE

PT.

1977

-IU

l3

-A

7N

1. o.or"··~·"'~~.o

1"

II

35

.FR

Ea.

IHZl

O.

5.

10

.IS

.2

0.

25.

30

.35

.FR

Ea.

lHll

30.

25

.20

.1

5.

10

.5

.

0.0

5.

10

.1

5.

20.

25.

30.

35

.F

RE

Q.

IHII

O.

5.

10

.1

5.

20.

25

.3

0.

35.

FREQ

.IH

Zl

I.

llYN

TEST

If'2

-SE

PT.

1977

-lU

I3

-A

3Il

I•

llYN

TEST

1f'2

-SE

PT.

1977

-lU

I3

-Ae

N

..... ......

U'1

,J~~

II

I5

.1

0.

15

.20

.25

.30

.3

5.

FREQ

.IH

lJO

.5

.10

.15

.20

.2

5.

30

.35

.FR

EQ.

IHZl

l'j

I1

.

I~llY

NTE

STIf

'2-

SEPT

.19

77-

lUI

3-

_llY

NTE

ST11

1'2-

SEPT

.19

77-

filii

3-

Il9N

llYN

TEST

1f'2

-SE

PT.

1977

-lU

I3

-AS

HOT

NTE

ST11

1'2-

SEPT

.19

77-

AIJ

I3

-A

IOIl

35.

FRE

a.(H

Z)3

0.

25.

20.

IS.

10.

5.

I.

35

.FR

Ea.

IHlJ

30.

25

.20

.1

5.

10

.5

.

I.

Fig

.4

.18

Th

ird

Sim

ula

ted

Ear

thqu

ake.

Fo

uri

erA

mpl

itud

eS

pec

tra

of

Acc

eler

atio

ns

Page 128: By Jack P. t·loeh 1e and A. Sozen

116

Level10 ----..... 1.000 -----1.000

9 0.973 0.972

8 0.943 0.939

7 0.885 0.876

6 0.807

5

4

3

2

80se

(a) First Steady -StateTest

(b) Second Steady-StateTest

Fig. 4.19 First-Mode Resonance Shapes Observed DuringSteady-State Tests

Page 129: By Jack P. t·loeh 1e and A. Sozen

117

Fig. 5.1 Comparison of Apparent Modal Frequencies with MaximumTenth-Level Displacement Previously Experienced by TestStructure

Page 130: By Jack P. t·loeh 1e and A. Sozen

118

I I

5.0 I--

o Free Vibration• Simulated EarthquakeoSteody - State... 4.0 - -%:..

""ucU::lCT 5.0~ -e 0/1.1:

u0'0

0:E 2.0 ..-- • 0 -I

0-co~ 0ii: •

1.0 I-- -

I I I I I r°0~--~2~O----4""O"""---6~O---~80"----...IIOO"""---12.&.O-~

Double - Amplitude Displacement I mm

Fig. 5.2 Comparison of Apparent First-Mode Frequency with MaximumTenth-Level Displacement Previously Experienced by TestStructure

Page 131: By Jack P. t·loeh 1e and A. Sozen

119

I I I I

30 10- Simulated 'FreeEarthquake Vibration

2nd MOdeC .. A3rd Mode I 0

025 I--

N 20~ -:::J:

enQ)

0'u •cQ):::JtT IS I--- -Q)~u.~

Q) •s=0'

:r::10 i---" • -

A

AA

51--- AA

I I 1 I Iool~----.L.'----~2----~3------14~---~5~""

First - Mode Frequency t Hz

Fig. 5.3 Comparison of Observed High Frequencies with First-Mode Frequency

Page 132: By Jack P. t·loeh 1e and A. Sozen

120

5.0

3.0o.....~~-----------------'----_..I-_ ....

2.0

Frequency, Hz

c 4.00-CU....Q. 3.0E~

::

0

" 2.00~

::Second Steady-State

1.0

Fig. 5.4 "Modal" Amplification Compared with Exciting Frequency inSteady-State Tests

Page 133: By Jack P. t·loeh 1e and A. Sozen

II

II

II

II

II

II

II

II

50

.01

.OO

SED

ISPL

ACE

MEN

TI

RUN

ON

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NIT

•MM

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../\

/'\

....

....

....

"..

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....

,.

"'\7~

"=

?'

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~--=

=----

=........-=

0:--

-50

.0

1.0

0I

BASE

AC

CEl

EFm

ION

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NO

NE,

UN

IT•

G

"'"

/I,A

A.

""It

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0._

CoA

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Afl

."

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VII

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0

50

.01

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ISPl

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EMEN

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.001

BASE

AC

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EfflT

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RUN

THRE

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=tt1

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0_/\~"""

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7

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00I

BASE

ActELERATI~N

/RU

NTH

REE.

UNIT

=G

......

N ......

0.0

0

-1.0

0

TSE

C0

.01

.02

.03

.0lI

.05

.06

.07

.08

.09

.01

0.0

11

.01

2.0

13

.01

4.0

15

.0•

•I

II

II

II

II

II

II

II

I

Fig

.5.

5M

easu

red

Sim

ulat

edE

arth

quak

eW

avef

orm

s

Page 134: By Jack P. t·loeh 1e and A. Sozen

122

1.0

OYN TEST HF2 - SEPT. 1977 - RUN 1 - ABN

1.0

5. 10. 15. 20. 25. 30. 35. fHEQ. 1HZ)

OYN TEST Mf2 - SEPT. 1977 - RUN 2 - ABN

1.0

OYN TEST HF2 - SEPT. 1977 - fll.!I 3 - ABN

30. 35. fAEQ. IHZI

25. 30. 35. fAEQ. lHll

Fig. 5.6 Fourier Amplitude Spectra of Simulated Earthquake Base Accelerations

Page 135: By Jack P. t·loeh 1e and A. Sozen

LEVE

L

10

9 8 1 6 5 \I 3 2 1

0.0

20

.0I

I

DISP

LACE

MEN

TSIM

M)

0.0

2.0

~I

LATE

RAL

FORC

ESIK

N)

0.0

10

.0I

I

SHEA

RS.

IKN)

0.0

20

.0t

I

M01

ENTS

IKN

-M)

--'

N W

TEST

STRU

CTUR

EM

F2-

TEST

RUN

1-

RESP

ONS

EAT

1.4

0SE

COND

S

Fig

.5.

7D

ispl

acem

ents

,L

ater

alF

orce

s,S

tory

Shea

rsan

dS

tory

-Lev

elt·1

omen

tst4

easu

red

Dur

ing

Sim

ulat

edE

arth

quak

es

Page 136: By Jack P. t·loeh 1e and A. Sozen

LEVE

L

10 9 8 7 6 5 It 3 2 1

0.0

50

.0I

I

DISP

LACE

MEN

TSIIt

1l

0.0

5.0

II

LATE

RAL

FORC

ESIK

Nl

0.0

20

.0I

I

SHEA

RSIK

N)

0.0

20

.0t

I

MOME

NTS

IKN

-M)

--'

N ~

TEST

STRU

CTUR

EM

F2-

TEST

RUN

2-

RESP

ONS

EAT

2.4

7SE

COND

S

Fig.

5.7

(Con

td.)

Dis

plac

emen

ts,

Lat

eral

Forc

es,

Sto

ryS

hear

s,an

dS

tory

Leve

lM

omen

tsM

easu

red

Dur

ing

Sim

ulat

edE

arth

quak

es

Page 137: By Jack P. t·loeh 1e and A. Sozen

LEVE

L

10 9 8 "1 6 5 II 3 2 1

0.0

50

.0I

I

DISP

LRCE

MEN

TS(M

Ml

0.0

S.O

II

LATE

RAL

fORC

ESIK

Nl

0.0

20

.0I

I

SHEA

RSIK

Nl

0.0

20

.0I

I

MOME

NTS

(~N-Ml

--'

N 01

TEST

STRU

CTUR

EM

F2-

TEST

RUN

3-

RESP

ONS

EAT

2.5

0SE

Cl'JN

DS

Fig.

5.7

(Con

td.)

Displacements~

Lat

eral

Forces~

Sto

ryS

hear

s,an

dS

tory

Lev

elM

omen

tsM

easu

red

Dur

ing

Sim

ulat

edE

arth

quak

es

Page 138: By Jack P. t·loeh 1e and A. Sozen

9I

IfI

,8

+/I

...

I.r7

+/I

+

6+

/I

...IJ

f

t/¥

......

,N

5+

/1+

en

4+

Iii

+,1

/,

,7,

3+

It·

+if

fII

/jor

2+

11/

+'I

r'l

r--

Des

ign

--

Sim

ulat

edE

art

hq

ua

ke-D

A----

Ste

ad

y-S

tote

Leve

l10

Bos

e

(0)

Te

stR

unO

ne(b

)T

est

Run

Tw

o(c

)T

est

Run

Th

ree

Fig.

5.8

Com

paris

onof

Mea

sure

dD

ispl

acem

ent

Shap

esan

dSh

apes

Cal

cula

ted

for

the

Sub

stit

ute

Str

uctu

reM

odel

Page 139: By Jack P. t·loeh 1e and A. Sozen

rI

II

'I

o1

00

20

03

00

40

0

Sp

ectr

um

Inte

nsi

ty1

mm

Fig

.5.

9C

ompa

rison

of

Max

imum

Ten

th-L

evel

Dis

plac

emen

tan

dSp

ectr

umIn

ten

sity

at

aD

ampi

ngF

acto

ro

f0.

20

Page 140: By Jack P. t·loeh 1e and A. Sozen

LEV

El.

10 ij

0.0

20

.0I

I0

.02

.0I

I

I0

.010

.0I

I0

.01

0.0

II

LEVE

L

10

0.0

20.0

II

0.0

2.0

~I

0.0

10.0

II

0.0

10.0

II

TEST

STRU

CTUR

EII

f2-

TEST

RUN

1-

RESP

ONS

ERT

2.2

6S

Eal

ND

STE

STST

RUCT

URE

IIf2

-TE

STRU

N1

-RE

SPO

NSE

RT2

.3q

SECO

NDS

OIS

I'IJI

C£I

£KTS

0Il

ILR

TEM

.Fl

lRC£

S10

0SI

£IlR

S10

0IIl

lItEI

ITS

IIOl-I

tIOISPLAC~IITS

0Il

ILA

TEM

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lRCE

SliN

)SH

EARS

IKH

lIIl

lItEI

ITS

111M

-HI

.... N 00

0.0

10

.0I

I

"MN

TS

IKH

-")

0.0

10

.0I

I

SHEA

RSIK

Hl

0.0

2.0

~I

LATE

RAL

FttlC

ESIII

NJ

0.0

20.0

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OIS

PLA

CEltE

NTS

0Il

I

ij9 6LEVE

1.

10

0.0

10

.0I

I0

.01

0.0

II

0.0

2.0

II

\0

.02

0.0

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2.1

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PLA

CEltE

NTS

LATE

M.

FttlC

ESSH

EAAS

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TS

0Il

IIII

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NlIK

H-"

)

9LEV

El.

10

TEST

STRU

CTUR

EII

f2-

TEST

RUN

1-

RES

PrlN

SERT

2.3

0SE

COND

STE

STST

RUCT

URE

Hf2

-TE

STRU

N1

-RE

SPO

NSE

RT2

.38

SECO

NDS

Fig

.5.

10M

easu

red

Res

pons

eTh

roug

ha

Hal

f-C

ycle

Incl

udin

gth

eM

axim

umD

ispl

acem

ent

Dur

ing

the

Fir

stSi

mul

ated

Ear

thqu

ake

Page 141: By Jack P. t·loeh 1e and A. Sozen

LEVE

L0

.02

0.0

II

0.0

2.0

II

0.0

10.0

II

0.0

20.0

II

LEVE

L

10

0.0

20.0

II

0.0

2.0

JI

0.0

10.0

II

I0.0

20.0

JI

019'

UlC

£l£N

TS

010

LRTE

M..

FllR

C£S

IlHJ

SHEA

I\SIlH

J_

tIT

SIK

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TEM

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lSH

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tKNl

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N-H

I

TEST

STRU

CTUR

E"f

2-

TEST

RUN

1-

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ONS

EFI

T2.

112

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NDS

TEST

STRU

CTUR

E"f

2-

TEST

RUN

I-

RESP

ONS

EFI

T2

.50

SECO

NDS

..J

N ~

0.0

20

.0I

I

HrlI1

ENTS

IKN

-Hl

0.0

10.0

II

SHEA

RSIK

Nl

0.0

2.0

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LRTE

ARL

FlIIC

ESlK

Nl

0.0

20

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I

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NTS

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~.

-

LEV

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10

0.0

20.0

II

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Hl

0.0

10.0

II

SHEA

I\SIK

Nl

0.0

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0.0

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NTS

010

9 2·6LEV

El

10

TEST

STRU

CTUR

EH

f2-

TEST

RUN

1-

RESP

ONS

EFIT

2.11

6SE

COND

STE

STST

RUCT

URE

Hf2

-TE

STRU

N1

-RE

SPO

NSE

FIT

2.5

ijSE

COND

S

Fig.

5.10

(Con

td.)

Mea

sure

dR

espo

nse

Thro

ugh

aH

alf-

Cyc

leIn

clud

ing

the

Max

imum

Dis

plac

emen

tD

urin

gth

eF

irst

Sim

ulat

edE

arth

quak

e

Page 142: By Jack P. t·loeh 1e and A. Sozen

130I I I I I I

15 I- --0-----0{)

Z~--'----

.¥ /~ 6

10 - /0 6'- /0Q) cfs::.

CJ) IQ)

~I0 1/2 x Maximum Double Amplitude

'"0 5 ° Peaks Observed Early In TestCDI Run OneI 6 Based On Measured w and Xi

II I I I I I

00 10 20 30 40 50 60

Tenth - Level Displacement, mm

-

-

Fig. 5.11 Comparison of Base Shear and 'Tenth-Level Displacement

w = apparent first-mode circular frequency; Xi = displacementat level i .

20

15 ~Maximum MeasuredBase Shear

-----------

:o

CD 0 Bose Shear forCalculated Mechanisms

5

109816542O'---.......- ......--L.-.....---II.------"""--......---'----I~o

Upper Story of Collapse Meehan ism

Fig. 5.12 Comparison of Measured Base Shear and Calculated CollapseBase Shears for Mechanism Acting Through Various Story Heights

Page 143: By Jack P. t·loeh 1e and A. Sozen

Ass

umed

Lo

ad

ing

Dis

trib

uti

on

w --'

--.

JO

.

I,.....

~

I

-~

~.....

~-"

'-~

-....

-

....-

....-

~

-~

....-

or

Clce

.....-

J'O

L.~

....--

~-

~....

-....

-

...n

.....-

J

Yie

lda

Col

umn

Bea

mFI

I;~

-~

~

~

~

~~

~j

jj

~

a)F

irst

Sto

ryC

olla

pse

Mec

hani

smB

ase

She

ar=

21kN

b)M

inim

umB

ase

-Sh

ea

rC

olla

pse

Mec

hani

smB

ase

Sh

ea

r=

12kN

c)F

ull

Be

am

-Yie

ldC

olla

pse

Mec

hani

smB

ase

She

ar=

14kN

Fig.

5.13

Cal

cula

ted

Col

laps

eM

echa

nism

san

dB

ase

Shea

rsfo

ra

Tri

angu

lar

Load

Dis

trib

utio

n

Page 144: By Jack P. t·loeh 1e and A. Sozen

132

605040

~ Test Run I

o Test Run 2

II Test Run 3

3020105

15

20

5

..Q)

.Q 10E~

z

­o

Displacement, mm

Fig. 5.14 Cumulative Number and Value of Displacement Peaks DuringSimulated Earthquakes

Page 145: By Jack P. t·loeh 1e and A. Sozen

Da

mp

ing

Fa

cto

r=

0.10

1.0

Ca

lcu

late

dfo

rM

ea

sure

dB

ase

Mo

tio

n

0.8

at .. c 0 -0.

60

I/

/~

\~

I.....

...

wCD

wCD U u <t

0.4

0.2

1.0

0.8

0.6

Pe

rio

dt

sec

0.4

Fre

quen

cyt

Hz

0'

I!

IJ

II

I,

~~

WW

5~2

Fig.

5.15

Com

paris

ono

fD

esig

nR

espo

nse

Spec

trum

and

Spec

trum

Cal

cula

ted

from

Fir

stSi

mul

ated

Ear

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Page 147: By Jack P. t·loeh 1e and A. Sozen

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APPENDIX A

DESCRIPTION OF EXPERIMENTAL WORK

A.l Concrete

The concrete was a small-aggregate type. The cement was high early

strength. Coarse and fine aggregates were, respectively, Wabash River

sand and fine lake sand. Mix proportions we~e 1.1 : 1.0 : 4.0 (coarse

fine: cement) by dry weight. A water: cement ratio of 0.74 was chosen

based on desired workability and compressive strength. A slump of 70 mm

was obtained.

The control specimens and the test specimen were cast from a single

batch. Age of the test specimen at testing was 47 days. The control

specimens were tested at 49 days. Similar treatment for both control

specimens and test frames was provided during the intervening period.

Control specimens comprised ten 100 by 200 mm cylinders for compression

tests, six 100 by 200 mm cylinders for splitting tests, and eleven

50 by 50 by 200 mm prisms for modulus-of-rupture tests.

The stress-strain relationship was determined from compression

tests on 100 by 200 mm cylinders. Strains were measured over a 125 mm

gage length with a O.OOl-in mechanical dial gage. It was not possible to

measure the descending portion of the stress-strain curve with any

accuracy because of equipment limitations. Figure A.l. shows the bounds

of all the stress-strain curves compared with the relation used in design.

The ultimate compressive strength, f~, had a mean of 38 MPa with a standard

deviation of 2.3 MPa. The secant modulus, Ec ' as determined from a

straight line drawn from the origin through the stress-strain curve at

20 MPa, had a mean value of 21000 MPa.

Page 148: By Jack P. t·loeh 1e and A. Sozen

136

The tensile strength of the concrete was determined by splitting 100

by 200 mm cylinders. The mean tensile strength, f t , was 3.59 MPa with a

standard deviation of 0.38 MPa.

The modulus of rupture, f r , was determined by loading 50 by 50 by

200 mm prisms at the center of alSO mm span. The mean modulus of rupture

was 7.88 t1Pa with a standard deviation of 0.72 f4Pa.

A.2 Reinforcing Steel

Longitudinal steel for beams and columns consisted of No. 13 gage

bright basic annealed wire (Wire Sales Company, Chicago). The wire was

ordered annealed and processed to a yield stress of approximately 400 MPa.

All wire was received in straight 3 m lengths.

Stress-strain properties of the No. 13 gage wire were determined

at a strain rate of 0.005/sec. From ten coupons tested, Young's modulus

was determined to be 200,000 MPa. The mean and standard deviation for

the yield stress were 358 MPa and 5.2 MPa.The mean stress-strain

relation is plotted in Fig. A.2.

Wire for the helical and spiral reinforcement was #16 gage annealed

wire. The wire was received in a roll. It was subsequently straightened

and turned on a lathe into the helical or spiral shape. Considering the

extent of overdesign with regard to shear failure, extensive testing of

the wire was not required. However, the yield stress of the wire was

determined to be approximately 750 MPa.

A.3 Specimen Details

(a) Frame Configuration

One test structure was built. It consisted of two ten-story, three-bay

frames cast monolithically with very stiff base girders. The overall

Page 149: By Jack P. t·loeh 1e and A. Sozen

137

configuration of a frame is shown in Fig. 2.1. Column lines were

regularly spaced. Story heights varied, those at levels one and ten

being approximately 20% taller than those at other levels. In addition,

an exterior-span beam was omitted at the first level in each frame

(Fig. 2.1). Stubs protruding from all beam and column ends were'provided

for development of reinforcing steel.

Nominal gross cross-sectional beam dimensions were 38 by 38 mm,

while those for columns were 51 by 38 mm. Owing to fabrication tolerances,

these dimensions differed slightly from the nominal values. The measured

gross dimensions are presented in Tables A.l through A.5. All depth

dimensions were measured in the plane of the frame. Width dimensions

were measured perpendicular to that plane. A key locating column lines

and East-West direct10ns is given in Fig. 2.1 Nominal beam and column

lengths varied as shown in Fig. 2.1. Measured lengths did not differ

from these values.

Holes were provided in the center of each beam-column joint to

facilitate supporting of a mass at each level (Fig. 2.18). These holes

were reinforced with steel tubing (12.7 mm outside diameter). Holes were

also provided in the base girders (Fig. A.3). Horizontal holes were

provided to facilitate the transporting of the frames from the formwork

to the test platform, while vertical holes were provided for fastening

the test structure to the test platform. Both horizontal and vertical

holes were reinforced with steel tubing (19 and 44 mm outside diameters,

respecti vely).

(b) General Reinforcement Details

Preparation of all steel was initiated by soaking in solvent and

then wiping clean. The longitudinal steel was then cleaned further with

acetoneo This process left the steel free of dirt and oil.

Page 150: By Jack P. t·loeh 1e and A. Sozen

138

The steel reinforcing cages were assembled by tying all reinforcing

elements with a ductile steel wire (0.91 mm diameter). Longitudinal

steel was continuous with the exception of cutoffs in the columns at the

lower levels (Fig. 2.19). No welding was performed except at the base

of the vertical steel where 3.2 mm thick steel plates were welded to

insure embedment into the base girders (Fig. A.3).

The completed cages were removed to a fog room. There they were

sprayed with ten percent hydrochloric acid solution and left for four

days to rust the steel in order to improve bond. The extent of rusting

was such that it had negligible effects on the steel force-strain

properties. All loose rust scales were removed with a wire brush prior

to placement of the cages in the forms.

(:c) Beam and Col umn Reinforcement

The distribution of beam and column reinforcement is given in Table

2.3. Typical details are shown in Fig. 2.16, 2.18, and 2.19. Steel

ratios for columns are computed as the ratio of the total longitudinal

steel to the nominal gross cross-sectional area. For four and eight bars

the steel ratios were 0.88 percent and 1.75 percent. For beams, the

steel ratios are computed as the ratio of the steel area per face to the

nominal effective area of the section (nominal width times nominal depth

to tension steel). Three bars per face gave a steel ratio of 0.74

percent. For two bars, the ratio was 1.11 percent. Nominal beam and

column cross-sections are shown in Fig. 2.16. Following testing, the mean

cover of longitudinal steel was determined to be 6.1 mm for columns and

6.7 mm for beams versus the nominal value of 6.6 mm.

Page 151: By Jack P. t·loeh 1e and A. Sozen

139

Development of the full flexural capacity of all members was of

primary concern in design. Development of this capacity required either

embedment or an adequate development of longitudinal steel. In general,

this was accomplished by having all steel continuous and developed into

protruding stubs at member ends (Fig. 2.18). In the stubs, the steel

was bent to the opposite face of the member. Column steel at the base

was developed 102 mm into the base girder and welded to steel plates

(Fig. A.3). Finally, where bar cutoffs were made in the columns, the

steel was developed 64 rom above floor level centerlines.

Transverse reinforcement consisted of #16 gage wire bent into a

helical shape. The outside dimensions. and pitch are shown i,n Fig. 2.18.

The quantity Avf dis (where A = cross-sectional area of the wire,y v

fy = yield stress, d = effective depth of beam, and s = spacing of

transverse reinforcement) was 9.0 KN (minimum) compared with a maximum

expected shear force of 2.6 KN.

(d) Joint Reinforcement

Two types of beam-column joint reinforcement were used. Number 16

gage spiral reinforcement provided joint confinement. The outside diameter

and pitch were 31.8 and 10.0 mm, respectively. The second type of

reinforcement, a steel tubing, served to reinforce the holes provided for

support of the concrete masses at each level. The locations within a

joint of each reinforcement type are shown in Fig. 2.18 and 2.19.

(e) Base Girder Reinforcement

The base girder was designed as a rigid element of each frame.

Fig. A.3 presents the details of the reinforcement.

Page 152: By Jack P. t·loeh 1e and A. Sozen

140

(f) Concrete Casting and Curing

The test specimen was cast monolithically in a horizontal position.

Formwork consisted of a steel form bed and steel side pieces. Casting

of both frames and of the control specimens was done simultaneously

from a single batch of concrete. Concrete was vibrated with a stud

vibrator. Vibration for the base girders was done by placing the

vibrator inside the formwork. Vibration for the rest of each test

specimen was done by vibration against the reinforcing cage. All

concrete was in place within one and one-half hours of mixing. Finishing

was done approximately one-half hour after placement had been completed.

The specimens were covered with a plastic sheet for 8 hours to help

prevent water loss. After this time) the sheet was removed and all side

pieces of the forms were removed. The specimens were sUbsequently

covered with wet burlap and plastic sheets for a period of 18 days.

Removal of the specimens from the forms immediately followed this period

of curing. This was done by first fixing the specimen to the formwork.

The formwork and the specimen were then lifted with a crane to an upright

position such that the weight of the specimens was supported by its base

and the formbed was supported by the crane. Removal of the bolts fixing

the specimen to the form allowed the form to be separated from the

specimen. All specimens were then sored in the laboratory for an

additional period of 29 days.

A.4 Dynamic Tests

(a) Earthquake Simulator

The dynamic tests of the structure were run on the University of

Illinois Earthquake Simulator. The earthquake simulator is located in

Page 153: By Jack P. t·loeh 1e and A. Sozen

141

the Structural Research Laboratory of the Civil Engineering Department at

the University of Illinois at Urbana-Champaign. Major components of the

system are a hydraulic ram, a power supply, a command center, and a test

platform. The overall configuration of the hydraulic ram and the test

platform is shown in Fig. A.4.

The test platform is 3.66 m square in plan. Four flexure plates

support the test platform so that it has essentially unrestrained free

motion in one horizontal direction. A 330 KN capacity hydraulic ram

drives the test platform. A flexure link connects the hydraulic ram and

the test platform.

Motion of the test platform is controlled by input from the command

center. An appropriate acceleration record is integrated twice and the

resulting displacement record is recorded on magnetic tape. This record

forms the input for a test run. A servomechanism uses the input to

control the hydraulic ram and reproduce the desired motion.

A more detailed description of the earthquake simulator and its

performance can be found in Reference [4] and.[6].

(b) Assembly of the Test Structure

The test structure was assembled on the simulator platform. It

consisted primarily of the two frames and their connections to the platform

and the ten masses with their connecting systems. The entire structural

system can be seen in Fig. 2.2 and A.4. Three stages of construction are

distinguished to be (1) stacking of the ten masses, (2) positioning of

the frames adjacent to the ten stacked masses, and (3) connection of the

masses to the frames.

Construction was begun by stacking ten story-masses on wooden blocks

on the earthquake simulator platform. The mass of each is presented in

Page 154: By Jack P. t·loeh 1e and A. Sozen

142

Table A.6. Each was positioned so that its known center of mass would

coincide with the appropriate story level. Bellows (Fig. 2.2) were

attached to each mass after it was positioned. The two test frames were

then positioned astride the stacked masses and the base girders fixed to

the test platform (Fig. A.4). Fixity was provided by bolting angle

sections across the base girders so as to bear down on them and by pro­

viding reaction angles at the end of each base girder (Fig. A.4).

The mass at each story-level was supported by two cross-beams which

protruded from beneath each mass in the transverse direction (Fig. 2.2).

The crossbeams were pinned at either end to perforated channels which

were in turn pinned through frame joints (Fig. A.5). Although the

connections through frame joints cannot be considered frictionless,

they were made only "snug" tight so as to reduce the transfer of moment

between a mass and a joint. In addition, washers were provided (Fig.

A.5) to further reduce moment transfer.

The mass-connecting system for levels two through ten was such that

each frame joint was ideally leaded with one~eighth of the total load

acting at that floor-level. The connection at the first level was

indeterminate (Fig. 2.2).

(c) Instrumentation

Displacements and accelerations were the two types of data directly

obtained in the dynamic tests of the structure. Displacements were

measured with differential transformers (LVDT's) and accelerations with

accelerometers. Locations and orientations of these instruments on the

structure are shown schematically in Fig. 3.1.

Page 155: By Jack P. t·loeh 1e and A. Sozen

143

LVDT's measured relative displacements of each side of the structure,

one at each level on a given frame. These were attached to the perforated

channels of the mass-supporting system, these channels being confined

to move identically with the frame at that level (Fig. A.5). The LVDT's

were mounted to an A-Frame which was rigidly fixed to the test platform

and which served as a rigid reference to the base. The natural frequency

at the A-Frame was approximately 48 Hz. In addition, one LVDT measured

displacements of the hydraulic ram. Mechanical calibrations were per­

formed by mechanically moving the rod of the LVDT. Machined aluminum

spacers were used to define the displacement of the rod in each mechanical

calibration. In addition, resistive electrical calibrations were made

throughout the tests.

Accelerations were measured in both horizontal and vertical directions

with two types of accelerometers (Endevco piezoresistive and Endevco

Q-Flex). Location and orientation of all accelerometers is shown

schematically in Fig. 3.1. Accelerometers which measured horizontal

accelerations of each frame in the direction of the input motion were

attached at each level to a perforated channel of the mass-supporting

system (Fig. A.5). Additional accelerometers were mounted one to the base

of each frame and one at the center of the tenth level mass to measure

in-plane motion at that point. Two accelerometers measured torsional

accelerations, that is acceleration out of the plane of the input motion.

These were attached at opposite ends of the tenth level mass (Fig. 3.1).

Finally, two accelerometers measured vertical acceleration. These were

mounted at the top of exterior columns, one at the side with the omitted

Page 156: By Jack P. t·loeh 1e and A. Sozen

144

beam and one at the side with beams at all levels. Mechanical calibra­

tion of all accelerometers was done by holding them vertical and then

rotating to a horizontal posHion for an acceleration of one g. All

accelerometers of a given type (piezoresistive or Q-Flex) were mechanically

calibrated simultaneously. Electric calibrations were performed for

accelerometers throughout the tests.

(d) Test Procedure

The tests were conducted in a single day. An outline of the test

procedure insured that the tests would be conducted smoothly and

reliably.

On the morning of the tests, the wooden blocks supporting the masses

were removed, transferring the weight of the masses to the test frames.

All connections were checked to insure a11ignment and to insure the

tightness of connecting bolts. All bolts connecting the frames to the

test platform were retightened to compensate for the creep that had

occurred under the high bearing stress.

Preparation of the earthquake simulator required that the hydraulic

ram be warmed up prior to the test. This was done by operating the ram,

free of the test platform, for one-half hour. After this time, the ram

was connected to the test platform~

Shrinkage cracks in the frames were checked both before and after

the masses had been connected to the frames, but before the first test

run. Cracks were located by spraying the frames with "Partek" Pl-A

Fluorescent (Magnaf1ux Corporation, Chicago, Illinois). The liquid

penetrated the cracks, reflecting under a "b1ack 1ight" to show the

crack patterns. Observed cracks were marked on the structure and

recorded on data sheets.

Page 157: By Jack P. t·loeh 1e and A. Sozen

145

The actual conduct of a test is given below.

(1) The test structure was given a small-amplitude free vibration

by laterally displacing and then releasing the tenth-level mass (Fig.

3.2).

(2) The test structure was subjected to the earthquake input

selected for that test run.

(3) The crack pattern resulting fron the test run was observed,

marked on the structure, and recorded on data sheets. Any spalling or

crushing was also noted.

(4) The test structure was given another small-amplitude free

vibration.

(5) The test structure was subjected to a sinusoidal base motion

starting at a frequency below the apparent resonance frequency and

sweeping in steps to a frequency above the observed apparent resonance

frequency.

The above sequence formed one test run. Three such runs were

performed. Electrical calibrations were made before and after each of

the steps (1), (2), (4), and (5). The voltages from free vibrations,

simulated earthquakes, steady-states, and electrical calibrations were

recorded on magnetic tape. A movie camera and a videotape machine

recorded the motion of the test structure during the test runs.

A.5 Data Reduction

Response measurements in all tests consisted of instrument voltage

responses. These voltage responses were amplified as required and

continuously recorded by four magnetic tape recorders. Each recorded

Page 158: By Jack P. t·loeh 1e and A. Sozen

146

13 voltage signals and one audio signal. One of the 13 voltage signals

was a signal common to all recorders, thereby allowing synchronization

of all response measurements.

In order to put the data in a more usable form, the analog records

were converted to a digital form using the Spiras-65 computer of the

Department of Civil Engineering. Data was digitized at 250 points per

second and the digitized data recorded on magnetic tape.

Using the digital tape, calibrations and zero levels for each test

event were determined using a computer program. Another computer

program was then used to calibrate and zero the digitized voltage

responses and to reorganize the data in terms of a series of time

histories, one for each instrument and test event. One option of this

computer program was used to record the reorganized data on another

magnetic tape. A second option allowed determination of amplitudes and

frequencies for use in the steady-state tests.

A series of computer programs was then used to manipulate the

response-time histories. The functions of these are destribed below.

(a) Story shear and moment histories were determined for simulated

earthquakes at each digitized time instant (250 per second) by considering

horizontal accelerations, displacements, story-masses, and story heights.

The P-delta moment was included. These histories were also recorded on

magneti c tape.

(b) Response-time histories were plotted (Chapter 4). A filtering

option utilizing the Fast Fourier Transform allowed specified harmonic

components of the histories to be filtered from the total response.

(c) Spectrum intensities and response spectra were determined at

various damping factors and the latter plotted (Chapter 4).

Page 159: By Jack P. t·loeh 1e and A. Sozen

147

(d) Fourier amplitude spectra were determined and plotted using the

Fast Fourier Transform. Dominant frequency components were determined

from these (Chapter 4).

(e) Response at any time instance could be determined. Distri­

butions of displacements, accelerations, lateral forces, story shears,

and story moments at the specified instant were determined and plotted.

These were used to observe changes in distributions throughout the test

runs.

Page 160: By Jack P. t·loeh 1e and A. Sozen

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Page 161: By Jack P. t·loeh 1e and A. Sozen

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.539

.4st

d.

dev.

0.40

0.43

0.33

0.52

0.43

0.51

0.54

0.64

Page 163: By Jack P. t·loeh 1e and A. Sozen

Tab

leA

.4M

easu

red

Gro

ssC

ross

-sec

tion

alC

olum

nD

imen

sion

s-

Sout

hFr

ame

Dim

ensi

ons,

mm.

Colu

mn

Lin

e1

Colu

mn

Lin

e2

Colu

mn

Lin

e3

Col

umn

Lin

e4

Sto

ryD

epth

Wid

thD

epth

Wid

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epth

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epth

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p50

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51.1

39.1

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38.4

38.4

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750

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50.5

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51.1

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51.1

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mea

n50

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.538

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d.

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0.30

0.46

0.29

0.46

0.33

0.48

0.29

0.37

Page 164: By Jack P. t·loeh 1e and A. Sozen

Tab

leA

.5Su

mm

ary

ofM

easu

red

Gro

ssC

ross

-sec

tion

alM

embe

rD

imen

sion

s

Dim

ensi

ons,

rrm.

Mea

nM

ean

Stan

dard

plus

min

usPa

ram

eter

Nom

inal

Mea

nM

inim

umM

axim

umD

evia

tion

Std

.D

ev.

Std

.D

ev.

Nor

thFr

ame

Colu

mn

Dep

th51

.050

.549

.351

.30.

4150

.950

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Colu

mn

Wid

th38

.039

.138

.140

.40.

5439

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.6--'

Beam

Dep

th38

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.60.

6338

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1N

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th38

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5839

.838

.6

Sout

hFr

ame

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mn

Dep

th51

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3051

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3739

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Page 165: By Jack P. t·loeh 1e and A. Sozen

153

Table A.6Measured Story Masses

Level

10987654321

t1ass(Kg)

461464463466464465465462465291

Page 166: By Jack P. t·loeh 1e and A. Sozen

Descript ion of Delilln Curve

fc'O ·c<Ofc ' f o[2(..!2.1 - (S)2} 0 < .c<.o

"0 41'0'

fc ' fo [I-150(.c- Eol] ·o<·c<·o+O.ool

40

30

ClQ.::IE

,;..CD 20..Ui

10

154

-- Measured Envelope--- Desion

2

Strain x 101

3 4

Fig. A.l Envelope of Measured Concrete Stress-StrainRelations and Design Relation

400~

358 '-- ,_-------------------------1300t-

Cl I-- 200,000 MPaQ.

::IE.: 200 i-- - Measured~ --- DesionU;

100

00I I I I I I I

4 8 II! 18 20 1!4 28

Strain x 101

Fig. A.2 Measured Mean Stress-Strain Relation andDesign Relation for No. 13 Gage Wire

Page 167: By Jack P. t·loeh 1e and A. Sozen

.......

CJ1

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(All

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Fig.

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orce

nent

Page 168: By Jack P. t·loeh 1e and A. Sozen

Ste

elP

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tal

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Page 169: By Jack P. t·loeh 1e and A. Sozen

CJ'1

'-l

Ma

ss--

Co

lum

n

Was

hers

Pin

ned

Inte

rio

rC

olum

n

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rfo

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ofr~ass-to-FrameConnection

Page 170: By Jack P. t·loeh 1e and A. Sozen

158

APPENDIX B

COMPLEMENTARY DATA

B.l Introductory Remarks

The purpose of this appendix is to compare various measured waveforms

so as to provide a check on the functioning of the experimental system. The

waveforms are presented separately from the main 'text because of their

limited importance concerning response of the test structure to earthquake­

type excitations.

B.2 Hori zonta1 Response Measurements

Absolute accelerations and relative 9;splacements were measured on

each of two frames which composed the test structure (Fig. 3.1). Waveforms

measured during the first simulated earthquake on each frame at levels

three, six, and nine are compared in Fig. B.l. Magnitudes of accelerations

measured during any earthquake simulation were essentially the same on

each frame at each level except for occasional peaks which could differ

by as much as ten percent. Magnitudes of displacements were found to

differ by a maximum of five percent. Despite these slight differences in

magnitude, waveforms plotted for a given level were nearly identical.

An accelerometer fixed to the tenth-level mass (Fig. 3.1) produced

the same acceleration waveform as observed for the tenth level of the test

frames. Therefore, the masses and frames can be assumed to have moved

i denti ca lly.

Page 171: By Jack P. t·loeh 1e and A. Sozen

159

B.3 Torsional Motions

Two accelerometers were fixed to the tenth level mass (Fig. 3.1) to

measure accelerations transverse to the line of input motion. The two

accelerometers were oriented so that response readings would be of the

same sign if the acceleration was torsional or of opposite signs if the

acceleration was caused by lateral sway of the test structure. Waveforms

obtained during the first simulated earthquake are plotted in Fig. B.2

(minor directional accel.) to a scale equal to that used for accelerations

in the figures for Chapter 4. Waveforms from other simulations were similar.

Most of the motion indicated in Fig. B.2 is torsional. The maximum measured

in any simulation was 0.13 g during the first simulation. A torsional

frequency of about three Hz could be obtained from the waveform.

B.4 Vertical Motions

Two accelerometers measured vertical accelerations at opposite ends

of the test structure (Fig. 3.1). Waveforms obtained during the first

earthquake simulation are plotted in Fig. B.2. Waveforms from other

simulations indicated increasing vertical acceleration with increasing

base motion intensity. The peak vertical acceleration was 0.18 g during

the third earthquake simulation. None of the obtained waveforms indicated

a definite rocking frequency of the test structure. nor were all accelera­

tions of a rocking nature. Accelerations of the same sense were often

evident at any given time. It is possible that vertical accelerations

measured on the test structure were induced by like accelerations of the

simulator test platform. However. this cannot be confirmed because vertical

accelerations of the test platform were not measured.

Page 172: By Jack P. t·loeh 1e and A. Sozen

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Page 173: By Jack P. t·loeh 1e and A. Sozen

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Page 174: By Jack P. t·loeh 1e and A. Sozen

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