REPORT NO.

EERC 76-12

FEBRUARY 1976

IPB 262 85S·

EARTHQUAKE ENGINEERING RESEARCH CENTER

SENSITIVITY ANALYSIS FOR HYSTERETIC DYNAMIC SYSTEMS: THEORY AND APPLICATIONS

by

D. RAY K. S. PISTER

E. POLAK

A report on research sponsored by the National Science Foundation

COLLEGE OF ENGINEERING

UNIVERSITY OF CALIFORNIA • Berkeley, California

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11. Report No. EERC 76-12

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5. Report Date

Sensitivity Analysis for Hysteretic Dynamic Systems: February 1976 Theory and Applications

7. A uthor(s)

D. Ray, K. S. Pister and E. Polak 9. Performing Organization Name and Address

Earthquake Engineering Research Center University of California, Berkeley 1301 So. 46th Street Richmond, California 94804

12 Sponsoring Organization Name and Address

National Science Foundation 1800 G Street, N. W. Washington, D. C. 20550

15. Supplementary Notes

16. Abstracts

6.

8. Performing Organization Rept. No. 76-12

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11. Contract/Grant No.

AEN 73-07732-A02

13. Type of Report & Period Covered

14.

Sensitivity analysis, Calculation of the rate of change of response variables with respect to design variables, is a critical corrtponent in the process of re-analysis for improvenent of trial designs or in seeking an optimum design. This report presents necessary theorems and provides details for numerical comDutation of sensitivity matrices for spatially discretized structural systems subjected to dynamic excitation. General results are presented for nonlinear (hysteretic) structures and explicit numerical examples illustrate the methodology applied to multi-story shear frames whose force-displacement relationship is bilinear hysteretic.

17. Key Words and Document Analysis. 170. Descriptors

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SENSITIVITY ANALYSIS FOR HYSTERETIC DYNAMIC

SYSTEMS: THEORY AND APPLICATIONS

by

D. Ray K. S. Pister

E. Polak

Prepared under the sponsorship of

National Science Foundation

AEN73-07732-A02

Report No. 76-12

Earthquake Engineering Research Center

College of Engineering

University of California

Berkeley, California 94720

February 1976

. IlL

ABSTRACT

Sensitivity analysis, calculation of the rate of change of response

variables with respect to design variables, is a critical component in

the process of re-analysis for improvement of trial designs or in seeking

an optimum design. This report presents necessary theorems and provides

details for numerical computation of sensitivity matrices for spatially

discretized structural systems subjected to dynamic excitation. General

results are presented for nonlinear (hysteretic) structures and explicit

numerical examples illustrate the methodology applied to multi-story

shear frames whose force-displacement relationship is bilinear hysteretic.

1. INTRODUCTION

For the purpose of analysis and design for dynamic loads, it is

customary to idealize complex structures as spatially discrete dynamic

systems whose degrees of freedom are associated with motion of a finite

set of nodal points, at which are represented mass, damping and internal

restoring force properties of the components of the structure. In gen-

eral spatial discretization is most easily carried out by employing the

finite element method, although in cases such as rigid frames, discretiz-

ation into beam and column elements follows in an obvious manner. For a

wide class of problems the resulting equations governing dynamic behavior

of the now-idea1i:zed structure can be put in the form

C[)[S,Z(S,T),t] = ° t E [O,t], t E [O,T] (1.1)

with initial conditions

z (s, 0) = 0,

* where z(S,t) denotes the N-dimensional state vector of the system at time

t, C[) is a differential or integro-differentia1 operator defining

system dynamics and S is a P-dimensional time-invariant parameter vector

characterizing both the properties of the structure as well as those of

the forcing function producing motion. For example, we may consider S

to be partitioned into sub-vectors which respectively characterize dis-

tribution of mass, geometric properties of structural components, con-

stitutive properties of materials and amplitude, frequency and

* In typical application, z is composed of ordered sets of displacements and velocities of nodal points; readers unfamiliar with this representation may find a discussion such as that contained in [1] helpful. State space formulation of the problem facilitates treatment of basic theorems under­lying the work as well as unifying results with those of other areas of application.

-2-

stationarity characteristics of the exciting force system. Here we

will postpone giving examples in favor of describing the general structure

of the problem and the significance of sensitivity analysis. Returning

to (1.1) we note that the present value of the state vector may depend

on the past history (path of evolution) of the dynamic process (such as

may occur in inelastic systems) and that T denotes the extent of the

time period of interest over which the system is observed.

In typical problems of prediction of structural response the vector

S is completely prescribed; i.e., distribution of mass, length and area

of members and their mechanical behavior as well as the dynamic excitation

function are given and the problem is to obtain the state vector as a

function of time (for the prescribed S) by direct numerical integration

of (1.1). Here we are interested in an inverse problem associated with

(1.1), applications of which are found in mathematical modeling of mechanical

behavior of structural components, optimal synthetic design or simply

conducting trade-off studies in attempting to achieve an improved (not

necessarily optimal) design of a structure. A common element in each of

these activities is sensitivity analysis, i.e., the capability to compute

efficiently the change in structural response (values of the state vector)

associated with changes in the parameter vector. In our problem format,

since both z and S are vectors, the resulting set of partial derivatives

constitutes a sensitivity matrix of size NxP whose elements are functions

of time and the parameter vector S.

A problem format including both mathematical modeling (parameter

identification) and optimal design is the following: Find

min f[S,z(S,t)] , t E [O,T] (1.2) S

-3-

subject to the system dynamics (1.1) and a set of constraints

q[B,z(B,t)] < 0, t E [O,T], (1. 3)

where the dimension of the vector q is M.

The objective, or cost function (1.2) in the case of a parameter

identification problem represents an error measure between a s.et (or sets)

of observed data and the prediction of a hypothesized mathematical model

whose parameter vector B is to be adjusted to minimize the error.

Equation (1.1) defines the dynamic properties of the test configuration

for which data are collected and constraints (1.3) reflect natural or

imposed limitations on values of the parameter and state vectors. Readers

interested in more specific details of this class of problems in the

context of structural mechanics may consult 14J. In design applications

undetennined components of 8 are usually taken to be member cross-sectional

areas (or functions thereof), while the components of 8 associated with

mass, member length and constitution, and input are prescribed. Here the

objective function (1.2) is some measure of cost of the structure, (1.1)

continues to govern dynamic response of the structure and (1.3) prescribes

limits on structural response, e.g., maximum stresses or displacements

in the structure. ~fihether dealing with the objective function or

constraints, in either the problem of identification or design, it is clear

that to calculate changes in cost or constraints, it is necessary (or at

least helpful)* to be able to calculate the sensitivity matrix ;~ .

For example, in executing the search procedure for an optimal design

* In direct search methods such calculations are not reqUired. In gradient methods and for trade-off studies, efficient calculation of the sensitivity matrix is demanded.

-4-

using a method of feasible directions, computations of gradients of

'active' constraint functions are required, I2]. Referring to (1.3), dq.

this calls for the major computational task of evaluating as~ CS,z(S,t)) J

for each constraint q. for which (1.3) is an equality. One method of ~

evaluating these gradients is by first obtaining ~~ (S,t), t E [O,T] as

the solution of a system of (NxP) matrix equations, called perturbation

equations, (see Appendix A) resulting from employing linear perturbation

analysis on the dynamic equations of motion (called system equations),

[2]. Then, premultiplying this matrix by t; (z(S,t)) provides the

required gradients. Since the dynamic equations of the system and the

perturbation equations have the same form, substantial savings in

computation time can be effected by carrying forward the solution of these

equations simultaneously; see II] for examples. In the sequel this

approach is associated with the term "first implementable form."

For maximum computational efficiency under certain circumstances it

is preferable to employ a second method of evaluating the sensitivity

matrix (and gradients of active constraints) in which use is made of the

adjoint of the perturbation equation, a vector equation with dimensions

(Nxl); in the sequel this approach is identified with the "second

implementable form." To give illustrations in which the choice of

implementable form is important, in an optimal design problem the optimal

structure is likely to be associated with a set of "tight constraints,"

i.e., most constraint functions will be active and the full sensitivity

matrix is required, necessitating use of the first computational method.

On the other hand if a trial design is far from optimal, with few

constraints active, or if one wishes to make selective comparisons of

design changes, the latter method is obviously superior from a computational

-5-

standpoint.

For linear system dynamics it is possible to give explicit results

for the calculation of sensitivity matrices, as shown for example in [1].

However, for nonlinear systems no such results are available. Therefore,

the purpose of this report is to present necessary theorems and provide

details enabling numerical computation of sensitivity matrices for

discretized dyna~Lc systems whose material properties are hysteretic.

The basic theorems for the perturbation equation and its adjoint,

applications of which were qualitatively discussed above, are contained

in Appendix A. For analytical simplicity these equations are given in

state-space representation of the system dynamics. In section 2 the

results obtained in Appendix A are transcribed into the more familiar

second-order integro-differentia1 format in order to take advantage of

symmetry in the mass, damping and tangent stiffness matrices. Explicit

representations of sensitivity equations are presented for a multi-story

shear frame with a bilinear, hysteretic force-displacement relationship,

subjected to earthquake ground motion and for which the parameter vector

components are moments of inertia of the column cross-sections of each

story. Alternative methods for calculating elements of the sensitivity

matrix are illustrated choice of which depends on the number of constraints

active at the particular stage of the design process. Section 3 describes

a numerical treatment of the material presented in the preceding sections,

while a discussion of the results for example problems appears in Section 4.

2. IMPLEHENTABLE SENSITIVITY ANALYSIS

2.1. Introduction

The theorems and corollary for calculating sensitivity matrix elements

-6-

presented in Appendix A appear in general form. Specialization for

particular structural systems and member force-deformation relationships

* provides the necessary detail to yield corresponding implementable forms

for applications. In this section the structural system chosen for

illustrative purposes is a shear-type frame with a bilinear force-deformation

relationship between story shear force and relative story drift see

Figure Al(b). The first theorem and corollary appearing in the Appendix

will be transcribed to yield two implementable forms, with a direct

transformation of the result given in Appendix (A-2) producing an alternative

numerically favorable to the particular structural model and force-

deformation relationship chosen here. Finally, it should be recognized

that the selections of structural system and hysteretic model, while

simplifying, are not formally restrictive on the field of application of

the basic theorems presented in the Appendix. Sensitivity equations for

other structural models, such as a rigid frame with flexible girders, or

other hysteretic material models, can be obtained in a similar fashion.

Before proceeding it should be recalled that the first form provides the

full sensitivity matrix by solving a system of (NxP) matrix equations

while in the second method the elements of the sensitivity matrix can be

calculated a row at a time by solving a vector equation of dimension

(Nxl) , where Nand P are the dimensions of the state vector and design

vector, respectively.

2.2. Structural System and Transcription of System Equations:

Structural Model - The form of equations and the ease with

* By implementable is meant computationally feasible.

-7-

which one can perform numerical analysis of the dynamic system equations

(1.1), (or alternatively (A-6) for the perturbation equations) depends

to a large extent on the model chosen for the hysteretic force-deformation

relationship of the structure. Although the bilinear model chosen here

has certain elements of simplicity, most of the algebraic and computational

complications of the sequel are a result of the fact that the tangent-

stiffness matrix :is discontinuous when a particular structural element

first yields, unloads from a plastic state or subsequently yields upon

re-loading. The reader should separate this largely "book-keeping"

complication from the logical structure underlying sensitivity analysis.

It is assumed that the structure is comprised of columns whose

cross-sectional area and elastic section modulus are continuously

differentiable functions of the moment of inertia of the cross-section,

[2]. Thus, the parameter vector, 6, for an N-story, one-bay, shear-type

( )T E N frame as shown in Fig. 1 can be expressed as S = 11 ,12"", IN JR +'

where for each i, I. is the moment of inertia of the cross-section of ~

a column with respect to its strong axis. As noted in section 2.1, we

adopt a bilinear structural model illustrated in Fig. A1(b). Let

t.(6), i E {1,2, .•. ,J} with t (6) = 0, be the set of points in time domain ~ 0

[O,T] at which any element of the structure's tangent-stiffness matrix

changes. For any t E [tj(S),tj +1 (6)] C [O,T], j = O,l, •.• ,J, the tangent­

stiffness matrix, denoted by Kj(S), remains constant and continuously

differentiable in 6. The transition points, t.(S), i E {1,2, ••• ,J} ~

correspond to changes in any or all element stiffnesses caused, either

by yielding of elements, or, by unloading and reloading of yielded

elements, or, both.

A Rayleigh damping matrix is considered in the sequel, i.e.,

-8-

(2.1)

where ao(S) and aleS) are determined by specification of only two modal

damping ratios and solving the system of two equations:

W(S) a(S) = 2E; (2.2)

where

1

W(S) = 1

T a(S) = (ao(s),al(S») , is the undetermined coefficient vector,

T ~ = (~1,E;2) , is the specified modal damping ratio vector, and M is the

diagonal mass matrix, assumed independent of S. The equation of motion

of such a system, initially at rest and subsequently subjected to

horizontal ground motion of acceleration, lig(t) E CO[O,T], may be

expressed as

Mli(S,t) + C(S) u(S,t) + Kj

(S)u(S,t) = -t [Ki-l(S)-K\S)] u(S,t. (13») ~l 1

u(B,O) = ° u(S,O) °

~

- Mlll (t), g

t E (tj(S),tj+l(S)] C (O,T],

¥j E {O,l, ••. ,J} (2.3)

where U(S,t), u(S,t) and u(S,t) are system acceleration, velocity and

-9-

displacement vectors relative to the base motion and 1 E'~N with

all components unity. We now relate the state vector z to the motion

u. In (A-4) let

with N = 2N

, :Vi E {O,l, •.. ,J}

and

(2.4)

Then, (A-4) yields, after integration, the system equation of motion

~.3)and corresponding initial conditions. Let F (S,t) be the restoring s

force vector whose ith component, F .(S,t), denotes the spring force s~

associated with the ith degree of freedom; let F(S,t) be the vector of

story shear force and x(S,t) be the relative ~tory drift vector. Define

L to be a constant, lower bidiagonal matrix with all diagonal terms 1

and lower first off-diagonal terms -1; all other terms are O. Then, for

a shear-type frame it follows that

and

T F (S,t) = L F(S,t), s

x(S,t) = Lu(S,t),

T . = L '[kJ]L

where,

-10-

(2.5)(i)

(2.5)(ii)

(2.5) (iii)

F (S,t) s

(2.5) (iv)

and [kj

] is an (NxN) diagonal matrix whose ith diagonal term represents

the current ith story stiffness, which may be either the elastic or

post yielding stiffness of the story. Now, combining the results of

(2.3), (2.4) and (2.5), we have the following familiar equations of

motion:

Mu(S,t) + Cu(S,t) + Fs(S,t) = -Miu (t), t E rO,T] g

2.3. First Implementable Form

(2.6)

Differentiating (2.4) with respect to z and using definitions (A-16),

we obtain the 2Nx2N constant matrices

A(s) = ~! (S,z(S,t),t) t I

@ : I

= --------~----------® : -M-1cUn

I

(2.7) (i)

where ® is an (NxN) null matrix and

I is an (NxN) identity matrix,

and

ag i t <]) : G> B,(s) = --~-- (S,z(S,t» = ----------r---------1. oZ I 1.

0) I -M-l<?(S) I

(2.7)(ii)

for ¥s E (ti(S),ti+

l (13)]. Using (2.4), (2.7) and performing appropriate

integration in (A.6), gives the following transcribed perturbation

. . . . dU equation for calculating components of the sens1.t1.vl.ty matrl.X ai3 :

-11-

M ~~ (S,t) + C(S) ~~ (S,t) + Kj(B) ~~n (B,t) ~, ~ N

t [Ki-l(B)_Ki(B) J {~~ (13: t. (B)) + lieS, t. (B) ~~i (B)} i=l oP~ J.. J.. Of-'~

= -

j dKi - l dKi ClKj - L [--- (13) - - (B)] u(B, t. (B)) - - (13) u(B, t)

i=l dS~ ClS~ J.. dB~

dC (13) ti(S, t), ---

dB,Q, t E (tj(B),tj+l(S)] C [O,T], ~ E {1,2, ..• ,N}

dU (13,0) = 0

dB,Q,

dU (13,0) 0 = dBg,

(2.8)

It may be noted that at any transition time ties), i E {1,2, ... ,J} at

which stiffness transition is caused by yielding of an element,

dF s (13, t) is a dis can tinuous f unc tion of t \vi th the j lU11p given by

dS~

dF s + '"\0 (S,t.(S» Of-'~ J..

dt. u(s,ti(B» dBJ.. (B)

g,

(2.9)

For those t.(S) at which a transition is caused by reappearance of ].

elastic behavior of elements (due to unloading or reloading of yielded

elements) a reversal in direction of motion occurs corresponding to a

condition of zero velocity. In these instances the discontinuity in

dF s

dSg, (B,t) vanishes as can be noted from (2.9). In general, however, when

a transition is a combination of both conditions, no such simplification

results.

-12-

Finally, for convenience let

aF 9- s j au

Qs(8,t) = - (8,t) - K (8) ~ (8,t), aS9- ~9-

tEIO,T],

f2- E {1,2, ... ,N} (2.10)

Then, using (2.10), (2.5)(iv) and its derivative with respect to 139-

along with (2.9), we obtain from (2.8) the required first implementable

form for calculation of the sensitivity matrix ~~ ,

M _ ~(Q) • (Q) 9- (Q ) ~ u ~,t - Qs

~,t , a89-

t E rO,T],

9- E {l,2, ••• ,N} (2.11)

Evaluation of Q9-(8,t), t E rO,T], will be discussed in section 3 on s

numerical experimentation.

2.4. Second Implementable Form:

To transcribe the result given by the second theor~~ in Appendix

A-4 to second order form, the following relations must be introduced

to describe conditions for stiffness transitions:

yield condition - xC .(S,t) and xC .(S,t) denote the positive and py1. ny1.

negative yield drift, respectively, of story i at any time t E [O,T];

* then, defining t.(S), the time corresponding to first yielding of 1.

element i, i E {1,2, ... ,N}, we have,

* (a) for t < t. (8), i E {l, 2, •.• ,N} 1.

c x .(S,t) = x .(8), py1. y1.

(2.12) (i)

c x .(S,t) = - x .(8), ny1. y1.

-l3-

where

(b)

x .(13) is the initial yield drift for element i. y~

* for t > t. (13) ~

(i) for x.(S,t) > ~

c x .(S,t) py~

c x .(S,t) nyJ.

0,

x.(S,t), = ~

xi(S,t) - 2x . (13) , = yJ.

(ii) for x.(B,t) < 0, J.

c x .(S,t) = x.(S,t) + 2x .(13), py~ ~ y~

c x .(S,t) = x.(S,t). ny~ ~

(2.12) (ii)

(2.12) (iii)

unloading or reloading condition - For any tj(S), j E {1,2, ••• ,J}

at which element i, i E {1,2, •.• ,N}, unloads or reloads, i.e., the

corresponding element stiffness changes from post-yielding stiffness

to its elastic stiffness, we have,

X.(S,t.(S» = 0 J. J

Now, from (2.12), if the mth element yields at any t.(S), then ~

x (S,t.(S» = x.(S,t. (13) + 2x (13), for xm(S,t~(S» > 0 m]. ].]. ym .L.

m

= x.(S,t. (S» - 2x (13), for x (S,t.(S» < 0 ].]. ym ID]' m

(2.l3)

(2.14)

where t. (13) corresponds to the most recent time at which the mth element J. ID

is unloaded or reloaded.

Then, using definition (A-15)(i) and (2.4), we have, for

-14-

(2.15)

But using relation (2.5)(ii), (2.5)(iii) and differentiating (2.14) and

using (2.13), we have

. at. [K

i-

1(S)-K

1CS)] u(S,ti(S») as 1

(S) .Q.

where, N. C {1,2, ..• ,N} is the set of elements which have yielded at 1

t. (S) 1

Di(S) = -LT[l.Iki JL

(2.16)

v. (S) = LTrl.lkiJL 1 m (2.17) ill

and where tl.lkiJ is an (NxN) diagonal matrix in which all elements,

except those yielded at t.(S), are zero, with mth diagonal, 1

il.lki.J = k k, mEN .. mm em ym 1

Also, il.lkiJ is an (NXl~) diagonal matrix, in which all elements except m

mth element, mEN., are zero, and wiCS) = L T,/(S), where yi(S) is an 1

(Nxl) vector with

m ~ N. 1

(2.18)

with E = 0, +1, or +2, depending on whether the first positive or m

-15-

negative yield point is the same as the most recent unloading point,

i.e., yielding or subsequent positive or subsequent negative yielding,

respectively.

Now, definin.g

U. (13) ::: [----~---l---~---l 1 -1 I

(2Nx2N) -H Ui (S): @

-V. (8)

1m (2Nx2N)

and

(2.19)

from (2.15), we have, for t E (tj

(S) ,tj+

1 (S)]

. j. j { d R~(S,t) = 2: ;1(8) + 2: D.(S),,~ (8,t.(8»)

N i=l i=l 1 O~t 1

+ R(t-ti(S) 2: Vi (S) ~~ (S,t i (S»l (2.20) m~. m t m 'J

1

where R(·) is the Reaviside step function. Now, let us partition

pet,s) in (A-2s) as

pet,s) = (2Nxl)

P.1 (t, s)

(Nxl)

pz(t,s)

(Nxl)

-16-

(2.21)

Using definitions (2.4), (2.7), (2.17), (2.18), (2.21) and relations

(2.20), we have from (A.19), for any S E (tj(B),tj+l(B)] C [O,T]

Pl(t,s) = - t{{8(S-t.(B» U.(B)T + L: 8(s-t. (B» V1"m(S)T}M-1P2(t,ti )

i=l 1 1 nFN. 1m

with

and

with

and

Pl(t,t) = ° Pl(t,t) = ~ (u(e,t»T au

P2(t,t) = ~2(t,t) = °

~ (u(S,t» asg. (t . T

= )0 P2(t,s) r~(S,s) ds

1

Now, defining

" -1 pet,s) = M P2(t,s), s E [O,t],

the desired second implementab1e form results:

~ _ ~t ~ dB (u(S,t» - pet,s) riCe,s) ds, i E {1,2, ... ,p},

~ ° t E [O,T]

where pet,s) satisfies, for any s E (tj(S),tj +l

(S)] C [O,t],

Mp"(t,s) - C(Q) pACt,S) + Kj(Q) pACt ) - ~ (t ) I-> f.), S - -p 1 ' s ,

with p(t,t) = °

(2.22)

(2.23)

(2.24)

(2.25)

(2.26)

: (2.27) p(t,t) = 0

-17-

where r (t,s) is given by (2.22) with (2.25), and 1

= - t {[ClKi

-l

(s) - ClKi (S)J u(S,tJ..' (S» + ClKj

(S) u(S,s)l i=l ClS~ ClS~ ClS~ J

ClC j . - - (S) ti(S ,s) - 2: wJ..(S), s E IO, t]

as~ i=l (2.28)

Thus, (2.26) through (2.22), (2.25) (2.27) and (2.28) constitutes the

second implementable form.

2.5. Third Implementab1e Form:

A third implementable form follows by directly treating the

transcribed second order perturbation equation given by (2.8) as the

starting point. Let us define, for j E {1,2, .•. ,J}, the sets

Jj - {i E {1,2, ... ,j}lt.(S) caused by at least one element yielding} y J..

Jj _ {i E {1,2, ..• ,j}lt.(S) caused by at least one element unloading u J.. or reloading}

Fact: Jj U Jj - {I 2 J'} and Jj n Jj mayor may not be a null set. y u - " ••• , y u

Then, using (2.5), and differentiating (2.14), with fact (2.13), l;ve have,

from (2.8), for any s E [O,t], t E (tj(S),tj+l(S)] C IO,T]

a" au j .. 1 a M ~ (S,s) + C(S) as- (S,s) + [Ko + L: R(s-t. (13» [KJ..(S) - KJ..- (S)]] Cl~ (l3 ,s)

asQ, Q, i=l J.. Q,

= - E w. (S) . J.. (2.29)

iEJJ u

-18-

with

a au u (8,0) = - (8,0) aB~ as,Q,

0, ,Q, E {1,2, ... ,N}

where W.(S) = LTr~kiJ L and where rlkiJ is an (NxN) diagonal matrix ~

in which all elements, except those unloaded or reloaded, are zero,

- i with the mth non-zero diagonal given by r6k J = k -k and all other nnn ym em

terms have been defined. Performing the same mathematical operations

as used in the proof of the second theorem in Appendix A-4, we have the

desired third implementable form:

a ~t T ~ (u(S,t)) = pet,s) r,Q,(S,s) ds, t E [O,T]

,Q, ° (2.30)

where

r~(S,s) is given by (2.28)

and pet,s), for any s E (ti(S),ti+l(S)] C IO,T], t E (tj(S),tj+l(S)]

C [O,T], satisfies the equation

.. . Mp(t,s) - C(S) pet,s) + Ki(S) pet,s)

L: W~(S) 6 (s-t. (8) {r p(t,T) dT] kEJJ K t (8)

k u

L:j 1: vT (8) o (s-tn (8»[f p(t,T) dT] , n

ncIy mENk m m t (8)

n

with

p(t,t) = ° (2.31)

-19-

3. A NUMERICAL TREATMENT OF IMPLEMENTABLE FORMS

3.1. Introduction

This section describes the numerical analysis that has been

utilized to compute with the basic model of system dynamics and three

forms of equations for sensitivity matrix elements presented in

Section 2 for the bilinear hysteretic shear frame. The integration

scheme chosen for complete analysis (dynamic analysis and sensitivity

analysis) is the familiar linear acceleration step-by-step method, [1].

While it is clear that study of alternative integration schemes for

dynamic analysis of nonlinear systems constitutes an important research

problem in itself, we have not addressed this issue here in view of the

broader objective of the report.

3.2. SOLUTION OF SYSTEM EQUATIONS

Let f>t denote the time step of integration, then f>u(S,t), the

increment in displacement vector in time f>t for any t E [O,T] such that

t.(S) ~ [t,t+f>t], for Vi E {1,2, ••• ,J}, is given by the following 1.

system of linear algebraic equations:

* * K (S,t) t,u(S,t) = f>r (S,t)

where,

and,

K * (S , t+ t, t) -- (f> : 2 ) M + (t,3t ) c ( S ) + K (S , t+f> t )

* f>r (S,t) = ·-Mill (t+f>t) + Ma(S,t) + C(S) beS,t) - F (S,t) g s

K(S,t) is the structure tangent-stiffness matrix at t, and,

a(S,t) = (:~) u(S,t) + 2u(S,t)

b(S,t) = 2u(S,t) + (6;) U(S,t).

-20-

(3.1)

Equation (3.1) can be solved by any of the standard techniques, namely,

* direct methods based on decomposition of K (S,t), or, iterative methods.

* Observing that K (S,t) in (A.2) is symmetric and tridiagonal, the Jacobi

method with Cholesky decomposition [3] is considered the most efficient

choice for the computer coding developed for numerical experimentation

in the next section. For t.(S) E [t,t+~t], for i E J, J C {1,2, .•. ,J}, ~

the system equation reduces to system of nonlinear algebraic equations

which is solved by an iterative procedure similar to what may be termed

a backward secant method belonging to the general class of Newton-like

methods, details of which can be found in [1].

3.3. Solution of First Implementable Form

The solution of (2.11) for t E [O,T] likewise reduces to a system

of linear algebraic equations:

i{* ~~u (S, t) = R.'\ s, t) R,

where, K* = (~:2) M + (;t) C(B) + K(B,t+~t)

and

(3.2)

= M ~ (B,t) + C(S) ~bB (B,t) - ~ (B) U(B,t+~t) - Q~(B,t+~t) aB~ ~ aB~ s

Evaluation of Q~(B,t+~t) s

Let k~ and k~ be stiffnesses of element i corresponding to time t ~ 1.

and t + ~t, respectively; if Q2(S,t+~t) is the (Nxl) vector with

components defined as:

!t 3F. at-x. Q'. (Q,t+ht) 1. (Q t+At) kn ~ (Q t) ~ i-> I..l = aB

2 f.l, I..l - i <lB

t >-', ,

by (2.5)

Q2(B, t+~t) s

-21-

¥~ E {1,2, ... ,N} (3.3)

¥i E {1,2, ..• ,N} ,

(3.4)

Now, let K(S,t) change to K(S,t+t.t):

(i) for i E {1,2, .•• ,r}, the element stiffnesses remain unchanged,

i.e. ,

(ii) for i E {r+l,r+2, ••• ,r+m}, elements have yielded,

and k~ = k . ~ y~

i.e. ,

(iii) for i E {r+m+l,r+m+2, •.. ,N}, elements have unloaded or reloaded,

i.e., k . and k~ = ke~' y~ ~ ...

Then, Q~(S,t+~t), ¥i E {1,2, ... ,N}, are computed from ~

(i)

of. ~

= - (S,t) ()SQ.

for ¥i E {1,2, ... ,r}

-c (x.(S,t)-x .(S,t»

1. y1.

-c ox . )

-~ (S,t) oSQ.

for Vi E {r+l,r+2, .•• ,r+m}

¥i E {r+m+l,r+m+2, .•. ,N}

where,

(~

= x- .(S,t), py~

I~

= x- .(S,t), ny~

for ~x.(S,t) > ° ~

for ~x.(S,t) < 0, Vi E {1,2, ••. ,N} J..

Q. Thus, (3.4) and (3.5) enable one to evaluate Q (S,t), t E rO,T].

s

(3.5)

The derivative of the damping matrix C(S) with respect to i3 is obtained

by direct differentiation of (2.1); this, of course, requires derivatives

-22-

of the first two elastic frequencies, wl

CS), w2

(S), of the system.

Using results from [2]:

where

aW. l. (13)

dS t

i = 1,2,

vt E {1,2, ••• ,N}, (3.6)

~l(S) and ~2(S) are eigen-vectors corresponding to wl(S) and w2(8),

respectively.

ClF Th .. S (Q A) Cla (Q A)' d db (Q ) e quan tl. tl.es as- jJ , t+LI t 'as jJ , t+LI t an as jJ, t+!:J. t are updated

t t t from the recurrence relations:

ClF s (S,t+!:J.t) =

aS t

a!:J.u QsCS,t) + K(S,t+!:J.t) aS

t (S,t),

3a (~) dAu

(S , t) - 6 db (S, t) - 2 ~~ (S, t) , ClS t

(13, t+!:J.t) !:J.t2 21S t

(!:J.t) 21S t 21S t

ab (8, t+!:J.t) 9 Cl!:J.u (S, t) - 2~ (S, t)

!:J.t 2a = (!:J.t) (2) as- (S, t) , 21S t aS t 38

t t vt E {l,2, •.• ,N}

Remark: It is recognized from (3.2) that the solution at any time

t E [O,T] requires prior knowledge of !:J.u(S,t) for tLme step !:J.t at t,

(3.7)

hence prior solution of (3.1). Moreover, (3.1) and (3.2) have the same

* coefficient matrix K (S,t) for tieS) ~ [t,t+!:J.t], Vi E {1,2, .•• ,J} and

* -K (8,t+!:J.t) for tieS) E [t,t+!:J.t], Vi E J C {1,2, ••• ,J}. Thus, in the

former case, once the necessary decomposition is achieved for solution of

(3.1), it can also be utilized for solution of (3.2). In the latter

situation, decomposition for (3.2) can be utilized for (3.1) in the next

-23-

time step of integration, etc. In either case, recognition of this fact

forms the basis of the concept of a "complementary pair" that is essen-

tial for efficient solution of both system and sensitivity equations in

the first implement able form.

3.4. Solution of Second Implementable Form:

From (2.26), one observes that the differential equation must be

integrated backward from s=t to s=O; otherwise, it is a piecewise linear

differential equation. Assuming a linear distribution of ~(t,s) in time

interval s and (s-~s), where ~s is the time step of integration, knowing

the state at s, the state at s-~s can be determined from:

p(t,s-~s) = P (t, s) ~p,

p(t,s-.6.s) (2)~A .6.s p + b (s) (3.8)

p(t,s-.6.s) 6 A

a(s) = -(-)~p + ~s2

where,

a(s) - (~6s-) ~(t,s) 2p(t,s), (3.9)

b (s) . ~ ..

- -2p(t,s) +:f pet,s)

Then, one needs to solve the system of algebraic equations

A

K(s-~s)~p = ~a (3.10)

where,

6H + 3 K - [-- - C + K(f3,s-~s)] (.6.s)2 lls

and lid - K ( 6, s-lls ) + Ha (s)

-24-

Evaluation of Pl(t,s-~s) -

From (2.22), Pl (t,t)= [~ (u(S,t»]T

(i) For tieS) $ [s-~s,s], i E {1,2, ..• ,J}, Pl

(t,s) remains constant, i.e.,

. Pl (t,s-~s) = Pl(t,s)

(ii) For tiCS) E [s-~s,s], for any i E J~, by direct integration of

(2.22) from (s-~s) to s, we have

Pl(t,s) + U.(S)Tp(t,t.) 1. 1.

(iii) For t.(S) E [s ~s s] for any i E Jj i 1. -" u'

= k , for some k E Jj m Y

and some m E Nk , then,

= is 1 C t, s) + L: V k (S) p ( t, tk (S» rrENk m

i=k m

(iv) For t.(S) E [s-~s,s] for any i E Jj n Jj 1. Y u

Fact:

i\ (t, s-~s) = i\ (t, s) + U i (S) p ( t , t i) + L: V k (S ) p ( t , tk (S ) ) rrENk m

i=k m

j U. (13), V. (S), i E J y ' mEN. are all symmetric matrices. Then, 1. 1. 1. m

(2.26) can be integrated by any standard method, such as the trapezoidal

rule or Gaussian quadrature. It may be noted that r,Q, (S, s), s E [0, t],

required for evaluation of (2.26) needs to be calculated according to

(2.22) during integration of the system equations of motion and made

available for evaluation of (2.26) backward and in parallel with the

step-by-step integration of (2.27).

3.5. Solution of Third Implementable Form

The solution of (2.31) is effected in almost the same way as has

-25-

been done for the previous case, the difference occurring in the treatment

at stiffness transition times resulting from the nature of (2,31). It

must be noted that for t.(S) ~ rs-~s,s], the forcing function vanishes ~

and integration for the step is carried out with no difficulty, as already .

described. From (2.31), it is obvious that pet,s) is discontinuous in s

at t.(S), i E Jj

• But jumps in ~(t,s) due to these discontinuities are ~ u

easily computed by integrating (2.31) locally across discontinuity points;

then, integration is carried out by resetting the state at these discon-

tinuity points.

4. EXAMPLES AND DISCUSSION

4.1. Introduction

The intent of this section is to illustrate and compare the numerical

procedures developed in the preceding sections. The examples chosen

involve shear-frame structural models with bilinear force-displacement

relationships to illustrate inelastic dynamic response of a class of

seismically loaded structures. The problems chosen and the ensuing dis-

cuss ion serve to emphasize three main points concerning the role of

sensitivity analysis in the area of seismic design: (1) modification of

a given (not necessarily feasible) design to meet performance constraints

and to possibly attain an optimal design (2) selection of an algorithm

and numerical analysis scheme that is suited to the problem under con-

sideration and (3) estimation of relative costs of various available

schemes for carrying out the sensitivity analysis.

In searching for a feasible design of a structure subjected to a

strong-motion earthquake in which nonlinear response occurs it is necessary

to satisfy performance constraints of the type described in Sec. 1. Typically,

-26-

such inequalities can be written

q(s) - max Iq(S,z(S,t»1 < ° tElO, T]

(4.1)

It is important to note that, unlike the problem of meeting ~Qnstraints

for a linear model of a structure, it is impossible to remove time from

(4.1). (For a linear system maximum response is usually estimated by

the square root of sum of squares of modal maxima, thus removing time

as a parameter of the constraint.) Accordingly, the effect of changing

the design vector S in (4.1) becomes an important computational problem

for design. Depending on the properties of the structure and the earth-

quake acceleration history, it is evident that more than one maximizer

may exist in (4.1), i.e., more than one element may exist in the set tr defined by

0' :: {t E [O,T] Ilq(p,z(p,t» I = q(S)} (4.2)

Therefore, it is essential to be able to calculate efficiently values of

"* for t Eccr in order to make rational design changes in the structure.

Finally, it may be noted that the second and third implementable

forms given in Sees. 2 and 3 are variations of the same basic theorem.

Since experience shows that the latter form is numerically more efficient

for locating stiffness transition times, the subsequent discussion is

limited to applications of the first and third forms.

4.2. Structure and Loading Characteristics

The structural models chosen for illustrative purposes include two-

and eight-story shear frames (Fig. 1). As noted in Sec. 2, the parameter

vector p consists of moments of inertia of column sections of each story,

-27-

i. e.,

frame. The columns are assumed to be structural steel with yield stress,

o = 36 ksi and elastic modulus, E = 30 x 103 ksi; empirical relations y

among column cross-sectional area, A in in2, elastic section modulus, S

in in3 , and in terms of I in in4 are assumed as follows [2J:

A = 0.80r1

/2

}

S = 0.7813/ 4 (4.3)

Referring to the Rayleigh damping matrix introduced in Sec. 2, the required

modal damping ratios for both first and second modes are taken to be 5%

of critical, i.e., ~1 = ~2 = 0.05. The force-deformation relationship

between each story shear force and relative drift is assumed bilinear,

hysteretic. The post-yield stiffness is assumed to be 10% of the initial

stiffness. Basic data of the example frames are shown in Table 1. The

maximum stress in an elastic column at story i at any time t is given by

M.(I,t) P.

0i (l,t) = S~ (W + A. (~.) (4.4) ~ ~ ~ ~

The relative yield drift, x . (1.), for any story i, is obtained by setting y~ ~

0. ° and given by 1. Y

-1/4 0.1755P.I.-3/4 x . (1.) = 5.05441. -y1. 1. 1. J. J.

(4.5)

The earthquake ground motion selected for numerical experimentation is

the North-South component of 1940, the El-Centro earthquake.

If x (S,t) is the relative drift at story m, m = 1,2, .•. ,N, the m ax

results presented are limited to presenting values of the matrix aSm (S,t), R-

m = 1,2, ..• ,N; ~ = 1,2, ..• ,N; t E [O,T]; note that q(u(S,t» of Sec. 2.4

and 2.5 is identic~l to (em)Tu(I,t), m = 1,2, ••• ,N; where, em is an (Nx1)

'::'28-

r .. ~

~

VA

RIA

BLE

S

STO

RY

STO

RY

HEI

GH

T (i

n)

STO

RY

2 M

ASS

(K-s

ec

lin

)

STO

RY

COLU

MN

LOAD

(K

)

COLU

MN

MOH

ENT

OF

4 IN

ER

TIA

(in

)

ELEM

ENT

STIF

FNE

SS

(K/i

n)

YIE

LD

DR

IFT

(in)

2-ST

OR

Y

FRAM

E

1 2

180

180

.20

8

.20

8

80

40

200

120

24

.69

1

4.8

1

1.

08

1. 3

3

8-ST

OR

Y

FRAM

E

1 2

3 4

5 6

7 8

180

180

180

180

180

180

180

180

.20

8

.20

8

.20

8

.20

8

.20

8

.20

8

.20

8

.20

8

I

320

280

240

200

160

120

80

40

I

1880

18

80

1280

12

80

680

680

380

380

23

2.1

0

23

2.1

0

15

8.0

2

15

8.0

2

83

.95

8

3.9

5

46

.91

4

6.9

1

0.5

7

0.6

0

0.6

5

0.6

8

0.7

8

0.8

3

0.9

8

1.0

6

TABL

E 1

. B

ASI

C

DA

TA O

F EX

AM

PLE

FRA

MES

N

I:fj

v"

STOR

Y M

1 2 3 4 5 6 7 8 .

TIM

E AT

W

HIC

H

Ix (l

,t)1

m

IS

MAX

IMUM

t

,sec

m 5.2

1

5.2

3

5.25

6.0

6

2.08

2.0

6

2.1

8

2.42

i ..

1

28.3

7561

[27.

9506

9]

-1.1

2519

1

-3.7

7612

0

3.47

4651

1. 2

1411

2

[1.1

0539

3]

.868

5165

1.83

4193

[1.

7565

49]

2.28

1240

Clx m

A

5

COM

PONE

NTS

OF ()I~

(I,t

m)

x 10

,

i =

1,2

, •.•

,8

2 _

3 4

5 6

-4.8

0386

-1

0.26

950

-10.

2908

9 -1

.026

152

3.43

0299

[-4.

8519

86]

[-9.

5534

37]

[-9.

3535

12]

[-.5

0757

99]

[2.3

2195

1]

24.2

5340

-10~04949

-8.5

9289

9 5.

6767

48

5.64

4728

-3.9

2320

6 35

.091

41

-11.

5309

9 -1

3.70

655

8.46

7581

.894

2530

.1

6735

84

-lI0

.25

62

6

50.4

9412

7.

3745

68

-3.6

5684

4 -1

4.68

171

-12.

6156

8 32

6.51

96

-116

.717

8

[-3.

7349

16J

[-14

.809

34]

[-12

.665

20J

[326

.767

5]

[-11

7.74

19]

.018

4787

0 -1

. 73

8183

-.

9113

435

-78.

2129

9 19

6.39

76

-7.9

9358

0 -2

0.38

371

-10.

7627

6 -1

89.9

170

-38.

2052

9

[-8.

0526

27J

[-20

.472

37]

[-10

.806

41]

[-19

1.52

76]

[-36

.480

84]

3.86

7979

7.

5294

73

4.38

4918

18

.818

57

-12.

0259

5

TABL

E 2.

D

ERlV

ATI

VZS

OF

MAX

L.'ill

M R

EI ••

D

RIF

TS

FOR

8-ST

OR

Y F

RAM

E

~---.-----

7 8

~():;(

I,tm)!

!~ -1

3.91

871

10.9

0006

36

.945

6235

1

[-15

.795

271

[6.1

1388

2]

10.6

7863

17

.160

17

Q) ~

36.9

7536

23

.304

00

R

Z p:

:

80.9

3469

5.

2935

93

N

!'::

.......

-ri

o-i

,....

-179

.868

1 -9

9.16

624

w

C"

!-,1

0

:>.

+J

Wo-i

tJ

Z

II

[-17

9.42

78]

[-99

.345

04]

<J)

-ri

>

'--'

s II

-88.

0204

7 -9

.00

19

l8

,.. 0 N

~

=

!'::

:>.

1252

.640

39

.619

74

=

<II

Q)

Zp::R

'"0

[125

1.95

2]

[39.

3819

1]

-ri

o-i tJ

\U

;:l

173.

3286

-1

95.1

931

~

:>.

.+

vector given by

e~ ={: j f m, j f m - 1

j = m - 1 (4.6) J

1 j m

~ mT Obviously, in Sees. 2.4 and 2.5 is equal to (e ) . au

4.3. Numerical Results:

Tables 2 and 3 summarize the results for the eight- and two-story

frames; the derivatives of the mth story relative drift x (I,t) with m

respect to the design vector I are evaluated for times t , at which the m

relative drift assumes an absolute maximum in [O,T]. Bracketed values

have been obtained using the third implementable form while unbracketed

values result from use of the first form. Comparison between the two

methods of computation are limited to stories 1, 5 and 7 in the eight-

story frame. It will be noted in Table 4, in which required drift

ductility factors of each story are tabulated, that inelastic deformation

occurs in stories 5, 6 and 7; thus a numerical comparison of the two'

methods is shown for inelastic response quantities.

4.4. Discussion of Results

The computations leading to Tables 2 and 3 were based on an integra-

tion algorithm employing a linear acceleration assumption in each time-

step, with a time-step of 6t = 0.01 seconds -- both for dynamic analysis

and sensitivity analysis. In view of the similarity in structure of the

differential equations appearing in the implementable forms of sensitivity

analysis it appears that the integration time-step for sensitivity

analysis has as large an acceptable value as that for dynamic analysis,

provided that the forcing functions in the former case are adequately

-29-

TIME AT WHICH dX 3 m "-COMPONENTS STORY Ix (I,t) I is

OF as£ (I,tm)x10

M

1

2

STORY

M

1

2

3

4

5

6

7

8

m MAXIMUM, t sec £ = 1 2 m

.8982965 19.73316 4.465

[ .8476618] [18.69639]

-5.846570 28.99335 2.0325

[-5.847385] [28.99365]

TABLE 3. DERIVATIVES OF MAXIMUM REL. DRIFTS FOR 2-STORY FRAME

maxlx (I,t)1 III

REQUIRED t

(in) DUCTILITY

0.5575 0.9766

0.4979 0.8362

0.6140 0.9472

0.5199 0.7635

1.2411 1. 5934

0.8912 1. 0717

2.6873 2.7375

0.9139 0.8596

TABLE 4, MAXil'1UM: REL. DRIFT AND REQUIRED DUCTILITIES FOR 8-STORY FRAME

- 19 G1 -

represented by the choice of ~t. The results in Tables 2 and 3 support

this observation.

We turn next to the question of selecting an algorithm for sensitivity

analysis appropriate to the problem at hand. The underlying motivation

is that of applications to design. For the optimization problem (1.2)

introduced in Sec. 1, with constraint functions given by (4.1), one

needs to compute gradients at times when the functions assume extreme

values. If the number of active constraints is found to be small (as

would occur in early stages of the design process), the second and third

implementable forms are superior to the first in that only vector equations

need to be solved as opposed to matrix equations of higher dimensionality

required by the first form. This means that one can exercise selectivity

over the choice of what constraint gradients are to be calculated when

the second or third forms are used. On the other hand for a design

closer to optimal or a "fully constrained" design, it would be expected

that gradients of all constraints would be required -- thus suggesting

the use of the first form. It should be noted that if one is interested

only in the effect on maximum response of changes in selected members in

the structure, use of the second or third forms is obviously called for.

In this report we have stressed the use of certain algorithms for

calculation of the gradients of either the cost function or constraint

functions which are required in a method of optimal design of structures

subjected to dynamic loads. It is natural to seek a comparison of the

efficiency of these rather sophisticated methods with a direct finite

difference approximation of the gradient calculations. To this end let

Td denote the computation time required to perform the analysis of the

dynamic structural system (shear frame), i.e., the time required to solve

-30-

an (Nxl) dimension vector differential equation over the time interval

of interest [O,T]. Then, each component variation of the design vector

requires solution of two (Nxl) vector differential equations, resulting

in a total computation time for gradient evaluation of 2PTd

, where P is

the dimension of the design vector. An important limitation of the

finite difference approach to gradient calculation is that the entire

coupled system of gradients must be calculated to obtain anyone par-

ticular element of the sensitivity matrix unlike forms two and three

discussed in this report.

Finally, we turn to a discussion of the computation time required

for the forms used in the report. We limit our attention to the case

in which P=N, i.e., the dimensions of the design vector and the struc-

tural response vector are equal (as in the shear frame studied). In

this case the computation time for the finite difference scheme is 2NTd •

For the first implementable form, employing the "complementary concept"

which takes advantage of the fact that the operators for dynamic analysis

and sensitivity analysis are the same [1], the computation time '.is T -= .1

~ NTd , a factor of four faster than the finite difference solution of

the same problem.

Continuing, we may compare the cost of the second or third form with the

the first, provided that the system response vector is large enough to

make the comparison meaningful. Referring to (2.28), let T be the time r

required to compute rQ,(I,tm), Q, E fl,2, ••• ,N} and tmthe time at which xm(I,t)

attains a maximuul. Using the second or third implementable form, the required

1 tm computation time is T2,3 = (N + 1) (1:)Td + Tr' while the same computation

~3l-

t using the first form would require Tl ~ ; NTd(T

m). If the complementary

pair concept is employed

time is modified to T2~3

in using the second or third forms as well, the A

t ~ (1 + 1) (~)T + T. The choice between

N 2 T d r

these two computational forms will obviously depend upon the size of the

system as well as the characteristics of the particular problem, which

will govern the computation of T • r

4.5. Concluding Remarks

In this report we have presented a method and illustrated its

application to a critical problem in the design of structures subjected

to dynamic loading. For a general nonlinear force-displacement relationship

characteristic of elastic-plastic behavior of materials, we have obtained

formulas for calculating the rate of change of structural response

variables with respect to parameters incorporated in the structural model.

In particular, examples are given for a bileanear model of a shear trame,

for which both maximum story drift, as well as the rate of change of

maximum story drift with respect to changes in selected column sizes,

are calculated. It has been shown that the calculation of such sensitivity

matrices can be carried out simultaneously with the dynamic analysis of

the system. Unification of this work with an optimization algorithm

capable of handling functional constraints (such as maximum over time)

is currently in progress. Likewise, adaptation of the basic algorithm

for other types of hysteretic structural models as well as incorporation

of ground motion parameters is under study.

-32-

REFERENCES

1. Ray, D., "Sensitivity Analysis for Hysteretic Dynamic Systems:

Application to Earthquake Engineering," Report No. EERC74-5, Earth­

quake Engineering Research Center, University of California, Berkeley,

1974.

2. Ray, D., Pister, K. S., Chopra, A. K., "Optimum Elastic Design of

Earthquake-re.sistant Shear Buildings," Report No. EERC74-3, Earth­

quake Engineering Research Center, University of California, Berkeley,

1974.

3. Isaacson, E., Keller, H. B., Analysis of Numerical Methods., John

Wiley & Sons, Inc., New York, 1966.

4. Pister, K. S., "Constitutive Modeling and Numerical Solutions of

Field Problems," Nuc1. Engin. and Design, 28, 1974, pp. 137-146

-33-

APPENDIX A - HATHEMATICAL FORMULATION

A.I Introduction

Here are presented in state space formulation a mathematical char-

acterization of the bilinear hysteretic force-deformation relationship

and two general theorems leading to sensitivity analysis for response

quantities relative to a time invariant- parameter vector. A corollary to

the second theorem provides an alternative more suitable for subsequent

numerical treatment found in Sec. 3.

A.2 State-Space Characterization of a Bilinear Hysteretic Model

To illustrate hysteretic behavior of a framed structure, we restrict

ourselves to the simplest case, viz. the single story frame in Fig. Al-(a)

with bilinear hysteresis, as shown in Fig. Al-(b), where

F =j[tK(S,X(S)'X(S»X(S)dS' The change in slope (loading effect) at point

° a results from yielding of the columns, while, when the force is reduced

at b (unloading effect) the slope increases again. Note that if starting

from b the force is reduced to zero, the deformation does not reduce to

zero. The residual deformation is given by x = x • r

Now, let the solution of (1.1) or equivalently (2.3) at t, from the

initial condition Zo = (xO,xO) at time to be denoted by x(t,to'zO'S).

Then, assuming that we start at to = ° with Zo = ° and trace out the graph

in Fig. Al-(b) as the motion proceeds, we can compute the times tl(S),

t 2 (S), etc., where x(t,O,zO'S) is equal to Xy' x2 ' x3 ' etc. recursively,

as follows.

(i) To compute tl (S), we set K(S,x,x) = ke(S) in the equation of

motion (2.3) and compute x(t,O,O,S), and x(t,O,O,S). Then tl (S) is

obtained as the solution of the equation.

Al

~(S'X(t1 (13),0,0, S),x(t1 (13),0,0, B))

~ xCt1 (13),0,0, B) - xy(B) = ° (A.1)

(ii) To compute t2CS), we set K(S,x,x) == kyCS) in the equation of

motion and compute x(t,t1 CS), zl,B) for t ~ t 1 CS), where

z = 1 (x(t1 CS),O,O,B),x(tzCS),O,O,S)). Then tZ(S) is obtained as the solution 0

0~(S'X(tZ(S),t1(S)'Zl,S),xCtzCS),t1(S)'Zl,B)

x(tZ(S),t1 (B),zl'S) = ° (A. Z)

since the velocity at b must be zero. Thus, if we wish to compute t 1 (B),

t2

CS) simultaneously, we must solve an equation of the form

CA.3)

222 where t (B) = (t1 (B),tZ(B) and s (B,t (13),13) = (z(t1 (13),0,0,13),

z(tZ

(S),t1 (S),z(t1 (13),0,0,6),6)), z = (x,x), and i: JR.P x JR4 is defined

Z 1 Z componentwise as follows: 01 = 01 and 0z is as in (A.Z). Thus, we see

that we get relations of the type used in Appendix A.3.

A.3 First Theorem:

Let operatorC[) defined in (1.1) have the representation

C[)cs,zes. ·),t) == z(S,t) - fCS,z(B,t),t) - j[tg(.,B,zeS,.»d., t E [O,T] -0 -

with z (13,0) = 0. The function f: JR.P x lRN x 1Rl + JRN is continuous in t

and is continuously differentiable in Band z. The function g is defined

piecewise, as follows: gCt,S,z) = g.(S,z) for tEl., where I = ~ ~ ° J

[0,t1 CS)], Ii = (t:i CS),ti+1 CS)], i = 1,2, .•• ,J, and U I. = (O,T]. The i=l ~

t.(S) are the instants of time at which some components of xCS,t) pass ~

through a slope discontinuity in the appropriate force-deformation

hysteresis graph as notes in Appendix AZ. It is assumed that there are

AZ

J such points in [O,T]. The times t.(6) are determined by an implicit ~

i relationship, as follows. For i = 1,2, .•. ,J, let t (8) = (tl (6),t2 (6),

T i i T ••• ,ti(S» and let ~ (S,t (S» = (z(S,tl (S», z(6,t2 (6», .•• ,z(6,ti (8») •

Then, the Eorce-deformation-hysteretic-graph defines a set of functions . p N. .

""~.' JR. x JR. ~ ~ JR.1.,' 1 2 J h h f . 1 2 J v ~ 1. = , , ••• , , suc t at or 1. = , , ••• ,

(A.5)

It is assumed that the model for hysteretic behavior is such that the

cr i(. ,.) are continuously differentiable. Under these assumptions, the

following results hold.

Theorem: The solution z(S,t) of (1.1) of Sec. 1 with operator CO defined

by (A.4), is differentiable with respect to 6, with .~~ (S,t) computable,

column by column, as the solution of the following set of integro-

differential equations

d dZ af dZ It.a£ az dt (asQ, (S,t» = a;(S,z(S,t),t)~(S,t) + ° az (1:,S,z(S,1:»a-s(S,1:)d1:

t . df 1 ~ j at] + as-(6,z(6,t),t) + as (T,S,z(6,T»dT + G 8(3(S),

Q, 0 Q, Q,

tEl. C [O,T], Q, E {1,2, .•. ,P} ]

(A.6)

with initial condition

dZ as;:-(8,0) °

where Gj is a (Nxj) matrix with columns G~ defined, for i = 1,2, ••• ,j, by ~

+ 11 lim get. (8),13,z) g(t.(S)+e:,I3,z), and 1.

s-+O l.

s>O

G~ g(t.(6),8,z) - + = get. (S),S,z) (A. 7) 1. 1. 1.

A3

For a proof of thi.s theorem, see [1]. The proof is established in

exactly the same way as that of the differentiability of the solution

of a differential equation with respect to parameters, except that

instead of the Bellman-Gronwall lenuna, one must make use of the fol-

lowing generalization:

Lemma 1: Let h(t) be a scalar function such that

t rt t o < h(t) ~ A + ~[~ h(s)ds + J

O ~ h(l)dlds] (A.8)

where A and ~ are positive constants, t ~ 0, and h(t) is continuous in

t E [O,T]. Then,

aT h(t) ~ c(~)e (A.9)

~ where c(~) > 0 is a constant and a = +~ 2

i. e. , a is the positive

root of the quadratic equation:

2 a - a~ - ~ ° (A. 10)

For a proof of this lemma, see [1].

A.4 Second Theorem:

Let q(z(S,t) be a real-valued function where z(S,t) satisfies (1.1);

then, ~ (z(S,t), ¥t E rO,T], ¥~ E {1,2, ... ,P} are given by ~

~qs (z(S,t») == it p(t,s)Tr (S,s)ds, t E [O,T] ~ 0 ~

(A. 11)

where pet,s) satisfies the following integro-differential equation

d ds pet,s) 3f T ~ T It = -- az (S,z(S,s),s) pet,s) - 3z (s,S,z(S,s)) (

s p(t,T)dl)

. j . T it -- 2:s~(S) 8(s-t.(s))( p(t,T)dT),

. 1 ~ ~ ~= tieS)

A4

s E [O,t]

p(t,t) = t;(Z(S,t»T

and

df r~ (S,s) = as-(S,z(S,s),s)

t

where,

and

j - - th j S.(S) is the (NxN)i column of S (13) matrix partitioned as: ~

sj (13) [sj ( ): S~ ( ) : · j] defined by ... · s. , (NxN. ) I · ]

]

sj (S) - -Gj [acr~ a~~ ]-l[acr~] a~] at] dS]

i _Gi[dcr~ dr;~ ]-l[dcri

] msz. (13) -as~ dt~ assz.

and 8(0) is the Dirac a-function.

Proof:

(A.12)

(A.13)

Differentiating (A.5) with respect to St' ~ E {1,2, ..• ,p}, we have

i i i i i i ~(Q,) = - [~ EL]-l(2.L + dO'. fu) a6~ dl;~ at i a6~ al;~ t·

(A.14)

(ixl) (ixNi) (Nixi) (ixl) (iX1~i) (Nixl)

Defining

and

i noting that y~(S,ti(S» = ~@Q, in (A.14),

AS

we have,

where,

i mQ, (S)

(Nxl)

and i - - th Sk(S) is an (N~~) k submatrix of SiCS) defined as

SiCS) = _Gi[~a~ a~~]-I[aa~] and partitioned as CN~~i) a~l at 1 a~l

SiCS) = [S~(S):s~(S): .....• ls~(S)]. (NxNi (NxN) (NxN) (NxN)

For simpIici~y of expression we now define functions

where

B(t) _ B. (t) J

ago Bj(t) :: ~(t,f3,zCf3,t»,

A(t) = ~;(S,z(S,t),t) ,

Rj (6, t) = t s~ (S)y Q, (s, tk (S»

k=1

- af it ~ -l- j rQ,(S,t) = as;S,Z(S,t),t) + 0 asQ, (S,T,z(S,T»dT . mQ,(S)

(A.15) (ii)

(A.16)

Using (A.15) and definitions (A.16), (A.6) may now be expressed, for

s E (tjCS),tj+ICS»), as

Y,Q,(S,s) = A(s)yQ,(S,s) + ~s B(T)YQ,(S,T)dT

j . + 2: H(s-tk (S»sJ

k CS)Yn(S,t, (6» + r (S,s). k=1 x- K Q,

(A.I7)

A6

Fact: A(s), B(s) and rt(S,s) are piecewise continuously differentiable

functions of s E [O,t]. Premultiplying by an as yet unspecified (NxN) ,

nonsingular and differentiable matrix function, ~(t,s) and integrating

from 0 to t, we have, from (A.17)

~(t,s)y (S,s)ds = ~(t,s)A(s)y (B,s)ds + r ~(t,s)( B(T)Y(S,T)dT)ds i t it t 1s

o ~ 0 t )0 0 ~

j t j 1s . + <p(t,s)(LH(s-t.(s» S~(S)O(T-t.(S»Yn(S,T)dT)ds

o i=l 1. 0 1. 1.:Iv

+ lt~(t,s)r (S,s)ds o t

(A.18)

Now,

t r ~(t,s)y (S,s)ds Jo ~

t

= ~(t,t)y~(S,t) - J( ~(t'S)Yt(S,s)ds (A.19) (i)

and

it s ~(t,s)( ( B(T)Yt(S,T)dT)ds

o Jo

t it = 1 ¢(t,S) H(S-T)B(T)Y (6,T)dTds o 0 ~

t t

= 1 [f ~(t,s)dsJB(T)Y (S,T)dT o T ~

t t = 1 [1 q.,(t,-r)dT]B(s)y (S,T)dT

o s !?-(A.19) (ii)

by similar arguments as in (ii)

i t j 18 .

q.,(t,s)(LH(s-t.(B» S~(B)cS(T-t.)y (S,T)dT)ds o i=l 1. 0 1. 1. !?-

i t It j . = [ <p(t,T)dT] l:S~(S)8(s-t.)y (s)ds

o t.(S) i=l1. 1. Q, 1.

(A.19) (iii)

A7

Finally, let ~(t,s) satisfy

~(t,s) = - ~(t,s)A(s) - [j[t~(t'T)d~]B(S) S

j it . - L [ ~(t,T)d·r]S~(S)8(s-t.(S», i=l t.(S) :L 1

1

~(t,t) I (A.20)

then, using (A.19)(i), (ii) and (iii) and (A.20) in (A.lS), we have

Define

(A.22)

we have, then, from (A.20), (A.21) and (A.22),

(A.23)

where,

T T it ~(t,s) = -A(s) pet,s) - D(s) [ p(t,T)dT] s

- ~lS~(3)T8(S-t.(S»[It p(t,T)dT] L..J 1. 1. i=l t.(S)

1

(A.24)

p(t,t) = [t;(z(S,t»]T Q.E.D.

A.S Corollary:

Let ll-(z(S,t» in Sec. A.4 be given by (A.ll), (A.12) and (A.13); a 8 Q,

then, it is also true that

(A.25)

AS

where,

pet,s) satisfies the following integro-differential equation:

d2 _ T d ---2 pet,s) + A(s) -- pet,s) ds ds

- B(s)Tp(t,s)

j . T It d L:S~(S) 8(s-t.(S)( [--d p(t,T)] i=ll. 1. t.(S) T

1.

d T),

with s E [O,t]

p(t,t) = ° d - (t )l = il(z(Q t»T

ds p ,s =t oz ~, (A.26)

where all terms have already been defined.

Proof:

Define the following transformation on pet,s):

d: pet,s) = pet,s) sE [O,t]

p(t,t) ° (A.27)

Then, the required result (A.25), (A.26) follows directly.

Q.E.D.

A9

I I · I I · I ·

b--rr.,.-,-, .... -r-r-r"7'""7"""r'.7"7"1 i -1 I · I

~ .... ~~21 ~ .

~~~~~~~1 2 t=~ ~1 M ·

Xj(,8,t)

( b)

Ug (t)

(0)

FIG. 1 - STRUCTURAL ~10DEL

BI

RIGID FLOOR

(a )

F

(b)

b,.,,7

I I I I I I I

FIG. A-l - BILINEAR HYSTERETIC MODEL

EERC 67-1

EERC 68-1

EERC 68-2

EERC 68-3

EERC 68-4

EERC 68-5

EERC 69-1

EERC 69-2

'EERC 69-3

EERC 69-4 ,

EERC 69-5

EAR1~QUAKE ENGINEERING RESEARCH CENTER REPORTS

"Feasibility Study Large-Scale Earthquake Simulator Facility," by J. Penzien, J. G. Bouwkamp, R. W. Clough and D. Rea - 1967 (PB 187 905)

Unassigned

"Inelastic Behavior of Beam-to-Column Subassemblages Under Repeated Loading," by V. V. Bertero - 1968 (PB 184 888)

"A Graphical Hethod for Solving the Wave Reflection­Refraction Problem," by H. D. McNiven and Y. Mengi 1968 (PB 187 943)

"Dynamic Properties of McKinley School Buildings," by D. Rea, J. G. Bouwkamp and R. W. Clough - 1968 (PB 187 902)

"Characteristics of Rock Motions During Earthquakes," by H. B. Seed, I. M. Idriss and F. W. Kiefer - 1968 (PB 188 338)

"Earthquake Engineering Research at Berkeley," - 1969 (PB 187 906)

"Nonlinear Seismic Response of Earth Structures," by M. Dibaj and J; Penzien - 1969 (PB 187 904)

"Probabilistic Study of the Behavior of Structures During Earthquakes," by P. Ruiz and J. Penzien - 1969 (PB 187 886)

"NuIl1erical Solution of Boundary Value Problems in Structural Mechanics by Reduction to an Initial Value Formulation," by N. Distefano and J. Schujman - 1969 (PB 187 942)

"Dynamic Programming and the Solution of the Biharmonic Equation," by N. Distefano - 1969 (PB 187 941)

Note: Numbers in parenthesis are Accession Numbers assigned by the National Technical Information Service. Copies of these reports may be ordered from the National Technical Information Service, 5285 Port Royal Road, Springfield, Virginia, 22161. Accession Numbers should be quoted on orders for the reports (PB --- ---) and remittance must accompany each order. (Foreign orders, add $2.50 extra for mailing charges.) Those reports without this information listed are not yet available from NTIS. Upon request, EERC will mail inquirers this information when it becomes available to us.

CI

EERC 69-6

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EERC 70-1

EERC 70-2

"stochastic Analysis of Offshore Tower structures," by A. K. Malhotra and J. Penzien - 1969 (PB 187 903)

"Rock Motion Accelerograms for High Magnitude Earthquakes," by H. B. Seed and I. M. Idriss - 1969 (PB 187 940)

"Structural Dynamics Testing Facilities at the University of California, Berkeley," by R. M. Stephen, J. G. Bouwkamp, R. W. Clough and J. Penzien - 1969 (FB 189 Ill)

"Seismic Response of Soil Deposits Underlain by Sloping Rock Boundaries," by H. Dezfulian and H. B. Seed - 1969 (PB 189 114)

"Dynamic Stress Analysis of Axisymmetric Structures under Arbitrary Loading," by S. Ghosh and E. L. Wilson - 1969 (FB 189 026)

"Sei.smic Behavior of Multistory Frames Designed by Different Philosophies," by J. C. Anderson and V. V. Bertero - 1969 (PB 190 662)

"stiffness Degradation of Reinforcing Concrete Structures Subjected to Reversed Actions," by V. V. Bertero, B. Bresler and H. Ming Liao - 1969 (PB 202 942)

"Response of Non-Uniform Soil Deposits to Travel Seismic Waves," by H. Dezfulian and H. B. Seed - 1969 (FB 191 023)

"Damping Capacity of a Model Steel Structure," by D. Rea, R. W. Clough and J. G. Bouwkamp - 1969 (PB 190 663)

"Influence of Local Soil Conditions on Building Damage Potential during Earthquakes," by H. B. Seed and I. M. Idriss - 1969 (PB 191 036)

"The Behavior of Sands under Seismic Loading Conditions," by M. L. Silver and H. B. Seed - 1969 (AD 714 982)

"Earthquake Response of Concrete Gravity Dams," by A. K. Chopra - 1970 CAD 709 640)

"Relationships between Soil Conditions and Building Damage in the Caracas Earthquake of July 29, 1967," by H. B. Seed, I. M. Idriss and H. Dezfulian - 1970 (PB 195 762)

cz

EERC 70-3

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EERC 71-1

EERC 71-2

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EERC 71-4

EERC 71-5

"Cyclic Loading of Full Size Steel Connections," by E. P. Popov and R. M. Stephen - 1970 (PB 213 545)

"Seismic Analysis of the Charaima Building, Caraballeda, Venezuela," by Subcommittee of the SEAONC Research Committee: V. V. Bertero, P. F. Fratessa, S. A. Mahin, J. H. Sexton, A. C. Scordelis, E. L. Wilson, L. A. Wyllie, H. B. Seed and J. Penzien, Chairman - 1970 (PB 201 455)

"A Computer Program for Earthquake Analysis of Dams," by A. K. Chopra and P. Chakrabarti - 1970 (AD 723 994)

"The Propagation of Love Waves across Non-Horizontally Layered Structures," by J. Lysmer and L. A. Drake -1970 (PB 197 896)

"Influence of Base Rock Characteristics on Ground Response," by J. Lysmer, H. B. Seed and P. B. Schnabel - 1970 (PB 197 897)

"Applicability of Laboratory Test Procedures for Measuring Soil Liquefaction Characteristics under Cyclic Loading," by H. B. Seed and W. H. Peacock -1970 (PB 198 016)

"A Simplified Procedure for Evaluating Soil Liquefaction Potential," by H. B. Seed and 1. M. Idriss - 1970 (PB 198 009)

"Soil Moduli and Damping Factors for Dynamic Response Analysis," by H. B. Seed and 1. M. Idriss - 1970 (PB 197 869)

"Koyna Earthquake and the Performance of Koyna Dam," by A. K. Chopra and P. Chakrabarti - 1971 (AD 731 496)

"preliminary In-Situ Neasurements of Anelastic Absorption in Soils Using a Prototype Earthquake Simulator," by R. D. Borcherdt and P. W. Rodgers -1971 (PB 201 454)

"static and Dynamic Analysis of Inelastic Frame structures," by F. L. Porter and G. H. Powell - 1971 (PB 210 135)

"Research Needs in Limit Design of Reinforced Concrete Structures," by V. V. Bertero - 1971 (PB 202 943)

"Dynamic Behavior of a High-Rise Diagonally Braced Steel Building," by D. Rea, A. A. Shah and J. G. Bouwkamp - 1971 (PB 203 584)

EERC 71-6

EERC 71-7

EERC 71-8

EERC 72-1

EERC 72-2

EERC 72-3

EERC 72-4

EERC 72-5

EERC 72-6

EERC 72-7

EERC 72-8

EERC 72-9

EERC 72-10

"Dynamic stress Analysis of Porous Elastic Solids Saturated with Compressible Fluids," by J. Ghaboussi and E. L. Wilson - 1971 (PB 211 396)

"Inelastic Behavior of Steel Beam-to-Column Subassemblages," by H. Krawinkler, V. V. Bertero and E. P. Popov - 1971 (PB 211 335)

"Modification of Seismograph Records for Effects of Local Soil Conditions," by P. Schnabel, H. B. Seed and J. Lysmer - 1971 (PB 214 450)

"Static and Earthquake Analysis of Three Dimensional Frame and Shear Wall Buildings," by E. L. Wilson and H. H. Dovey - 1972 (PB 212 904)

"Accelerations in Rock for Earthquakes in the Western United States," by P. B. Schnabel and H. B. Seed -1972 (PB 213 100)

"Elastic-Plastic Earthquake Response of Soil-Building Systems," by T. Minami - 1972 (PB 214 868)

"Stochastic Inelastic Response of Offshore Towers to Strong Motion Earthquakes," by M. K. Kaul - 1972 (PB 215 713)

"Cyclic Behavior of Three Reinforced Concrete Flexural Members with High Shear," by E. P. Popov, V. V. Bertero and H. Krawinkler - 1972 (PB 214 555)

"Earthquake Response of Gravity Dams Including Reservoir Interaction Effects," by P. Chakrabarti and A. K. ChoprC\ - 1972 (AD 762 330)

"Dynamic Properties on Pine Flat Dam," by D. Rea, C. Y. Liaw and A. K. Chopra - 1972 (AD 763 928)

"Three Dimensional Analysis of Building Systems," by E. L. Wilson and H. H. Dovey - 1972 (PB 222 438)

"Rate of Loading Effects on Uncracked and Repaired Reinforced Concrete Members," by S. Mahin, V. V. Bertero, D. Rea and M. Atalay - 1972 (PB 224 520)

"Computer Program for static and Dynamic Analysis of Linear Structural Systems," by E. L. Wilson, K.-J. Bathe, J. E. Peterson and H. H. Dovey - 1972 (PB 220 437)

C4

EERC 72-11

EERC 72-12

EERC 73-1

EERC 73-2

EERC 73-3

EERC 73-4

EERC 73-5

EERC 73-6

EERC 73-7

EERC 73-8

EERC 73-9

EERC 73-10

EERC 73-11

EERC 73-12

"Literature Survey - Seismic Effects on Highway Bridges," by T. Iwasaki, J. Penzien and R. W. Clough -1972 (PB 215 613)

"SHAKE-A Computer Program for Earthquake Response Analysis of Horizontally Layered Sites/' by P. B. Schnabel and J. Lysmer - 1972 (PB 220 207)

"Optimal Seismic Design of Multistory Frames ," by V. V. Bertero and H. Kamil - 1973

"Analysis of the Slides in the San Fernando Dams during the Earthquake of February 9, 1971 / " by H. B. Seed, K. L. Lee, I. M. Idriss and F. Makdisi -1973 (PB 223 402)

"Computer Aided Ultimate Load Design of Unbraced Hultistory steel Frames," by M. B. EI-Hafez and G. H. Powell - 1973

"Experimental Investigation into the Seismic Behavior of Critical Regions of Reinforced Concrete Components as Influenced by Moment and Shear," by M. Celebi and J. Penzien - 1973 (PB 215 884)

"Hysteretic Behavior of Epoxy-Repaired Reinforced Concrete Beams," by M. Celebi and J. Penzien - 1973

"General Purpose Computer Program for Inelastic Dynamic Response of Plane Structures," by A. Kanaan and G. H. Powell - 1973 (PB 221 260)

"A Computer Program for Earthquake Analysis of Gravity Dams Including Reservoir Interaction," by P. Chakrabarti and A. K. Chopra - 1973 (AD 766 271)

"Behavior of Reinforced Concrete Deep Beam-Column Subassemblages under Cyclic Loads," by O. Kustu and J. G. Bouwkamp - 1973

"Earthquake Analysis of Structure-Foundation Systems," by A. K. Vaish and A. K. Chopra - 1973 (AD 766 272)

"Deconvolution of Seismic Response for Linear Systems," by R. B. Reimer - 1973 (PB 227 179)

"SAP IV: A Structural Analysis Program for static and Dynamic Response of Linear Systems," by K.-J. Bathe, E. L. Ivilson and F. E. Peterson - 1973 (PB 221 967)

"Analytical Investigations of the Seismic Response of Long, Multiple Span Highway Bridges," by W. S. Tseng and J. Penzien - 1973 (PB 227 816)

EERC 73-13

EERC ·73-14

EERC 73-15

EERC 73-16

EERC 73-17

EERC 73-18

EERC 73-19

EERC 73-20

EERC 73-21

EERC 73-22

EERC 73-23

EERC 73-24

EERC 73-25

EERC 73-26

"Earthquake Analysis of Multi-Story Buildings Including Foundation Interaction," by A. K. Chopra and J. A. Gutierrez - 1973 (PB 222 970)

"ADAP: A Computer Program for static a.'1.d Dynamic Analysis of Arch Dams," by R. W. Clough, J. M. Raphael and S. Majtahedi - 1973 (PB 223 763)

"Cyclic Plastic Analysis of structural Steel Joints," by R. B. Pinkney and R. W. Clough - 1973 (PB 226 843)

"QUlID-4: A Computer Program for Evaluating the Seismic Response of Soil structures by Variable Damping Finite Element Procedures," by I. M. Idriss, J. Lysmer, R. Hwang and H. B. Seed - 1973 (PB 229 424)

"Dynamic Behavior of a Multi-story Pyramid Shaped Building," by R. M. Stephen and J. G. Bouwkamp - 1973

"Effect of Different Types of Reinforcing on Seismic Behavior of Short Concrete Columns," by V. V. Ber1:ero, J. Hollings, O. Kustu, R. M. Stephen and J. G. Bouwkamp - 1973

"Olive View Medical Center Material studies, Phase I,ll by B. Bresler and V. V. Bertero - 1973 (PB 235 986)

"Linear and Nonlinear Seismic Analysis Computer Proqrams for Long Multiple-Span Highway Bridges," by W. S. Tseng and J. Penzien - 1973

"Constitutive Models for Cyclic Plastic Deformation of Engineering Haterials," by J. M. Kelly and P. P. Gillis - 1973 (PB 226 024)

"DRAIN - 2D User's Guide," by G. H. Powell - 1973 (PB 227 016)

"Earthquake Engineering at Berkeley - 1973" - 1973 (PB 226 033)

Unassigned

"Earthquake Response of Axisymmetric Tower Structures Surrounded by Water," by C. Y. Liaw and A. K. Chopra -1973 (AD 773 052)

"Investigation of the Failures of the Olive View stairtowers during the San Fernando Earthquake and Their Implications in Seismic Design," by V. V. Bertero and R. G. Collins - 1973 (PB 235 106)

EERC 73-27

EERC 74-1

EERC 74-2

EERC 74-3

EERC 74-4

EERC 74-5

EERC 74-6

EERC 74-7

EERC 74-8

EERC 74-9

EERC 74-10

EERC 74-11

EERC 74-12

"Further studies on Seismic Behavior of steel Beam­Column Subassemblages," by V. V. Bertero, H. Krawinkler and E. P. Popov - 1973 (PB 234 172)

"Seismic Risk Analysis," by C. S. Oliveira - 1974 (PB 235 920)

"Settlement and Liquefaction of Sands under Multi-Directional Shaking," by R. Pyke, C. K. Chan and H. B. Seed - 1974

"optimum Design of Earthquake Resistant Shear Buildings," by D. Ray, K. S. Pister and A. K. Chopra -1974 (PB 231 172)

"LUSH - A Computer Program for Complex Response Analysis of Soil-Structure systems," by J. Lysmer, T. Udaka, H. B. Seed and R. Hwang - 1974 (PB 236 796)

"sensitivity Analysis for Hysteretic Dynamic Systems: Applications to Earthquake Engineering," by D. Ray -1974 (PB 233 213)

"Soil-Structure Interaction Analyses for Evaluating Seismic Response," by H. B. Seed, J. Lysmer and R. Hwang - 1974 (PB 236 519)

Unassigned

"Shaking Table Tests of a Steel Frame - A Progress Report," by R. N. Clough and D. Tang - 1974

"Hysteretic Behavior of Reinforced Concrete Flexural Members with Special Neb Reinforcement," by V. V. Bertero, E. P. Popov and T. Y. Wang - 1974 (PB 236 797)

"Applications of Reliability-Based, Global Cost Optimization to Design of Earthquake Resistant Structures," by E. vitiello and K. S. Pister - 1974 (PB 237 231)

"Liquefaction of Gravelly Soils under Cyclic Loading Conditions," by R. T. i'long, H. B. Seed and C. K. Chan -1974

"Site-Dependent Spectra for Earthquake-Resistant Design," by H. B. Seed, C. Ugas and J. Lysmer - 1974

EERC 74-13

EERC 74-14

EERC 74-15

EERC 75-1

EERC 75-2

EERC 75-3

EERC 75-4

EERC 75-5

EERC 75-6

EERC 75-7

EERC 75-8

EERC 75-9

"Earthquake Simulator Study of a Reinforced Concrete Frame," by P. Hidalgo and R. W. Clough - 1974 (PH 241 944)

"Nonlinear Earthquake Response of Concrete Gravity Dams," by N. Pal - 1974 (AD/A006583)

"Modeling and Identification in Nonlinear Structural Dynamics, I - One Degree of Freedom Models," by N. Distefano and A. Rath - 1974 (PB 241 548)

"Determination of Seismic Design Criteria for the Dunmarton Bridge Replacement Structure, Vol. I: Description, Theory and Analytical Modeling of Bridge and Parameters," by F. Baron and S.-H. Pang - 1975

"Determination of Seismic Design Criteria for the Dunmarton Bridge Replacement Structure, Vol. 2: Numerical Studies and Establishment of Seismic Design Criteria," by F. Baron and S.-H. Pang - 1975

"Seismic Risk Analysis for a Site and a Metropolitan Area," by C. S. Oliveira - 1975

"Analytical Investigations of Seismic Response of Short, Single or Hultiple-Span Highway Bridges," by Ma-·chi Chen and J. Penzien - 1975 (PB 241 454)

"An Evaluation of Some Methods for Predicting Seismic Behavior of Reinforced Concrete Buildings," by Stephen A. Mahin and V. V. Bertero - 1975

"Earthquake Simulator Study of a Steel Frame Structure, Vol. I: Experimental Results," by R. W. Clough and David T. Tang - 1975 (PB 243 981)

"Dynamic Properties of San Bernardino Intake Tower," by Dixon Rea, C.-Y. Liaw, and Anil K. Chopra - 1975 (AD/A008406)

"Seismic Studies of the Articulation for the Dunmarton Bridge Replacement Structure, Vol. I: Description, Theory and Analytical Modeling of Bridge Components," by F. Baron and R. E. Hamati - 1975

"Seismic Studies of the Articulation for the Dumbarton Bridge Replacement Structure, Vol. 2: Numerical Studies of Steel and Concrete Girder Alternates," by F. Baron and R. E. Hamati - 1975

EERC 75-10

EERC 75-11

EERC 75-12

EERC 75-13

EERC 75-14

EERC 75-15

EERC 75-16

EERC 75-17

EERC 75-18

EERC 75-19

EERC 75-20

EERC 75-21

EERC 75-22

EERC 75-23

"Static and Dynamic Analysis of Nonlinear Structures," by Digarnbar P. r10ndkar and Graham H. Powell - 1975 (PB 242 434)

"Hysteretic Behavior of Steel Columns," by E. P. Popov, V. V. Bertero and S. Chandramouli - 1975

"Earthquake Engineering Research Center Library Printed Catalog" - 1975 (PB 243 711)

"Three Dimensional Analysis of Building Systems," Extended Version, by E. L. Wilson, J. P. Hollings and H. H. Dovey - 1975 (PB 243 989)

"Determination of Soil Liquefaction Characteristics by Large-Scale Laboratory Tests," by Pedro De Alba, Clarence K. Chan and H. Bolton Seed - 1975

"A Literature Survey - Compressive, Tensile, Bond and Shear Strength of Masonry," by Ronald L. Mayes and Ray W. Clough - 1975

"Hysteretic Behavior of Ductile Moment Resisting Reinforced Concrete Frame Components," by V. V. Bertero and E. P. Popov - 1975

"Relationships Between Maximum Acceleration, Maximum Velocity, Distance from Source, Local Site Conditions for Hoderately Strong Earthquakes," by H. Bol.ton Seed, Ramesh Murarka, John Lysmer and I. M. Idriss - 1975

"The Effects of Method of Sample Preparation on the Cyclic Stress-Strain Behavior of Sands," by J. Paul Mulilis, Clarence K. Chan and H. Bolton Seed - 1975

"The Seismic Behavior of Critical Regions of Reinforced Concrete Components as Influenced by Moment, Shear and Axial Force," by B. Atalay and J. Penzien - 1975

"Dynamic Properties of an Eleven Story Masonry Building," by R. M. Stephen, J. P. Hollings,· J. G. BoUwkamp and D. Jurukovski - 1975

"State-of-the-Art in Seismic Shear Strength of Masonry -An EVuluation and Review," by Ronald L. Mayes and Ray W. Clough - 1975

"Frequency Dependencies Stiffness Matrices for Viscoelastic Half-Plane Foundations," by Anil K. Chopra, P. Chakrabarti and Gautam Dasgupta - 1975

"Hysteretic Behavior of Reinforced Concrete Framed Walls," by T. Y. Wong, V. V. Bertero and E. P. Popov - 1975

EERC 75-24

EERC 75-25

EERC 75-26

$5.00 EERC 75-27

EERC 75-28

EERC 75-29

EERC 75-30

EERC 75-31

EERC 75-32

$4.00 EERC 75-33

EERC 75-34

$5.00 EERC 75-35

EERC 75-36

EERC 75-37

"TE!sting Facility for Subassemblages of Frame-Wall Structural Systems," by V. V. Bertero, E. P. Popov and T. Endo - 1975

"Influence of Seismic History on the Liquefaction Characteristics of Sands," by H. Bolton Seed, Kenji Mori and Clarence K. Chan - 1975

"The Generation and Dissipation of Pore Water Pressures DUJ::-ing Soil Lique faction, It by H. Bol ton Seed, Phillippe P. Martin and John Lysmer - 1975

"Identification of Research Needs for Improving a Seismic Design of Building Structures," by V. V. Bertero - 1975

(PB 248 136) "E"!laluation of Soil Liquefaction Potential during Earth­quakes," by H. Bolten Seed, I. Arango and Clarence K. Chan 1975

"Representation of Irregular Stress Time Histories by Equivalent Uniform Stress Series in Liquefaction Analyses," by H. Bolton Seed, L 1-1. Idriss, F. Makdisi and N. Banerjee 1975

"FLUSH - A Computer Program for Approximate 3-D Analysis of soil-Structure Interaction Problems,lI by J. Lysmer, T. Udaka, C.-F. Tsai and H. B. Seed - 1975

"ALUSH - A .Computer Program for Seismic Response A.,alysis of Axisymmetric Soil-Structure Systems," by E. Berger, J. Lysmer and H. B. Seed - 1975

"'I'RIP and TRA\-"'EL - Computer Progra.."llS for Soil-Structure Interaction Analysis with Horizontally Travelling Waves,u by T. Udaka, J. Lysmer and H. B. Seed - 1975

"Predicting the Performance of Structures in Regions of High Seismicity," by J. Penzien - 1975 (PB 248 130)

":t::fficient Fi."'1ite Element Analysis ·of Seismic Structure Soil - Direction," by J. Lysmer, H. Bolton Seed, T. Udaka, R. N. Hwang. and C.-F~)Tsai - 1975

"'J21e Dynamic Behavior of a First Story Girder of a Three­St:ory Steel Frame Subjected to Earthquake Loading," by., Ray W. Clough and Lap-Yan Li - 1975 (PB 248 84i)

"Earthquake Simulator Study of a Steel Frame Structure, Vc)lume II - Analytical Results I " by David T. Tang - 1975

"ANSR-I General Purpose Computer Program for Analysis of Non-Linear Structural Response," by Digambar P. Mondkar and Graham H. Powell - 1975

L 10

..

EERC 75-38

EERC 75-39

EERC 75-40

EERC 75-41

EERC 76-1

EERC 76-2

EERC 76-3

EERC 76-4

EERC 76-5

EERC 76-6

\ EERC 76-7

EERC 76-8

EERC 76-9

"Nonlinear Response Spectra for Probabilistic Seismic Design and Damage Assessment of Reinforced Concrete Structures I" by Masaya Murakami and Joseph Penzien 1975

"Study of a Method of Feasible Directions for Optimal Elastic Design of Framed Structures Subjected to Eart.'lquake Loading," by N. D. Walker and K. S. Pister - 1975

"An Alternative Representation of the Elastic-Viscoelastic Analogy I" by Gautam Dasgupta and Jerome L. Sackman - 1975

Effect of Multi-Directional Shaking on Liquefaction of Sands,·t by H. Bolton Seed, Robert Pyke and Geoffrey R. Martin - 1975

"Strength and Ductility Evaluation of Existing Low-Rise Reinforced Concrete Buildings - Screening Method," by Tsuneo Okada and Boris Bresler - 1976

"Experimental and Analytical Studies on the Hysteretic Behavior of Reinforced Concrete Rectangular a..-rd T-Beams," . by Shao-Yeh ~1arshall Ma, Egor P. Popov and Vitelmo V. Bertero - 1976 .

"Dynamic Behavior of a Multistory Triangular-Shaped . Building," by J. Petrovski, R. M. Stephen, E. Gartenbaum and J. G. Bouwkamp - 1976

"Eart."'quake Induced Defonnations of Eart.'" Da.l!'.s, 11 by Norman Serff and H. Bolton Seed - 1976

"Analysis and Design of Tube-Type Tall Building Structures 1 n

by H. de Clercq and G. H. Powell - 1976

"Time and Frequency Domain Analysis of Three-Dimensional Ground Notions, San Fernando Earthqual{e / " by Tetsuo Kubo and Joseph Penzien - 1976

"Expected Performance of Uniform Building Code Design Masonry Structures," by R. L. Mayes, Y. Omote,S. W. Chen and R. w. Clough - 1976

/

"Cyclic Shear Tests on Concrete Masonry Piers," R. L. Mayes, Y. Ornote and R. W. Clough - 1976

"A SUbstructure Method for Earthquake Analysis of Structure­Soil Interaction," by Jorge Alberto Gutierrez a..'1d Anil K. Chopra - 1976

C 11

EE:RC 76-10

EERC 76-11

EERC 76-12

"Si:abilization of Potentially Liquefiable Sand Deposits Using Gravel Drain Systems," by H. Bolton Seed, and John R. Booker - 1976

"Influence of Design and A.'lalysis Assumptions on Computed InE~lastic Response of Moderately Tall Frames, fI by G. H. Powell and D. G. Row -1976

"SEmsitivity Analysis for Hysteretic Dynamic Systems: ThE~Ory and Applications," by D. Ray, K. S. Pister and . E. Polak - 1976

C 12