SNS COLLEGE OF ENGINEERING

RESEARCH SEMINAR PRESENTATION 18.01.14

Dr.D.Vijayalakshmi.

Professor & Head

Department Of Civil Engg

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Research is Desire to face the challenge in solving the unsolved problems Desire to get intellectual joy of doing some creative work Desire to be of service to society Desire to get respectability. 2

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Logical theoretical Quantitative, experimental Qualitative, observational

Thesis Organization

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Research is your life, not your supervisor’s.

EXPERIMENTAL AND THEORETICAL STUDIES ON CONFINED STEEL CONCRETE COMPOSITE BEAMS

UNDER COMBINED BENDING AND TORSION

BY

D. VIJAYALAKSHMI(06ZA003)

Dr. R. Mercy Shanthi Dr. D. Tensing Joint Research Supervisor Research Supervisor

OUTLINE OF PRESENTATION Introduction Literature Survey Experimental Programme on CSCC beams Test Procedure and Test Results Analysis of Ultimate Strength of CSCC beams under

combined loading Evaluation of Test results Finite Element Analysis Discussion of Test Results Conclusions and Recommendations

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1. INTRODUCTION

General Composite Construction Steel Concrete Composite Construction Confined Steel Concrete Composite Beam

Concrete beam shuttered with cold formed steel sheet by means of shear connectors and top bracings

Research Methodology Research Schedule

7

RESEARCH SCHEDULEWork Plan

Material

study

TEST FOR1)

AGGREGAT

ES,2)

TENSION

TEST FOR

COLD FORMED SHEE

ET,3)

CUBE COM

PRESSION TEST

Element

study

BEAM UNDE

R 1)

PURE BENDING2)

PURE TORSI

ON3)

COMBINE

D BENDING AND

TORSION

Theoretical investigation

Generating equation for BM and TM

Numerical validation

Using finite element analysis

8

OBJECTIVES OF PRESENT STUDY Behaviour of CSCC beam under combined loading

(bending and torsion) Interaction equation between bending and torsion Effect of bending moment on the torsional strength Effect of shear connectors on the ultimate strength of

beam Effect of bond force on the ultimate strength of beam Effect of dimension of beam on the ultimate strength of beam Effect of spacing of bracing on the ultimate strength of beam Comparison of Deflection results with ANSYS

9

SCOPE OF PRESENT STUDY 32 Nos of CSCC beams - pure bending, pure torsion and

combined bending and torsion Beam size

150 x 230 x 2300mm and

150 x 300 x 2300mm Sheet thickness – 1.2 mm and 1.5 mm Bracings – 148 x 10 mm Spacing of bracings – 100 mm and 150 mm M25 grade of concrete Reinforcement: 2 nos of 8 mm diameter Mix ratio - 1:1.47:2.72 with W/C 0.45

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EXPERIMENTS ON BEAM ELEMENTS 32 beams under four groups

Method of construction-Fabrication of trough and concreting

The various parameters of test programme includes Thickness of sheet Crossection Spacing of bracing

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4. TEST PROCEDURE AND RESULT4.1 Pure Bending

Group A-8 beams Two point loading Test setup with instrumentation

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OBSERVATION

Initial separation of sheet First crack at 40% of ultimate load Propagation of crack, crushing of concrete, failure of

bracing and yielding of steel13

4.2 PURE TORSION Group D-8 beams Test setup

Test setup for Pure Torsion 14

OBSERVATION ABOUT THE BEHAVIOR OF BEAMS Diagonal cracks close to 45degrees at top Bracings act as ties and restrict the torsional deflection

and improves the torsional capacity Well defined failure

Separation of sheet occurs Inclined cracks develop at top and propagates to

longitudinal sides and crack widens followed by failure of connectors

Failure occurs at vicinity of bottom face and rotation about longitudinal axis near bottom face

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4.3 COMBINED BENDING AND TORSION Group B- 8beams 30% of ultimate theoretical torque

followed by the flexural load till failure Group C- 8beams 60% of ultimate theoretical torque

followed by flexure till failure. Test setup

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OBSERVATION ABOUT THE BEHAVIOR OF BEAMS Angle of twist and twisting moment increases linearly Sheets are separated first Bracing at top delays the failure Crack widens Rotation at failure occurs near the top face

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THEORETICAL INVESTIGATION5. ANALYSIS

Crack pattern under pure torsion

18

Failure of a piece of chalk under torque

Beam subjected to flexural moment and torsion

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MODES OF FAILURE

Idealised pattern for Mode 1 failure

Idealised pattern for Mode 2 failure

Idealised pattern for Mode 3 failure 20

Equation for Mt1

External moments are due to

1. Bending

2. Twisting

Internal moments are due to

3. Component of tensile force in the bottom sheet.

4. Component of tensile force along longitudinal reinforcement.

5. Component of tensile force in the side sheet.

6. Component of bond force at bottom between The concrete and sheet The concrete and connector

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5) Component of bond force at sides between The concrete and sheet The concrete and connector

From the equilibrium of internal and the external moments about an axis parallel to the neutral axis and located at mid-depth of the equivalent compression zone, the following equation is obtained

22

111112111

211111

11 mcqnrclpczfAMb

cM ytstbt

cdhh 01

101 2 c

b

hb

bK

23

)2

( 11011

xkhz

111

yst

ss

fA

ftbp

111

yst

BCCrstudstud

fA

fnnAq

111 2 ysy

BCS

fA

fbLr

b

xkh

m 211

1

211

201

11

xkh

b

Knl

Equation for X1

Forces considered to derive x1 acting perpendicular to the plane

which contains neutral axis and is perpendicular to the top face of the beams are;

1. Component of tensile force in longitudinal reinforcement

2. Component of tensile force in bottom sheet

3. Component of bond force at bottom between

a) The concrete and sheet

b) The concrete and connector

4. Force in concrete compression zone

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From the equilibrium of forces acting perpendicular to the plane which contains the neutral axis and is perpendicular to the top face of the beam, the following equation is obtained

25

211

1111

21

0111

1 85.0 Lkfc

cqrpbc

KbfA

xyst

bhCm 21

COMPARSION OF THEORETICAL AND EXPERIMENTAL RESULTS

Description No

Mode-1 Mode-2 Mode-3Exp values Predicted

mode of failure

Observed mode of failure

the the the

Mt Mb Mt Mb Mt Mb Mt Mb

A - Beams Subjected t o 0% Torque

A1 T1 2 0 51.10 0 36.90 0 16.20 0 52.20

MODE-1

A1 T2 2 0 52.20 0 40.50 0 18.40 0 50.52

A2 T3 2 0 82.40 0 40.60 0 30.70 0 60.20

A2 T4 2 0 83.50 0 44.60 0 31.20 0 75.00

B - Beams Subjected to 30% Torque and Bending till Failure

B1 T1 2 4.84 46.47 3.14 25.89 1.60 15.15 4.67 45.80

MODE-1

B1 T2 2 5.06 48.02 3.44 28.38 1.78 16.90 4.82 47.15

B2 T3 2 5.93 69.26 3.05 28.47 2.22 25.71 4.30 58.00

B2 T4 2 6.57 76.62 3.35 31.28 2.46 28.70 5.20 68.12

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Description No

Mode-1 Mode-2 Mode-3Exp values

Predicted mode of failure

Observed mode of failure

the the the

Mt Mb Mt Mb Mt Mb Mt Mb

C - Beams Subjected to 60% Torque and Bending till Failure

C1 T1 2 9.16 24.84 6.28 14.79 3.19 8.65 8.52 23.90

MODE-1C1 T2 2 10.12 27.49 6.88 16.22 3.56 9.66 9.49 26.78

C2 T3 2 11.87 39.57 6.12 16.20 4.42 14.69 9.10 38.40

C2 T4 2 13.13 43.78 6.72 17.87 4.92 16.40 9.15 41.84

D - Beams Subjected to 100% Torque and Zero Bending

D1 T1 2 15.27 0 10.47 0 5.32 0 14.84 0

MODE-1D1 T2 2 16.87 0 11.47 0 5.94 0 15.15 0

D2 T3 2 19.78 0 10.17 0 7.34 0 18.49 0

C2 T4 2 21.89 0 11.17 0 8.20 0 19.27 0

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CONCLUSIONS

BEHAVIOUR IN PURE BENDING Bracings at top delays the separation of sheet and there by

failure Followed by local buckling of sheet, formation of cracks and

crushing of concrete and yielding of steel The deflection varies linearly up to the yield point in pure

bending Local buckling of sheet starts at 40-50% of the ultimate load

at pure bending

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BEHAVIOUR IN PURE TORSION The bracings at top contribute significantly to the torsional

strength of the beam Failure observed in two stages – before cracking and after

cracking Before cracking behaviour is affected very little After cracking mode of failure is observed by width of

cracks and rotation at vicinity of the beam Cracks starts at 25-30% of ultimate torque value in pure

torsion and combined bending and torsion

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BEHAVIOUR IN COMBINED BENDING AND TORSION The composite beams subjected to combined bending and

torsion is characterized by three modes of failure The mode of failure predicted in the analysis do not agree

with the observed mode of failure Upward deflection in Group C beams In combined bending and torsion, both B and C group beam

exhibits Mode 1 failure. This may be due to the confinement of sheet on three sides and the interfacial bond between the concrete and connectors

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RECOMMENDATIONS The effect of shear is not accounted in generating the

equations of ultimate strength under combined loading. The research can be extended to include the effect of shear and the shear strength capacity of the connectors

The effect of placing the shear connectors at salient locations of the beam must be studied

The equations can be developed for the beams subjected to constant bending moment and applying twisting moment till failure

The equation can be developed to find the angle of twist under combined loading and comparison can be made for both theoretical and experimental value of angle of twist

The research can be extended with profiled sheeting as confinement

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Extension of analysis to formulate the design methodology of the composite beams under pure torsion and combined bending and torsion can be made

The beams can be tested for negative bending Extension of analysis to formulate the design methodology

of the composite beams under pure torsion and combined bending and torsion can be made

The beams can be tested for negative bending The cross-section other than the rectangular cross sections

can be tried for combined loading in composite beams

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