SNS COLLEGE OF ENGINEERING RESEARCH SEMINAR PRESENTATION Dr.D.Vijayalakshmi. Professor & Head Department Of Civil Engg

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EXPERIMENTAL AND THEORETICAL STUDIES ON CONFINED STEEL CONCRETE COMPOSITE BEAMS UNDER COMBINED BENDING AND TORSION BY D. V IJAYALAKSHMI (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 6

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 SCHEDULE Work Plan Experimental Study Material study TEST FOR 1) AGGREGATES, 2) TENSION TEST FOR COLD FORMED SHEEET, 3) CUBE COMPRESSION TEST Element study BEAM UNDER 1) PURE BENDING 2) PURE TORSION 3) COMBINED 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

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 11

4. TEST PROCEDURE AND RESULT 4.1 Pure Bending  Group A-8 beams  Two point loading  Test setup with instrumentation 12

OBSERVATION  Initial separation of sheet  First crack at 40% of ultimate load  Propagation of crack, crushing of concrete, failure of bracing and yielding of steel 13

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 15

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 16

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 17

THEORETICAL INVESTIGATION 5. ANALYSIS Crack pattern under pure torsion 18

Failure of a piece of chalk under torque Beam subjected to flexural moment and torsion 19

MODES OF FAILURE Idealised pattern for Mode 1 failure Idealised pattern for Mode 2 failure Idealised pattern for Mode 3 failure 20

Equation for M t1 External moments are due to 1. Bending 2. Twisting Internal moments are due to 1. Component of tensile force in the bottom sheet. 2. Component of tensile force along longitudinal reinforcement. 3. Component of tensile force in the side sheet. 4. Component of bond force at bottom between  The concrete and sheet  The concrete and connector 21

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

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Equation for X 1 Forces considered to derive x 1 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 24

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

COMPARSION OF THEORETICAL AND EXPERIMENTAL RESULTS DescriptionNo Mode-1Mode-2Mode-3 Exp values Predicted mode of failure Observed mode of failure the MtMt MbMb MtMt MbMb MtMt MbMb MtMt MbMb A - Beams Subjected t o 0% Torque A 1 T MODE-1 A 1 T A 2 T A 2 T B - Beams Subjected to 30% Torque and Bending till Failure B 1 T MODE-1 B 1 T B 2 T B 2 T

DescriptionNo Mode-1Mode-2Mode-3 Exp values Predicted mode of failure Observed mode of failure the MtMt MbMb MtMt MbMb MtMt MbMb MtMt MbMb C - Beams Subjected to 60% Torque and Bending till Failure C 1 T MODE-1 C 1 T C 2 T C 2 T D - Beams Subjected to 100% Torque and Zero Bending D 1 T MODE-1 D 1 T D 2 T C 2 T

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 28

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 29

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 30

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 31

 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 32

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