dissertation vinh 2010

Behaviour of Steel-ConcreteComposite Beams Made of Ultra

High Performance Concrete

Der Wirtschaftswissenschaftlichen Fakultatder Universitat Leipzig

DISSERTATION

zur Erlangung des akademischen Grades

Doktor-Ingenieur

(Dr.-Ing.)

vorgelegt von

M.Eng. Bui Duc Vinh

geboren am 07 April 1972 in Vinh Phuc - Vietnam

Leipzig, 9th October 2010

Foreword

This thesis was the results of a long hard working period of the author, is wouldnot have been possible without the contribution of a great number of people:

First of all, I would like to thank to my supervisor Prof. Dr.-Ing. habil. NguyenViet Tue for giving me the opportunity to join his research group and giving methis challenging research project. I had learn a lot of thing from many hoursdiscussion with him. He was not only always able to push up my spirits while Iwas in despair with my results but also sharing with me in sad moment which Ihad spent, and I am very grateful for that.

The experiments of this study could not have been performed without the helpand technical expertise of the laboratory personnel, as of Dipl.-Ing. Holger Busch,Dipl.-Ing. Immanuel Wojan and many staffs at MFPA-Leipzig for conducting theexperiments. I would like to express my thanks for their support.

My gratitude also goes to Dr.-Ing. Nguyen Duc Tung, Dr.-Ing. Jiaxin Ma,Dr.-Ing. Michael Kuchler, Dipl.-Ing. Jiabin Li, Dipl.-Ing. Stephan Mucha, Dipl.-Ing. Gunter Schenck etc. my colleagues in IMB (Institut fur Massivbau undBaustofftechnologie, Uni-Leipzig) for many valuable suggestions and discussionhours. Grateful appreciation is also due to Mrs. Sigrid Fritzsche and Mrs. SylviaProksch for their warm friendship and constant help during my stay in Leipzig.

I wish to thank the German Research Foundation (DFG- Deutsche Forschungs-gemeinschaft) for finance support the research project SPP 1182, which allowsme take up doctoral studies at University of Leipzig, Germany.

Last but not least, I want to sincerely thank my parents and especially my wifeVan Anh and son Nhan for their great support and patience during my study. Ihope in the future I can return all their love.

iv Foreword

Biography

Bui Duc Vinh was born in Vinh Phuc, Vietnam, on the 7th April 1972. In October1991 he started his studies in Civil Engineering at Ho Chi Minh University ofTechnology (HCMUT), where he received his Bachelor degree in 1996, specializein Coastal Engineering. He started joint Faculty of Civil Engineering (FCE),HCMUT and worked as research assistant. Two year after, 1998, he obtainedMaster Degree in Mechanic of Construction from University of Liege, Belgium.He continued his studies on structural engineering and focused on high strengthconcrete material, modelling of concrete structures.

In Dec. 2006, he jointed research team of Prof. Dr.-Ing. habil. Nguyen Viet Tue,at Institute for Structural Concrete and Building Materials, University of Leipzig(IMB, Uni-Leipzig). At here, his work concentrates on investigation structuralbehaviour of steel-concrete composite beams made of ultra high performanceconcrete. March 2010 he finished his dissertation under the supervision of Prof.Nguyen Viet Tue.

Leipzig, October 2010 Bui Duc Vinh

vi Biography

Dedicated to my parents, my wife Van Anh and my son Bui Hoang Nhan

viii Biography

Abstract

Ultra-High Performance Concretes (hereafter, UHPC) have high mechanicalstrengths (fc > 150 MPa, ft > 7 MPa) and exhibit quasi-strain hardening intension. Their very density improve durability and extend long service life. Thesteel-concrete composite beams with concrete slab made of UHPC possess ad-vanced properties give significant improvement in ultimate strength of the com-posite beams. The research reported in this thesis aimed to determine the perfor-mance and structural behaviour of composite steel-UHPC elements in bending.In addition, the continuous Perfobond based shear connectors that belong to thebeams was investigated as well.

The Experimental assessment of the shear connector was conducted through 11series Push-Out test with 27 specimens. In order to predict shear capacity, char-acteristic load-slip curves as well as contribution of constituents. The connec-tors without any reinforcement show very poor ductility, the characteristic slipreached lower 1.5mm only. They could be classified as non-ductile connector.The headed stud show better characteristic load-slip response, but this connec-tor often failed by shanked at the base of connector. The shear connector withadded reinforcement in front cover and dowel exhibits better performance thanheaded stud connection in both terms of load capacity and ductility. The testpointed out that embedded rebars in dowel play an important role in improve-ment performance of the connector. The contribution of steel fiber less importantthan and It is not obviously when steel fiber vary in range of 0.5% to 1.0%.

The structural response of the composite members under bending with the UHPCslab in compression was investigated with four points bending test of six full scalecomposite beams. The concrete mix contained either 1% fibres or 0.5% (by vol-ume) of straight steel fibres with concrete strength of approximately 150 MPa.The experimental study demonstrates that the use of UHPC slab with contin-uous shear connector is possible, and it enhances the performance of compositeelements in terms of resistance and stiffness.

The finite element analysis of the Push-Out specimens and composite beamswhich tested in this investigation was carried out using software ATENA. Fullthree dimension models for both Push-Out specimens and composite beams weredeveloped in order to taken into account complexity of geometry. The concrete

was modelled using a Microplane M4 with parameters were calibrated accom-panying to uni-axial compression and RILEM bending test. Modelling resultshowed a reasonable agreement with the experimental data. The FE simulationis not only provide ultimate strength, global behaviour but also explained localdamage area as well process of collapse occurred in structures. However, the FEanalysis need more improvement in concrete material model, in order to used forparameter studies.

Finally, based on result of experimental and numerical investigation a numerousrecommendations are issued for practical design. The results form this workprovide to better knowledge on using new UHPC in composite structures. It alsocontribute to provision of design code.

Contents

Foreword iii

Biography v

Abstract ix

Abbreviations xv

List of Symbols xvii

List of Figures xix

List of Tables xxvii

1. Introduction 11.1. State of the art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2. Context and motivation . . . . . . . . . . . . . . . . . . . . . . . . 31.3. Objectives of study . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.4. Scope of work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.5. Structure of the thesis . . . . . . . . . . . . . . . . . . . . . . . . . 6

2. Consideration aspects of steel-concrete composite beams 72.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.2. Single span composite beams under sagging moment . . . . . . . . 9

2.2.1. Basic Structural Behaviour . . . . . . . . . . . . . . . . . . 92.2.2. Structural composite beam with continuous shear connection 12

2.3. Perfobond shear connector (PSC) . . . . . . . . . . . . . . . . . . . 142.3.1. Conventional Perfobond shear connector . . . . . . . . . . . 142.3.2. Modified pefobond shear connectors . . . . . . . . . . . . . 18

2.4. Development of concrete technology . . . . . . . . . . . . . . . . . 202.5. Composite beam made of UHPC . . . . . . . . . . . . . . . . . . . 212.6. Finite Element modelling . . . . . . . . . . . . . . . . . . . . . . . 22

2.6.1. modelling of composite beams . . . . . . . . . . . . . . . . . 222.6.2. Modelling of Push-Out test . . . . . . . . . . . . . . . . . . 24

2.7. Design of composite beam . . . . . . . . . . . . . . . . . . . . . . . 25

xii Contents

2.7.1. Limit state design philosophy . . . . . . . . . . . . . . . . . 252.7.2. Methods for analysis and design . . . . . . . . . . . . . . . 262.7.3. Resistant capacity of composite beam under sagging moment 262.7.4. Partial shear connection . . . . . . . . . . . . . . . . . . . . 282.7.5. Ductile and non-ductile shear connectors . . . . . . . . . . 28

2.8. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3. Characterization material properties of UHPC 313.1. Development of UHPC-A Historical perspective . . . . . . . . . . . 313.2. Constituent materials of Ultra High Performance Concrete . . . . . 33

3.2.1. Principle of UHPC . . . . . . . . . . . . . . . . . . . . . . . 333.2.2. Composition of UHPC . . . . . . . . . . . . . . . . . . . . . 343.2.3. Cost of UHPC . . . . . . . . . . . . . . . . . . . . . . . . . 363.2.4. Material used in this work . . . . . . . . . . . . . . . . . . . 37

3.3. Relevant material properties . . . . . . . . . . . . . . . . . . . . . . 383.3.1. Properties of fresh UHPC . . . . . . . . . . . . . . . . . . . 383.3.2. Time dependent properties of UHPC . . . . . . . . . . . . . 393.3.3. Durability . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

3.4. Mechanical behaviour characterization . . . . . . . . . . . . . . . . 423.4.1. Development of compressive strength . . . . . . . . . . . . . 423.4.2. Stress-strain behaviour in uni-axial compression . . . . . . . 433.4.3. Bi-axial behaviour of UHPC . . . . . . . . . . . . . . . . . . 463.4.4. Flexural and direct tension behaviour of UHPC . . . . . . . 483.4.5. Fracture properties of UHPC . . . . . . . . . . . . . . . . . 49

3.5. Concluding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . 51

4. Experimental study for perfobond shear connector in UHPC 534.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534.2. Experimental programs and specimens . . . . . . . . . . . . . . . . 54

4.2.1. Push-Out test specimens . . . . . . . . . . . . . . . . . . . 544.2.2. Arrangement for Push-Out series . . . . . . . . . . . . . . . 594.2.3. Standard Push-Out test setup . . . . . . . . . . . . . . . . . 604.2.4. Loading procedure . . . . . . . . . . . . . . . . . . . . . . . 62

4.3. Test results and observations . . . . . . . . . . . . . . . . . . . . . 624.3.1. Resistance and slip results . . . . . . . . . . . . . . . . . . . 624.3.2. Behaviour of headed stud shear connectors in UHPC . . . . 634.3.3. General behaviour of perfobond shear connector in UHPC . 654.3.4. Influence of dowel profile and test setup . . . . . . . . . . . 674.3.5. Influence of fiber content to load slip-behaviour . . . . . . . 684.3.6. Influence of transverse reinforcement arrangement . . . . . 714.3.7. Influence of embedding reinforcement through concrete dowel 72

Contents xiii

4.4. Summary conclusions for Push-Out test . . . . . . . . . . . . . . . 73

5. Experimental investigation on the structural behaviour of steel-UHPC composite beams 755.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755.2. Experimental program for composite beams . . . . . . . . . . . . . 75

5.2.1. Aim and Objectives . . . . . . . . . . . . . . . . . . . . . . 755.2.2. Design and construction of test specimens . . . . . . . . . . 765.2.3. Test set-up and instrumentation . . . . . . . . . . . . . . . 79

5.3. Analysis of the test results and observations . . . . . . . . . . . . . 815.3.1. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815.3.2. Structural behaviour and Observations of beam B1 and B2 835.3.3. Structural behaviour and Observation of beam B3 and B4 . 895.3.4. Test results and observing of beam B5 . . . . . . . . . . . . 935.3.5. Test results and observing of beam B6 . . . . . . . . . . . . 97

5.4. Shear flow distribution in composite beam . . . . . . . . . . . . . . 1015.4.1. Load-slip behaviour in composite beam versus Push-Out test1015.4.2. Distribution of longitudinal shear forces . . . . . . . . . . . 103

5.5. Summary conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 104

6. Material models for Finite Element Modelling 1076.1. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1076.2. Material models for structural steel and reinforcement . . . . . . . 1086.3. Microplane M4 material model for concrete . . . . . . . . . . . . . 109

6.3.1. Aspects of concrete material model . . . . . . . . . . . . . . 1096.3.2. Microplane M4 material model in ATENA . . . . . . . . . . 110

6.4. Parameter study of Microplane . . . . . . . . . . . . . . . . . . . . 1156.4.1. Setting up virtual test . . . . . . . . . . . . . . . . . . . . . 1156.4.2. Input parameter and sensitivity analysis . . . . . . . . . . . 1176.4.3. UHPC experimental data . . . . . . . . . . . . . . . . . . . 1176.4.4. Results of M4 model parameters investigation and discussion118

6.5. Proposed set of parameter for UHPC . . . . . . . . . . . . . . . . . 1236.5.1. Adjustment strategy for model parameters . . . . . . . . . 1236.5.2. Result of compression and bending modelling with M4 . . . 123

6.6. Concluding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . 124

7. Finite Element Modelling 1277.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1277.2. Modelling of Push Out Test . . . . . . . . . . . . . . . . . . . . . . 128

7.2.1. Finite element model . . . . . . . . . . . . . . . . . . . . . . 1287.2.2. Experimental validation finite element model . . . . . . . . 132

xiv Contents

7.2.3. Local behaviour Push-Out specimens . . . . . . . . . . . . . 1357.2.4. Proposed model for prediction ultimate capacity of perfor-

bond shear connector . . . . . . . . . . . . . . . . . . . . . 1417.3. Modelling of composite beam . . . . . . . . . . . . . . . . . . . . . 146

7.3.1. Finite element model . . . . . . . . . . . . . . . . . . . . . . 1467.3.2. Validation of the FE model . . . . . . . . . . . . . . . . . . 1497.3.3. Local stress distribution in steel girder and shear connectors1557.3.4. Shear flow on concrete dowel . . . . . . . . . . . . . . . . . 157

7.4. Summary conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 157

8. Conclusions and Future Perspective 1598.1. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

8.1.1. Ultra high performance concrete . . . . . . . . . . . . . . . 1598.1.2. Composite beam members made of UHPC under static load 1608.1.3. Perfobond based shear connectors in UHPC . . . . . . . . . 1618.1.4. Modelling of composite beams . . . . . . . . . . . . . . . . 162

8.2. Recommendations for further research . . . . . . . . . . . . . . . . 162

A. Appendices: Concrete mix proportional 165A.1. List of tables for constituent materials . . . . . . . . . . . . . . . . 165

B. Appendices: Standard Push-Out Test 169B.1. Experimental results of Standard Push-Out test . . . . . . . . . . . 169B.2. List of drawings and charts . . . . . . . . . . . . . . . . . . . . . . 169

C. Appendices: Bending test of composite beam 181C.1. Design of steel-concrete composite beams for bending test . . . . . 181C.2. List of drawings and charts . . . . . . . . . . . . . . . . . . . . . . 181

D. Appendices: Tool for ATENA 203

Bibliography 207

Abbreviations

FE Finite ElementFEA Finite Element AnalysisFEM Finite Element MethodsNFEA Nonlinear Finite Element AnalysisFES Finite Element SimulationFEMD Finite Element ModellingSG Strain gaugeLVDT Linear Variable Displacement TransducerCMOD Crack Mount Opening DisplacementNSC Normal Strength ConcreteCSC Conventional Strength ConcreteHPC High performance ConcreteUHPC Ultra High Performance ConcreteUHPFRC Ultra High Performance Fiber Reinforced ConcreteRPC Reactive Powder ConcreteCB Composite beamSCCB Steel Concrete Composite BeamUHPCSCCB Steel Concrete Composite Beam Made of UHPCSHC Shear ConnectorSPOT Standard Push-Out TestHSSC Headed Stud Shear ConnectorPFSC Perfobon Shear ConnectorODW Open dowelCDW Closed dowelM4 Bazants Miroplane material model for concreteEC4 EuroCode 4RILEM International Union of Laboratoies and Experts

in Construction Materials, System and Structures

xvi Abbreviations

List of Symbols

Greek characters

c stress of concreteuk characteristic value of slip capacity degree of shear connection curvature diameter of concrete dowel

Latin lower case letters

bo bottom width of shear surface in dowel aread depth of shearing conendw numer of dowel in the Push-Out specimenhsc height of steel ribtsc thickness of steel ribqu shear capacity per perfobondPdw shearing capacity of plain concrete dowelPr contribution of rebar in dowel to capacity of PSCPfr contribution of rebar in front cover to capacity of PSCPa contribution of steel rib to capacity of PSC

Latin upper case letters

A Cross-sectional area of the effective composite sectionneglecting concrete in tension

Aa cross-sectional area of the structural steel sectionAb cross-sectional area of bottom transverse reinforcementAbh cross-sectional area of bottom transverse reinforcement in a

haunchAc cross-sectional area of concreteAcc cross-sectional area of concrete shear per connector

Acd cross-sectional area of dowelAct cross-sectional area of the tensile zone of the concreteAfc cross-sectional area of the compression flangeAr area of embedded reinforcement in concrete dowelArf amount area of reinforcement in front coverLe span of composite beamM Bending momentD uiameter of concrete dowelPu ultimate resistance of Push-Out specimenPu,test ultimate resistance of Push-out specimen from testPu,pred predicted ultimate resistance of Push-out specimenPRk ,1 characteristic value of the shear resistance of a single connectorPRk characteristic value of the shear resistance of Push-Out specimen

Mechanical Properties

fc Cylinder compressive strengthfc,cube Cube compressive strength (150 mm)fck Characteristic value of the cylinder compressive strength of

concretefct Tensile strength of concretefc,28d compressive strength of concrete at 28 daysfy Nominal value of the yield strength of structural steelfy,r yield strength of reinforcementEc elastic modulus of concreteEa elastic modulus of structural steelEa,r elastic modulus of reinforcementGf Fracture Energylch Characteristic length Possions ratiov Partial factor for design shear resistance of a shear conector

List of Figures

1.1. Karl-Heine footbridge in Leipzig-Germany: concrete filled steeltube structures, after Koenig (56) (left), and the composite floorof a residential building in London(26) (right) . . . . . . . . . . . . 1

1.2. Basic mechanism of composite action . . . . . . . . . . . . . . . . . 21.3. Perfobond shear connection in composite beam . . . . . . . . . . . 4

2.1. Typical cross sections of composite beams (26) . . . . . . . . . . . 72.2. Typical shear connectors, after Oehlers and Bradford (68) . . 82.3. Stages of composite beam at different load levers(26) . . . . . . . 102.4. Longitudinal shear force on connectors(26) . . . . . . . . . . . . . . 102.5. Typified VFT-WIB composite section (above) and application

in Vigaun bridge project, after Schmitt et al. (94) . . . . . . . . 142.6. Push-Out specimens and test setup, a) general specimen

(Oguejiofor and Hosain (83)), b) specimen with profile steelsheet (Kim et al. (55)). . . . . . . . . . . . . . . . . . . . . . . . 16

2.7. Shear transfer mechanism from concrete slab to steel rib . . . . . . 172.8. Various kind of Perfobond Shear connector in composite beam . . 182.9. Push-Out test of the VFT-WIB connector (93) . . . . . . . . . . . 192.10. Discrete and continuous model for shear connector in composite

beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232.11. Elasto-Fracture-Plastic based material models for steel and

concrete in Finite element modelling of Push-Out test and com-posite beam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2.12. Push-Out specimen model of Kraus and Wurzer (57) . . . . . . 252.13. Ideallized tress-strain diagrams used in the plastic method, (26; 27) 262.14. Plastic analysis of composite section under sagging moment, 1a-

neutral axis in concrete slab; 1b-neutral axis at the bottom of com-posite slab; 2a-neutral axis lies within top flange of steel section;2b- neutral axis in the web . . . . . . . . . . . . . . . . . . . . . . 27

2.15. Design method for partial shear connection (47; 48) . . . . . . . . 27

3.1. Historical development of UHPC . . . . . . . . . . . . . . . . . . . 323.2. Comonents of a typical UHPC . . . . . . . . . . . . . . . . . . . . 34

xx List of Figures

3.3. Relative density vesus w/c ratio, after Richard andCheyrezy (90) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

3.4. Estimation cost of constituent materials for UHPC, (a):UHPCwithout steel fiber, (b) with 1% steel fiber (58) . . . . . . . . . . . 37

3.5. Autogeneous shrinkage of UHPC with and without coarse aggre-gates, after Ma et al. (69; 70) . . . . . . . . . . . . . . . . . . . . 39

3.6. Creep of UHPC with and without coarse aggregates, after Ma andOrgrass (71; 73) . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3.7. Porosity of UHPC with and without heat treated, afterCwirzen (23) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

3.8. Comparison durability properties of NSC, UHP and UHPC. AfterSuleiman et al. (99) . . . . . . . . . . . . . . . . . . . . . . . . . 41

3.9. Development compressive strength, after Ma (74) . . . . . . . . . . 423.10. Test setup for stress-strain response under uni-axial compression . 443.11. Loading procedure for uni-axial compression test . . . . . . . . . . 443.12. A comparison of stress-stress curves of NSC, HPC and UHPC(left),

and Poinssons ratio (right). After (Tue et al.) (101) . . . . . . . 443.13. Relation elastic modulus vesus compressive strength.(Tue et

al. (101; 70)) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453.14. Comparison influence of grain size and fiber content to bi-axial

strength increment, modified from Curbach and Hampel (22) . 473.15. Proposal reduction strength under compression-tension load, mod-

ified from (Fehling et al. (29)) . . . . . . . . . . . . . . . . . . . 473.16. Flexural tensile stress-deflection diagram of G7-UHPC, by Tue

et al. (108) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483.17. Notched beam three points bending test(left) and Wedge splitting

test (right) to determine fracture energy of concrete . . . . . . . . 493.18. Characteristic length versus versus compressive strength (32) . . . 50

4.1. Behaviour of headed stud shear connector in NSC, after John-son (47) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

4.2. Standard Push-Off Test, Setup 1 (a) and Setup 1 (b) . . . . . . . . 554.3. Typical stress-strain curve of structural steel at room temperature,

modified Outinen et al. (85) . . . . . . . . . . . . . . . . . . . . 564.4. Typical stress-strain curves of Bst500 reinforcement . . . . . . . . 564.5. Material responses of G7-UHPC 1% steel fiber, stress-strain di-

agram in compression test (left) and stress-deflection in RILEMbeam test(right) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

4.6. Casting Push-Out specimens . . . . . . . . . . . . . . . . . . . . . 58

List of Figures xxi

4.7. CDW (above line) and ODW (below line) shear connectors, (a &e)-without rebar, (b & f)-rebar in dowel, (c & g)-rebar in frontcover, (d & h)-rebar in dowel and front cover . . . . . . . . . . . . 60

4.8. Push-Out specimen in 4000 kN load frame and controller system . 614.9. Instrumentation setup in SPOT Setup 1(left) and Setup 2 (right) . 614.10. Load history for SPOT . . . . . . . . . . . . . . . . . . . . . . . . . 624.11. Load-slip diagram of headed studs shear connectors in UHPC . . 644.12. Crack opening in concrete surfaces . . . . . . . . . . . . . . . . . . 644.13. Failure process and shanked of HSSH at footing . . . . . . . . . . . 654.14. Basic mechanics of perfobond shear connector (left), stress state

in concrete dowel, after Kraus and Wurzer (57)(right) . . . . . 664.15. Deformation of the steel ribs after test . . . . . . . . . . . . . . . . 664.16. Overview behaviour of perfobond shear contectors . . . . . . . . . 664.17. Load-Slip behaviour of CDW and ODW (1 % steel fiber) . . . . . . 684.18. Influence of fiber content on load-slip behaviour series 8: 0.5% and

series 9: 1% vol. steel fiber . . . . . . . . . . . . . . . . . . . . . . 694.19. Crack opening curves of series 8 and 9 . . . . . . . . . . . . . . . . 694.20. Crack pattern of SPOT with UHPC 0.5% (left) and 1% (right)

steel fiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 704.21. Crack on the concrete surface, without reinforcement in cover (left)

and with reinforcement(right) . . . . . . . . . . . . . . . . . . . . . 704.22. Effect of transverse reinforcement arrangement on load-slip be-

haviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714.23. Influence of reinforcement thought dowel . . . . . . . . . . . . . . . 72

5.1. Sketch layout of Beam B1 and B2 . . . . . . . . . . . . . . . . . . 775.2. Sketch layout of Beam B3 and B4 . . . . . . . . . . . . . . . . . . 775.3. Design layout of Beam B5 and B6 . . . . . . . . . . . . . . . . . . 785.4. Instrumentation for flexural test of composite beams Series 1 . . . 805.5. Instrumentation for flexural test of composite beams Series 2 . . . 805.6. Equipment for flexural test of composite beams Series 1-2 . . . . . 815.7. Force-deflection curve before and after remove residual strain . . . 825.8. Load-deflection behaviour of composite beam B1 and B2 . . . . . . 835.9. Plastic of steel girder and crushed of concrete slab . . . . . . . . . 835.10. Moment curvature relationship of beam B1 and B2 . . . . . . . . . 855.11. Strain development in concrete slab (left) and steel girder(right)

of composite beam B1 and B2 . . . . . . . . . . . . . . . . . . . . . 865.12. Strain development in cross section of composite beam B1 and B2 865.13. Longitudinal slip of beam B1 (left) and B2 (right) . . . . . . . . . 875.14. Lateral strain surround hole of perforated strip . . . . . . . . . . . 885.15. Load-deflection behaviour of composite beam B3 and B4 . . . . . . 89

xxii List of Figures

5.16. Failure of beam B3 due to collapse of shear connector in right side 905.17. Load-strain behaviour of composite beam B3 and B4, concrete slab

(left) and steel girder (right) . . . . . . . . . . . . . . . . . . . . . . 925.18. Load-strain development in cross section beam B3(left) and B4

(right) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 925.19. Diagram Load-longitudinal slip in beam B3 and B4 . . . . . . . . . 935.20. Load - deflection behaviour diagrams of beam B5 . . . . . . . . . 945.21. Load - strain response of beam B5 . . . . . . . . . . . . . . . . . . 955.22. Longitudinal slip of beam B5 . . . . . . . . . . . . . . . . . . . . . 955.23. Slip development of beam B5 . . . . . . . . . . . . . . . . . . . . . 965.24. Load - deflection diagrams of beam B6, UHPC G7 0.5 % fiber

content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 975.25. Load - slip behaviour of beam B6 . . . . . . . . . . . . . . . . . . . 985.26. Failure progress of composite beam B6 . . . . . . . . . . . . . . . . 995.27. Load-Strain at middle span section of beam B6 . . . . . . . . . . . 1005.28. Strain development in middle span section (left) and one third

section (right) of beam B6 . . . . . . . . . . . . . . . . . . . . . . . 1005.29. Stress-strain over slab thickness . . . . . . . . . . . . . . . . . . . . 1015.30. Comparison load slip behaviour of shear connector in composite

beam and push out test . . . . . . . . . . . . . . . . . . . . . . . . 1025.31. Comparison load slip behaviour of shear connector in composite

beam and push out test . . . . . . . . . . . . . . . . . . . . . . . . 1025.32. Slip distribution versus degree shear connection . . . . . . . . . . . 1035.33. Longitudinal shear force in composite beams . . . . . . . . . . . . 103

6.1. Bilinear Elasto-plastic material model for structural steel . . . . . 1086.2. Calculation macro stress scheme in microplane model . . . . . . . 1116.3. Strain component on a micro plane . . . . . . . . . . . . . . . . . . 1116.4. Microplane boundary . . . . . . . . . . . . . . . . . . . . . . . . . . 1136.5. FE simulation RILEM (left) bending test and uni-axial compres-

sion (right) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1166.6. Typical stress-strain of uni-axial compression test (left) and bend-

ing stress-displacement diagram of RILEM three points bendingtest (right) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

6.7. Effect of changing elastic modulus to flexural and compressionspecimens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

6.8. Effect of k1 parameter . . . . . . . . . . . . . . . . . . . . . . . . . 1196.9. Influence of parameter c1 . . . . . . . . . . . . . . . . . . . . . . . 1206.10. Influence of parameter c3 . . . . . . . . . . . . . . . . . . . . . . . 1206.11. Influence of parameter c5 . . . . . . . . . . . . . . . . . . . . . . . 1216.12. Influence of parameter c7 . . . . . . . . . . . . . . . . . . . . . . . 121

List of Figures xxiii

6.13. Influence of parameter c8 . . . . . . . . . . . . . . . . . . . . . . . 1226.14. Influence of parameters c4, c10, c11 and c12 . . . . . . . . . . . . . 1226.15. Stress-displacement and Stress-strain response of G7-UHPC (1%

vol. steel fiber) with Microplane M4 material model adjusted pa-rameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

6.16. Stress-displacement and Stress-strain response of B4Q-UHPC (1%vol. steel fiber) with Microplane M4 . . . . . . . . . . . . . . . . . 124

7.1. Geometry of push-out test specimens . . . . . . . . . . . . . . . . . 1287.2. Finite Element model of Push-Out specimen . . . . . . . . . . . . . 1297.3. Loading, boundary conditions and constrain DOFs at contact sur-

faces between steel and concrete . . . . . . . . . . . . . . . . . . . 1317.4. Comparison load-slip response of experimental and FE analysis for

Push-Out series 3 and 4 (open dowel) . . . . . . . . . . . . . . . . 1347.5. Comparison load-slip response of experimental and FE analysis for

Push-Out series 6 and 7 (closed dowel) . . . . . . . . . . . . . . . . 1347.6. Local deformation of the series 4 - Open dowel with test setup 2 . 1367.7. Local deformation of the series 7 - Closed dowel with test setup 1 . 1367.8. Local stress distrubution in the steel rib . . . . . . . . . . . . . . . 1377.9. Local strain distribution in concrete block . . . . . . . . . . . . . . 1387.10. Stress concentration distribution in rebars of Series 4 (ODW) and

7 (CDW) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1407.11. Simplified shearing cone assumption . . . . . . . . . . . . . . . . . 1407.12. Geometry of composite beam for FE modelling . . . . . . . . . . . 1467.13. Finite Element mesh of a composite beam model . . . . . . . . . . 1477.14. Interface between steel and concrete surface . . . . . . . . . . . . . 1477.15. Deformed shape of the beam B1 and FE simulation . . . . . . . . . 1507.16. Comparison test and modelling results of beam B1 and B2, force

- deflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1517.17. Comparison test and modelling results of beam B3 and B4, force

- deflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1517.18. Comparison test and modelling results of beam B1, force-strain . 1527.19. Comparison test and modelling results of beam B2, force-strain . 1527.20. Comparison test and modelling results of beam B3, force-strain . 1537.21. Comparison test and modelling results of beam B4, force-strain . 1537.22. Comparison local slip of beam B1 (left) and B2 (right) . . . . . . . 1547.23. Stress distribution in girder, beam B1 to B4 . . . . . . . . . . . . . 1557.24. Stress distribution in steel rib . . . . . . . . . . . . . . . . . . . . . 1567.25. Longgitudinal stress in steel rib of shear connector, beam B1 and

B2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

xxiv List of Figures

B.1. Push-Out test setup S1 and S2 . . . . . . . . . . . . . . . . . . . . 170B.2. Rebars arrangement of Push-Out specimens . . . . . . . . . . . . 171B.3. Push-Out test reults: Load-Slip and Crack opening, Series

1-Headed stud shear connector, specimen-1(a), specimen-2(b),specimen-3(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

B.4. Push-Out test reults: Load-Slip, Series 2-ODW without rebar(left), Series 3-ODW with rebar in core(right) . . . . . . . . . . . . 173

B.5. Push-Out test reults: Load-Slip and Crack opening, Series 4-Opendowel with rebar in core and front cover, specimen-1(a), specimen-2(b), specimen-3(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

B.6. Push-Out test reults: Load-Slip and Crack opening, Series 5-CDWwithout Reinforcement, specimen-1(a), specimen-2(b), specimen-3(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

B.7. Push-Out test reults: Load-Slip and Crack opening, Series 6-CDWwith rebar in core, specimen-1(a), specimen-2(b), specimen-3(c) . . 176

B.8. Push-Out test reults: Load-Slip and Crack opening, Series 7-Opendowel with rebar in core and front cover, specimen-1(a), specimen-2(b), specimen-3(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . 177

B.9. Push-Out test reults: Load-Slip and Crack opening, Series 8-CDW with rebar in cover-UHPC 0.5% steel fiber, specimen-1(a),specimen-2(b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178

B.10.Push-Out test reults: Load-Slip and Crack opening, Series 9-CDW with rebar in cover-UHPC 1.0% steel fiber, specimen-1(a),specimen-2(b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179

B.11.Push-Out test reults: Load-Slip and Crack opening, Series 10-11-CDW with rebar in core and front cover-UHPC 1.0% steel fiber,8mm-(a), 12mm-(b) . . . . . . . . . . . . . . . . . . . . . . . . . 180

C.1. Design of the composite beam B1 . . . . . . . . . . . . . . . . . . . 182C.2. Design of the composite beam B2 . . . . . . . . . . . . . . . . . . . 183C.3. Design of the composite beam B3 . . . . . . . . . . . . . . . . . . . 184C.4. Design of the composite beam B4 . . . . . . . . . . . . . . . . . . . 185C.5. Design of the composite beam B5 . . . . . . . . . . . . . . . . . . . 186C.6. Design of the composite beam B6 . . . . . . . . . . . . . . . . . . . 187C.7. Experimental setup of the composite beam B1 . . . . . . . . . . . 188C.8. Experimental setup of the composite beam B2 . . . . . . . . . . . 189C.9. Experimental setup of the composite beam B3 . . . . . . . . . . . 190C.10.Experimental setup of the composite beam B4 . . . . . . . . . . . 191C.11.Experimental setup of the composite beam B5 and B6 . . . . . . . 192C.12.Beam B1, Load-deflection and Load-rotation (a), strain in girder

section 1-1 (b) and strain in girder section 2-2 (c) . . . . . . . . . . 193

List of Figures xxv

C.13.Beam B1, Load-strain in concrete slab (a), strain in steel rib (b)and slip (c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194

C.14.Beam B2, Load-deflection and Load-rotation (a), strain in girdersection 1-1 (b) and strain in girder section 2-2 (c) . . . . . . . . . . 195






C.20.Beam B5, Load-deflection (left), strain in girder and concrete slabat section 1-1 (right) . . . . . . . . . . . . . . . . . . . . . . . . . . 201

C.21.Beam B6, Load-deflection and Load-rotation (a), strain in girderand concrete slab section 1-1 (b) . . . . . . . . . . . . . . . . . . . 201

C.22.Beam B6, strain in girder and concrete slab section 2-2 (a), Load-longitudinal slip along left and right side of the beam (b) . . . . . 202

D.1. Structure of the program . . . . . . . . . . . . . . . . . . . . . . . 203D.2. Flow chart of calibration model parameter of microplane M4 . . . 204D.3. Main screen of the program . . . . . . . . . . . . . . . . . . . . . . 205D.4. Result extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205D.5. Quick plot experiment results . . . . . . . . . . . . . . . . . . . . . 206D.6. Atena datafile editor . . . . . . . . . . . . . . . . . . . . . . . . . . 206

xxvi List of Figures

List of Tables

3.1. Diameter range of granular class for UHPC, after Richard andCheyrezy (90) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

3.2. Mixture proportion of UHPC . . . . . . . . . . . . . . . . . . . . . 383.3. title of table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413.4. Fracture parameters of UHPC for different mix designs, after

Ma (74) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503.5. Tensile fracture properties of UHPC with steel fiber, modified

Fehling et al. (32) . . . . . . . . . . . . . . . . . . . . . . . . . . 52

4.1. Mechanical properties of steel grade S355 and reinforcing bar Bst500 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

4.2. Material properties of UHPC . . . . . . . . . . . . . . . . . . . . . 574.3. Parameter for Push-Out test program . . . . . . . . . . . . . . . . 594.4. Summary Standard Push-Out Test results . . . . . . . . . . . . . . 63

5.1. Description of composite beams . . . . . . . . . . . . . . . . . . . . 765.2. Transverse reinforcement arrangement in concrete slab . . . . . . 765.3. Summary of test result of the composite beams . . . . . . . . . . . 825.4. Comparison of ultimate strength, deflection and stiffness of beams

B2 with B3 and B4 . . . . . . . . . . . . . . . . . . . . . . . . . . 905.5. Peak slip location versus actual shear connection degree . . . . . . 103

6.1. Boundaries for the microplane model parameters . . . . . . . . . . 1176.2. Value of M4 model parameters for UHPC G7 and B4Q . . . . . . 124

7.1. Comparison of ultimate capacity predicted by ATENA with ex-perimental values . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133

7.2. Push-Out test and modelling data for linear regression analysis . . 1437.3. Push-Out test and modelling data for linear regression analysis

(cont) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1447.4. Verification prediction model with experimental and simulation data1457.5. Description of composite beams for experimental and modelling . . 1507.6. Ultimate load and deflection results for the experimental and nu-

merical analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

xxviii List of Tables

1. Introduction

1.1. State of the art

The term Composite Construction is normally understood within the contextof buildings and other civil engineering structures, to imply the use of Steel andConcrete combine together as a unified component. The aim is to archive a higherlevel of performance than would be have been the case had the two materialsfunctioned separately. Steel and concrete can be used in mixed structural sys-tems, for example concrete cores encircled by steel tubes, concrete slab gluedwith steel girder via shear connection in order to form composite beam whichmost widely used in practical construction. Moreover, composite columns offermany advantages over bare steel or reinforced columns, particularly in reducingcolumn cross-sectional area. Another important consideration is fire resistance.Figure 1.1 shows Karl-Heine pedestrian bridge in Leipzig (Koenig (56)), and thecomposite floor of a residential building in London (26) . They are the typicalillustration of using hybrid structures in construction.

Figure 1.1.: Karl-Heine footbridge in Leipzig-Germany: concrete filled steel tube structures,after Koenig (56) (left), and the composite floor of a residential building inLondon(26) (right)

The basic mechanics of composite action is best illustrated by analysis a com-posite beam under bending load which demonstrated in Fig. 1.2. In the caseof non-composite (a), the concrete slab is not connected to the steel section and

2 1. Introduction

therefore behaves independently. As it is generally very weak in longitudinalbending it deforms to the curvature of the steel section and has its own neutralaxis. The bottom surface of the concrete slab is free to slide over the top flangeof the steel section and considerable slip occurs between the two. The bendingresistance of the slab is often so small that it is ignored.

Alternatively, if the concrete slab is connected to the steel section (b), both acttogether in carrying the service load. Slip between the slab and steel sectionis now prevented and the connection resists a longitudinal shear force. Conse-quently, the load bearing capacity of the second beam (b) is few times greaterthan the first beam (a).

slip

strain stressNon-composite section

strain stressComposite section

Shear connectors

Composite beam

Non-Composite beam

+

-

a)

b)

Na

Nc

concrete slabsteel girder

Figure 1.2.: Basic mechanism of composite action

The characteristic of the steel-concrete composite is exhibited by resistance ofeach contributed material portion and the resistance of shear connection. Whenthe connection cannot resist all of the forces applied then considered as partialconnection, otherwise full shear connection.

Most frequently, composite beam is designed to carry bending load. Regardingthe stress and strain distribution of composite section as shown in Fig. 1.2b,

1.2. Context and motivation 3

the neutral axis dose not often fall at the interface. Good design will attemptlocate this axis close to this position. Thus whole concrete slab is subjected tocompressive force, whereas steel girder to be concerned tension force. In prac-tical constructions, the composite beam is often made of either normal strengthconcrete (in short NSC) or high strength concrete (in short HSC) for slab andhigh strength steel for girder.

1.2. Context and motivation

Recent development of concrete technology resulting a new type of concrete withmany advanced properties, it is called in common name Ultra High PerformanceConcrete (in short UHPC). The key benefits of UHPC are considered in applica-tion point of view as follows:

very high in compressive strength and tensile strength which are ideal tocarry compression load in the composite beams.

addition steel fiber will enhanced ductility behaviour

reduce total weight of structural member

with high flow ability properties, concrete can be complete fulled for com-plex geometry members.

extraordinary durability compare to conventional concrete, reduce maintaincost during service time.

most disadvantage of UHPC is highly cost at the moment, it may be de-creasing in the near future when increasing amount of applications. Thedetail characteristic of UHPC will be mentioned in the chapter 3.

In the structural member behaviour outlook, with NSC the resistance of concreteslab is often less than steel girder, the neutral line lie in the web.

By substituting UHPC to NSC/HSC, the resistance of concrete materials couldbe reached resistance capacity of steel easily. Consequently obtaining optimalload caring of each contribute material. The replacement is not only increasethe stiffness and overall ultimate strength but also reduce cross section of thecomposite beams.

Fig. 1.3 illustrates the idea using perforated steel rib as continuous shear connec-tion in the composite beam. This type of shear connector was first introduced byLeonhardt (62). Perforation strip are welded on top flange of steel girder or cut

4 1. Introduction

directly from web. At construction phase, UHPC will be flowed through perfo-rated hole the dowels formed. Under loading, interaction is developed by concreteengaging with perforations strip, the working mechanism of shear connector canbe illustrated similar to the action of a dowel. In principle, this method bringsto many advantages in practical construction, while load transfer performance isstill guaranteed.

Figure 1.3.: Perfobond shear connection in composite beam

It is well known that, at interaction area between perforated strip and UHPCdowel, the behaviour is combination of tension-shear and compression. TheUHPC with very high compressive strength but less ductility must be treatedto satisfy characteristic ductility requirement of shear connector in compositebeam. The application of this device for shear connection incorporating steelgirder still requires further verification.

Due to the high cost of UHPC material and testing, the experimental studyis unable to cover all range of interested problems. Consequently, numericalsimulation play an important role in this works. However, the behaviour ofUHPC is different with conventional concrete, therefore suitable material modelis required to illustrate mechanism of beam as well concerned problems.

1.3. Objectives of study

The present study aims to investigate performance and structural behaviour ofsteel-concrete composite beam made of UHPC under bending, and it also provide

1.4. Scope of work 5

a better knowledge of perfobond shear connector response in Push-Out test andconjugate with steel girder. More precisely, the following points are explored:

Characteristic of UHPC would be better known and understood, especiallyfocus on basic mechanical properties.

A better knowledge on response of the perfobond shear connectors inUHPC, appropriate choice of shear connector for UHPC composite memberwould be achieved.

Experimental investigation of UHPC composite beam subjected flexuralload, which provides structural behaviour of member under serviceabilityand ultimate limit state, in order to answer the following questions:

- Is it possible to build composite UHPC-Steel elements with monolithicbehaviour; and how can the advantageous UHPC properties be exploited in suchcomposite elements?

- What do resistance and failure modes of UHPC-Steel elements would beshown under bending?

- How do local deformations, stresses and cracking evolve in the composite

members under monotonic load?

Nonlinear finite element models must be evaluated and developed in orderto predict the structural behaviour of shear connectors and UHPC-Steelcomposite beams. The simulation should be explored following aspects:

- Are existing material models appropriate to simulate behaviour of UHPC?

- How to construct suitable structural models for shear connector and com-posite beams?

- What do local behaviour would be shown?

- How to improve performance of the UHPC-Steel composite beam?

On the basis of the results, a design model and guidelines are developed forpractical application of UHPC composite members.

1.4. Scope of work

This work is part of priority research program SPP 1182: Sustainable Buildingwith Ultra High Performance Concrete, which collaborate by numerous of uni-versities in Germany. The concrete material and design of composite were priorplanned, and oriented to the trend of this project. The flexural behaviour of sin-gle span composite beams were limited to sagging moment only. The continuous

6 1. Introduction

beam with hogging moment (negative moment) at support is not considered inthis work.

1.5. Structure of the thesis

The thesis consists of eight chapters. Chapter one is the outline introductionto innovation context of development of UHPC and its application into hybridsteel-concrete structures. The main aspect and objective of this research workwas also mentioned.

Chapter two presents relevant literature review of the behaviour of steel-concretecomposite beams made of UHPC. The content includes material properties as-pect, load transfer mechanism in the beam, as well as experiment and modellingof composite beams.

In Chapter three, the state of the art of UHPC are brief introduced, propertiesof UHPC are characterized and main properties which influence on behaviour ofstructures under loading service are to be discussed in details.

Chapters four and five present an experimental program to investigate the be-haviour of shear connectors and composite beams. The structural tests are con-ducted on standard Push-Out test (SPOT) specimens according to guideline ofEuro Code 4 (EC4), the beams are performed on large scale. Experimental frame-work is divided into two phases namely Push-Out test of shear connectors, thenbending test for composite beam. The discussion and analysis of the experimentalresults are presented.

The first part of chapters six presents briefly material the model for structuralsteel and reinforcement was well. Principally, this chapter focuses on the Mi-croplane M4 material model for concrete. Based on parameter investigation, aset of model parameters for UHPC was introduced.

Chapter seven describe a development of three dimension model for simulation ofPush-Out specimens and composite beams. The parameter study was carried outfor various type of shear connectors (SHC) and steel-concrete composite beams(SCCB). Discussion on modeling results and conclusion were drawn.

The last chapter of this dissertation presents final conclusion based on this re-search project and provide future prospective concerning to SCCB and hybridstructures made of UHPC.

2. Consideration aspects of steel-concretecomposite beams

2.1. Introduction

The most important and most frequently encountered combination of construc-tion materials is that of steel and concrete, with applications in multi-storeybuildings and constructions, as well as in bridges. These materials can be usedin mixed structural systems, for example concrete slab glued with steel girder, aswell as in composite structures where members consisting of steel and concreteact together. Steel and concrete have the same expansion coefficient, and eachmaterials is strong in either compression or tension. Concrete also provides cor-rosion protection and thermal insulation to the steel at elevated temperaturesand additionally can restrain slender steel sections from local or lateral-torsionalbuckling. These essentially different materials are completely compatible andcomplementary to each other.

Composite beams, subjected mainly to bending, consist of a steel section actingcompositely with one (or two) flanges of reinforced concrete. The two materialsare interconnected by means of mechanical shear connectors. For single spanbeams, sagging bending moments, due to applied vertical loads, cause tensileforces in the steel section and compression in the concrete deck thereby allowingoptimum use of each material. Fig. 2.1 and Fig.2.2 show several compositebeam cross-sections and shear connectors respectively, which are widely used inpractical construction.

I-beam with steel girder

Haunched-slabwith steel sheet Steel box girder

I beam with precast concrete slab

Figure 2.1.: Typical cross sections of composite beams (26)

8 2. Consideration aspects of steel-concrete composite beams

Figure 2.2.: Typical shear connectors, after Oehlers and Bradford (68)

The shear connectors in composite beams are used to develop the compositeaction between steel girder and concrete. They are provided mainly to resistlongitudinal shear force, therefore must meet a various requirements, such as(26):

transfer direct shear at their base.

create a tensile link into the concrete.

economic to manufacture and welding.

The most common type of mechanical shear connector is the headed stud shownin Fig. 2.2a. It can be welded to the upper flange either directly in the factoryor through thin galvanised steel sheeting on site. The Behaviour and ultimatestrength of connectors can be examined by Push-Out test according to availablestandards such as EuroCode4 (27). For the design of headed stud, the fol-lowing aspects are considered; shear strength of stud shank, bearing strength ofconcrete, additional contribution of chemical bonding and friction. In spite of itswide application, the headed stud has many deficiencies such as a slip Behaviourbetween stud and concrete, and fatigue failure at welding zone. (26; 80; 47; 55)

Recently, a very high strength cement based composite called Ultra High Perfor-mance Concrete (UHPC) has been developed. It provides many enhancementsin properties compared to conventional and high strength concrete (HSC). In

2.2. Single span composite beams under sagging moment 9

the composite beams, the replacement of normal strength concrete (NSC) withUHPC lead to an improvement in the load carrying in the compression zone. Gen-erally, a significant increase in load bearing capacity and stiffness of the beamis achieved, resulting in saving dead load, reducing construction depth as wellas construction time. However, as reported in Johnson (47), Hegger et al.,Tue et al. (105) the headed stud shear connector is not appropriate in theHSC/UHPC slab due to restrict deformation surrounding stud area. The combi-nation of perfobond shear connector in UHPC will be optimized in both term ofmaterial and structural system.

This chapter aims to review researches relevant to the Behaviour of compositebeams under bending load, which focuses to composite beam/slab with perfobondshear connector. Different aspects of the problem are discussed such as the basicBehaviour of composite beams, innovation of concrete technology, mechanicalshear connection. The numerical modelling of the structural composite beamsand the currently available design procedures will be also mentioned.

2.2. Single span composite beams under sagging moment

2.2.1. Basic Structural Behaviour

The way in which a composite beam behaves under the action of low load, mediumand the final failure load can be briefly described in stages as follows (26):

Stage 1

Under very low loads the steel and concrete behaves in an approximately linearway. The connection between the two materials carries very low shear stresses andit is unlikely that appreciable longitudinal slip will occur. The beam deforms sothat the strain distribution at mid span is linear, as in Fig. 2.3a, and the resultingstress is also linear.

It can be seen from the strain diagram that, if the slab is thick enough thenthe neutral axis lies within the concrete. As a result some of the concrete is intension. If the slab was thin, it is possible that the neutral axis would be in thesteel and then the area of steel above the axis would be in compression. Thisstage corresponds to the service load situation in the sagging moment region ofmost practical composite beams.


strain stress

+

-Shear force

Bending moment a) stage 1strain stress

Shear force

Bending moment b) stage 2strain stressShear force

Bending momentc) Stage 3

Figure 2.3.: Stages of composite beam at different load levers(26)

Longitudinal shear

a b c d

slip

Load on shear connector

abc

d

Longitudinal shear

a b c d

slip

Load on shear connector

ab

c d

slip

Load on shear connectora b c d

Longitudinal shear

a b c d

a)

b)

c)Figure 2.4.: Longitudinal shear force on connectors(26)

Stage 2

In this stage applied load was increased, thus caused rise to deformation in theshear connection. This deformation is known as slip and contributes to the overall


deformation of the beam. Fig. 2.3b shows the influence of slip on the strainand stress distribution. This stage corresponds to the service load stage thatcomposite beams class has been designed as partially shear connection. However,for many composite beams slip is very small and may be neglected.

Stage 3

The steel girder achieves yield limit strain first, plasticity develops and then al-most part of steel section becomes plastic. It occurs as similar fashion in concreteslab. Stress block of whole section changes from triangular to shape shown inFig. 2.3c that is very difficult to express in mathematical form. In ultimate limitstate (ULS) it is assumed to be a rectangular block.

If longitudinal shear resistance is big enough the slip can be neglected. Thestrain in concrete slab could lead to over stress, then it is potentially possiblethat explosive brittle failure of the slab would occur. However, in most practicalcase this situation could ever arise due to the deformation of shear connectors.The response of shear connector in load stage is illustrated as follows:

As the load increases the shear strain, the longitudinal shear force between theconcrete slab and steel girder increases in proportion. For single span compositebeam under uniformly load, it is assumed to deform in an elastic manner andthe longitudinal shear force between slab and steel section can be expressed asT = VS/I (96). Hence longitudinal shear force is directly proportional to thevertical shear force, thus the force on the end connectors is the greatest. Forlow loads the force acting on a connector produces elastic deformation. The slipbetween the slab and the steel section will be greatest at the end of the beam.The longitudinal shear and deformation of a typical composite beam, at this stageof loading, are shown in Fig. 2.4a.

If the load is further increased the longitudinal shear force increases too, and theload on the end stud may cause plastic deformation. The ductility of the connec-tors means that the connectors are able to deform plastically whilst maintainingresistance to longitudinal shear force. Fig. 2.4b shows the situation when the endconnectors are deforming plastically. By increasing applied load, the connectorsnear to the midspan section also begin sequentially to deform plastically. Failureoccurs when once all of the connectors have reached their ultimate resistance asshown in Fig. 2.4c. The failure pattern is dependent upon the plastic defor-mation of shear connector. As exhibited, the end connector must be consideredbefore other one close to the midspan area reaches its ultimate capacity. Therequirement for ductility of shear connector is necessary.


It can be seen that the failure of the composite beam is dictated by the resis-tance of its three main components: steel girder, concrete slab as well as shearconnector. the interaction of these components is very complex, in design thestress-strain relation of these materials are usually assumed as elastic- perfectplasticity (27).

2.2.2. Structural composite beam with continuous shear connection

Steel-concrete composite beam with perforbond shear connectors have been rarelyinvestigated. Jurkiewiez and Hottier (50; 51) studied Behaviour of simplesupport composite beams whose steel beam is an Tee girde without upper flange.Horizontal shear connection was designed as dovetail-shape (a variant of per-fobond) and cut directly on the web of I steel section. By taking symmetriccharacteristic of shear connector, two steel beams obtained with only a cuttingline. To improve the shear capacity and ductility, concrete dowel and horizontalwas combined acting together to resist longitudinal shear force. Normal strengthconcrete with compressive strength of 48 MPa at 28 days was used for slab. Nu-merous large scale specimens were constructed, three points bending tests wereconducted under static and fatigue load.

Experimental results shows global Behaviour of the beam with novel shear con-nector is similar to that with usual connectors. The response includes elasticity,yielding and plasticity domains as well. A flexural failure occurred with a plastichinge in the mid-span cross section accompanied by yielding of the steel girderand crushing of the concrete. The shear connectors did not fail during the testand allowed to efficiently transmit shear forces from the slab to the girder. Thenew proposed shear connector is satisfactory in the bending Behaviour in accor-dance with requirements of design codes.

In different context, Kim and Jeong (53; 46; 54) carried out experimentalinvestigations on the ultimate strength of steel-concrete composite bridge deckwith profiled steel sheeting and perfobond rib shear connectors. In fact, compositeaction of one way bridge deck behaves similar to composite beam in flexuralmode. The perforate steel rib with holes of 50mm diameter was welded directlyinto steel sheet and form continuous shear connectors. The parameters such assteel deck profile, perfobond rid, reinforcement as well as concrete strength wereconsidered. The Push-Out with the same shear connection of the deck was carriedout to determine the capacity of shear connector.

The proposed deck system outperforms a typical cast in place (CIP) reinforceconcrete deck in several ways: its ultimate load-carrying capacity is approxi-mately 2.5 times greater; its initial concrete cracking load is 7.1 times greater;


and it weighs about 25% less. Cconsequently, reduction in the permanent loadmay lead to lighter superstructures and extend longer span deck. The test resultsalso confirm that the perfobond rib shear connection designed in this study canbe effectively used for the proposed deck system.

However, in the Push-out test specimens was taken into account the resistanceof concrete at bottom of the perforated strip 1, this is not accompanying to con-tinuous shear connection which used in the deck specimens. Therefore, ultimatestrength result from Push-Out test gives higher than its real capacity. The con-clusion on the estimated horizontal shear resistance greater than two times of therequired horizontal shear strength is not exact.

Composite truss girders having longer spans that requires higher resistance capac-ity. Machacek and Cudejko (76) have proposed to use CTU perforate shearconnector for shear connection system. The ultimate capacity of composite trusssystem as well as longitudinal shear distribution was investigate by experimentand three dimensional finite element analysis. The test and numerical resultswere compared to approximate solution according to EuroCode4 (27). Accord-ing to test results the perforate shear connector show excellent performance inboth case of full and part shear connection. Within elastic region the distri-bution of longitudinal shear is generally highly non-uniform, exhibiting peaksabove nodes of the composite truss. And within the yielding region, longitudinalshear is redistributed and depending on characteristic load-slip diagram of theconnector.

Recent development of composite beam in Germany with continuous shear con-nection was introduced and have been applied in practical construction. Thecommercial product lines namely VFT-WIB (also known as VFT-constructionmethod) which developed by Schmitt et al., Seidl et. al. (93; 94; 39).In fact, The cross-section of composite beam is composed of two prefabricatedelements with halved rolled girders, working as bottom flange. The compositedowels are manufactured by cutting directly from web of rolled steel profiles.The height of section was designed relatively low to reduce slender of the sec-tion. Steel girder works as external reinforcement as shown in Fig. 2.5. In theVFT-WIB composite beam, the failure mode of shear connector was identifiedin three modes: the shear resistance, yielding due to bending of the dowel and inthe fatigue limit state by fatigue cracks due to dynamic loading. The experimen-tal study on Standard Push-Out test (SPOT) according EuroCode4(27) wascarried out with static and fatigue load. In the tests failure of concrete as wellas steel was observed, It indicated that, the ultimate strength of the steel part isalmost independent on the shape of the dowel. Fatigue cracks caused by a very

1reaction force Rbr in Fig. 2.6


high level of stress amplitude. And the fatigue cracks has limited propagationdue to steel part is compressed in the SPOT. The optimize shape of dowel hasbeen performed by finite element simulation. The several beam test was alsotaken to verify load bearing capacity of structural VFT-WIB beams (39).

shear connectorSteel girder

Concrete beam

Concrete casted in place Reinforcement

Figure 2.5.: Typified VFT-WIB composite section (above) and application in Vigaun bridgeproject, after Schmitt et al. (94)

The VFT-WIB construction method was successfully applied in the road bridgeover the railway line to Poecking (Bavaria, Germany) in 2004 (93). And otherroad bridge project in Vigaun (Austria) which used the same structural systemwas done and service began 2008 (94).

2.3. Perfobond shear connector (PSC)

2.3.1. Conventional Perfobond shear connector

To overcome the disadvantages of headed stud connector, several new type ofshear connector has been developed and used as alternative solutions. Among

2.3. Perfobond shear connector (PSC) 15

of them Perfobond shear connector is known to be a highly effective method interm of construct ability and fatigue resistance. Conventional Perfobond rib shearconnector is made from a rectangular plate with perforated holes as indicated inFig. 2.8a. During casting concrete slab, concrete will flow through holes andconcrete dowels formed. (62; 83).

A considerable amount of experimental tests have been done to establish theBehaviour of different types of perfobond shear connectors. Leonhardt etal. (62) proposed a formula to evaluate strength of the PSC as given in equation2.1. It depends on the compressive strength of concrete rather than yield strengthof steel.

qu = 1.6ld2fck/v (2.1)

Hosaka et al. (44) have proposed another expression for the calculation of aPerfobond connector resistance, corresponding to each holes contribution:

qu = 3.38D2

tscD

fck 39 (2.2)

Oguejiofor and Hosain (83; 83) performed an extensive experimental studywith different Perfobond connector geometries on normal strength concrete. Infact that specimens and Push-Out test setup are shown in Fig. 2.6. The thick-ness of concrete slab, diameter of rib holes as well as spacing between holes wastaken into account, the thickness and transverse reinforcement are not changedin all of the specimens. The full size of composite beam with discrete shear con-nectors was tested to verify performance of the shear connectors. Additionally,a numerical study of the Behaviour of PSC was established. The three dimen-sion model was generated and nonlinearity was taken into account, in order toconsider complexity of material and geometry of specimens. Numerical modelswere validated and showed good agreement with test data. Through parameterstudy and linear regression analysis the prediction model was obtained and givenin equation 2.3.

qu = 4.47htfc + (3.30Acd + 0.01Acc)

f c + 0.90Atr fyr (2.3)

or

qu = 4.50hsctscfck + 0.91Atr fy + 3.31nD2

fck (2.4)

where qu is the shear capacity per Perfobond; h and t are height and thickness ofsteel rib respectively; Acd is concrete area of the dowel; Acc is the concrete shear


per connector that equals to the slab longitudinal area minis the connector area;Atr is reinforcement areas presents in the concrete dowel.

P

W 200

X 59

Concrete slabs

100

712

337

375

100

Rbr

Rdw

d

thickness-t

a)

b)P

Figure 2.6.: Push-Out specimens and test setup, a) general specimen (Oguejiofor and Ho-sain (83)), b) specimen with profile steel sheet (Kim et al. (55)).

In a similar manner based on Push-Out test results, Medberry andShahrooz (79) have proposed a more general formula for estimation strength ofPSC as given in equation 2.5.

qu = 0.747bh

fck + 0.413bf Lc + 0.9Atr fy + 1.66npiD2

4

fck (2.5)

where b is slab thickness; h is slab height downward the connector; bf steel section


flange width; Lc is contact length between the concrete and the flange of the steelsection.

Kim et al. (55) conducted test of with Perfobond connectors on normal weightconcrete for building structures. The influence of dimension of steel rib and re-inforcing bars placement on load carrying capacity were investigated. Jeong etal. (46; 53) conducted several tests of perfobond connector with profile sheet-ing, fig. 2.6 shows specimen for POT. Subsequently, the test results was used todesigned shear connection for concrete composite bridge decks.

Neves et al. (110; 14) investigated Behaviour and strength of PSG as well as T-Perfobond which derived from original PSG. The specimens and test setup as wellas evaluation results were performed according to EuroCode4. A comparisonexperimental result with other authors was established.

Through research work mentioned above, it can be seen that the contributionsfor the shear resistance of perfobond rib shear connector can be evaluated assummation of three terms; dowel action of the concrete holes, shear resistance ofhole crossing reinforcement, and the concrete end-bearing resistance.

dxVa

NaMa

Va

Na

VcNc

McNc

Mc+dMc+dNc

Vc +dVc

+dNa

+dVa

Ma+dMaVLVL

Ps Ps Ps

NcRsh

NcRshRst

a) b) c)

Figure 2.7.: Shear transfer mechanism from concrete slab to steel rib

The mechanism of shear transfer between concrete slab in composite beam isillustrated in Fig. 2.7. In fact, if continuous shear is used (Fig.2.7b) then theresistance is generated by only concrete dowel (included reinforcement if any).The prediction equation 2.3 to 2.5 as well as test data can not be used in this case.The predicted shear strength of shear connector overestimate its actual capacity,there are some misunderstanding in translating from Push-Out test result todesign shear connection such as (53; 54). The end-bearing resistance componentsbeing accounted if and only if discrete shear connector is used (Fig. 2.7c). Theadvantage is that the shear strength of each PCS is increased, but the numberof shear connector along beam is reduced due to essential space between shearconnectors. Consequently, the overall shear connection degree may not higherthan continuous shear connector.


2.3.2. Modified pefobond shear connectors

From practical application point of view the traditional PSC have disadvantagesin construction, especially for placing reinforcement into concrete dowel duringform works are enclosed. However, the concrete dowel has small diameter is notoptimal in term of using material by follow reasons:

failure always occurs in concrete dowel rather than steel rib

large amount of wasted material after cutting

high producing cost for cutting by special equipment required

If the diameter of dowel is increased, then thickness of concrete slab is also greaterthan requirement, particularly in the case of high strength concrete is used. Thereare several different types shear connectors which are modified from original PSChave been studied, proposed and used as shown in Fig. 2.8.

a) Perfobond b) CTU Perfobond

d) Puzzle saw/VFT-WIB

c) Open dowel

e) Puzzle strip/crestbond f) CR connector/crestbondFigure 2.8.: Various kind of Perfobond Shear connector in composite beam

The CTU Perfobond connector was early developed by Studnicka andMachacek at 1994, it was modified from original PSC and the half holes wereadded in the front side of steel rib which contacts with concrete, aimed to increaseresistant capacity (Fig. 2.8b). The Behaviour of CTU connector was elevated forother geometries, hole size, concrete strength. Several Push-Out test series wasconducted with full size of specimens (98; 75). Chromiak and Studnicka (21)adapted CTU PSC for slightly modified on half opening to use with standardwelded reinforcing mesh.

Verissimo et al (109)) have developed a new type of connector as an alternativeto the Perfobond, named Crestbond (or CR). This new shear connector wasformed by an indented steel rib. Fig. 2.8e and 2.8f) shown CR connector aswell as its variation. The open holes provides resistance to longitudinal shearand makes the assembly of the reinforcing bar into concrete slab easier. Thestructural Behaviour of Crestbond connector was studied by Push-Out test andcompare to other existing connectors. Tracing back experimental work, it canbe seen that the specimens and test setup was designed that reaction force atending steel plate is accounted as early mentioned (Fig. 2.6). According to test


results the connector CR50 with reinforcement 12mm and concrete compressivestrength of 28.5 MPa gives ultimate capacity over of 350kN per connector andexcellent characteristic slip also derived. This result is 45% higher than thecorresponding open dowel shear connector made of UHPC which tested by Tueet al. (108). Once again, it can be noted that, the data obtained from above testsetup is not able to used in the composite beam with continuous shear connector.

Figure 2.9.: Push-Out test of the VFT-WIB connector (93)

Schmitt et al. (93) introduced a connector called Puzzle saw (Fig. 2.8d) thatpossibility used for bridges. The ultimate capacity is achieved from Push-Outtest as described in sketch 2.9. Based on test data, the cutting line for Puzzleconnector was modified, in order to achieve better fatigue resistance performanceunder dynamic load. The Puzzle connector was used in composite beam of theVigaun bridge project (94).

It can be seen from figure two foam blocks are placed at bottom of steel rib.Thus the end-plate bearing component is ignored in summation of resistance ofthe connector. This test setup is different from other POT as above mentioned.

Hottier and Jurkiewiez (51)) have proposed the Dovetail-shape connectiontype which similar Puzzle saw connector. The connector exhibits efficient in loadcarrying, reducing wasted material by utilize symmetric of geometry. The beamtest was taken to verify possibility of proposed connector.


Beside many advantages, in the production point of view the modified Perfobondconnector more difficult to make a cutting line, especially if profile contains manyround angles. Generally, it requires high precision cutting machine with auto-matic controller (CNC cutting machine). The cutting work may be performed infactory only.

2.4. Development of concrete technology

During the 1970s, concrete having a compressive strength of 60 to 70 MPa beganspecified for column in high rise buildings , because of reduced column cross sec-tion that offers more architectural space (4). The concrete properties is not onlyoffer high strength but also high durability and other desirable characteristics.Therefore the name has been change to High Performance concrete (HPC). Forthe few past decades, HPC has demonstrated its superior performance in engi-neering applications such as Water Tower Place (Chicago, USA), Petronas TwinTower (Kuala Lumpur, Malaysia), Tsing Ma Bridge (Hong Kong, China) etc.

The advent of Ultra High Strength (UHSC) and Ultra High Performance Concrete(UHPC) is a relatively recent development in concrete technology. The excellentproperties of UHPC could be briefly explained as follow: very high strengthin compression (>150MPa) and tension (> 10MPa), high elastic modulus (>45GPa), the stress - train relation linearly up to 70% or 80% of strength. Theextremely dense matrix allows increasing significantly durability, reducing per-meability to structures working in extreme condition. Properties of fresh UHPCwith high self compacting, fast development strength at early age and does notrequire any heat or pressure curing condition (74; 34). The details on UHPC willbe discussed in chapter 3.

The increases of strength and extraordinary properties is accompanying increasematerial cost and a general reluctance to use new materials in practical appli-cations. To reduce the gap between material development and application ofnew materials in routine design, researchers must optimize the use of UHPC instructural design to take advantage of the incredible increase in strength andother material properties. Then the use of UHPC and other high performancematerials can become more common in structural applications.

2.5. Composite beam made of UHPC 21

2.5. Composite beam made of UHPC

The UHPC filled tube with high bearing capacities and sufficient ductility havebeen investigated by Tue et al. (101; 106). Generally, the hybrid structuralmember can be applied to buildings and bridges. In this work, the UHPC filledsteel tube columns was compared to composite column with steel core and showsbenefit in the costs per load unit as well as possibility to the realization. In addi-tion, some structural solutions for joint element which needed to transfer loadingfrom UHPC composite columns to conventional concrete slab were proposed aswell. Several tests were conducted to evaluate performance of joint elements.

Fehling et al. (31; 28) introduced the pedestrians bridge project cross Fuldariver in Kassel-Germany. This is the first construction in European using UHPCcomposite structure. The bridge deck consists of precast prestressed UHPC slabelements. The longitudinal structure comprise of a continuous truss girder systemwith triangular cross section. The truss girder was made of two upper chords ofprecast prestressed UHPC and a lower chord and diagonals made of tubular steelsections. Glued connections are used between the upper chords and the deck aswell as between the deck plates. The project have been built in period 2005-2006and began service since the end of 2006. In the same manner, the combination ofUHPC panel and steel girder in bridge have been successfully applied to retrofitthe Kaag bridges Netherlands, further detail can be found in Kaptijn andBlom (52).

Within a collaborative research project SPP1182, the study on shear connec-tion and composite beam made of UHPC was performed at University of Leipzig(Uni-Leipzig) and RWTH Aachen University (Uni-Aachen). In fact, the compos-ite beam with continuous Perfobond based shear connectors was used. Heggeret al. (40; 105; 42) investigated shear connector with puzzle and saw toothshapes, while Tue et al. (105; 108) deals with closed and opened circles con-nectors. Many series of Push-Out test was conducted to assess general Behaviour,load bearing capacity, local deformation and influence of reinforcement to per-formance of shear connectors. Furthermore, the bending test of composite beamwith various design were conducted. Ultimate strength, load-defection, local slip,strain as well as mode of failure could be determined and compared to existingdesign codes.


2.6. Finite Element modelling

2.6.1. modelling of composite beams

Composite structures exhibit complex Behaviour in both term of geometry aswell as material response. It is not possible for one individual to be master ofall the required inputs. They must, recognize,appreciate and know how best toutilize the contributions of others so that the whole is considerably more than justthe sum of the parts. In the structural engineering research, experimental studyis most important and often used in study a new type of structures. However,the condition for testing is not always available by many reasons. Even if in thecase of testing would be able to perform then it also may not cover all respectedproblems due to highly cost of materials, labour work and time. Consequently,a numerical simulation is carried out correspondingly to experiment research.Today with faster and cheaper of computer hardware, Nonlinear Finite Elementmodelling is a powerful tool to analysis general structures as well as specially incomposite constructions.

The modelling of composite beam can be divided into primary approach accordinggeometry items: One dimensional element or full three dimensional. The firstapproach is usually in practical design by advantages in computation time andreasonable precision of results. While the achieved results from last approach cangive more detail of Behaviour and local response. Moreover result is generallyhigher accuracy than simple model. Therefore it is favoritelly used in research.

Ranzi and Zona (87) presented an analytical model for full/partial shear con-nection including deformability of the of steel girder. The formulation is obtainedby coupling the Euler-Bernoullis beam for concrete slab to Timoshenkos beamfor the steel girder. The composite action is provided by a continuous shear con-nection which enables relative longitudinal displacements to occur between thetwo components. The structural steel and reinforcement are modelled by usinglinear elastic laws, while linear viscous-elastic integral-type constitutive law isused to taken into account time dependent Behaviour of the concrete slab.

Gatteso (33) proposed a numerical procedure for the analysis of compositebeams. In particular the most refined stress-strain constitutive relationships ofmaterials were used as input parameters. For shear connectors distributed bondmodel is used (Fig. 2.10) and the nonliear load-slip relationship adapted fromPush-Out test. The favorable comparisons between the proposed method withexperimental results was done. This procedure is capable in predicting the struc-tural Behaviour of composite beams over the whole loading range up to failure.The program may be helpful in design as well as parameter study.

2.6. Finite Element modelling 23

Figure 2.10.: Discrete and continuous model for shear connector in composite beams

s,1

s,2

Bi-axial loading

fy Esh

Esh

Es

fy

TensionCompression I

s

Uni-axial loading Uni-axial loading

fct

fck

Tension

Compression

c

1 0

EcEo

cd fct

fck

TensionCompressionc,2

c,1

Bi-axial loading

Figure 2.11.: Elasto-Fracture-Plastic based material models for steel and concrete in Finiteelement modelling of Push-Out test and composite beam

Queiroz et al. (86) used commercial finite element software ANSYS to analyzecomposite beam with full and partial shear connection. Quadrilateral shell ele-ment (SHELL43) and 8 nodes brick concrete element (SOILD65) was employed tosimulate the steel section and concrete slab, respectively. Discrete stud shear con-nector was represented by nonlinear spring element, the load slip curves for studare obtained from push-out tests (Fig. 2.10a). The effect of full or partial shearconnection were taken into account. In the analysis model, both longitudinal andtransverse reinforcement are modeled as smeared reinforcement throughout thesolid elements. Bilinear Elasticity-Plastic material model is used for structuralsteel and reinforcement (Fig. 2.11a) and fracture plastic based model describesfor nonlinear Behaviour of concrete (Fig. 2.11b). The proposed Finite Element(FE) model was validated with test data, some parameter study for various caseof composite have been performed.

Liang et al. (64) investigated ultimate flexural and shear strength of simplesupport composite beams in combined bending and shear actions. By usingthe general purpose ABAQUS software, a three dimension (3D) FE model hasbeen developed to account for geometric and nonlinear material of compositebeams. The concrete slab and steel girder were modeled by four-node doublycurved thick/thin shell elements with reduced integration. 3D beam was usedto represent for discrete stud shear connectors. The material models for both


steel and concrete are the same with Queirozs work. The developed model wasmade valid with experiment and then performed case studies of composite beam.Based on analysis results, a design model has been proposed for the compositebeam subjected combined bending and shear load.

2.6.2. Modelling of Push-Out test

A numerical study of the Perfobond rib shear connector was early conducted byOguejiofor and Hosain (82). In fact the general purpose FE software ANSYSwas used to generate the model and analysis. Taking advantage of symmetry toreduce the size of the problem, only one-quarter of the specimen was selected andmodeled. The push-out test specimen was modeled using two types of elementsfrom the ANSYS element library: SOLID65 for concrete slab; SHELL41 for bothsteel section and perfobond rib connectors. The reinforcing bars were smearedinto the three-dimensional reinforced concrete solid elements. Coincident nodeson the contact surface were either constrained in particular directions or mergedcompletely. In order to make appropriated relative movement between steel andconcrete under applied load. Afterwards the Push-Out model was calibrated withthe test data before used to study shear capacity of PSC. Finally, linear regressionanalysis was conducted to achieve formula for prediction ultimate strength of PSCas expressed in equation 2.4.

It can be seen that Oguejiofors model was simplified up to possible, theconcrete dowel and thickness of steel rib were ignored in the model. There-fore it can not capture the local damage at concrete dowel which caused bytension-shear stress state. And contribution of bearing reaction at bottom plateis not accounted correctly in general case. From FE modelling point of view, theOguejiofors model can not be used to assess local Behaviour well as evaluationload-slip relation of the PO specimens.

In the independent work, Kraus and Wurzer (57) developed 3D layered Push-Out model for open dowel specimen within Finite Element code ADINA (Fig.fig:Kraus-POT-model). In fact that concrete slab, steel flange and ribs are mod-elled by 3D solid element. The FE mesh used very small element size had tobe used in concrete dowel as well as the area that near contact surface. Thenonliear stress-strain relationship based material model which includes post-failure Behaviour and three dimensional failure envelope are used for concrete.The plastic-Multilinear was used for reinforcement and structural steel. Onlythree components was taken into account in contribution to resistance capac-ity: concrete dowel; embedded reinforcing bars in dowel as well as transversereinfor

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