Ultimate strength behaviour of steel concrete steel sandwich composite beams and shells

Ultimate strength behavior of the SCS sandwich beams with shear connectors and ULCC were evaluated through one- or two- point loading tests on 18 sandwich beams.. A theoretical model by

ULTIMATE STRENGTH BEHAVIOR OF CONCRETE-STEEL SANDWICH COMPOSITE

STEEL-BEAMS AND SHELLS

YAN JIABAO

NATIONAL UNIVERSITY OF SINGAPORE

2012

ULTIMATE STRENGTH BEHAVIOR OF CONCRETE-STEEL SANDWICH COMPOSITE

STEEL-BEAMS AND SHELLS

YAN JIABAO

(B.Eng., Central South University; M.Eng., Xi’an Jiaotong University)

A THEIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CIVIL AND ENVIRONMENTAL

ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE

2012

DECLARATION

I hereby declare that the thesis is my original work and it has

been written by me in its entirety

I have duly acknowledged all the sources of information which

have been used in the thesis

This thesis has also not been submitted for any degree in any

university previously

Yan Jiabao

24 May 2012

  I 

ACKNOWLEDGEMENTS

Firstly, I would express my sincerest appreciation and gratitude to my supervisors, Prof Liew Jat Yuen, Richard and Prof Choo Yoo Sang for their full support, supervision, encouragements, constructive advices, generous guidance on my research work, paper writing and presentation skills during the PhD study I would also like to thank Prof Zhang Min-Hong, Prof Marshall Peter William, and Assistant Prof Qian Xudong for their helpful suggestions and valuable discussions

My sincere appreciation is dedicated to Dr Kazi Md Abu Sohel, Dr Chia Kok Seng, Dr Liu Xuemei, Dr Lee Siew Chin, Mr Xiong Dexin, Mr Xiong Mingxiang, Mr Li Ya and

Mr Wang Tongyun for their continuous supports on research works and discussions

My thanks also extend to all staff members at Concrete and Structural Engineering Laboratory Special thanks go to Mr Koh Yian Kheng, Mr Ang Beng Oon, Mr Ishak Bin A Rahman, Mr Choo Peng Kin and Ms Annie Tan for their generous, patient and continuous help during the experiments

I would thank all the friends and colleagues at my office during the year 2008 to 2012 and friends at the Centre for Offshore Research & Engineering (CORE), NUS for every happy moment we have shared during those years

Finally, I would thank my wife (Ms Chen Guiling), my parents, and my brother for their moral supports, continuous love, understanding and encouragements This thesis is

II    dedicated to my family

  III 

TABLE OF CONTENTS

ACKNOWLEDGEMENT……… I TABLE OF CONTENT……… III SUMMARY……….… IX List of Tables……… XIII List of Figures……… …XV List of Symbols and Anronyms……… XXI

CHAPTER 1 Introduction……… - 1 -

1.1 Overview……… - 1 -

1.2 Research Background……… …- 2 -

1.3 Research Objectives and scopes……… - 6 -

1.4 Thesis organization……… - 9 -

CHAPTER 2 Literature Review……….…- 15 -

2.1 General……… - 15 -

2.2 SCS sandwich composite structure………- 15 -

2.2.1 SCS sandwich composite structure without shear connector………… - 16 -

2.2.2 SCS sandwich structure with shear connector……… - 17 -

2.3 Curved SCS sandwich composite structure and curved reinforced concrete structure……….- 22 -

2.3.1 Curved reinforced concrete (RC) structure or RC shell structure………- 22 -

2.3.2 SCS sandwich shell structure………- 25 -

2.4 Strength of SCS sandwich composite beam and plate structure………- 26 -

2.4.1 Shear strength of the mechanical shear connectors……… - 26 -

2.4.2 Description on shear load-slip curves……… - 30 - 2.4.3 Tensile capacity of the mechanical shear connectors (or pull-out

IV    

strength)……… ……… - 33 -

2.4.4 Strength of the SCS sandwich composite beams……… - 39 -

2.4.5 Strength of SCS sandwich composite plates………- 42 -

2.4.6 Punching shear strength of concrete shell………- 49 -

2.4.7 Strength of SCS sandwich shell without shear connectors……… - 51 -

2.5 Finite element (FE) analysis on SCS sandwich structure……… - 52 -

2.6 Summary of observations from the literature review………- 53 -

CHAPTER 3 Novel shear connectors for SCS sandwich Composite structures ………- 63 -

3.1 Introduction………- 63 -

3.2 Types of connectors……… - 64 -

3.3 Prototype testing program……… - 66 -

3.3.1 Specimens for the test……….………… - 67 -

3.3.2 Material property……… - 68 -

3.3.3 Test setup……… - 69 -

3.4 Test results……….- 70 -

3.4.1 Failure modes and ultimate loads……….- 70 -

3.4.2 Load-deflection behaviors………- 71 -

3.5 Analysis and discussion of test results……… - 72 -

3.5.1 Analysis on strength of SCS sandwich beams with UCU connectors… - 73 -

3.5.2 Comparisons between UCU connectors and J-hook connectors……… - 76 -

3.5.3 Comparison between J-hook connectors and headed shear studs………- 77 -

3.6 Summary………- 78 -

CHAPTER 4 Behaviour and strength of shear connectors in steel-concrete-steel sandwich structures……….- 89 -

4.1 Introduction………- 89 -

4.2 Shear strength of J-hook connectors……… - 91 -

4.2.1 Experimental program……… - 92 -

4.2.2 Test results………- 96 -

4.2.3 Discussion on test results……… - 98 -

4.2.4 Shear strength of J-hook connectors……… - 100 -

4.2.5 Load-slip behaviors of J-hook connectors……… - 103 -

  V 

4.3 Tensile strength of J-hook connectors embedded in concrete……….- 119 -

4.3.1 Experimental program………- 120 -

4.3.2 Test results of tensile test………- 122 -

4.3.3 Discussions on test results……… - 123 -

4.3.4 Analytical model on tensile (Pull-out) strength of J-hook connectors - 127 -

4.4 Strength of J-hook connectors subjected to combined shear and tension loads ……….- 156 -

4.4.1 Push-out test results………- 156 -

4.4.2 Tensile test results……… - 157 -

4.4.3 FE model……….- 157 -

4.4.4 FE verifications against test results………- 162 -

4.4.5 FE analysis of J-hook connectors subjected to combination of tension and shear forces……….- 163 -

4.4.6 Analytical method on strength of J-hook connectors subjected to combination of shear and tension loads……… ………… - 164 -

4.4.7 Strength of J-hook connectors subjected to combined tension and shear loads………- 166 -

4.5 Summary……… - 176 -

CHAPTER 5 Strength of steel-concrete-steel sandwich composite beams with ultra lightweight cementitious composite (ULCC)………- 179 -

5.1 Introduction……… - 179 -

5.2 Experimental Investigation……… - 180 -

5.2.1 In-filled core material……….- 180 -

5.2.2 SCS sandwich composite beams and test setup ……….- 181 -

5.2.3 Strength of mechanical shear connector………- 181 -

5.3 Analytical analysis on strength of SCS sandwich composite structure…… - 182 -

5.3.1 Key concept………- 182 -

5.3.2 Strength of mechanical connectors……….- 183 -

5.3.3 Moment resistance of sandwich beam………- 185 -

5.3.4 Transverse shear resistance of sandwich beam……… - 189 -

5.3.5 Deflection……… - 190 -

5.3.6 Strength of beam under combined bending moment and transverse shear ………… ……… - 193 -

VI    

5.4 Push out test and tensile test results………- 193 -

5.4.1 Push out test results………- 193 -

5.4.2 Pull out test results……….- 194 -

5.5 Beam test results and discussion……….- 195 -

5.5.1 Load deflection behavior………- 195 -

5.5.2 Failure modes & maximum loads……… - 195 -

5.5.3 Effect of shear span-to-beam thickness ratio……….- 196 -

5.5.4 Effect of thickness of the steel face plate……… - 197 -

5.5.5 Effect of core material strength ……….- 197 -

5.5.6 Effect of spacing of the shear connectors……… - 199 -

5.6 Finite element analysis on SCS sandwich composite beams with J-hook shear connectors………- 199 -

5.6.1 General………- 199 -

5.6.2 Material model………- 200 -

5.6.3 Element type and geometry of the model……… - 200 -

5.6.4 Contact and restraint conditions ……….- 201 -

5.6.5 Loading and boundary conditions……….- 201 -

5.6.6 Verifications of FE model……… - 202 -

5.7 Verifications of the Analytical Model……….- 202 -

5.8 Comparisons between beams with J-hook connectors and headed studs……- 204 -

5.9 Summary……… - 204 -

CHAPTER 6 Experimetnal study on steel-concrete-steel sandwich composite shell under point load……….- 229 -

6.1 Introduction……… - 229 -

6.2 Development of SCS sandwich composite shell structure……… - 231 -

6.2.1 Concept of using mechanical shear connectors ……….- 231 -

6.2.2 Concept of using ULCC……….- 232 -

6.3 Static tests on SCS sandwich composite shells……… - 233 -

6.3.1 Test program……… - 233 -

6.3.2 Preparation of the specimens……….- 235 -

6.3.3 Test setup and instrumentation……… - 237 -

6.4 Test results and discussions………- 240 -

6.4.1 General behavior……….- 241 -

  VII 

6.4.2 Ultimate strength and failure mode………- 242 -

6.4.3 Measured deflections of the shell……… - 246 -

6.4.4 Strain distribution……… - 249 -

6.4.5 Load-transfer mechanism of the SCS sandwich shell under point load.- 250 - 6.4.6 Effect of variables on the punching shear strength of the shell ……….- 251 -

6.5 Summary……… - 256 -

CHAPTER 7 analysis on Punching shear strength of steel-concrete-steel sandwich composite shell structure……… - 297 -

7.1 Introduction……… - 297 -

7.2 Applications and considerations……… - 298 -

7.3 Analysis on punching shear strength of SCS sandwich shell ……….- 302 -

7.3.1 Modified controlled perimeter for SCS sandwich composite shell……- 302 -

7.3.2 Punching shear strength of the core material……… - 304 -

7.3.3 Punching shear strength of the steel face shell……… - 306 -

7.4 Comparisons between the test results and predictions………- 307 -

7.5 Comparisons between the test results and the ice-pressure……….- 311 -

7.6 Design recommendations……….- 311 -

7.6.1 Calculating punching shear strength of the SCS sandwich composite shell (calculate the first peak strength of the structure)……… - 311 -

7.6.2 Calculating punching shear strength of the surface skin steel shell (for second peak strength of the structure)………- 312 -

7.6.3 Determine the ice-contact pressure from ISO 19906 and compare the determined strength with the calculated punching shear resistance of the shell……….- 312 -

7.7 Summary……… - 312 -

CHAPTER 8 Conclusions and recommendations……… - 321 -

8.1 Review of completed research work………- 321 -

8.2 Conclusions……… - 323 -

8.3 Recommendations for future works……….- 328 -

References……… - 331 -

Publications………- 343 -

VIII    

An innovative study aiming to develop novel shear connectors for the SCS sandwich structure was carried out Concepts of nine types of mechanical shear connectors were proposed The general advantages and disadvantages of these developed shear connectors were discussed and compared Comparative studies on structural performances of the selected cable connector, J-hook connector and headed shear studs were carried out by tests on the prototype beams with them The test results showed that the beams with the cable connectors exhibited equivalent ultimate strengths but lower elastic stiffness compared with the beams with J-hook connectors The beams with the J-hook connectors exhibited equivalent strength, ductility and stiffness to the beams with the headed shear studs Design formulae on SCS sandwich beams with UCU connectors are developed

As the basic components of the SCS sandwich structure, the strengths of the J-hook shear connectors were studied by the test and FE methods The shear and tensile strengths of

X    

the J-hook connectors embedded in normal weight concrete (NWC), lightweight concrete (LWC) and ULCC were widely investigated through 102 push-out tests and 79 tensile tests The push-out tests show the shear strength of the J-hook connectors are significantly influenced by the geometry and strengths of the steel and concrete materials Based on the push-out test results, design formulae were developed to predict the shear strength and describe the load-slip behaviors, respectively Design approaches for tensile strength of the J-hook connectors were also developed by modifying the ACI 318 and PCI codes Strength of the J-hook connectors under combined shear and tension loads were obtained through FE analysis All these developed design approaches offer the basic design guides

on the prediction of the SCS sandwich members

Ultimate strength behavior of the SCS sandwich beams with shear connectors and ULCC were evaluated through one- or two- point loading tests on 18 sandwich beams Through the experimental investigation, it reveals that shear span significantly influence the failure modes and ultimate strength Thickness of the steel plates, core material strength, and spacing of the connectors influence the strength of the sandwich beams Through the comparisons between the strengths of the beams with the J-hook connectors and headed shear studs, it revealed that the J-hook shear connectors provided equivalent ultimate strength, ductility and stiffness to the beams with headed studs Theoretical model was developed to predict the strength of the SCS sandwich beams under combined shear force and bending moment The predicted strengths by this theoretical model agree well with the test results Moreover, nonlinear 3D FE model was developed for the analysis of the sandwich beams with the J-hook connectors The FE model exhibits good agreements on the ultimate strength, deforming shape of the beams and cracks developed in the core material This offers a useful method for the analysis of the SCS sandwich beams

  XI 

To date, there are no available design guides or tests on the SCS sandwich composite shell structure with shear connectors In this thesis, the ultimate strength performances of the SCS sandwich composite shells were investigated to fill the missing information Nine SCS sandwich shells were tested under patch loading The test results revealed that curvature of the shell, thickness of the steel face shell, strength of the core material, and spacing of the connectors have significant influences on the punching shear resistance of the SCS sandwich shell Introducing the mechanical shear connectors greatly improves the strength of the sandwich shell A theoretical model by modifying Eurocode 4 was developed to predict the punching shear resistance of the SCS sandwich composite shell structure Compared with the test results in this paper and 11 test results from the reference (Shukry, 1986), the developed model offers the best predictions compared with other design guides or methods Compared with the local ice contact pressure obtained from the API RP 2N and ISO 19906, it is found that all the tested sandwich shells exhibited much larger punching shear resistance

The proposed novel shear connectors offer more choices to design the SCS sandwich composite structures The developed design formulae on predicting strength of the J-hook connectors provide the basis for designing of the SCS sandwich beams, plates and shells with such type of connector The analysis model and numerical model developed in this thesis will be useful to predict the ultimate strength of the connector, sandwich beams and shells The experimental and analytical investigations on the SCS sandwich shell fill up the missing information on the SCS sandwich composite shells with shear connectors

XII    

  XIII 

LIST OF TABLES

Table 3.1 General comparisons among different connectors ……… …- 80 -

Table 3.2 Details of the prototype beams……… - 81 -

Table 3.3 Results of prototype testing……… - 81 -

Table 4.1 Details of specimens in Batch A for push-out test ……….- 106 -

Table 4.2 Details of specimens in Batch B for push-out test……… - 107 -

Table 4.3a Concrete material properties of specimens in Batch A (At 28 day)…… - 108 -

Table 4.4 Push-out test results and predictions by Eq 4.2 of specimens in Batch A - 109 - Table 4.5 Push-out test results and predictions by Eq 4.2 of specimens in Batch B - 110 - Table 4.6 Coefficients for proposed design formulae ……….- 111 -

Table 4.7 Material properties of the concrete mixture………- 135 -

Table 4.8(a) Specimen for tensile test and results……….- 136 -

Table 4.8(b) Specimen for tensile test and results……….- 138 -

Table 4.9(a) Predictions by groups of equations method A~E……… - 140 -

Table 4.9(b) Predictions by groups of equations method A~E……… - 142 -

Table 4.10(a) Details of push-out test specimens……… - 167 -

Table 4.10(b) Details of push-out test specimens……… - 168 -

Table 4.11 Comparisons between FE predictions and test results……… - 169 -

Table 4.12 Detailed information and FE results of FE models……… - 169 -

Table 5.1 Beam test specimen and specifications……… - 207 -

Table 5.2 Push out test specimens and specifications of J-hook connector…………- 208 -

Table 5.3 Details of the pull out test specimens……… - 208 -

Table 5.4 Shear resistance of concrete………- 208 -

Table 5.5 Shear resistance provide by steel connector………- 209 -

Table 5.6 Push out test results and predictions………- 209 -

XIV    

Table 5.7 Pull out test results summary and predictions by different approaches proposed

in Chapter 4 Part B……… - 210 -

Table 5.8 Comparisons between the FE prediction and the test results……….- 210 -

Table 5.9 Experimental and calculated moment resistances……… - 211 -

Table 5.10 Experimental and calculated shear resistances……… - 212 -

Table 5.11 Comparison of experimental and theoretical central deflections at two-thirds of the maximum test loads……… - 213 -

Table 5.12 Strength of B series beams and J series beams……… - 214 -

Table 6.1 Details of the SCS sandwich composite shells………- 259 -

Table 6.2(a) Property of the core material of the SCS sandwich composite shell… - 259 -

Table 6.2(b) Property of the surface skin and shear connector……….… - 260 -

Table 6.3(a) Ultimate strength of the composite shells and corresponding strains at the five critical locations………- 261 -

Table 6.3(b) Strains of ε1~ ε5 relate to the corresponding readings of rosettes in Fig.6.5………- 262 -

Table 6.4 Dimension of the punched concrete cone………- 262 -

Table 6.5 Observed cracks in the core material at different load stages……….- 263 -

Table 6.6 Test results of the SCS sandwich composite shells……….……- 264 -

Table 7.1 Details of the SCS sandwich composite shell tested by Shukry (1986)… - 315 -

Table 7.2 Comparisons between the test results and predictions by proposed design formulae and design codes……… - 316 -

  XV 

LIST OF FIGURES

Fig 1.1 Ice-resisting wall for platforms in Arctic Ocean……… - 12 - Fig 1.2 Concept for fluted shell Arctic structure (Marshall, 2009)……… - 12 - Fig 1.3 Details of curved shell, radial bulkhead, and internal framing (Marshall, 2010)……… - 13 - Fig 1.4 Double skin structure (Wright and Oduyemi, 1991) ……… - 13 - Fig 1.5 Illustrations on strengths of the SCS sandwich composite beam and shell structure……….- 14 -

Fig 2.1 Double skin SCS sandwich composite structure (Wright and Oduyemi, 1991) - 55 - Fig 2.2 Illustration on linking the shear cracks of the overlapped shear studs………- 55 - Fig 2.3 Bi-steel structure……… - 55 - Fig 2.4 Different types of mechanical connectors (GARCÍA, 2004)……… - 56 - Fig 2.5 Test set-up of shells under concentrated loading (Birdy et al., 1985)……….- 56 - Fig 2.6 Test set-up and dimensions of the specimens (Long, 1988; McLean et al., 1990)……….- 57 - Fig 2.7 Test set-up of the SCS sandwich shells (Shukry, 1986)……… - 57 - Fig 2.8 Failure modes of for anchors under tension force (a) Steel failure; (b) Pullout failure; (c) Concrete breakout failure; (d) Side-face blowout ; (e) Concrete splitting (ACI 318-08, 2008) ……… - 57 - Fig 2.9 Design philosophies on concrete breakout strength (Pallarés and Hajjar, 2010)……… - 58 - Fig 2.10 Strut and tie model for analysis of SCS sandwich beams (Xie et al., 2007) - 58 - Fig 2.11 Stress block and the resultant force in the section ……… - 58 - Fig 2.12 Dimension of the controlled perimeter……… - 59 - Fig 2.13 Stress block and the resultant force in the section……….- 59 -

XVI    

Fig 2.14 Resultant forces in unit length of the SCS sandwich composite plate…… - 60 -

Fig 2.15 Yield line analysis method for SCS sandwich composite plate……….- 60 -

Fig 2.16 FE model used for SCS sandwich plates (Shanmugam, 2002)……… - 61 -

Fig 2.17 FE model used for SCS sandwich plate with J-hook connector (Sohel, 2008)……… - 61 -

Fig 2.18 Illustration of the parameters of the concrete shells……… - 62 -

Fig 3.1 Illustration of different developed mechanical shear connectors for SCS sandwich composite structure………- 82 -

Fig 3.2 Dimension and test set-up of the SCS sandwich beams……… - 83 -

Fig 3.3 Tensile test of steel cable……… - 84 -

Fig 3.4 Fabrication procedures of SCS sandwich member with UCU connector……- 85 -

Fig 3.5 Failure shapes of the tested SCS sandwich prototype beam ……… - 86 -

Fig 3.6 Load-deflection curves of the beam test……… - 87 –

Fig 4.1 Different types of shear connectors ……….- 112 -

Fig 4.2 Push-out test specimen……….- 112 -

Fig 4.3 Stress strain curve of normal and high strength steel reinforcements…… - 112 -

Fig 4.4 Coarse and fine aggregate used for the push-out test specimen………- 113 -

Fig 4.5 Compression and flexural tension behaviors of ULCC……….- 113 -

Fig 4.6 ULCC grout before and after float table test……… - 113 -

Fig 4.7 Test set-up of push-out test………- 114 -

Fig 4.8 Determination of slip capacity……… - 114 -

Fig 4.9 Failure modes observed in the push-out tests with J-hook connectors…….- 114 -

Fig 4.10 Typical load-slip curves of specimen in batch (a) B1 with NWC; (b) B1 with ULCC; (c) B1 with LWC; (d) B2 with NWC; (e) B2 with ULCC; (d) B2 with LWC………- 115 -

Fig 4.11 Effect of hs /d on PJ for specimens ……….- 116 -

Fig 4.12 Effect of d on PJ……… - 116 -

Fig 4.13 Effect of fck on PJ (BA=Batch A; BB=Batch B)……….- 116 -

Fig 4.14 Predictions verified against the experimental ones ……….- 117 -

Fig 4.15 Scatter of ratios of test-to-prediction by different design equations………- 117 - Fig 4.16 Test and predicted load-slip curves (a) for NWC in Batch A; (b) for NWC in Batch B; (c) for LWC in Batch A; (d) for LWC in Batch B; (e) for ULCC in Batch A; (f)

  XVII 

for ULCC in Batch B ……….- 118 -

Fig 4.17 Failure modes of anchorage under tensile loading: (a)Steel failure; (b) pullout concrete; (c) breakout; (d) side-face blowout; (e) concrete splitting (ACI 318, 2008)………- 144 -

Fig 4.18 Methods of test on tensile strength of a pair of J-hook connectors……….- 144 -

Fig 4.19 Geometry illustration of the tensile-test specimens ……….- 144 -

Fig 4.20 Test set-up of the tensile test of J-hook connectors ……….- 145 -

Fig 4.21 Failure modes observed in tensile test of J-hook connectors……….- 146 -

Fig 4.22 Effect of concrete strength on tensile strength of J-hook connector…… - 147 -

Fig 4.23 Effect of diameter of connector on tensile strength of connector…………- 147 -

Fig 4.24 Effect of embedment depth on tensile strength of J-hook connector…… - 148 -

Fig 4.25 Effect of D/d ratio Fig 4.26 Effect of fiber content………- 148 -

Fig 4.27 Principles of calculating concrete breakout strength of the shear connector……… - 148 -

Fig 4.28 Calculation of projection area AN of the connector………- 152 -

Fig 4.29 Frequency distribution of ratios of test results-to-prediction ratios by (a) Eqn 4.6 for concrete breakout failure (CBF); (b) Eqn.4.12a for CBF; (c) Eqn.4.12b for CBF; (d) Eqn 4.12c for CBF; (e) Eqn 4.12d for CBF; (f) Eqn 4.13 for hook straighten .- 153 - Fig 4.30 Comparisons between the test results and predictions by design approaches A~E……… - 155 -

Fig 4.31 Comparisons between the push-out test results and predictions………… - 170 -

Fig 4.32 load-slip curves of push-out test……… - 170 -

Fig 4.33 Load-elongation curve of pullout test……… ………- 170 -

Fig 4.34 FE Stress-strain curve for ULCC………- 170 -

Fig 4.35 FE Stress-strain curve of steel… ……… - 170 -

Fig 4.36 Influence of friction coefficient μ………- 171 -

Fig 4.37 Simplified mode for push-out test specimen with J-hook connectors…….- 171 -

Fig 4.38 Different mesh size used in the FE model………- 172 -

Fig 4.39 Effect of mesh size on the FE prediction………- 172 -

Fig 4.40 a~f FE results verified against push-out test results……… - 173 -

Fig 4.41 Comparison of failure modes between test and FE simulation………… - 174 -

Fig 4.42 FE load-elongations curve verified against the test ones……….- 174 -

Fig 4.43 FE model for shear connector under shear and tension……… - 174 -

Fig 4.44 3D and 2D stress illustration in shank of J-hook……….- 175 -

XVIII    

Fig 4.45 Tension-shear interaction strength of connectors………- 175 -

Fig 4.46 Ratio of tension-shear interaction………- 175 -

Fig 5.1 Different types of mechanical connectors: (a) headed shear stud; (b) friction welded connectors in Bi-steel; (c) angle connectors; (d) J-hook connector; (e) ‘U’ Shape connecting system with steel cables………- 215 -

Fig 5.2 Stress-strain curve of the core material used in SCS sandwich composite beams……… - 215 -

Fig 5.3 Test setup of sandwich beams………- 216 -

Fig 5.4 Push test set up and specifications of specimen……….- 217 -

Fig 5.5 Tensile test setup ……… - 217 -

Fig 5.6 (a) 45° cone method (b) concrete capacity design (CCD) method……… - 217 -

Fig 5.7 (a) beam cross-section; (b) strain distribution; (c) stress distribution block; (d) elastic force distribution; (e) plastic force distribution………- 218 -

Fig 5.8 Comparisons between the predictions and test results of push out test (J-hook)………- 218 -

Fig 5.9 Comparisons of the generalized P/Pu-δ curves between the test and predictions………- 218 -

Fig 5.10 Failure modes observed from the push out test………- 219 -

Fig 5.11 Observed failure modes from pull out test ……….- 219 -

Fig 5.12 Load-elongation curve of pull out test……….- 219 -

Fig 5.13 Scatters of test-to-prediction ratios by the proposed design approaches in Chapter 4, section 4.3 ……….- 219 -

Fig 5.14 Effect of the parameters on the strength of the SCS sandwich composite beams……… - 223 -

Fig 5.15 Flexural failures………- 224 -

Fig 5.16 Vertical shear failures……… - 224 -

Fig 5.17 Connector failure……….- 224 -

Fig 5.18 Proposed FE model for SCS sandwich composite beams with J-hook connector……… - 225 -

Fig 5.19 FE verifications against the test results………- 226 -

Fig 5.20 (a)~(f) Comparisons of the cracks in the core material between the FE model and test……….- 227 - Fig 5.21 Scatter of the ratio of the experimental deflection-to-predicted deflection - 228 -

  XIX 

Fig 6.1(a) Dimension of the SA1……… - 265 - Fig 6.1(b) Dimension of the SA2……… ……… - 265 - Fig 6.2 (a) Dimension of SCS sandwich composite shell SB1~SB3……….- 266 - Fig 6.2 (b) Dimension of SCS sandwich composite shell SB4……….- 267 - Fig 6.2 (c) Dimension of SCS sandwich composite shell SB6……….- 268 - Fig 6.2 (d) Dimension of SCS sandwich composite shell SB7… ……….- 269 - Fig 6.3 A step-by-step precedure of fabricating curved SCS sandwich composite structure……… - 270 - Fig 6.4 Casting of the curved SCS sandwich shell………- 270 - Fig 6.5(a) Layout of LVDTs on SA1 and SA2……… - 271 - Fig 6.5(b) Location of strain gauges on SA1 and SA2……… - 271 - Fig 6.6 (a) Location of LVDTs on SB1~SB7……….- 271 - Fig 6.6 (b)~(d) Rosette location of specimen SB1~SB3………- 271 - Fig 6.6 Layout of the transducers and strain gauges……….- 272 - Fig 6.7 Test setup of SA1 and SA2………- 273 - Fig 6.8 Test setup on SB1~SB7 and material test……… - 273 - Fig 6.9 Load-deflection curves of specimen SA1 and SA2………- 274 - Fig 6.10 (a) Load-central deflection curves of specimen SB1~SB3……… - 274 - Fig 6.11 Punching shear failure of the outer top steel shell in different specimens - 278 - Fig 6.12 Cracks in the core material of the specimens……….- 278 - Fig 6.13 Deformed shapes of SB1~SB6 at different load levels………- 285 - Fig 6.14 Deformed shapes of SA1……… - 286 - Fig 6.15 Deformed shapes of SA2……… - 287 - Fig 6.16 Load-strains curves in the steel shells of SB1~SB7……….- 292 - Fig 6.17 Load-deflections curves and effect of different variables………- 296 -

Fig 7.1 Inclination angle along arch direction………- 317 - Fig 7.2 Illustration of control perimeter for the punching shear strength………… - 317 - Fig 7.3 Illustration of tension membrane effect……….- 318 - Fig 7.4 Scatters of ratios of test results-to-predictions by code or proposed formulae……… - 318 - Fig 7.5 Comparisons of test results with predictions by codes and proposed formulae……… - 319 - Fig 7.6 Comparisons of test results with predictions by code and proposed

XX    formulae……… - 319 -

   XXI 

LIST OF SYMBOLS AND ANRONYMS

A Ice floe area

0

N

A Projected area of one anchor at the concrete surface unlimited by edge influences

or neighboring anchors, idealizing the failure cone as pyramid with a base length

or in the case of a group of anchors, from a line through a row of adjacent anchors

s

A Cross section area of the shear connector

D Inner diameter of the bent hook

c

E Elastic Young’s modulus of concrete

s

E Elastic Young’s modulus of steel material

H Height of the headed shear stud connector

I Second moment of area

t

K Elastic stiffness of the mechanical shear connectors in the tension zone of concrete

under shear forces

c

K Elastic stiffness of the mechanical shear connectors in the compression zone of

concrete under shear forces

J

N Tension capacity of the J-hook connector

P Applied shear load on the connector

R Inner radius of the bent hook

S Averaged relative slip occurred on the interface between concrete and steel

V Shear resistance of the structure

c

V The shear resistance contributed by the concrete

s

V The shear resistance contributed by the connectors or shear reinforcements

d Diameter of the headed shear stud connector

t Thickness of the tension steel plate, mm

w Density of the concrete, kg/m3

s Spacing of connectors

x The distance from the neutral axis to the top compression fiber of the concrete in beam section

   XXIII 

ACRONYMS

3D Three dimensional

AASHTO American Association of State Highway and Transportation Officials

ABA Angle-steel bar-angle connecting system

ACA Angle-C channel-angle connecting system

ACI American Concrete Institute

AHA Angle-steel hoop-angle connecting system

AIA Angle-I beam-angle connecting system

API American Petroleum Institute

ASTM American Society for Testing and Materials

AT Angle-T beam connecting system

BS British standard

CEB-FIP Euro-International Committee for Concrete (CEB)-International

Federation for prestressing (FIP) DNV Det Norske Veritas

EC Eurocode

FE Finite element

HPC High performance concrete

ISO International organization for standard

LWC Lightweight concrete

LVDT Linear varying displacement transducer

NWC Normal weight concrete

PVA Polyvinyl Alcohol

RC Reinforced concrete structure

SCS Steel-concrete-steel sandwich composite structure

UCU U connector-cable-U connector connecting system

ULCC Ultra lightweight cementitious composite

USU U connector-steel bar-U connector connecting system

WBW Wave connector-steel bar-wave connector connecting system

XXIV  

SCS sandwich shell is the curved form of SCS sandwich structure It is made of infill core concrete sandwiched by two steel face shells SCS sandwich composite shell structure was used as oil reservoirs built at the seabed for the deep sea oil production system (Montague, 1975; Shukry, 1986; George, 1998) More recently, curved SCS sandwich structure was proposed as the ice-resistant wall to resist the ice loading and provide

Ultimate strength of the SCS sandwich structure is one of the main concern when we design such type of structures For most of the design codes, the SCS sandwich structure

is treated as the RC structure to check the flexural and shear resistance (Eurocode 4) Similar to RC structure, the SCS sandwich structure probably fails in flexural failure, brittle failure (shear failure or punching shear) or combined failure of the both, which will be greatly depended on the structure itself as well as applied loads (Stein, 2007) For ice-resistant wall structures in Arctic region, the main concern for designing is punching shear resistance that considers the local ice contact pressure acting on the structures (API

RP 2N, 1995)

1.2 Research Background

To meet the rapid growing demand of oil and gas for the bursting industries of the world, the search of oil now extends to deep sea and Arctic region The Arctic region is found to

be the last region with the highest unexplored potential resources for oil and gas as well

as unconventional hydrocarbon resources such as gas hydrates Most of the offshore

  ‐ 3 - 

petroleum production system in the Arctic requires platforms that can be used as oil storage and maintaining facilities Due to the harsh environment with moving ice sheets, ridges and icebergs, an ice-resistant wall around the perimeter of the oil production platforms will be used to resist the produced ice loading and transmit these loads to the foundation This ice-resistant wall system is shown in Fig 1.1 The exterior ice-resisting wall is composed of flat or curved plates stiffened by the bulkheads and thrust beams Marshall et al (2009, 2010) proposed a concept for ice-resistant platform with a SCS sandwich structure to be used in sea water depths ranging from 10 to 100 m (as shown in Fig 1.1c, 1.2 and 1.3) The proposed ice-resistant structure is in a conical shape with a slope angle of 45°~50° to the horizontal sea level It was observed that sloping structures would encounter smaller ice forces compared with vertical-sided structures The ice sheet would ride up the slope and fail in flexural bending rather than crushing as that occurred

to a vertically-sided structure Curved SCS sandwich system was proposed as the resistant wall for this arctic platform

ice-Since the curved SCS sandwich structure was chosen for the protection of the platforms,

it is of great interest to obtain strength of this type of structure for design purpose Unfortunately, there are no related design guidelines for this SCS sandwich shell structure The EC4 or ANSI/AISC only specifies the strength of the flat steel-concrete composite structures Moreover, few literatures are available for this topic in the public domain The SCS sandwich shells subjected to external pressure and local concentrated load were studied by Shukry (1986) However, these investigated curved SCS sandwich structures were designed without any bond measures between the concrete and steel plates There were some research works done to study the ultimate strength of concrete shells made of both normal and lightweight concrete (Birdy and Bhula, 1985; McLean et al., 1990; Phan, 1993; Sabnis and Shadid, 1994) Nevertheless, those research works were limited to the

‐ 4 -    

concrete shells that were different from the SCS sandwich structures

In SCS sandwich structures, cohesive materials and mechanical shear connectors are widely used to achieve composite action SCS sandwich structure with the cohesive material such as epoxy was proved to be weak in sectional shear strength due to sole shear capacity contributed by the pure concrete (Solomon, 1976; Ong and Mansur, 1985) Compared with cohesive material, shear connectors exhibited advantages on providing cross sectional shear resistance There are several representative types of mechanical connectors used in SCS sandwich structures The most widely used shear connector in SCS sandwich structure was the headed shear stud or Nelson stud SCS sandwich structure with overlapped headed shear stud namely ‘Double skin structure’ was originally devised for submerged tunnels as shown in Fig 1.4 (Wright and Oduyemi, 1991) Another representative type of connector is the one used in ‘Bi-steel’ sandwich structure (Bowerman et al., 1999) Friction technology was used to fabricate this type of sandwich composite structure Though this type of structure exhibited excellent performances, the only disadvantage was that the thickness of Bi-steel structure was limited to 0.2~0.7 m to fit the friction welding equipment during fabrication SCS sandwich structures with angles were also applied in port and harbor structures (Malek et al., 1993) Experimental studies on this type of sandwich structure were carried out by Malek et al (1993) and Sohel (2003) However, due to shallow embedment of the angle connectors, this type of structure exhibited weak cross section shear resistance J-hook connectors were proposed to be used in SCS sandwich composite structure by Liew et al (2008) The J-hook shear connector was named after its shape like the English character

‘J’ The J-hook connectors were found to be capable of providing effective bond and cross sectional shear resistance under different loading conditions (Liew et al., 2009;

  ‐ 5 - 

Sohel, 2008; Dai, 2008; Sohel and Liew, 2011) However, as the basic components, the shear and tensile strength of the J-hook connectors embedded in the core concrete have not been systematically studied

LWC concrete is used in SCS sandwich composite structure to reduce self weight Present research explores the newly developed concrete mixture namely Ultra Lightweight Cementitious Composite (ULCC) The ULCC exhibits high compressive strength ( f ck

=65 MPa) but with a low density of only 1450 kg/m3 (Chia et al., 2011) The ULCC uses very fine aggregate (Cenosphere) and exhibits excellent workability This advantage can greatly reduce the honeycomb voids in the structure with normal weight concrete Finally, ULCC is chosen as the core material for the SCS sandwich composite structure

Since the ULCC is used in the SCS sandwich structures, corresponding design methods need to be developed Therefore, it is necessary to develop design approaches or check currently available design guidelines for research and design purposes So far, most of the design formulae on the strength of the mechanical connectors are empirical ones and greatly depend on the library of the tested specimens The SCS sandwich structure with new types of connectors and core material are out of scope of these design codes Previous research works were focused on strength of SCS sandwich structure with NWC

or LWC (Oduyemi and Wright, 1989; Roberts et al., 1995; Roberts et al., 1996; Narayanan et al., 1997; Liew et al., 2009; Sohel and Liew, 2011) Most of the design codes were developed for the steel-concrete composite structure with headed shear studs (EC4, ANSI/AISC)

To date, there are few literatures on the strength of SCS sandwich shell structures Previous studies were either on the concrete shells or SCS sandwich shell without mechanical shear connectors (Phan, 1988; Sabnis and Shadid, 1994; McLean et al., 1990;

‐ 6 -    

Shukry, 1986; Shukry and Goode, 1990) It is necessary and important to carry out experimental investigations to obtain the structural performances of the SCS sandwich composite shell structure Furthermore, as specified in API RP 2N, the localized ice loads need to be considered for both steel and concrete structures (API-RP-2N, 1995) Therefore, the punching shear capacity of the SCS sandwich composite shell structure becomes a main concern for the further research

1.3 Research Objectives and scopes

As mentioned above, information on the strength of SCS sandwich shells (or curved SCS sandwich plates) are quite limited In order to achieve full composite action at the interface of the steel and concrete, mechanical connectors are used The newly developed ULCC is chosen as the core material to achieve a lightweight structure So far, structural behaviors of SCS sandwich structures with new mixture-ULCC have not been investigated Moreover, the shear and tensile strengths of the proposed J-hook connector have not been systematically studied The structural performances of the SCS sandwich composite structure with the mechanical shear connectors and ULCC should be studied for the flat panels The relationship among the strength of the structure and strength of the connectors were shown in Fig 1.5 The research objectives are listed below:

1) To carry out feasibility study on mechanical connectors for the SCS sandwich shell structures and to recommend suitable connectors for curved sandwich structure 2) To systematically study the shear and tensile strength of the J-hook connectors embedded in different concrete mixtures including NWC, LWC and ULCC; to obtain the strengths of the J-hook connectors subjected to shear, tension and combined shear and tension loads To develop design formulae on prediction of these strengths

3) To experimentally investigate the ultimate strength behavior of the proposed

  ‐ 7 - 

sandwich beams with the newly developed mixture ULCC To develop FE and analytical models to predict the strength of these SCS sandwich beams with the mechanical connectors and ULCC

4) To carry out experimental study on the SCS sandwich shells with mechanical connectors and ULCC These experimental studies are set to investigate the structural performances of sandwich shells under patch loading

5) To develop analytical methods to predict the punching shear strength of the SCS sandwich shell structures with mechanical connectors and ULCC

To achieve the above objectives, the research scopes are as follows:

1) In order to find the suitable shear connectors to be used in the SCS sandwich shell structure, several types of novel shear connectors were developed and proposed The performances of the selected connectors were investigated through the tests on the prototype SCS sandwich composite beams with them Through the comparative studies, recommendations on the most suitable connectors are made for the further research

2) To investigate the shear strength, tension capacity and strength of the J-hook connectors under combined shear and tension forces of the proposed J-hook shear connectors, a series of push-out tests, tension tests and finite element analysis are conducted, respectively Parametric studies are carried out to investigate the influences of different variables on the shear and tension capacity All these test programs are focused on the strength of the J-hook connectors embedded in different concrete mixtures especially in the ULCC

3) Ultimate strength of SCS sandwich beams with the ULCC is also one of the research scopes Structural behaviors of the SCS sandwich beams with ULCC are investigated

‐ 8 -    

through a series of three-point or four-point bending tests The tests are also carried out to investigate the influences of different parameters on the strength of sandwich beams Analytical models are proposed and compared with finite element (FE) method to predict the strength of SCS sandwich beams The experimental results are used to verify the developed analytical model and FE model

4) Finally, the ultimate strength behavior of SCS sandwich composite shell is investigated A two-phase experimental programme is carried out to investigate the structural behavior of the SCS sandwich shells under concentrated loading In the test program, the bond enhancement by the connector, thickness of the steel shell, strength of the concrete, spacing of the connectors, curvature of the shell are considered The tests focus on the strength of the shell under point load Experimental results are used to verify the analytical method to predict the strength

of the SCS sandwich shell

The research work reported in this thesis aims to fill the missing information on SCS sandwich composite shell structures with shear connectors Design guidelines are proposed to predict the strength of the SCS sandwich composite shell structure under local concentrated loading The developed design guides to calculate the strengths of J-hook connectors will supplement the existing design approacheson the shear connectors used in SCS sandwich composite structure Nevertheless, this developed design guides enlarge the application scopes of the formulae for connectors embedded in more types of core concrete Therefore, these researches clear the obstacles of applying the SCS sandwich composite structure with the J-hook connectors The ultimate strength behaviors of the SCS sandwich composite beams with mechanical shear connectors and new core material ULCC will be investigated through the test on these sandwich beams

  ‐ 9 - 

The design approaches are hopefully developed for the SCS sandwich composite beams with mechanical shear connectors and ULCC Finite element model will also be developed to analyze the structural performances of the SCS sandwich beams with the J-hook connectors and ULCC

1.4 Thesis organization

Chapter 1 introduces the development of SCS sandwich structure especially for the SCS sandwich shell structure Development of mechanical shear connectors used in SCS sandwich structures is also introduced Research objectives, scopes and significance are presented in this chapter

Chapter 2 gives literature reviews on SCS sandwich composite structures, concrete shell structures and SCS sandwich shell structures SCS sandwich composite structures with different bonding measures are reviewed Research work on investigating the strengths of mechanical shear connectors including shear, tensile and strength under combinations of shear and tensile loads are reviewed Ultimate strength tests on SCS sandwich composite beams and plates were also reviewed

Chapter 3 performs feasibility studies on the novel connectors for used in SCS sandwich shells Through the comparative study, bonding effectiveness of the studied mechanical shear connectors is discussed and observed Recommendations on suitable shear connectors are made for the further research

Chapter 4 presents the research achievements on the strength of the J-hook connectors used in the SCS sandwich composite structure The shear strength and tensile strength of the J-hook connectors are systematically studied through push-out tests and pull-out tests, respectively Based on these push-out test results, regression analysis are carried out and

‐ 10 -    

design formulae on predicting shear strength of the J-hook shear connectors embedded in different concrete mixture are proposed for design purpose Moreover, design formulae describing the load-slip behaviors the J-hook connectors are also proposed through analysis on amounts of the load-slip curves obtained from the test Design guidelines in ACI and PCI are also used to predict the pull-out strength of the J-hook connectors Predictions are verified against the pullout test results A FE model is developed and used

to investigate the strength of J-hook connectors under combinations of shear and tensile loads

Chapter 5 investigates the structural behaviors of the SCS sandwich beams with shear connectors and ULCC Two series of SCS sandwich beams are designed with J-hook connectors and headed shear studs respectively Different parameters influencing the ultimate strength of the SCS sandwich beams are studied and discussed Analytical design formulae predicting the ultimate strength of the SCS sandwich beams are developed Moreover, FE model is also developed to describe the structural response of the SCS sandwich beams with the ULCC and shear connectors

Chapter 6 describes the structural behavior of the SCS sandwich composite shells under local concentrated loading The investigated SCS sandwich composite shells are designed with mechanical connectors (including J-hook and headed shear stud connectors) and ULCC The experimental study focus on the punching shear resistance of the SCS sandwich shells subjected to local concentrated loading

Chapter 7 presents the analytical model to predict the punching shear strength of SCS sandwich composite shell structures The analytical predictions are compared with those from experiments Moreover, strengths of the SCS sandwich composite shells are also checked by the ice contact pressures that are specified in API and ISO 19906 Through

‐ 12 -    

(a) Oil production platform in Northstar Island,

Alaskan Beaufort Sea

(b) Oil production platform-Molikpaq,

Canadian Beaufort Sea

(c) Generic Arctic oil & gas platform (Marshall, 2010) Fig 1.1 Ice-resisting wall for platforms in Arctic Ocean

Fig 1.2 Concept for fluted shell Arctic structure (Marshall, 2009)

  ‐ 13 - Fig 1.3 Details of curved shell, radial bulkhead, and internal framing (Marshall, 2010)

Fig 1.4 Double skin structure (Wright and Oduyemi, 1991)