IMPACT PERFORMANCE OF CEMENT COMPOSITE FILLED PIPE-IN-PIPE STRUCTURES WANG YU NATIONAL UNIVERSITY OF SINGAPORE 2014 IMPACT PERFORMANCE OF CEMENT COMPOSITE FILLED PIPE-IN-PIPE STRUCTURES WANG YU (B. Eng., HIT) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CIVIL & ENVIRONMENTAL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2014 DECLARATION I hereby declare that this 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. Wang Yu 01 August 2014 Acknowledgement ACKNOWLEDGEMENT I wish to express my sincerest gratitude to my supervisors Professor Liew Jat Yuen, Richard, Professor Zhang Min-Hong and Associate Professor Qian Xudong for their invaluable support, guidance and encouragement on my research work. Sincere thanks are further expressed to Dr. Chia Kok Seng, Dr. Kazi Md Abu Sohel, Dr. Lee Siew Chin, Dr. Wang Tongyun, Dr. Xiong Dexin, Dr. Xiong Mingxiang, Dr. Yan Jiabao and Ms. Zheng Jiexin for their help in my research work. Thanks are also extended to all staff members at Concrete and Structural Engineering Laboratory for their generous, patient and continuous help during the experiments. I would also like to thank all friends and colleagues in National University of Singapore during the past four years for sharing with me their happiness. Special thanks to my parents and girlfriend for their moral supports, continuous love, understanding and encouragement. Finally, I would like to acknowledge the finiancial support from the Center for Offshore Research and Engineering in the National University of Singapore and the research scholarship provided by the China Scholarship Council. i Table of contents TABLE OF CONTENTS ACKNOWLEDGEMENT . i TABLE OF CONTENTS ii SUMMARY . vi LIST OF TABLES . viii LIST OF FIGURES x LIST OF SYMBOLS . xvii CHAPTER ONE INTRODUCTION 1.1 Background . 1.2 Objectives and Scopes . 1.3 Significance and Contributions . 1.4 Outline of the Thesis . CHAPTER TWO LITERATURE REVIEW 2.1 Introduction . 2.2 Hollow Steel Pipes Subjected to Transverse Loads 2.2.1 Hollow Steel Pipes Subjected to Static Transverse Loads 2.2.2 Hollow Steel Pipes Subjected to Transverse Impacts . 14 2.2.3 Indentation Limits for Hollow Steel Pipes 21 2.3 Steel-Concrete-Steel (SCS) Composite Panels Subjected to Transverse Loads . 23 2.4 Concrete-Filled Steel Tubes (CFST) Subjected to Transverse Loads . 28 2.4.1 Concrete-Filled Steel Tubes (CFST) Subjected to Static Transverse Loads . 28 2.4.2 Concrete-Filled Steel Tubes (CFST) Subjected to Transverse Impacts 32 2.5 Concrete-Filled Pipe-In-Pipe Composite Structures . 36 2.6 Filler Materials for Composite Structures . 41 2.7 Observations Arising from the Literature Review 43 ii Table of contents CHAPTER THREE DROP WEIGHT IMPACT TEST 3.1 Introduction 46 3.2 Test Specimens and Set-up 47 3.2.1 Test Specimens 47 3.2.2 Ultra Lightweight Cement Composite (ULCC) . 49 3.2.3 Test Set-up and Test Procedure . 51 3.3 Test Results and Discussion 55 3.3.1 Damage Mechanisms . 57 3.3.2 Impact Force 59 3.3.3 Global Displacement 62 3.3.4 Local Indentation . 64 3.3.5 Strains 67 3.3.6 Post-peak Mean Force 72 3.3.7 Global Bending Deformation Energy 74 3.3.8 Energy Absorption Capacity 75 3.3.9 Effects of PVA Fibers 77 3.3.10 Comparison of the Impact Performance 79 3.3.11 Multiple Impacts 79 3.4 Summary 84 CHAPTER FOUR FINITE ELEMENT ANALYSIS 4.1 Introduction 87 4.2 Finite Element Modeling . 88 4.2.1 Material Models . 88 4.2.2 Finite Element Models . 92 4.2.3 Contact Model 94 4.3 Validation of Finite Element Analysis . 95 4.4 Finite Element Parametric Study . 101 iii Table of contents 4.4.1 Impact Velocity Effect 102 4.4.2 Indenter Shape Effect 104 4.4.3 Inner Pipe Effect 107 4.4.4 Steel Strength Effect 108 4.4.5 Cement Composite Strength Effect . 110 4.4.6 Filler Material Effect . 112 4.5 Summary . 113 CHAPTER FIVE LOAD-INDENTATION RELATIONSHIP 5.1 Introduction . 115 5.2 Experimental Investigation 116 5.2.1 Test Specimens and Set-up 116 5.2.2 Test Results . 118 5.2.3 Comparison with Analytical Models for Hollow Pipes . 123 5.3 Finite Element Investigation . 125 5.3.1 Finite Element Modeling . 125 5.3.2 Validation of the FE Analysis . 126 5.4 Load-Indentation Relationship for Hollow Pipes 129 5.5 Two-Stage Load-Indentation Formulation for Pipe-In-Pipe Composite Structures 131 5.5.1 Theoretical Model for Hollow Pipes . 131 5.5.1.1 Ring model 133 5.5.1.2 Generator model 135 5.5.1.3 P-δ relationship for hollow pipes 137 5.5.2 Two-Stage Approach for Cement Composite Filled Pipe-In-Pipe Structures . 137 5.5.2.1 Composite stage . 138 5.5.2.2 Separation stage . 142 5.5.3 Validation 143 5.6 Load-Indentation Relationship for Cement Composite Filled Pipes . 147 5.6.1 Localized Indentation Phase 147 iv Table of contents 5.6.2 Indentation Propagation Phase . 149 5.6.3 Load Redistribution Phase . 150 5.6.4 Validation . 153 5.7 Summary 154 CHAPTER SIX THEORETICAL ANALYSIS 6.1 Introduction 157 6.2 Theoretical Analysis 158 6.2.1 Dynamic Deformation Response . 158 6.2.2 Load-Indentation Relationships for Simply Supported Pipes 163 6.2.3 Numerical Procedure . 166 6.3 Validation of Theoretical Analysis 169 6.4 Parametric Study 176 6.4.1 Material Strength Effect . 176 6.4.2 Geometric Property and Impact Velocity Effect 180 6.4.3 Validation against Numerical Simulations . 185 6.4.4 Simplified Impact Response Formulation for Pipe-In-Pipe Composite Structure . 188 6.5 Summary 192 CHAPTER SEVEN CONCLUSIONS 7.1 Brief Overview 194 7.2 Main Findings and Conclusions 196 7.3 Recommendations for Future Research . 203  REFERENCE . 204 LIST OF PUBLICATIONS 218 v Summary SUMMARY Circular hollow sections have wide applications in both onshore and offshore infrastructures, including offshore jacket and jackup structures, oil and gas pipelines, etc., due to their low resistance to fluid flow, easy handling in construction, transportation and erection. Protection of pipelines against impact loadings has become an important concern in engineering as external impact loadings are a primary threat and a frequent cause of damage in onshore and offshore pipelines. Most of the current studies on this problem have focused on the impact performance of hollow steel pipes, which demonstrate limited structural capacity under impact loads, coupled with large global and local deformations. Concrete-filled pipe-in-pipe composite structures have recently emerged as a popular solution to enhance the structural resistance against external loadings. Engineering applications of such composite structures in a harsh offshore environment requires a comprehensive understanding on the impact behavior for these pipe-in-pipe composite structures. The objective of this research is, therefore, to develop a framework to predict the impact response of ultra lightweight cement composite (ULCC) filled pipe structures, validated by detailed experimental and numerical investigations. This study carries out drop weight impact tests to investigate the impact behavior for three types of pipe specimens, including hollow pipe specimens, ULCC-filled pipe specimens and ULCC-filled pipe-in-pipe specimens. Besides the experimental investigation, this study simulates the impact process for the pipe specimens by using the nonlinear finite element (FE) software LS-DYNA and conducts an FE parametric study to extend the understanding of the impact performance for pipe-in-pipe composite structures. The pipe specimens experience global deformations and local indentations under the transverse impact. This study conducts lateral indentation tests to explore the load-indentation (P-δ) vi Conclusions 7.3 Recommendations for Future Research The following are further research work recommended to achieve an insight into the impact behavior of pipe-in-pipe composite structures: (1) Research work investigates the impact behavior for pipe-in-pipe composite structures under the combined transverse impacts and various levels of external or internal pressure to simulate the working condition of pipelines in the offshore environment. (2) Research work investigates the impact behavior for pipe-in-pipe composite structures subjected to the combined transverse impacts and axial pre-loads to simulate the working condition of onshore and offshore pipelines. (3) Experimental study focuses on the ultra lightweight cement composite (ULCC) through bending tests, biaxial and triaxial compressive test, etc., to improve the understanding of the material behavior and to develop the material model for the ULCC in the finite element (FE) analysis. (4) In the current study, the cement composite strength and the inner steel pipe thickness demonstrate slight influence on the impact performance for the pipe-in-pipe composite structures than the outer pipe strength and its thickness. Research work may explore the impact behavior for pipe-in-pipe composite structure filled with more lightweight materials than the ULCC and utilize FRP inner pipe to further reduce the structural weight. 203 References REFERENCE AIJ. Standards for Structural Calculation of Steel Reinforced Concrete Structures. Tokyo: Architectural Institute of Japan. 1987. AIJ. Recommendations for Design and Construction of Concrete Filled Steel Tubular Structures. 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Int J Impact Eng, 72, pp. 1-16. 2014. Wang, Y., Qian, X., Liew, J. Y. R., & Zhang, M-H.Impact of Cement Composite Filled Steel Tubes: An Experimental, Numerical and Theoretical Treatise.Thin-Walled Struct, 87, pp. 7688. 2015. Wang, Y., Qian, X., Liew, J. Y. R., & Zhang, M-H. Concrete-Filled Pipe-In-Pipe Composite Structure under Transverse Impact Loading. In Proc. 10th International Conference on Advances in Steel Concrete Composite and Hybrid Structures, July 2012, Singapore, pp. 11071114. Wang, Y., Qian, X., Liew, J. Y. R., & Zhang, M-H. Experimental Behavior of Cement Composite Filled Pipe-In-Pipe Sandwich Structures under Transverse Impact Loading. In Proc. 10th Pacific Structural Steel Conference, October 2013, Singapore, pp. 630-635. Wang, Y., Qian, X., Liew, J. Y. R., & Zhang, M-H. Experimental Behavior of Cement Filled Pipe-In-Pipe Composite Structures under Lateral Indentation. In Proc. 26th KKHTCNN Symposium on Civil Engineering, November 2013, Singapore. 218 [...]... generator model in the pipe- in -pipe composite structure ti Thickness of the inner pipe in the pipe- in -pipe composite structure to Thickness of the outer pipe in the pipe- in -pipe structure or thickness of the hollow steel pipe or thickness of the steel pipe in the cement composite filled pipe structure tring Equivalent thickness for the ring model in the pipe- in -pipe composite structure t1 Time instant when... Maximum impact force Po Indentation resistance of the outer pipe Pp Peak load of the tubular joint (Lu et al., 1994) Ps Serviceability strength of the tubular joint (Lu et al., 1994) Pu Ultimate strength R Radius of the pipe Rc External radius of the infilled cement composite cylinder Rci Failure stress of the cement composite in ith direction Ri External radius of the inner pipe in the pipe- in -pipe composite. .. radius of the outer pipe in the pipe- in -pipe structure or external radius of the hollow steel pipe or external radius of the steel pipe in the cement composite filled pipe structure R1 Radius of the bottom arc in a deformed ring R2 Radius of the upper arc in a deformed ring S Continuous deformation field SB Local effects factor defined in Eq (2.10) S BS Coefficient defined in Eq (2.30) Ts Tensile force in. .. steel pipes C3 , C 4 , C5 Coefficients in the recommended P-δ relationship for simply supported hollow steel pipes D Diameter of the pipe Di External diameter of the inner pipe in the pipe- in -pipe composite structure Dmax Maximum diameter of the pipe Dmin Minimum diameter of the pipe Do External diameter of the outer pipe in the pipe- in -pipe structure or external diameter of the hollow steel pipe or... predict the impact response of ULCC -filled pipe- in -pipe structures and to provide design implications on this composite pipe To achieve this target, the specific objectives are: (1) To investigate experimentally the transverse impact performance of the three types of pipe structures, i.e., the hollow pipe structures, the ULCC -filled pipe structures and the ULCC -filled pipe- in -pipe composite structures. .. develop finite element (FE) models to simulate the impact process and to have a deep understanding on the impact behavior of the pipe- in -pipe composite structures (3) To examine the load-indentation (P-δ) response for the pipe- in -pipe composite structures based on a combined experimental and numerical investigation (4) To develop theoretical methods to estimate the impact response of the pipe- in -pipe composite. .. stiffness of SCS composite beams (Liew et al., 2009) Kp Plastic contact stiffness of SCS composite beams (Liew et al., 2009) xviii List of symbols L Length of the pipe Lf Crushing failure length of the cement composite in the x-z plane Lo Clear span length of the pipe Lt Total length of the cement composite under the indenter in the x-z plane Lxz Length of the load-resistance area of the cement composite in. .. impact response for the pipe- in -pipe composite structures 1.3 Significance and Contributions This study will contribute to the existing literatures and hopefully lead to the recommendation of design guidelines for the practical use of the ULCC -filled pipe- in -pipe composite structure in pipeline applications against transverse impacts This study will extend the understanding of the impact behavior of. .. or the cement composite g Gravitational acceleration k Coefficient defined in Eqs (2.14) to (2.16) kd Internal scalar multiplier in MAT_72R3 in LS-DYNA m Coefficient defined in BS 5400-part 5 (2005) md Mass of the drop weight mo Coefficient defined in CIDECT (1995) mp Mass of the pipe n Strain-hardening exponent p Mean pressure of the cement composite in MAT_72R3 in LS-DYNA pi Internal pressure of the... the steel pipe (Gresnigt et al., 2007) r Radius of the semi-cylindrical indenter head xxii List of symbols  rf Strain rate enhancement factor in MAT_72R3 in LS-DYNA si Deviatoric stress tensor s1 Length of the bottom arc in a deformed ring s2 Length of the upper arc in a deformed ring s3 Half-length of the flat segment in a deformed ring t Thickness of the pipe tc Thickness of the cement composite . IMPACT PERFORMANCE OF CEMENT COMPOSITE FILLED PIPE- IN -PIPE STRUCTURES WANG YU NATIONAL UNIVERSITY OF SINGAPORE 2014 IMPACT PERFORMANCE OF CEMENT COMPOSITE. types of pipe specimens, including hollow pipe specimens, ULCC -filled pipe specimens and ULCC -filled pipe- in -pipe specimens. Besides the experimental investigation, this study simulates the impact. the pipe specimens by using the nonlinear finite element (FE) software LS-DYNA and conducts an FE parametric study to extend the understanding of the impact performance for pipe- in -pipe composite