Blast resistance of steel concrete composite structures

BLAST RESISTANCE OF STEEL-CONCRETE COMPOSITE STRUCTURES KANG KOK WEI B.Eng (Hons.), NUS A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CIVIL & ENVIRONMENTAL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2012 i 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. _________________ Kang Kok Wei 29th October 2012 ii ACKNOWLEDGEMENT First and foremost, I would like to thank God to providing me with the opportunity go through a candidature for a PhD as such opportunities not befall most. I would like also to thank my wife. Kareen, for all the physical and emotional support and love that she has showered upon me throughout these years, especially now when we have one additional member in our family. At the university, I would like to express my heartfelt gratitude to my supervisor, Professor Richard Liew. It is an honour to be under his supervision and I appreciate the support especially during periods when my candidature was converted to part-time. He still finds the time to talk and remind me constantly of the objectives of the PhD. I would also like to thank Dr. Lee Siew Chin for constantly pushing me to improve the contents of my thesis and her guidance, discussions and encouragement in numerical techniques. In addition, I would like to thank the staff at the structural laboratory for their assistance and guidance in the conduct of the laboratory tests that were carried out in this thesis. I would like to mention fellow researchers, Patria and Andy, who went through a week of field tests during ETSC08 at Pulau Senang. The conditions during the tests weren’t the best but the comradeship fostered in working together to pursue the success of one another’s test on that island. The completion of the PhD was not an easy and straight forward one. There are ups and there are downs. Regardless of the outcome of this dissertation, the intangible fruits that came with all the arduous process will have a longer lasting effect than the few pages bounded in this book. iii TABLE OF CONTENTS DECLARATION .ii ACKNOWLEDGEMENT . iii TABLE OF CONTENTS iv SUMMARY . viii LIST OF TABLES xi LIST OF FIGURES .xii LIST OF SYMBOLS xix INTRODUCTION . LITERATURE REVIEW 2.1 General 2.2 Explosive Attacks 2.2.1 Types of Explosives . 13 2.2.2 Nature of blast loading . 15 2.3 Background on Protective and the Protection of Structures 18 2.3.1 Protection of Key Structural Elements 19 2.4 Methodologies in Explosive Dynamic Analysis . 21 2.4.1 Analytical Methodologies 22 2.4.2 Experiment Methodologies 24 2.4.3 Numerical Methodologies 29 2.5 Structural Materials under Blast Loading . 33 2.5.1 Masonry . 34 2.5.2 Reinforced Concrete 35 2.5.3 Steel 38 2.5.4 Composite (Steel-Concrete) . 42 ANALYSIS OF CONCRETE FILLED STEEL TUBULAR COLUMN SUBJECTED TO BLAST LOADING . 44 3.1 General 44 3.2 Material Response Under Dynamic Loading 47 3.2.1 Concept of High Strain Rate Effects 47 3.2.1.1 Fundamentals . 48 3.2.1.2 Concepts behind the Phenomenon . 51 3.2.2 Experimental Programme to Examine the Basis of DIF of Concrete 52 3.2.2.1 Objective 53 3.2.2.2 Specifications of Concrete Studied (Granite & Stalite) . 53 3.2.2.3 Experimental Setup and Instrumentation . 54 iv 3.2.2.4 Test Results and Discussion . 59 3.3 Design of CFST Column . 66 3.3.1 Assumptions . 66 3.3.2 Methods of Analysis 68 3.3.2.1 Equivalent System of Structural Element based on SDOF 68 3.3.2.2 Equivalent System of Structural Element based on RigidPlastic Analysis 80 3.4 Analytical Study of CFST Column . 84 3.4.1 Specification of Composite Column 84 3.4.2 Static and Blast Loading 86 3.4.3 Comparison and Discussion of Results 88 3.5 Numerical Study of CFST Column . 92 3.5.1 Finite Element Solution Scheme 92 3.5.1.1 Geometry and Design of Column 93 3.5.1.2 Type of Elements Selected . 93 3.5.1.3 Selection of Material Models . 94 3.5.1.4 Steel-Concrete Interface Modelling . 98 3.5.1.5 Blast Loading . 98 3.5.2 Comparison with Analytical Models . 99 3.5.3 Further Discussion on CFST Columns 103 3.6 Summary . 109 EXPERIMENTAL PROGRAMME OF STEEL-CONCRETE-STEEL (SCS) SANDWICH PANELS UNDER STATIC AND BLAST LOADINGS . 112 4.1 General 112 4.1.1 Concept of SCS Sandwich Panels 116 4.1.2 Objectives 118 4.1.3 Design and Construction of Specimen . 118 4.2 Material Static Properties 127 4.2.1 Steel 128 4.2.1.1 Instrumentation 128 4.2.1.2 Results and Discussions . 129 4.2.2 Concrete . 132 4.2.2.1 Instrumentation 133 4.2.2.2 Results and Discussions . 135 4.3 SCS Sandwich Panels Design Capacity under Static Loading 138 4.3.1 Analytical Properties of SCS Sandwich Panels . 142 4.4 Experimental Study on the Static Capacity of SCS Sandwich Panels 144 v 4.4.1 Experimental Setup and Instrumentation . 144 4.4.2 Test Results 145 4.4.3 Discussion and Comparison with Analytical Solution 154 4.5 Numerical Study on Static Capacity of SCS Sandwich Panels . 156 4.5.1 FE Solution Scheme . 156 4.5.1.1 Geometry and Design of SCS Panel 157 4.5.1.2 Type of Elements Selected . 159 4.5.1.3 Selection of Material Models . 160 4.5.1.4 Contact Interface Modelling 162 4.5.2 Comparison of FE Model with Experimental and Analytical Results . 163 4.5.2.1 Specimen SP 163 4.5.2.2 Specimen SCSNE 165 4.5.2.3 Specimen SCSN . 167 4.5.2.4 Specimen SCSN4 . 169 4.5.2.5 Specimen SCSL . 171 4.5.2.6 Specimen SCSH . 173 4.6 SCS Sandwich Panels Design Capacity and Failure Modes under Blast Loading . 175 4.6.1 Analytical Solution of the Blast Response of SCS Sandwich Panel Specimen to Blast Loadings 176 4.7 Experimental Programme on the Blast Resistance of SCS Sandwich Panels 177 4.7.1 Experimental Setup and Instrumentation . 178 4.7.1.1 Procedure and Design of Experiment 178 4.7.1.2 Blast Loading . 179 4.7.1.3 Reinforced Concrete Support Structure . 180 4.7.1.4 Instrumentation 183 4.7.2 Test Results 185 4.7.2.1 Blast Response and Failure Mode 185 4.7.2.2 Pressure Signal Records . 192 4.7.2.3 Acceleration Signal Records 194 4.7.2.4 Strain Gauge Records . 194 4.7.3 Discussion and Deductions from Experimental and Analytical Results 199 4.8 Numerical Study on the Blast Resistance of SCS Sandwich Panels . 205 4.8.1 FE Solution Scheme . 206 4.8.1.1 Geometry and Design of Test Setup and Specimens . 206 vi 4.8.1.2 Type of Elements Selected . 208 4.8.1.3 Selection of Material Models . 208 4.8.1.4 Steel-Concrete Interface Modelling . 208 4.8.1.5 Blast Loading . 209 4.8.2 Comparison of FE Model with Experimental and Analytical Results 211 4.8.2.1 Specimen SCSNE 211 4.8.2.2 Specimen SCSN . 213 4.8.2.3 Specimen SCSN4 . 216 4.8.2.4 Specimen SP 217 4.8.2.5 Specimen SCSL . 218 4.8.2.6 Specimen SCSH . 220 4.8.3 Further Discussion on the Dynamic Design of SCS Sandwich Panels 220 4.9 Summary . 226 CONCLUSION 229 BIBLIOGRAPHY 234 APPENDIX A A-1 APPENDIX B B-1 APPENDIX C C-1 vii SUMMARY Steel-concrete composite structural design is becoming common and more prominent in the modern construction industry and this can be attributed to the facility of construction and its capacity to harness the strength of both concrete and steel. However, modern structures face an increasing threat due to the increasing presence of terrorism with their access to destructive technologies through asymmetric warfare. One of these concerns which arose is the use of explosives against commercial or governmental buildings. Therefore it is now important for civil engineers to understand dynamic designs and incorporate them into buildings to resist loads generated from such an environment. This study attempts to develop an analytical method to accurately capture the dynamic inelastic behaviour of concrete filled steel tubular (CFST) columns subject to blast loading. The proposed approach will possess a closed form solution approach and the capability to analyse a structure, which respond both in flexural as well as in shear. The thesis will also study the blast resistant performance of steel-concrete-steel (SCS) sandwich panels through analytical, experimental and numerical study. In the design of structural members against blast loading, the Single-Degree-ofFreedom (SDOF) method is commonly used to approximate the dynamic response of structures. One of the limitations of this method is the inability to capture the multifailure modes of the structural members. The Rigid-Plastic method is thus proposed in this thesis to estimate the blast response of CFST columns. The Rigid-Plastic results are compared with SDOF calculations as well as validated numerical models in order to assess the competency of this proposed method. Due to the assumption of rigid- viii plastic material behaviour, the accuracy of this method is influenced by the extent of plastic deformation of the structural member. For the case of impulsive blast loading, the Rigid-Plastic estimations are found to be closer to the numerical results than those obtained using the SDOF method. This study also encompasses a study into the performance of a composite column as compared to that of a reinforced concrete one and a significant improvement in the blast resistance of the composite column was observed. Another phase of this study includes an experimental study to investigate the response of SCS sandwich panel of various configurations under quasi-static and dynamic loadings. The quasi-static experiment series utilised a three-point laboratory load setup and the dynamic study was carried out with actual explosives in an outdoor firing range. The differences in response of six configurations of sandwich composite panels, which differed in the thickness of steel plates, the concrete properties of the sandwich core and the connectors, were investigated under both quasi-static and dynamic loads. Both experimental series showed the enhancement effects by the increased steel plate thickness and the presence of concrete core. In addition, the comparison between quasi-static and the dynamic test series has emphasised the differences between static and dynamic resistance. Specimens of high static resistance may not necessarily perform well under dynamic load due to the brittle nature of the concrete cores. Results from the experimental study are also used to validate the numerical models and the analytical design approach, which has shown to be conservative in static and in most dynamic cases. These numerical models are further extended to demonstrate the effectiveness of incorporating steel plates between the top and bottom steel face plates to enhance the blast resistance. In addition, the use of ix lightweight concrete could be used in blast resistance SCS panels provided sufficient strength is designed in the concrete. x APPENDIX B Time Phase Deflection Shape Governing Equations Boundary Conditions Figure B.1 Response of a simply-supported member with υ ≤ B-1 Time (s) Velocity (m/s), Deflection (m) Time Phase Deflection Shape Governing Equations Boundary Conditions Time (s) where, Figure B.2 Response of a simply-supported member with < υ ≤ 3/2 B-2 Velocity (m/s), Deflection (m) Time Phase Deflection Shape Governing Equations Boundary Conditions where, where, where, where, B-3 Time (s) Velocity (m/s), Deflection (m) Figure B.3 Response of a simply-supported member with υ > 3/2 B-4 Time Phase Deflection Shape Governing Equations Boundary Conditions Figure B.4 Response of a fixed-end member with υ ≤ B-5 Time (s) Velocity (m/s), Deflection (m) Time Phase Deflection Shape Governing Equations Boundary Conditions where, Figure B.5 Response of a fixed-end member with < υ ≤ B-6 Time (s) Velocity (m/s), Deflection (m) Time Phase Deflection Shape Governing Equations Boundary Conditions where, where, where, where, B-7 Time (s) Velocity (m/s), Deflection (m) Figure B.6 Response of a fixed-end member with υ > B-8 APPENDIX C Time Phase Deflection Shape Governing Equations Boundary Conditions where, C-1 Time (s) Velocity (m/s), Deflection (m) Figure C.1 Response of a simply-supported member with η ≤ C-2 Time Phase Deflection Shape Governing Equations Boundary Conditions where, where, C-3 Time (s) Velocity (m/s), Deflection (m) where, where, where, Figure C.2 Response of a simply-supported member with η > C-4 Time Phase Deflection Shape Governing Equations Boundary Conditions where, C-5 Time (s) Velocity (m/s), Deflection (m) Figure C.3 Response of a fixed-end member with η ≤ C-6 Time Phase Deflection Shape Governing Equations Boundary Conditions where, where, C-7 Time (s) Velocity (m/s), Deflection (m) where, where, where, Figure C.4 Response of a fixed-end member with η > C-8 [...]... properties of concrete- infilled steel column 86 Table 3-9 Applied blast loading 87 Table 3-10 Blast response of column at stand-off distance of 10 m (impulsive regime) 88 Table 3-11 Blast response of column at stand-off distance of 12.5m (dynamic regime) 88 Table 3-12 Blast response of column at stand-off distance of 15m (dynamic regime)88 Table 3-13 Blast. .. the need of formworks Composite structures harness the strength of both concrete and steel to optimise on the usage of materials in design In view of the significant performance of steel- concrete composite structural members over conventional steel or reinforced concrete structures in static design, there is a need to research on such system to quantify the performance of these columns against blast loading... of column at stand-off distance of 10m 99 Table 3-14 Blast response of column at stand-off distance of 12.5 m 99 Table 3-15 Blast response of column at stand-off distance of 15 m 100 Table 4-1 Specifications of the configurations of the specimens 119 Table 4-2 Tabulation of the key parameters from the tensile test 132 Table 4-3 Lightweight concrete mix 133 Table 4-4 HSC concrete. .. Schematic of J-hook connector 125 Figure 4-9 Specimen preparation photos of (a) positioning of jig, (b) welding of Jhook connectors, (c) placement of top and bottom plate prior to welding of the side and end plates, (d) preparation of specimens with J-hook connectors prior to casting of concrete core, (e) preparation of specimens without J-hook connectors prior to casting of concrete and (f) concrete. .. 3-41 Comparison of displacement-time histories of RC and CFST columns 104 Figure 3-42 Comparison of effective mean stress-time histories of the element at the mid-span of RC and concrete- filled steel composite columns 105 Figure 3-43 RC column with comparable properties as the concrete- filled steel composite column in Figure 3-36 106 Figure 3-44 P-M Interaction curves of CFST and RC columns... the understanding of the design and response of steelconcrete composite structural components which are subjected to blast loading through reviews and to come up with a proposal of analytical design approach for steel- concrete composite columns and slabs against blast loading The analytical study 1 is coupled with numerical modelling and an experimental programme to ensure validity of the result and... description of the scope of work, of which the sequence of these work will be detailed in the subsequent paragraphs of this chapter:  Review the state -of- the-art in analytical, numerical and experimental works in deriving the structural response to blast loading  Conduct of quasi-static and dynamic tests of construction materials against dynamic loading  Validation of application of the Single Degree of. .. models of Specimen SCSL 219 Figure 4-95 Deflection profile of Specimen SCSL with fringe levels of deflection 219 Figure 4-96 Midspan displacement histories of numerical models of Specimen SCSH 220 Figure 4-97 Comparison of the response of Specimen SCSN and SCENE 221 Figure 4-98 Comparison of the response of Specimen SCSN and SCEN4 222 xvii Figure 4-99 Comparison of. .. the result and ascertain the performance of certain assumptions that were made in the design process The specific objectives of this thesis are as follow: • Develop an analytical method to accurately capture the dynamic inelastic behaviour of concrete filled steel tubular (CFST) subject to blast loading • Study the blast resistant performance of steel- concrete -steel (SCS) sandwich panels through analytical,... Actual positions of instrumentation 185 Figure 4-64 Deformation of Specimen SP (a) onsite (left) and (b) in the laboratory 186 Figure 4-65 Deformation of Specimen A was obstructed by the steel I-beam 186 Figure 4-66 Local buckling of the steel plates of Specimen SP 187 Figure 4-67 Steel fracture on the top steel plate at the midspan of the specimen 187 Figure 4-68 Deformation of Specimen SCSN . need of formworks. Composite structures harness the strength of both concrete and steel to optimise on the usage of materials in design. In view of the significant performance of steel- concrete. of concrete- infilled steel column 86 Table 3-9 Applied blast loading 87 Table 3-10 Blast response of column at stand-off distance of 10 m (impulsive regime) 88 Table 3-11 Blast response of. stand-off distance of 12.5m (dynamic regime) 88 Table 3-12 Blast response of column at stand-off distance of 15m (dynamic regime)88 Table 3-13 Blast response of column at stand-off distance of