Finite Element Analysis for Seismic Behavior of Bolted Beam-Column Connections in CFT Structures

傳統梁柱接頭抗彎變形能力不足，接頭破壞常發生在梁端銲道。螺栓式梁柱接頭是為工廠銲接、工地栓接，可避免工地銲接之品質問題。螺栓式梁柱接頭並於梁端加銲翼翅擴板(wing plate)，以提升梁端彎矩強度之容量，使塑性鉸遠離銲道。前人實驗已經驗證螺栓式梁柱接頭耐震能力優良，只要設計恰當即可符合國內外耐震接頭之要求。試驗的試體是有限的，使用數值分析若可準確模擬試驗結果，則可做更多參數變化。故本文採用ABAQUS有限元素分析程式分析翼翅擴板、端板及翼板間加勁板對螺栓式梁柱接頭之影響，以及分析整個接頭之耐震行為。經由收斂性分析配合 “Riks” 分析程序(本文先經由收斂性分析得到所建立有限元素模型的合理性，再以靜力分析模擬試體在反覆載重下之耐震行為，可得到挫屈前的包絡線，最後則利用單調遞增之靜力分析模擬出挫屈後耐震行為，可得到與實驗結果相近似的力與位移包絡線。分析結果證明，只要翼翅擴板的長度與寬度符合本文所修正之設計公式，翼翅擴板可有效使梁端塑鉸遠離銲道；只要端板厚度符合AISC-LRFD提出之計算公式，搭配三角加勁板，可有效防止端板因彎撬現象之發生而破壞；在梁端塑鉸處加銲翼板間加勁板，可有效延緩局部挫屈塑鉸發生的時機，亦即延後最大強度的發生時機，進而增加整體接頭的韌性。對矩形鋼管混凝土單向螺栓式接頭而言，分析也證明矩形鋼管寬厚比之設計能改變主要之消能構件，寬厚比較小者，鋼管厚度較大，可由鋼梁來消能；寬厚比較大者，鋼管厚度較小，可由交會區來消能；若符合臨界寬厚比，則可由鋼梁與交會區共同消能。對矩形鋼管混凝土雙向螺栓式接頭而言，分析證明雙向螺栓預力可大大提升交會區之強度及勁度，因此皆由鋼梁來消能；分析也證明圓形鋼管混凝土螺栓式梁柱接頭之適用性；並證明只要設計得宜，螺栓式接頭確為優良耐震接頭。From researches, the deformation capacity of the conventional beam-column connections is seriously inadequate. The brittle failure usually occurs at the welding zone. The design of bolted beam-column connections is that welding is carried out at the shop and bolting at the site, thus the guality of the welding can be assured. Moreover, wing plates are welded at beam ends in bolted beam-column connections to make sure that plastic hinges are away from the welding zone. Researches proved that the bolted beam-column connections have excellent seismic resistance satisfying seismic design codes of Taiwan and the US as long as the width-to-thickness of columns, end-plate thickness and wing-plate width suffice for the corresponding limits. In this dissertation, the finite element program ABAQUS is adopted to analyze the influences of wing plates, end plates and stiffeners between flanges to bolted connections, and the seismic hehavior of bolted beam-column connections. Through the convergence analyses collocating the analysis procedure “Riks”, the numerical load-displacement envelope curves are close to the experimental envelope curves. From numerical results, it is proved that the plastic hinge is away from the welding zone as long as the wing-plate width and length are allowable from caculating the design formulas; the brittle fracture of the end plates can be prevent as long as the end-plate thickness is allowable from caculating the design formulas and the upstanding ribs are used; the occurrence of the plastic hinges can be delayed as long as the stiffeners are welded between flanges. For uni-directional bolted connections of rectangular CFT structures, numerical results prove that the design of width-to-thckness ratio of the steel tube can change the main energy-dissipation component. The energy is dissipated by beams when the width-to-thckness ratio is smaller. The energy is dissipated by the panel zone when the width-to-thckness ratio of the steel tube is larger. The energy can be dissipated by the panel zone and the beam at the same time when the width-to-thckness ratio of the steel tube is critical. For bidirectional bolted connections of rectangular CFT structures, numerical results prove that the strength and stiffness of the panel zone can be improved by the pre-stresses of the bidirectional bolts, thus the main energy-dissipation component is the beam. For circular CFT structures, numerical results prove the feasibility of the bolted beam-column connections. Overall, the bolted beam-column connection is certainly a kind of excellent seismic resistant connection.誌謝 iii 摘要 v Abstract vii 1. INTRODUCTION 1 2. MECHANICAL THEORY OF BOLTED BEAM-COLUMN CONNECTIONS 9 2.1 WING PLATE 9 2.2 END-PLATE 11 2.3 PANEL ZONE 12 2.3.1. Rectangular CFT Column 12 2.3.2. Circular CFT Column 16 3. EXPERIMENTAL DESIGN 21 3.1 WING PLATE 29 3.2 END-PLATE 31 3.3 STIFFENER BETWEEN FLANGES 32 3.4 WHOLE CONNECTION 34 3.4.1. Rectangular CFT Column 35 3.4.2. Circular CFT Column 36 4. FINITE ELEMENT ANALYSES 39 4.1 MATERIAL MODEL 39 4.1.1 Steel 39 4.1.2 Concrete 40 4.1.3 Contact 47 4.1.4 Constraint 47 4.2 ELEMENT TYPE 47 4.3 ANALYSIS PROCEDURE 48 4.4 CONVERGENCE ANALYSES FOR TEST PARAMETERS 48 4.4.1 Wing Plate 49 4.4.2 End-plate 59 4.4.3 Whole Connection 75 5. RESULTS AND DISCUSSIONS 91 5.1 WING PLATE 91 5.1.1 Ductility Ratio, Strength and Stiffness 92 5.1.2 Failure Mode 98 5.1.3 Discussion on the Width of the Wing Plates 106 5.2 END-PLATE 110 5.2.1 Specimens with enough wing-plate widths 111 5.2.2 Specimens with critical wing-plate widths 114 5.2.3 Existence of upstanding rib 117 5.3 STIFFENER BETWEEN FLANGES 120 5.3.1 Influence of existence of stiffeners between flanges 120 5.3.2 Influence of number of stiffeners between flanges 124 5.3.3 Influence of d, b and tf to length of plastic hinge 127 5.4 WHOLE CONNECTION 129 5.4.1. Connections with Rectangular CFT Column 130 5.4.2. Connections with Circular CFT Column 139 6. CONCLUSION 145 6.1 WING PLATE 145 6.2 END-PLATE 146 6.3 STIFFENER BETWEEN FLANGES 146 6.4 WHOLE CONNECTION 147 6.4.1. Rectangular CFT Column 147 6.4.2. Circular CFT Column 147 ACKNOWLEDGEMENT 147 REFERENCE 148 APPENDIX A: Design of Wing plates 153 APPENDIX B: Displacement Measurement 157 APPENDIX C: WORKED EXAMPLE FOR END PLATES 161 APPENDIX D: CONTACT PROPERTY 167 APPENDIX E: CONSTRAINT PROPERTY 169 APPENDIX F: ELEMENTS INTRODUCTION 171 APPENDIX G: ANALYSIS PROCEDURES INTRODUCTION 17