面內挫屈斜撐之耐震行為

Abstract

本研究之目的為設計斜撐使斜撐於受壓時之挫屈為面內挫屈，其一為將斜撐端部翼板切削，使其產生塑鉸，另外為以連接板連接斜撐與接合板，於連接板產生凹折區域，達成斜撐面內挫屈，探討其強度及遲滯迴圈。研究方法採有限元素分析建立數值模型，研究不同參數對於斜撐行為之影響；進而以有限元素分析之參數研究結果規劃試驗試體，共設計六組試體，進行往復載重實驗，驗證斜撐遲滯行為。有限元素分析結果顯示，切削型式採單接合板接斜撐腹板，因斜撐腹板局部變形不易於切削處產生塑性鉸，惟可以加勁腹板改善；而採雙接合板之斜撐皆於切削處產生預期的塑性鉸。切削型式的參數中，切削的深度對於斜撐強度與局部行為之影響較大，切削的長度則影響有限。連接板型式皆於連接板產生凹折，達成斜撐面內挫屈，惟在斜撐翼板端點與連接板處有應力集中的現象，導致連接板開裂破壞。試驗結果顯示六組試體皆具有穩定非線性行為與消散能量之能力。四組斜撐採切削型式試體遲滯迴圈達4~5%弧度之層間變位角，表現如預期一樣斜撐產生面內挫屈並最終於斜撐中點發生斷裂。切削量小時，斜撐端部勁度大，集中於斜撐之變形量就會越大，以致斜撐中點產生之裂縫較早，導致較早的斷裂破壞。從面內變形量也發現，雙接合板也比單接合板有著較大的斜撐面內變形量。連接板型式試驗結果為一組試體於連接板產生斷裂，肇因於接合板與斜撐翼板力量的直接傳遞，而喪失有效寬度的意義。令一組試體則因銲接不良於斜撐與連接板接合處發生斷裂。整體而言，斜撐採端部切削型式可達成斜撐面內挫屈，具有典型的斜撐的非線性行為並消散能量。

This paper aims to design bracing members to achieve in-plane buckling of the braces while subjected to compression, and to study the strength and hysteretic behavior. The ways to lead the brace buckle in-plane are either reducing brace section at both ends of the brace to form a hinge, or using a connecting plate between the gusset plate and the brace to create a rotational area to buckle the brace in-plane. Finite element analysis was conducted to establish the numerical model for parametric study. On the basis of the analytical results, six specimens were designed and tested to validate the hysteretic behavior of the specimens. The results of the finite element analysis indicate that for the brace with reducing brace section and a single gusset plate the formation of the plastic hinge is not distinct because of the distinguish local deformation of the brace web to which the gusset plate was welded; however, the local deformation of the brace web can be attenuated by adding stiffeners. The brace with reducing brace section and double gusset plate can form expected hinge at both ends of the brace. Among the design variables, the depth of the reducing section has major effect of the strength and local behavior of the brace, while the width of the reducing section has minor effect. The brace designed to have connecting plate can achieve in-plane buckling; however the stress concentration occurred at the connection between brace and connecting plate may cause the failure of the brace. The test results demonstrated that all six specimens attained stable nonlinear behavior and dissipating energy. Four specimens with reducing section achieved 4 to 5% rad of the interstory drift angle, buckled in-plane, and fractured at the middle of the brace as predicted in the analysis. One specimen behaved premature failure of the fracture due to the crack occurred at the middle of the brace because of the less reducing section causing higher stiffness at the brace ends and large deformation at brace middle part. Moreover, the braces in-plane deformation of the brace with double gusset plate is larger than those with single gusset plate. The test results revealed that one of the specimens with connecting plate fractured at the connecting plate owing to the direct force transferring between gusset plates and brace flanges, losing the concept of the effective width of the connecting plate. The other specimens with connecting plate failed due to fracture occurred at the weld between the brace and connecting plate, causing by the weld defect. In summary, the brace designed by reducing section at both ends can achieve in-plane buckling of the brace, possesses typical inelastic behavior, and dissipate energy.