二層樓夾型挫屈束制斜撐鋼構架受反覆側向位移下中等韌性箱型鋼柱耐震性能之有限元素分析

Abstract

本研究延續覃文康 (2022) 之研究，欲以有限元素分析箱型鋼柱在構架中的耐震行為。首先針對兩種不同尺寸的夾型挫屈束制斜撐，以兩種方法在 ABAQUS 中建立了有限元素模型，再以覃文康 (2022) 之實驗構架為目標建立了完整的構架模型，並將實驗與模擬結果進行了詳細的比較。以此為基礎，總共建立了三組構架模型，共六種鋼柱斷面，以探討寬厚比 (b/t) 及初始軸力比 (P/P_y) 對於鋼柱及對於構架的耐震行為。 研究發現，在寬厚比愈大的試體中，柱底挫屈的程度愈大，發生挫屈的時間愈早，嚴重影響整體構架的行為；在初始軸力愈大的柱中，柱底挫屈愈嚴重，柱的軸向縮短量愈大，造成構架產生不對稱的行為。結果顯示，對於承受高軸力的箱型鋼柱而言，寬厚比設為高等韌性構件與中等韌性構件之平均寬厚比限制，其最大側位移角能力可達到 0.04 rad.，然而若寬厚比恰為中等韌性構件時，則其最大側位移角能力僅有 0.015 rad.；而對於受到中軸力的箱型鋼柱而言，其最大側位移角能力可達 0.03 rad.，且在受中軸力的柱行為中可以發現構架之傾覆作用使得構件的反應並不對稱，當構架往負向，使柱所受軸力較初始軸力小時，即便是寬厚比遠小於中等韌性構件之限制，其行為仍保持飽滿。

This study builds upon the research conducted by Tam (2022) and aims to investigate the seismic behavior of built-up box columns in a BRB frame using finite element analysis. Two different sizes of sandwiched buckling-restrained braces (SBRB) were initially modeled using two different methods in ABAQUS. Subsequently, a complete BRB frame model was developed based on the experiments conducted by Tam (2022), and a detailed comparison was made between the experimental and simulation results. Based on this foundation, a total of three sets of BRB frame models were established, consisting of six steel column cross sections, to explore the seismic behavior of both the columns and the frame concerning the width-to-thickness ratio (b/t) and initial axial load ratio (P/P_y). The study findings indicate that in specimens with larger aspect ratios, the bottom column buckling is more severe, occurring earlier and significantly affecting the overall behavior of the frame. In columns with higher initial axial loads, the severity of bottom column buckling increases, leading to larger axial shortening of the columns and causing asymmetric behavior in the frame. The results demonstrate that for box steel columns subjected to high axial forces, when the aspect ratio was set to the average value between the limits for highly ductile members and moderately ductile members, the maximum story drift angle capacity could achieve 0.04 rad. However, when the aspect ratio precisely falls within the limit for moderately ductile members, the maximum story drift angle capacity is only 0.015 rad. As for box steel columns subjected to intermediate axial forces, the maximum lateral displacement angle capacity reaches 0.03 rad. It can be observed that the overturning effect of the frame leads to asymmetric responses of the components. When the frame goes toward the direction which causes axial force smaller than the initial axial force, the behavior remains satisfactory, regardless of the aspect ratio being far below the limit for moderately ductile members.