長跨挫屈束制支撐結合強脊構架二元系統鋼構架耐震設計與分析

Abstract

跨樓層長跨斜撐設計為近年因應高樓層建築興起之結構配置。比起跨單層之斜撐，此配置擁有接頭數量少、建築空間靈活度高等優點。而桁架圍束式挫屈束制支撐TC-BRB有高軸力強度、低自重的優點正適合應用於長跨斜撐，而強脊系統能均勻層間位移角。本研究設計與分析長跨BRB結合強脊之BRB-SBF二元鋼構架系統，觀察長跨TC-BRB之受力、位移需求與整體結構行為。 本研究提出四種結構配置，應用於位於台北二區的23層建築例，擇BRB與強脊斜撐皆橫跨4樓之配置B4-S4進行設計。以容量設計法設計BRBF梁柱構件與檢核強脊構架SBF彈性標準，利用ETABS結構分析完成結構斷面設計。所得前三模態分別於45°、135°水平振動及垂直向旋轉，週期分別為2.11、1.98及1.11秒。 本研究另建立PISA3D模型，參考2021年縮尺寸TC-BRB實驗數據，擬合BRB材料模型參數。使用21組地震紀錄，依規範進行加速度縮放，進行非線性歷時分析(NRHA)。SLE、DBE及MCE危害度地震下，各最大平均層間位移角分別約0.005、0.012及0.015弧度，變異係數COV皆約為0.0045弧度；轉換層間位移角最大分別約0.0025、0.007及0.008弧度，COV皆約為0.003弧度。MCE下殘餘層間位移角小於0.005弧度，結構可輕易修復。垂向旋轉角於DBE、MCE為0.001及0.002弧度。BRB強度在MCE最大應變硬化因子Ω = 1.6, 核心應變ε = 0.007, 累積塑性應變CPD = 116，因此BRB應不會破壞；且發現BRB於多數地震下可同時降伏。三種危害度地震下之平均系統超強分別為1.2、2.4及2.7，且SBF剪力佔比從27%(SLE)增加至40%(MCE)，SBF可在BRB降伏後幫助提供側向勁度。NRHA結果顯示前述容量設計法適當，BRBF柱與容量設計所估的最大軸力比值為0.88；但梁軸力最大比值為2.7，有低估之情況。SBF除了高樓層斜撐與梁，其餘構件在MCE地震下皆保持彈性。以增量式動力分析執行易損性分析， MCE下結構達到防止崩壞性能點CP之機率約0.01，崩塌機率相當低。

Long-span brace which spans multiple floors has the advantage of fewer brace members and connections, and higher flexibility of architectural planning compared to the conventional single-story brace. Moreover, truss-confined buckling-restrained braces (TC-BRB) which have a higher axial strength and lower self-weight is favorable for long-span applications. The strong-back system can promote a uniform story drift distribution. In this study, structural designs and seismic responses of dual systems consisting of long-span TC-BRBs and strong-back frame are discussed. This study proposed four different structural configurations, which were applied to a prototype 23-story building in Taipei Seismic Zone 2. Configuration B4-S4 in which both BRBs and strong-back braces span 4 floors was selected. Beam and column members of buckling-restrained brace frame (BRBF) and strong-back frame (SBF) were designed and checked by capacity design method. The first three natural vibration modes are translations at 45°, 135°, and vertical torsion, respectively, with periods of 2.11, 1.98 and 1.11 seconds. A PISA3D model is constructed using BRBs’ material parameters calibrated from using recent TC-BRB experiment results. Nonlinear response history analysis (NRHA) using 21 historical earthquake ground motions, scaled to the SLE, DBE and MCE hazard levels. Peak averaged inter-story drifts are 0.5%, 1.2% and 1.5% rads, while those of the 4-story drifts are 0.25%, 0.7% and 0.8% rads, respectively, under the SLEs, DBEs and MCEs. Coefficient of variance (COV) of the peak averaged inter-story drifts is 0.45%rad, while COV for the 4-story drifts is 0.3% rad. The peak averaged residual story drift in MCEs is less than 0.5% rad, suggesting that the structural repair is feasible. The floor rotations are 0.1% and 0.2% rads in DBE and MCE, respectively. BRBs’ maximum strain hardening factor is 1.6, the peak averaged core strain was 0.7%, the maximum averaged cumulative plastic deformation CPD is 116 in MCE. Moreover, BRBs yielded almost at the same time during most MCEs. The averaged system overstrength under three hazard level earthquakes are 1.2, 2.4 and 2.7, respectively. The averaged base shear ratios of SBF are increased from 27% (SLE) to 40% (MCE). The averaged ratio of BRBF column axial force computed in MCEs to that estimated from the capacity design method is 0.88. However, the ratio of maximum beam axial force in MCEs to that from capacity design is 2.7. Fragility curve constructed from incremental dynamic analyses indicates that the probability of the structure reaching the CP performance point during the MCEs is 0.01.