挫屈式韌性斜撐之耐震性能試驗與分析

Abstract

本研究針對預彎拱鈑進行一系列元件測試與耐震性能試驗，探討其力學特性及建築抗震應用之可行性。元件測試結果顯示，預彎拱鈑之遲滯迴圈相當穩定，且隨鈑厚及擾動振幅之增加而愈趨飽滿。ANSYS應力分析與試驗結果有相當程度之契合，有助於對預彎拱鈑元件力學行為之掌握。為能進一步預測結構之地震反應，本研究採用廣義文氏模型(Generic Wen’s Model)來描述預彎拱鈑之力學行為，並以四階Runge-Kutta法求解非線性微分方程，藉由調整形狀控制函數之各項參數，使其遲滯迴圈與元件測試結果相符，並結合狀態空間法求解運動方程式，經由疊代過程完成結構之非線性動態分析。耐震性能試驗結果顯示，以預彎拱鈑為核心結合H-型鋼所組成之韌性斜撐可大幅提高結構低振態之等效阻尼比，降低其振動反應，但也因韌性斜撐之加勁作用而放大高振態之反應。減震效能隨地震強度之增大而愈趨明顯，主要是預彎拱鈑之降伏程度增加所致。模擬分析與試驗結果呈現不錯之相關性，惟仍存在不容忽視之誤差。誤差之來源應為分析模型中忽略斜撐(H-型鋼)的存在，因而高估結構勁度之結果。建議未來在建立結構系統時，應將斜撐考慮進去。

In this study, a series of component tests and seismic performance tests on the pre-bent steel strip has been conducted to explore its mechanical properties and the feasibility of using it for earthquake resistance of building structures. Component tests show that the hysteresis loops of the pre-bent steel strips are pretty stable, and richness of the hysteresis increases with the thickness of the strips as well as the disturbing amplitude. Stress analysis by ANSYS agrees well with the experimental results, which helps in getting insight of the mechanical behavior of the pre-bent steel strips. In order to further predict the seismic structural responses, the Generic Wen's Model is adopted in this study to simulate the mechanical behavior of the pre-bent steel strips. In form of a nonlinear differential equation, the Generic Wen's Model is resolved by using the fourth-order Runge-Kutta method, with parameters of the shape function calibrated to comply with the hysteresis obtained by the component tests. The nonlinear dynamic analysis of the structure is then carried out via an iterative process using the state-space approach. Seismic performance tests show that the ductile braces, consisting of the pre-bent steel strips and wide-flange steel beams (H-beams), significantly enhance the equivalent damping ratios in the lower modes of the structure, and therefore reduce the overall dynamic responses. While the higher mode responses are somewhat amplified due to stiffness strengthening by the ductile braces. The seismic performance of the ductile braces becomes more pronounced with the quake intensity increased, due to increase in the extent of yielding of the pre-bent steel strips. Simulation results of the seismic performance tests are fairly correlated with the experimental data, although the discrepancies are not negligible. The source of errors is believed to come from neglecting the H-beams in the modeling which results in over-estimation of the stiffness. It is suggested that the H-beam should be taken into account in modeling the structural system in the future.