若建築物受到強震作用後進入塑性變形，結構體仍然可發揮韌性，不至於崩塌。規範依據能量相等法則和位移相等法則，將韌性容量換算為地震力折減係數，以制定非彈性設計震譜。本研究依據921集集地震測站實測紀錄來產生與彈性設計震譜相符的人工地震，以進行彈塑性振動歷時分析，檢核規範地震力折減係數是否保守，發現規範公式在中週期處高估地震力折減係數，造成地震力之低估。再以兩層樓均質剪力屋架為例，比較彈塑性反應歷時分析和規範反應譜分析在樓層剪力、樓層傾倒彎矩和層間變位的差異。

If a building vibrates in a state of elastic deformation under a strong earthquake, then its ductility is well used to avoid collapse. On the basis of energy-equal and displacement-equal rules, a yield strength reduction factor is obtained from a ductility capacity in common seismic codes to set up an inelastic design spectrum. A lot of artificial earthquakes compatible with elastic design spectra are generated through real records of 921 Chi-Chi earthquake in order to analyze elastoplastic vibration. It is found that the code formula will overestimate the yield strength reduction factor in the region of middle period, and then underestimate the seismic force. Take a two-story building idealized as a homogeneous shear frame for example, comparing the difference of story shears, story overturning moments and story drifts in analyses of elastoplastic-time-history and response-spectra.

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