以瞬時功率及譜加速度評估鉛心橡膠隔震系統 隔震位移之研究

Abstract

隔震系統透過延長結構物之基本振動週期，以有效降低上部結構所承受之地震力，為常見之耐震設計策略。然而，當結構遭遇含長週期速度脈衝之地震動時，隔震器可能產生過大位移而導致破壞，因此，建立一套能準確評估隔震位移反應之地震強度指標，對於隔震設計之安全性與可靠性具有重要意義。 本研究旨在驗證既有文獻中提出之強度指標—瞬時功率IP—是否能有效捕捉鉛心橡膠隔震系統之最大隔震位移，並進一步探討其計算方式與納入設計規範之可行性。研究首先以單自由度鉛心橡膠隔震系統為對象，選取脈衝型與非脈衝型地震紀錄，縮放至四個不同強度等級，分別進行單向與雙向地震輸入之非線性歷時分析，以評估瞬時功率在不同濾波區間與積分範圍設定下對隔震位移預測能力之影響。 在確立適當之瞬時功率計算參數後，進一步隨機生成上部結構與隔震系統配置，建立多自由度隔震模型並進行非線性歷時分析，以驗證單自由度系統所得結論之適用性。分析結果顯示，採用IP(T_int=3s)可有效評估隔震系統在地震作用下之最大位移反應。 最後，本研究建立三棟五層樓隔震建築作為案例模型，探討以地震歷時紀錄之IP分佈作為地震紀錄篩選依據，是否能降低隔震位移反應之離散性。研究結果顯示，將IP納入地震紀錄選取條件，可有效降低隔震設計中位移評估之不確定性，並建議未來相關設計規範將地震紀錄之IP值納入考量，以提升隔震系統設計之穩定性與可靠性。

Seismic isolation systems are widely adopted as an effective seismic design strategy by lengthening the fundamental vibration period of structures to reduce seismic forces transmitted to the superstructure. However, when subjected to ground motions containing long-period velocity pulses, isolation bearings may experience excessive displacement demands that can lead to failure. Therefore, establishing a reliable seismic intensity measure capable of accurately evaluating isolation displacement responses is essential for improving the safety and reliability of seismic isolation design. This study aims to verify whether the intensity measure Instantaneous Power (IP), previously proposed in the literature, can effectively capture the maximum displacement response of lead–rubber bearing (LRB) isolation systems, and to further investigate its calculation procedure and applicability in seismic design provisions. The study first examines a set of single-degree-of-freedom (SDOF) LRB-isolated systems subjected to both pulse-like and non-pulse-like ground motions scaled to four intensity levels. Nonlinear response history analyses (NRHA) are conducted under unidirectional and bidirectional ground motion inputs to evaluate the influence of different filtering bands and integration ranges on the predictive capability of IP for isolation displacement. After identifying appropriate calculation parameters for IP, a series of multi-degree-of-freedom (MDOF) isolated structural models are randomly generated by varying superstructure and isolation system properties. NRHAs are performed to assess the applicability of the SDOF-based findings to more realistic structural systems. The results indicate that IP evaluated at a period of 3 seconds, IP(T_int=3s), provides an effective indicator for capturing the maximum displacement response of seismic isolation systems. Finally, three five-story base-isolated buildings are developed as case-study models to investigate whether selecting ground motion records based on the distribution of IP values can reduce the dispersion of isolation displacement responses. The results demonstrate that incorporating IP-based criteria in ground motion selection effectively reduces uncertainty in displacement demand estimation. Accordingly, this study recommends that IP be considered along with Sa in future seismic design guidelines for base-isolated structures to enhance the robustness and reliability of isolation system design.