中間樓層隔震結構之模態耦合效應研究

Abstract

近年來，我國隨著隔震技術逐漸成熟，除了基礎隔震建築物外，因應經濟預算考量、建物特性、高人口密度等因素，中間樓層隔震建築物亦與日俱增。然而中間樓層隔震建築物並無設計規範可遵循，僅能依照現行基礎隔震建築規範進行設計建照，除了下部結構勁度之考量外，設計興建時相對於基礎隔震是否還有其他特殊考量，需要多加探討。 從以前的文獻中得知中間樓層隔震結構相對於基底隔震結構動態行為更為複雜，不能單純考量下部結構勁度的影響，上部結構勁度同樣會影響隔震效果。其中非設計預期之模態耦合效應會造成中間樓層隔震結構無法發揮預期之隔震效果，然這方面的研究為現象性之描述，對於相關的結構動態特性並無實際試驗佐證，無法提供實務設計上有效之依據，仍有待進一步研究。 故本文主要研究模態耦合效應對中間樓層隔震結構的影響，希望以試驗結果驗證理論分析結果，研究方法由中間樓層隔震結構簡化模擬成三個堆積質量節點之三自由度結構，改變上下部結構之質量比與頻率比進行參數分析，以興建中的台大土木系研究大樓為中間樓層隔震結構之實例做分析研究，並設計規劃中間樓層隔震結構縮尺振動台試驗，進一步驗證模態耦合效應並探討結構動態特性。以期提供工程界實務設計一個良好的參考依據，更進一步於規範中列入考量，使有效發揮結構隔震效益。

The excellent performance of seismically isolated buildings during the past earthquakes is encouraging for the extensive adoption of the isolation design. Correspondingly, isolation design guidelines have been implemented or refined in various seismic design codes. However, these design guidelines have been provided specifically for the base-isolated structures. For the mid-story isolation design in which the isolation layer is frequently designated at the top of the first or other lower stories of the buildings to facilitate the construction and efficiently utilize the limited site, there indeed exists the difference between the mid-story isolated and the base-isolated buildings such as the flexibility effect of the structure below the isolation layer as well as the interaction of the structures below and above the isolation layer. Therefore, for the mid-story isolated structures, a simplified three-lumped-mass structural model is adopted to perform the equivalent linear analysis to appropriately reflect the effect of vibration characteristics of the structures above and below the isolation layer, and to have a better insight on the basic dynamic characteristics in this study. Accordingly, the shaking table tests on the scale-down models were conducted to validate the numerical analysis results. It is concluded that for the mid-story isolated buildings, the participation and the undesired coupling effect of the higher modes should be especially taken into account in the equivalent lateral response design procedure.