基於鉛心橡膠支承基底隔震建築之高寬比探討
Other Title
Study of Aspect Ratios for Base Isolated Buildings With Lead-Rubber Bearings
Journal
結構工程
Journal Volume
39
Journal Issue
1
Start Page
51
End Page
74
ISSN
1021-7878
Date Issued
2024-03
Author(s)
Abstract
隔震結構乃利用低側向勁度之隔震支承，延長結構的第一自然週期，使該週期遠離地震之主要頻率內涵，進而降低上部結構之加速度反應。然而，如果上部結構的高寬比過高，會引致較大的傾覆彎矩，進而對隔震支承產生軸拉力，造成支承破壞。再者，對於國內常見的彈性支承而言，因橡膠材料並與鋼板積層堆疊黏著，其力學更加複雜且具備耦合之特性，需考慮支承甚或整體隔震結構之穩定性。然而，傳統隔震設計所採用之分析模型，往往未能忠實呈現軸拉力及傾覆彎矩。因此，本研究針對採用彈性支承之建築結構，根據理論、推導及分析，系統性探討支承的穩定性及破壞。於模型中，將整體隔震結構簡化為兩集中質量，上部結構採單自由度模擬，隔震系統含兩個隔震支承並以一剛性樓板與上部結構相連；彈性支承採Koh-Kelly模型，以呈現剪切、撓曲與軸向複合作用，進而推導運動方程。於推導中，彈性支承以不受拉力為目標，可得簡化之隔震結構建議高寬比，加上前述理論模型，以非線性歷時分析進行探討與驗證。理論分析中，考慮多項因素，包含上部結構週期、隔震週期、斷層考量與支承數量，以便驗證高寬比建議式之適用性。模擬結果顯示，本文所提之高寬比建議式，相對日本規範之建議，較為保守；然以本文之範例而言，確實呈現無或甚低之機率於支承發生拉拔。因此，本文之建議高寬比，可供工程師在進行初設時，先期掌握或估算隔震結構之極限高寬比，以判斷支承在地震時有無受軸拉力破壞之疑慮，增進結構設計之效率。
Seismic isolation shifts the fundamental frequency of structures away from the dominant frequencies of earthquakes by employing bearings with low horizontal stiffness, resulting in reduced responses of superstructures. However, an isolated building with a higher aspect ratio may introduce excessive overturning moments that can further cause tensile failure to bearings. Moreover, the elastomeric bearings, which are familiar and common in Taiwan, consist of laminated rubber layers with in-between steel shims, yielding complicated and coupled mechanics. Thus, the stability of the isolation bearings and the overall structural system should be concurrently considered. Such complicated behavior for an isolated building with elastomeric bearings as mentioned above may not be simulated or presented by conventional analysis in practical application. Therefore, this research studies the coupling effect for base isolated buildings with lead-rubber bearings, and then the relationship between aspect ratios and selected isolation bearings is constructed. In this research, the superstructure is simplified to be single-degree-of- freedom and mounted on an isolation system consisting of a rigid floor and two bearings. Each bearing is modeled by a simple mechanical model proposed by Koh and Kelly to consider the coupling effect. Based on the tension prevention of bearings, an aspect ratio criterion is also derived and proposed. This aspect ratio criterion is further verified by time history analyses which consider various factors, such as the period of superstructure, isolation period, fault effect, and layout of bearings. As found in the parametric study, an isolated building designed by the proposed aspect ratio formula has a pretty low probability of tensile failures on bearings, as compared to the recommendation in the Japanese design code. Thus, the proposed aspect ratio criterion is more conservative and can be consequently a reference for engineers in the preliminary design phases of base isolated buildings with lead-rubber bearings.
Subjects
基底隔震
彈性支承
穩定性
高寬比
非線性歷時分析
base isolation
elastomeric bearing
stability
aspect ratios
nonlinear time history analysis
Type
journal article