棒狀模型非線性歷時分析與消能評估

Abstract

現今業界，不論在做結構設計或是阻尼器設計，皆把結構視為彈性作分析，在外力小的情況下，最後分析結果或許是可接受的，但一旦發生大規模地震，由於結構會進入非線性，此差異會導致最後分析結果超出預期，造成結構設計上的危險。有鑑於此，本研究主要是探討結構非線性行為，對結構歷時分析的反應以及阻尼器消能效果之影響。因此，本文將提供一套分析的方法，如何利用套裝軟體ETABS的非線性側推分析(Nonlinear pushover analysis)，所得到的容量曲線，來模擬結構的非線性行為。側推分析中，塑鉸則採用內建塑鉸，並利用國家地震中心的鋼筋混凝土實驗試體，來確保內建塑鉸的合理性。而即使決定了結構主體的非線性行為，對於3D結構計算量亦十分龐大，故有必要將3D結構簡化成棒狀模型(Stick model)。 以高樓結構的歷時分析結果來看，在設計上如果以線性結構做設計分析，並和非線性結構分析結果作比較，結構的位移反應會被低估，加速度、基底剪力會被高估。而阻尼器的消能效果，由於忽略了結構本身的消能能力，因此消能效果會被高估，且阻尼器設計上所需側位移、最大側力也會被低估，阻尼會無法達到預期效果，故結構非線性分析是有必要的。

Today, elastic structural analysis is conducted for the design of structures without and with dampers in the industry. When earthquakes are small, analysis results may be acceptable. However, when earthquakes are severe enough, structures may exceed elastic limits. Analysis results may not be the same as expected and the design may not be conservative enough. Therefore, nonlinear behavior of structures without and with velocity- and displacement dampers is investigated through time-history analysis in this thesis. Capacity curve is obtained from nonlinear pushover analysis by using ETABS and nonlinear spring for each story is established from the relationship of story shear and inter-story displacement. In the nonlinear pushover analysis, default plastic hinges built in ETABS are adopted. The feasibility of the default plastic hinges is verified by the experimental results provided by the National Center for Research on Earthquake Engineering. Since it is very time-consuming to perform 3D nonlinear structural time-history analysis, the nonlinear structure is simplified to stick model. From the case analysis of a high-rise building, if the structure is assumed to be elastic, displacements are underestimated but absolute accelerations and base shear are overestimated compared with those obtained from nonlinear structural analysis. When velocity- or displacement-dependent dampers are added to the structure, elastic analysis overestimates the effect of dampers because energy dissipated by the structure is ignored. Moreover, the lateral displacement and lateral force demands of the dampers are underestimated. The effectiveness of the dampers cannot be as developed as expected. Therefore, nonlinear analysis is necessary for structures under earthquake loads.