磚牆在面內水平加載下之位移推估及其耐震評估應用

Displacement of Masonry Wall under Horizontal In-Plane Loading and It’s Seismic Assessment Application

磚砌古蹟及歷史建築如何在地震前之修復過程適切掌握每道牆體之結構行為，並進而評估整體結構系統之耐震能力，對古蹟及歷史建築保存而言，實為相當重要之基礎工作。
為使磚牆在水平力作用下之面內變形行為得到更合理之預測及耐震評估應用，本文將垂直主壓應力方向之軟化效應納入位移估算。經由實例之計算及比較，發現當牆體不考慮此軟化效應時，牆體水平加載-位移推估曲線與實驗曲線有相當大之差異，而考慮軟化效應時，此推估曲線與實驗曲線大致相近，因此建築師或設計者以壓力斜撐來模擬分析磚牆在水平力下之面內行為時，主拉應變對於主壓方向之強度衰減及軟化效應不容加以忽略。
為說明水平加載-位移推估曲線之評估應用，本文以台南市市定古蹟「原台灣總督府專賣局台南支局（台南出張所）」來進行實例操作。基本上，依本文方式所建立之水平加載-位移推估曲線，可有效評估各道受面內水平力牆體之安全指標及檢討是否合乎空間性能等級需求，並進一步對牆體相垂直之橫向壁體之面外安全性做評估檢討。

In Taiwan, the wall element is the most important part that provides the earthquake resistance for a masonry historic building. Thus, during conservation design, the complete behavior of the wall under earthquake is needed to assess the resistant capacity of the structure. To predict the behavior of the brick wall under in-plane loading reasonably, the softening of principal compressive stress was counted in the calculation of the load-displacement relationship curve (P-△curve). By comparing the computation with test results, it shows that the calculated load-displacement curves without considering the softened effect are quite different from the test curves. However, the calculated curves considering the softened effect obtain good agreement with the test results. This comparison also shows the softening of principal compressive stress due to the principal tensile strain should not be ignored when using the compressive truss model to analyze the masonry shear wall. For explaining the seismic assessment application of the load-displacement relationship curve, the Historical Site of Tainan City, Suboffice of Taiwan Tobacco and Wine Monopoly Bureau in Japanese Colonial Period, is chosen to run the seismic assessment. The P-△ curve calculated by using the formula established in this paper can effectively assess the in-plane safe index of the wall and whether the seismic performance reaches the legal standard. Besides, it also can use to assess the out-of-plane safe of the wall which is perpendicular to the assess in-plane wall.