Performance Evaluation of Unreinforced Masonry via Fragility Analyses

摘要

The objective of this study is to develop a methodology to investigate the performance of unreinforced masonry (URM) via fragility analyses, describing the probability of a set of limit states being reached given the ground motion severity. It has been well recognized that many existing URM in the world such as the Sichuan Province of China and the mid-west area of America were not designed for seismic forces and will not meet the current seismic design requirements. Their vulnerability under earthquake excitations is therefore, a serious concern for engineers. In this study, vulnerability of such buildings is defined in terms of probability of seismic demand exceeding building capacity for a specific limit state over a given period of time. The demands consist of wall drift, slip between wall and diaphragm, and dynamic impact of diaphragm on the walls. These responses can be obtained by performing numerical analyses (e.g., a 3-D finite element dynamic response analysis under a suit of ground motion excitations). Frequently, URM fails to provide sufficient lateral resistance against earthquake excitations. One of the reasons is the poor design in the connection between the wall and diaphragm such as the buildings in the Mid-America region. In this region, many of the diaphragms of the URM are seated on the walls with a small number of anchors. The connection largely relies on dry fiction between the diaphragm and the wall. From the inspection in the post-Wenchuan earthquake, similar design is found and thus, the methodology proposed here, which is originally developed for the mid-America region, maybe suitable for the performance evaluation of URM in Sichuan Province if relative information (e.g., seismic excitation records and the wall-to-diaphragm connection details) is provided.