Vulnerability of un-reinforced masonry buildings in Mid-America

A methodology is developed for probabilistic evaluation of performance of existing and retrofitted un-reinforced masonry building under earthquake excitations. Since most buildings in mid-Amerca have not been designed for seismic forces, the vulnerability of such structures is a serious concern as in many other areas of moderate seismicity. A finite element model based on ABAQUS was developed. Due to the lack of data of ground motions of engineering interest, simulation is used. Ground motions were generated such that they are consistent with the regional seismicity and uniform hazard target response spectra. Nonlinear and hysteretic structural components behaviors are properly considered. An incremental dynamic analysis (IDA) is also performed to assess the building capacity against collapse. For retrofit, the center core method of embedding the reinforcing bars within an existing un-reinforced masonry wall and wall/diaphragm connection strengthening are considered. Results show that wall-strengthening does not enhance building performance as would be expected. The slip between wall and diaphragm can cause the diaphragms falling off from the walls or impacting out-of-plane walls and hence collapse of the building. Retrofitting the diaphragm/wall interface to prevent the slip may be more effective.