SEISMIC PERFORMANCE EVALUATION OF URM BUILDINGS

Abstract

Substantial research has been carried out on unreinforced clay brick masonry structures worldwide to understand their behavior during earthquake. But, the heterogeneity and variation in material, quality of clay and differences in construction methodologies make this research output questionable for application in Indian conditions. In India, research efforts have been taken on masonry, particularly focused on material properties, but not prominent on the behavior of components. This lack of knowledge had contributed in the devastation of unreinforced masonry buildings during past earthquakes and makes them a serious threat to safety of life and property. In this work, an attempt has been made to understand the seismic behavior of Indian URM buildings through experimental investigations on the masonry walls and analytical investigations to study the performance and vulnerability of the existing school buildings in the seismically active region of Uttarakhand. To study the material properties, compressive strength tests have been carried out on the masonry prisms to determine the strength and elastic properties of masonry. The tests have shown large variation in the strength and modulus of elasticity of masonry. Seismic resistance in URM building is mainly due to in-plane action of piers. Therefore, detailed study on in-plane behavior of piers becomes necessary. To study the in-plane behavior, a test setup has been developed to test masonry piers under in-plane lateral cyclic load with constant vertical stress. The test setup also facilitates to test piers with different aspect ratio and different vertical loads. An experiment carried 'out on a pier has given information about future modification needed for testing and maximum size of the specimen that can be tested considering the capacity of the actuators and maximum vertical stress. The pier tested for in-plane load has shown sliding shear failure under low level of vertical stress. The pier has shown large deformation capacity and low stiffness degradation per cycle. Also the drift values shown are very large comparative to those given by FEMA 356, which suggests the need of further research for Indian conditions. iii Performance of typical school buildings in rural areas of Uttarakhand built in unreinforced masonry has been evaluated by Pushover Analysis according to FEMA-356/440. The performance has been studied for different material qualities and different PGA levels. The performance of the building is Life Safety in DBE for Zone IV and Collapse Prevention for Zone V, for all material qualities given in FEMA-356. For the properties reported for Indian masonry by Krishna and Chandra, the building has shown Life Safety level. However in MCE, the building has shown `Collapse'. Vulnerability assessment of the building for the same material qualities and PGA has also been done based on probabilistic approach. The HAZUS Methodology has been used to find the probability of damages. The approach based on capacity spectrum has been applied, in which spectral displacements have been assigned as the median threshold values for different damage states. The variabilities have been taken from HAZUS manual. The study has shown very high probabilities of damage and collapse for the considered type of buildings under major (MCE) earthquakes expected in seismic zone IV and V. iv