Seismic Capacity Assessment of Unreinforced Concrete Block Masonry Buildings in Pakistan Before and After Retrofitting

Abstract

This article presents the results of an experimental study on the performance of a full-scale unreinforced concrete block masonry (URCBM) building system tested under quasi-static loading. The configuration and materials used for the single-story URCBM building are typical of those found in the northern areas of Pakistan affected by the 2005 Kashmir earthquake. The retrofitting of the building was done using ferro-cement overlay and cement based grout injection. Combined shear and flexure failure was observed during the test before retrofitting. The lateral load capacity of the retrofitted building was significantly improved (more than 200% of the original strength) and the damage mechanism was transformed from mixed compression-flexure-shear to a more stable flexural rocking mode. Damage patterns and force-deformation behavior of the retrofitted structure are compared with those of the intact structure to quantify the beneficial effects of retrofitting scheme, which is proposed as an efficient approach for the rehabilitation of the existing buildings. Experimental data were analyzed and presented in the form of force-deformation hysteresis loops and envelope curves. Based on the measured data, different performance levels before and after retrofitting of the structure have been established. Response modification (R), displacement ductility (μD), and displacement amplification (Cd) factors were also derived. The results from this study are expected to guide future efforts on development of design recommendations and vulnerability assessment of buildings in Pakistan.