SEISMIC PERFORMANCE AND RETROFIT EVALUATION OF REINFORCED-CONCRETE STRUCTURES

A procedure for evaluating the seismic performance and retrofit of exi sting low-to-midrise reinforced concrete (RC) buildings is proposed. T he procedure is derived from the well-known capacity spectrum method a nd is intended to provide practicing engineers with a methodology for estimating the margin of safety against structural failure, A series o f seismic story demand curves is established from modal superposition analyses wherein changes in the dynamic characteristics of the structu re at various response phases ranging from elastic to full failure mec hanism are considered. These demands are compared to the lateral story capacities as determined from an independent inelastic pushover analy sis. The distribution of lateral forces used in the progressive pushov er analysis is based on stiffness dependent incremental story shear de mands and forms a critical aspect of the methodology. Tile proposed te chnique is applied to a one-third scale model, three-story reinforced concrete frame building that was subjected to repeated shaking table e xcitations, and that was later retrofitted and tested again at the sam e intensities. This study indicates that the procedure can provide rel iable estimates of story demands versus capacities for use in seismic performance and retrofit evaluation of structures.