Seismic performance and retrofit evaluation of reinforced concrete structures

A procedure for evaluating the seismic performance and retrofit of existing low-to-midrise reinforced concrete (RC) buildings is proposed. The procedure is derived from the well-known capacity spectrum method and is intended to provide practicing engineers with a methodology for estimating the margin of safety against structural failure. A series of seismic story demand curves is established from modal superposition analyses wherein changes in the dynamic characteristics of the structure at various response phases ranging from elastic to full failure mechanism are considered. These demands are compared to the lateral story capacities as determined from an independent inelastic pushover analysis. The distribution of lateral forces used in the progressive pushover analysis is based on stiffness dependent incremental story shear demands and forms a critical aspect of the methodology. The proposed technique is applied to a one-third scale model, three-story reinforced concrete frame building that was subjected to repeated shaking table excitations, and that was later retrofitted and tested again at the same intensities. This study indicates that the procedure can provide reliable estimates of story demands versus capacities for use in seismic performance and retrofit evaluation of structures.