Seismic Performance and Retrofit Evaluation of Reinforced Concrete Structures

TLDR

The capacity spectrum method is a well‑known approach for estimating the margin of safety against structural failure in reinforced concrete buildings. The study proposes a procedure to evaluate seismic performance and retrofit of existing low‑to‑midrise reinforced concrete buildings. The method constructs seismic story demand curves via modal superposition across elastic to failure phases, compares them to capacities from an independent inelastic pushover analysis using stiffness‑dependent incremental shear demands, and is validated on a one‑third‑scale three‑story RC frame tested before and after retrofit on a shaking table. The procedure reliably estimates story demands versus capacities, supporting seismic performance and retrofit evaluation of reinforced concrete structures.

Abstract

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.