Seismic rehabilitation of a reinforced concrete flat-slab structure

Abstract

The effectiveness of seismic rehabilitation techniques used to eliminate punching shear failures was assessed for flat-slab structural systems. This type of retrofit was evaluated for a four-story reinforced concrete (RC) frame office building damaged during the 1994 Northridge Earthquake. This structure had no serious damage in its perimeter moment frames, but experienced several punching shear failures at its interior slab-column connections. Previous research has led to the conclusion that these buildings may be retrofitted by limiting their lateral drift and/or retrofitting their interior connections. This study focused on evaluating the effectiveness of stiffening the structure using vertical bracing in the perimeter frames. An analytical model in DRAIN-2DM of the study building was used to evaluate different retrofit strategies. Various aspects of the selection and design of steel bracing systems for the seismic retrofitting of reinforced concrete frames were considered. The bracing configuration within the exterior frame was varied and the effects of allowing the braces to behave outside of the elastic range were assessed. As part of the evaluation of various bracing configurations, both static and dynamic nonlinear analyses were performed. The ground motion records used for the dynamic nonlinear analyses included a ground motion recorded within 0.6 mi. (1 km) of the study building and a synthetic ground motion representative of the mid-west and east coast area of the United States.