Gravity-Load-Designed Reinforced Concrete Buildings: Seismic Evaluation of Existing Construction and Detailing Strategies for Improved Seismic Resistance

Abstract

An analytical investigation of the performance of reinforced concrete buildings designed primarily for gravity loads is presented. In the first part, the seismic performance of non-ductile reinforced concrete frame buildings in regions of low to moderate seismicity is evaluated. Several significant aspects of non-ductile detailing are modeled using rational simplifications of expected member behavior at critical sections. The detailing configurations included in the analysis are: 1) discontinuous positive flexural reinforcement; 2) lack of joint shear reinforcement; and 3) inadequate transverse reinforcement for core confinement. Inelastic time history analyses are carried out under moderate to severe earthquake excitations. The first phase of the investigation established that most of the structural damage could be attributed to non-seismic details at beam-column joints or interfaces. Consequently, the second part of the study was concerned with examining the effects of improving these details in a marginal way so that the seismic performance could be enhanced without resorting to a full seismic design. An extensive parametric study of the same buildings with refined detailing characteristics is carried out to establish simple techniques to improve the seismic resistance of gravity-load-designed buildings. The important feature of the study is that the buildings are not redesigned for lateral forces, but only that the detailing in critical regions is altered to achieve improved performance.