On the Post-Peak Ductility of Shear-Critical Beams

Abstract

This paper describes how code procedures for the seismic design of reinforced concrete structures are increasingly incorporating performance-based criteria. The push-over analyses is being incorporated into these criteria and becoming an accepted means of demonstrating sufficient energy-absorbing capacity. Therefore, in concrete frame structures containing shear-critical structural elements, the post-peak load-deformation response of these members becomes of practical importance. A series of shear-critical beams was tested recently, patterned after the classic set of beams tested by Bresler and Scordelis forty years ago. In the current tests, particular attention was paid to capturing the post-peak response. The details and results of these beams are presented, providing data useful in testing and calibrating analytical procedures. Nonlinear finite element analyses were undertaken to determine current ability to accurately model post-peak ductility in shear-critical members. Results indicate that current procedures are of marginally acceptable accuracy, and that further developmental work is warranted. A case study, involving a large concrete frame structure built in a high seismic region and containing shear-deficient members, is discussed. This case underscores the importance of accurately calculating the post-peak ductility of shear-critical beams.