A Review of Research on Shear Strength Decay in Members under Load Reversals

Abstract

In the design of reinforced concrete earthquake-resisting frame members, it is critical that shear distress be limited in order to ensure acceptable deformation capacity and reduce damage. Accordingly, several ACI Building Code1 provisions for beams and columns of frames categorized as “special moment frames” are aimed at minimizing shear distress. Pertinent requirements include using a capacity design approach to calculate demand, neglecting any contribution of the concrete to nominal shear strength in beams, and limiting hoop spacing to one-fourth of the effective (beams) or overall (columns) member depth. These provisions are largely based on findings from early research aimed at understanding the behavior of frame members subjected to cycles of load reversals. The aim of this paper is to review relevant research on the behavior of frame members under earthquake-type demands, beginning with the first tests of flexural members subjected to fully reversed loads and ending with the 1983 ACI Building Code2, as it was the first ACI Code edition to incorporate several provisions aimed at minimizing shear strength decay. This paper describes the basis for pertinent ACI Building Code provisions (other code or design documents were not included in this review), emphasizes the importance of low shear stress demands, and highlights reinforcement detailing options that have been shown to improve member behavior. This review should therefore be of interest to students and structural engineers, particularly those learning or involved in earthquake-resistant design of reinforced concrete structures.