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


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

Author(s): Remy Lequesne and Gustavo Parra-Montesinos

Publication: Special Publication

Volume: 311


Appears on pages(s): 1-16

Keywords: shear, strength decay, beam, column, seismic

Date: 9/1/2016

Early research on the behavior of frame members subjected to reversed cyclic displacements has been reviewed, with an emphasis on the phenomenon of shear strength decay. Information is provided about variables that affect shear strength decay and measures that can be taken to mitigate this phenomenon, which should be of interest to students and structural engineers learning or involved in earthquake resistant design of reinforced concrete structures. Starting in the 1950s, the effect of reversing the loading direction on the flexural response of beams was investigated experimentally. Among other findings, tests showed that single and repeated reversals of load had little influence on flexural strength, but that loading history does influence the deformation capacity and stiffness of members. Although several researchers emphasized the importance of providing adequate transverse reinforcement confining the member core, the role of shear stresses on the response of frame members was not well understood until the early 1970s. Tests by Brown and Jirsa, Wight and Sozen, and Popov, Bertero and Krawinkler, showed that member strength can decay under reversals of load if shear stress demands are large or if inadequate transverse reinforcement is provided. In particular, it was shown by Wight and Sozen that maintaining the integrity of the concrete core through use of closely spaced transverse reinforcement with enough area to resist the entire shear demand without yielding is essential, although not necessarily sufficient. Changes to the ACI Building Code aimed at minimizing shear strength decay were first adopted in 1983 and have remained in subsequent editions of the Code with relatively minor changes.