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Transverse reinforcement in reinforced concrete (R/C) frame buildings designed to older seismic codes is typically inadequate, rendering their members vulnerable to shear failure subsequent, or prior, to yielding of their longitudinal reinforcement. This can eventually lead to loss of axial load-bearing capacity of columns and initiate vertical progressive collapse.
The development of a member-type model for the full-range response of substandard elements is presented herein. The basis of post-peak behaviour modelling is the ascription of post-shear failure deformations to shear strains alone and their concentration at a critical length defined by a diagonal failure plane. The parameters defining the critical angle of this plane and the in-cycle shear strength degradation after the onset of shear failure are identified and empirical models are put forward. To this end, a rather large database of experimental results of rectangular shear and flexure-shear critical R/C columns has been compiled.