Constitutive model for steel buckling-restrained braces

Buckling restrained braces (BRBs) can develop axial yielding in compression in addition to axial yielding in tension, permitting an hysteretic behaviour of the BRB similar to that of its core material. As a result, BRBs with steel core could be modelled using cyclic models already available for structural steel. However, commonly adopted available models do not address completely some highly desired requirements: description of significant isotropic hardening and non symmetric tension-compression response as observed experimentally, explicit computation of the plastic component of the deformation as required in BRB capacity models, smoothness of the transition from the elastic to the plastic range to improve convergence rate, limited number of input data parameters to facilitate its implementation and use. In this paper an elastoplastic constitutive model for steel BRBs is presented following a simple and consistent approach based on a rheological scheme that requires the use of only one internal variable. The adopted formulation allows a straightforward interpretation and identification of its constitutive properties as well as the explicit computation of response quantities related to failure and dissipated energy. Response results obtained using the proposed model are discussed and compared to experimental test results available in the literature.