Hysteretic model for buckling-restrained braces

The yielding core of 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 the core material. As a result, BRBs with steel core could be modelled using cyclic models already available and commonly used in the literature for structural steel. However, available models do not address completely some highly desired requirements: appropriate isotropic hardening, 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, simple implementation and limited number of input data parameters to facilitate its implementation and use. Therefore, 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 formulation adopted 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.