Numerical Model for Buckling Restrained Braces Using An Alternative Confining Material

Abstract eng:
Buckling restrained braces are metallic dissipators made up of a core of ductile steel, designed to resist similar tensile and compressive forces, by confining the core and preventing global and local buckling. Generally, mortar is used as confining material. The main objective of this research is to determine the properties required of an alternative material to be used as confining material in a BRB and to predict analytically the behavior of the brace subjected to cyclic loads. First, a model that represents the behavior of a beam on an elastic foundation was used to determine the Euler´s critical BRB buckling load and the required value of shear modulus G of the material, in order to restrict buckling of the steel core made of different commercial plates. Next, a 3D finite element model was developed with ANSYS 15.0 software which considers geometric non-linearity, and nonlinear materials and contacts. An isotropic hardening law was used for the steel core model. In order to validate the model, cycles from available experimental data of BRB filled with mortar were compared with the numerical results. A significantly larger maximum strength and asymmetric compression hardening are predicted by the model with respect to the experimental results. This effect is minimized when a softer material is used. A parametric analysis for different values of shear and bulk moduli, friction between the steel core and the confining material and the confined length of the device was performed. Monotonic and cyclic displacements of increasing amplitude were applied to the model and cycles and critical buckling loads were determined. This analysis allowed to identify the influence of the main variables on the stress distribution and the level of confinement, and to predict the critical buckling loads

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