# Buckling-Restrained Bracing System with Ultra-High-Performance Fiber Concrete
## 1 Introduction
They came to the conclusion that the length of the core plate does not affect buckling behavior and provided a standard for local buckling restraint failure. [PERSON] (2010) prepared a sandwiched BRB 3D numerical model to provide a better understanding of the compressive behavior of BRBs under buckling loading. In this model, the concrete behavior was assumed to be elastic [18]. They checked whether the BRB components affect elements such as the core plate size in terms of its behavior. [PERSON] (2012) developed an all-steel BRB 3D FEM model by focusing on the overall buckling behavior [19]. They studied the effect of the air gap between the core and the restrainer and concluded that the contact frictional magnitude coefficient had a significant effect on the behavior of the device. [PERSON] (2012) also developed a 3D model for all-steel BRBs with reduced lengths using the bilinear steel material model [20]. There are several researchers working on developing numerical material modeling. The aforesaid BRB FEM models were developed using the finite element commercial software Abaqus; the concrete was modeled as an elastic material and the steel material was modeled with diverse material models, such as simple bilinear and complex combined hardening. However, in the cyclic material models, some key cyclic characteristics were not considered. A range of models were developed to expose the cyclic BRB behavior in numerical studies using truss finite elements: an elasto-plastic bilinear model with 110% axial compressive strength of the tensile and post-yield stiffness set as zero [21]; a force-deformation bilinear relationship with post-yield stiffness set as 0.05 [22]; a force-deformation trilinear analytical model (with two inelastic truss elements in parallel) representing the BRBstrength raise from isotropic hardening [23]; the Bouc-Wen smooth law [24]; the modified Ramberg-Osgood smooth law with isotropic and kinematic strain hardening as well as a yield load in compression increased by 10% [25]; the Menegotto-Pinto smooth law with kinematic and isotropic hardening [26]. All uni-axial constitutive models have their own advantages and disadvantages. Bilinear laws are uncomplicated and capture the overall BRB hysteretic behavior in cases with proper hardening rules. Nevertheless, these models do not have the ideal response efficiency and the estimate of the actual load-deformation behavior is not sufficient and is enhanced just to a limited extent by tri-linear laws. Nevertheless, the conventional BRBs had some restrictions which have limited the extensive acceptance of BRBFs in the design community. For instance, the yielding core element of BRB supposed to dissipate hysteretic energy during an earthquake event. This absorbed energy is capable of causing cumulative damage, reducing fatigue life and even ruptures in the element, possibly compromising BRB efficiency for following earthquakes. Another issue is the difficulty of detecting and tracking damage in a core element of a conventional BRB aftermath of a severe earthquake, which can be destructive. Furthermore, the buckling-restraining element of a well-designed ordinary BRB should remain elastic when damages occur in its restrained yielding segment. However, it is inconvenient to reuse the buckling-restraining elements of ordinary BRBs, which does not help achieve the sustainable design objective. Most studies in the literature focused on investigation of the BRB behavior by changing the core material, and the design effect of filler material was neglected. Hence, [PERSON] (2023) conducted an experimental test, focusing on the effect of conventional concrete mixed with steel, micro silica, fly ash and polypropylene and their mixture percentage on a BRB performance. The findings of this research indicated that conventional concrete with steel fibers yielded the most favorable outcome, enhancing the compressive capacity of BRBs by 25% [27].