## 1 Introduction  
Buckling restrained braces (BRBs) are typically composed of core components and external restraining members [1; 2]. The core component is directly subjected to axial loads and laterally restrained during compression buckling by the external restraining members. It is a principal bearing and energy-dissipating member. The core is often constructed of steel with a low yield point to meet ductility standards. The outer load for the external restraint system, which is not directly subjected to axial pressure, is the lateral extrusion dispersed load acting on the core part, a flexural component. The external restraining members increase the bearing capability of the core member by providing lateral restraint, preventing overall instability and resulting in a complete hysteresis curve and superior energy dissipation performance of the BRB. BRBs can provide stable lateral stiffness and bearing capacity subject to earthquakes and wind loads; under medium or large earthquakes, the core is the first to enter yielding, consuming the earthquake's energy input, reducing the energy input to the main structure from the earthquake, and playing the role of energy dissipation and earthquake reduction. In addition, the torsional vibration pattern may control the structure's design for systems with severe plane abnormalities. The frame's stiffness can be increased in this case by modifying the BRB to meet the structure's initial vibration mode, which is a flat dynamic vibration mode, successfully reducing the system's torsion effect. The existing BRBs are categorized into three categories based on their external restraining members: reinforced concrete restrained BRBs [3; 4], steel and concrete restrained BRBs [5], and all-steel restrained BRBs [6; 7]. At present, the reinforced concrete restrained BRB is rarely used in the structural design, considering that reinforced concrete is easy to crack and the restraint effect is poor. The design methods of the steel and concrete restrained BRB and all-steel restrained BRB are relatively mature, and these BRBs are widely used in structural design. [PERSON] et al. [8] proposed a novel type of angle steel buckling-restrained brace (ABRB) and investigated its elastic buckling load, load resistance, and hysteretic performance numerically and experimentally. [PERSON] et al. [9] proved the short-core all-steel BRB could effectively reduce the story drifts of the frames. [PERSON] et al. [10] investigated the failure mode and hysteretic performance of the web-restrained BRB under cyclic load. [PERSON] et al. [11; 12; 13] investigated the elastic buckling behavior, load resistance, and hysteretic performance of all-steel BRBs such as triple-truss-confined BRB (TTC-BRB), and shuttle-shaped BRB (SS-BRB), numerically and experimentally. [PERSON] et al. [14] numerically investigated the failure modes and buckling behavior of all-steel fish-bone-shaped BRB (FB-BRB). [PERSON] et al. [15] studied the buckling behavior and hysteretic performance of steel angles assembled BRBs. Other research like [PERSON] et al. [16], [PERSON] et al. [17], [PERSON] et al. [18], and [PERSON] et al. [19], also investigated the hysteretic performance of all-steel BRBs. Recently, the core assembling of BRBs has been commonly fabricated. However, the existing BRBs generally use a single core, and their bearing capacity is limited. [PERSON] et al. [20; 21] and [PERSON] et al. [22] presented and studied the elastic buckling load, load resistance, and hysteretic performance of all-steel core-separated BRB (CS-BRB) theoretically, numerically, and experimentally. However, the all-steel rectangular tube-constrained BRB chord is welded by four plates of steel to a very flat rectangular steel tube, which is difficult to manufacture. The test proves that its rectangular steel tube is prone to tear damage at the welding seam under the extrusion force of the in-line core. [PERSON] et al. [23] proposed and studied an all-steel assembled double-cores BRB (DCBRB).