Theoretical And Experimental Study On Design Methods For Double Square Tube Assembled Buckling-restrained Brace

The assembled buckling-restrained brace(BRB) is a new king of BRB, and the components constituting the external restraining member are assembled by high strength bolts. For example, the square tube assembled BRB’s external restraining member consist of two square tubes with extension plates bundled by high strength bolts. The assembled BRB has advantages of high construction precision, conveniently assembled at construction site, and easy replacement of core member after the earthquake, and the external members are reusable.A Refined finite element(FE) analysis on a simplified BRB was firstly carried out in this study, the development of contact between the core and external member, core waveform variation, core contact force distribution and external member stress were discussed. The impacts of some parameters on the performance of BRB stress were also investigated, such as the core initial imperfection form, external member initial imperfection amplitude, gap between the core and external restraining members, external member strength and stiffness, core length, core width-to-thickness ratio and core thickness.After that, pinned BRB with extended core member was also studied. The BRB stress state under conditions of core member single wave overall deformation and multiwave buckling was analyzed intensively. In addition, the theoretical derivation was employed to calculate the most unfavorable bending moment on the extended portion of the core member, core member contact force, bending moment distribution on the external restraining member, etc. Finally, based on stress characteristics of BRB components, the design criteria of external restraining member and the core member strengthening portion were established to perfect the design theory of pinned integrated BRB. The assumptions made in the corresponding theoretical derivation and its results were verified by the numerical method. Also, the influence of nine design parameters on the core contact force and the external member stress were also analyzed.As the discrete layout of the connection bolts has adverse impact on the integral restraining stiffness of the external restraining members, the theoretical derivation and numerical verification were employed to study how to quantify the external restraining stiffness of the square tube assembled BRB. After considering the bolt discrete impact on the external restraining stiffness and the local stress of panels between the bolts, this study put forward a set of design method suitable for square tube assembled BRB. In addition, imaginary BRB cases were also designed and tested, which verified the design theory. Finally, the square tube assembled BRB bolt design theory was made and the applicable bolt design method was put forward.The numerical analyses on the square tube assembled BRB was carried out in this study; the impact of design parameters on BRB performance, the possible failure modes and influence factors of BRB were investigated. Besides, the impact of different connection constructions between BRB and frame on BRB performance and the superiority and inferiority of different connection constructions were also discussed.Finally, the experimental study on the square tube assembled BRB was carried out, which verified the safety and the reliability of the design theory in this study. The rationality of BRB construction details was also examined by the test, which provides a sufficiently reliable basis for the engineering application.