Cyclic tests for assembled X-shaped buckling restrained brace using two unconnected steel plate braces

Cyclic loading tests for a novel type X-shaped buckling-restrained brace (X-BRB), comprising two unconnected steel plate braces encased in an assembled steel panel or assembled X-shaped restraining members, were carried out to investigate the hysteretic behavior of five X-BRBs. Besides, three diagonal BRBs with similar constructional details were tested for a direct comparison. The effects of configuration and size of restraining members, gaps between the restraining members and plate braces and the distance between bolts on the working behavior were mainly examined. The restraining members were constructed by steel parts or steel-concrete composite parts. Tests reveal that, compared with diagonal BRBs, in-plane gaps between the restraining members and plate braces have direct impacts on the interaction between them in X-BRBs, as well as on the overstrength of X-BRBs after yielding of plate braces. Larger gaps enlarged the amplitudes of residual flexural deformation of plate brace. The maximum strength of each diagonal BRB or X-BRB is much larger than its yield strength due to strain hardening and frictional action, as well as the in-plane interaction in X-BRBs. When appropriate spacing of assembled bolts was ensured, either steel or steel-concrete composite restraining members nearly remained intact. All specimens achieved great ductility and energy dissipation capacity and eventually failed due to tension fracture of the plate braces. Whereas, large spacing of bolts induced local bending failure of restraining members. When two parts of each broken plate brace contacted again under further large drifts, the compressive resistance was revived in some degree. The assembled configuration realized reuse of restraining members and would facilitate inspection or replacement of encased braces in application. In this paper, configurations of assembled steel or steel-concrete composite restraining members were proposed to allow the two encased diagonal braces to pass through each other freely, to improve bearing capacity of restraining members, etc. Moreover, cyclic loading tests for five X-shaped BRBs and three diagonal BRBs were conducted to examine the effects of the constructional details on the hysteretic behavior of the assembled BRBs. The configuration details of the specimens and preparation of tests were introduced first, and then both the test results and evaluation on the hysteretic behavior, failure modes, ductility and energy dissipation, etc. were p