Performance testing and comparison of buckling-restrained braces with H and crisscross cross section unrestrained segments

Abstract

Buckling-restrained braces (BRBs) deliver ductile, stable, and repeatable hysteretic behavior. The plastic deformation capacity of the BRBs indicates the good indexes both in terms of ultimate deformation and in terms of energy dissipation capacity. In this paper, the load-carrying elements of BRBs were fabricated with steel (Chinese Q235), and four layers of plastic film (0.2 mm in thickness) were used as unbounded materials to prevent the buckling of inner cores in higher modes and provide spaces to facilitate its lateral expansion in case of compression. The differences of ultimate compression and tension loads were controlled in a small range. The transformation of the unrestrained segment's section from crisscross shape to H shape can significantly improve the moment-resistance capacity of the unrestrained segment, avoiding buckling instability effectively due to evident moment stiffness enhancement. The experimental results of pseudo-static tests (PSTs) under cyclic load indicate: BRB with H cross section unrestrained segments can undergo fully-reversed axial yield cycles without loss of stiffness or strength, which have large ductility and superior seismic energy dissipation ability. There is obvious strain intensification in tension and compression phases. But there is evident decreasing of stiffness and strength on BRB with crisscross section unrestrained segments due to the buckling of unrestrained segment under compression, the ductility and energy dissipation ability decline distinctly.