Research and application of buckling restrained braces

In recent years, experimental and analytical researches have been conducted in NTU to investigate the effectiveness of various kinds of unbonding material, the brace-to-gusset connection details, analytical models and the design procedures for the buckling restrained braces (BRBs). Tests conducted on more than 50 specimens confirm that the proposed BRBs employing double steel cores encased in twin steel tubes and infill concrete can stably sustain severe inelastic cyclic axial strain reversals. The double-cored BRBs can be conveniently connected to the gusset plate as in the traditional double-tee brace to gusset plate connections. Experiments include cyclic tests of BRB components and large scale single bay V-shaped buckling restrained braced frames (BRBFs). Test results indicate that the 2 mm thick silicon rubber sheets are effective in minimizing the difference between the cyclic peak compressive and tensile forces of the BRBs. The three V-shaped BRBF tests confirm that the steel brace core strain demands can be satisfactorily predicted from the story drift demand by geometry and incorporating the inelastic core length ratio. Test results also reveal that at a large story drift, the tensile strain in the tension brace was always greater than the compressive strain in the compression brace. This paper also introduces fully detachable BRB designs, non-destructive evaluation techniques for damage detections of BRBs. Finally, the paper concludes with the applications of the proposed BRBs in seismic retrofit as well as new construction projects in Taiwan. Keywords：Buckling restrained braces, unbonded braces, cyclic loading tests, cumulative plastic deformatio