Local Buckling of Buckling Restrained Braces

Abstract eng:
After extensive tests in the Center for Research on Earthquake Engineering (NCREE) and Taiwan University laboratories, buckling restrained braces (BRBs) have gained wide acceptance in seismic building applications in recent years. In order to facilitate cost-effective production, the cross-section optimization of the BRB is studied in this research. In order to slim down the BRB cross section, the role of the concrete strength in preventing the local buckling of the brace core is investigated using five full scale BRB specimens. Test results confirmed that the confinement requirements developed based on the lateral compressive stiffness of the infill concrete are not sufficient in the slimed BRB. Test results indicated that the wave length of the high mode buckling of brace core is about 2.25 times the width of core steel plate. Based on the flexural mode of the confining concrete under the lateral compression of core steel plate, it can be found that the required stiffness of the infill concrete is a function of the core steel plate width to confining concrete height ratio (w/h) and the core steel plate width to thickness ratio (w/t). It is found that if the brace core is made from ASTM A572 Grade 50 steel, the required concrete Young’s modulus Ec (in kg/cm2) has to be greater that 18000(w/h)3(w/t). The paper concludes with seismic design recommendations for the slimed BRBs.

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