Deformation concentration to lower stories in high-rise steel buckling-restrained braced frames subject to long-period earthquake ground motions

We study the dynamic response of high-rise steel buckling-restrained braced frames (BRBFs). Three BRBFs designed using different design base shear are subjected to two types of artificial ground motions: One is the long-period ground motion with peak value of 250 cm/s around a dominant period of 3 sec in the velocity response spectrum, expected to take place at Sannomaru site in Nagoya City. The other type is the design ground motion with constant velocity response spectrum of 100 cm/s in the long-period range. For the former type of ground motion, deformation concentrated to lower stories when the ground motion was amplified more than 1.3 times in the BRBF with the highest design base shear. For the later type of ground motions, the deformation concentration was observed when they were amplified more than 1.5 times in the BRBFs with lowest and middle design base shear. Care should be taken when the natural period of a BRBF is smaller than a dominant period of the long-period ground motion even when the design base shear is high. It should be emphasized that the deformation concentration was not observed when the post-yield story stiffness was positive, or when the p-delta effect was neglected.