Abstract
One of damping braces used for super high-rise steel building frames is a buckling-restrained brace. Low-yield steel used for the brace deform plastically so that they can stably absorb the energy of earthquakes. However, it is known that the low-yield steel cause low-cycle fatigue by being subjected to repeated loads. Therefore, there is a possibility that the damping function of buckling-restrained braces are lost under disturbances such as long-duration earthquakes. In this study, behaviors of a super high-rise steel building frame with buckling-restrained braces subjected under a long-duration earthquake motion were simulated. Numerical models of the building with and without buckling-restrained braces were constructed with linear Timoshenko beam elements. The adaptively shifted integration (ASI)-Gauss code with a fatigue fracture algorithm based on experimental results was used in the analyses. According to the repeated loading experiment of buckling-restrained braces, fatigue fracture occurred after 18 repetitions. The numerical results had shown the reduction of displacement and acceleration of the building owing to buckling-restrained braces. However, it had also shown a transition of dynamic characteristics during long-duration earthquake motion, due to fatigue damages of damping braces located in lower floors.