Probabilistic seismic demand assessment of steel frames braced with reduced yielding segment buckling restrained braces

Buckling-restrained braces have adequate seismic performance characteristics such as high energy absorption due to their symmetric behaviour in compression and tension. However, low post-yield stiffness is one of the main disadvantages of these braces. The stiffness values of buckling-restrained brace frames can highly degrade when the core segments are yielded. Reducing the length of the yielding segments of buckling-restrained braces is being proposed and investigated by many researchers, considering the high strain capacity of steel in the post-elastic region. This article focuses on a type of buckling-restrained brace called reduced yielding segment buckling restrained brace or in short, 'reduced length buckling restrained brace'. In such frames, the length of the yielding part is reduced and placed in one end of the brace element. In this research, the seismic performances of the above-mentioned buckling-restrained braces were investigated through probabilistic approach and compared with those of conventional buckling-restrained braces. Their performances were quantitatively assessed in terms of two limit states, immediate occupancy and collapse prevention. The fragility curves, the mean annual limit states frequencies and the seismic demand hazard curves of the frames were plotted using probabilistic seismic demand analysis. According to the results obtained for immediate occupancy limit state, the frames braced with reduced length buckling restrained braces show better seismic performances compared to those braced with conventional buckling-restrained braces. However, for collapse prevention limit state, it is hard to comment accurately because in some cases, reduced length buckling restrained braced frames show enhanced seismic performance while in other cases, conventional ones exhibit improved response.