Probabilistic residual drift assessment of rocking buckling restrained braced frames under crustal and subduction ground motion records

Buckling restrained braced frames (BRBFs) are widely used as a lateral force resisting system due to their advantageous characteristics such as elimination of brace buckling in compression, high ductility and energy dissipation. BRBFs may have damage concentration in one or few stories during severe seismic excitations, because buckling restrained brace (BRB) yields in a certain story and the stiffness of that story significantly decreases. Drift concentration is undesirable as it can lead to general instability resulting from P-Δ effects or residual drift. For controlling damage concentration in one or few stories and achieving a uniform distribution of drifts in all stories, a new system entitled rocking buckling restrained braced frame (RBRBF) can be used. RBRBF system generates uniform story drifts over the height of structure and prevents the damage concentration in one or few stories. Unlike conventional or suspended zipper braced frames, the braces on one side of the braced span along with the adjacent columns and ties are part of a vertical truss system that is hinged at the base and designed to remain elastic until the near collapse limit state is reached. This vertical truss system works as a strong support for preventing damage concentration in one or few stories of the braced frame. The braces on the other side of the braced span are BRBs and are designed to provide energy dissipation. RBRBFs are designed according to a displacement‐based approach. The novelty of this paper is investigating the residual drift performance of this new structural system under the effect of subduction ground motion records, which have higher significant durations compared with crustal ground motion records. In this study, 4-, 8-, and 12-story structures with RBRBF and BRBF systems are considered, and their residual drift capacity values given four maximum residual interstory drift ratio (MRIDR) levels of 0.2%, 0.5%, 1.0% and 2.0% are computed using incremental dynamic analyses (IDAs). IDAs are performed on two-dimensional models of the structures using 22 pairs of short-duration crustal and long-duration subduction ground motion records. After computing the capacity values given these four MRIDR levels, the residual drift margin ratios (RDMR), and the mean annual frequencies (MAFs) of exceeding different MRIDR levels (λRD) are obtained. The results demonstrate that all the RBRBFs have better residual drift performance than the BRBFs. Based on these results, the use of RBRBF dramatically reduces BRBF weaknesses including the concentration of damage in a certain story and low post-yield stiffness. For example, the ratios of the total λRD value given MRIDR= 2.0% for the BRBF system to its corresponding value for the RBRBF system for the 4-, 8-, and 12-story structures are 21.10, 4.06, and 3.21, respectively. In addition, for most of the structures, as the MRIDR level increases, the ratio of the RDMR value under crustal records to that under subduction records increases.