Defining Design Parameters for Controlled Rocking Braced Frames to Control Seismic Losses

Controlled rocking braced frames (CRBFs) are a self-centering lateral force-resisting system aimed at reducing structural damage potential. Previous research has shown that relatively low design forces for rocking and for structural elements in CRBFs would be acceptable based on collapse fragility analysis. However, past studies have also highlighted the potential for significant story drifts and for increased demands on acceleration-sensitive nonstructural components installed in buildings with CRBFs. Therefore, while CRBFs have demonstrated acceptable performance in terms of collapse across a wide range of design options, these design options must be evaluated considering the performance of nonstructural components if the intended low-damage potential of CRBFs is to be fully realized. To address this need, this paper investigates the influence of two key design parameters on seismic losses of buildings with CRBFs, namely the response modification factor (R) for the rocking joint design and the amplification factor (gamma) used to incorporate higher-mode forces into the capacity design of frame members. Three different heights of CRBF buildings are designed using different design options, with values of R ranging from 5 to 12 and with higher-mode forces considered based on two seismic intensity levels: the design earthquake (DE) and the maximum considered earthquake (MCE). Then, following an assessment of structural responses, the paper's primary emphasis is on earthquake-induced economic losses. While the computed total expected annual losses (EALs) using various design options are remarkably similar, the distribution of losses attributed to collapse or to nonstructural components varies. The CRBFs with lower resistance to rocking exhibit greater losses attributed to collapse and to drift-sensitive nonstructural components, but this is counterbalanced by a simultaneous reduction in losses related to acceleration-sensitive nonstructural components. Furthermore, in taller CRBF buildings, using amplified higher-mode forces based on the MCE level slightly decreases total EALs compared to those using the DE level, primarily due to a reduction in collapse losses.