Probabilistic seismic evaluation of suspended zipper-braced frames

Inverted-V-Braced Frames often face seismic challenges, notably the buckling of compression braces on a specific floor, leading to a consequential reduction in overall structural strength and lateral stiffness. To address this challenge, one of the proposed solutions is the implementation of Suspended Zipper-Braced Frames (SZBFs). However, the actual effectiveness of SZBFs remains uncertain in the face of earthquakes with various spectral acceleration intensities associated with the level of seismicity. This study is dedicated to the probabilistic evaluation of the seismic performance of SZBFs, with a focus on assessing their safety margins and collapse capacities. The study utilizes a thorough probabilistic evaluation, taking into account four sources of uncertainty, and performs nonlinear analyses on 18 Suspended Zipper-Braced Frames serving as archetypes. These archetypes are designed in compliance with seismic provisions related to the lower bound of Seismic Design Category D (SDC D_min) and are categorized into six performance groups with varying heights and bracing angles based on FEMA P695 methodology. The research incorporates nonlinear modelling for both structural components and gusset plate connections in both static and dynamic analyses. Archetypes are subjected to 44 different earthquakes with varying intensity and frequency content. The analysis of collapse margin ratios for the archetypes, compared to acceptable values in FEMAP695, indicates that the seismic design parameters integrated during the initial design phase of these frames have established a safety margin exceeding twice the specified limits. Additionally, the achieved Overstrength factor of 3 is higher than what is suggested for Special Concentrically Braced Frames (SCBFs) in design codes. According to the results, the findings imply that SZBFs can be designed to not only achieve a satisfactory margin of safety but also to incorporate economic structural elements.