Seismic response of concentrically braced frames with staggered braces in split-x configurations

Special concentrically braced frames (SCBFs) are used in high-seismic regions to provide adequate lateral strength, stiffness, and ductility to a structural system. Although these frames help the structure to survive the lateral seismic actions, high uplifting/settling forces in the bracing columns may, sometimes, damage the structural integrity. This detrimental effect can be mitigated by distributing the concentrated uplifting forces among the columns using braces in staggered arrangement. Thus, the primary aim of this study is to understand the seismic response of SCBFs with staggered braces arranged in split-X configurations as compared to the conventional single-stack braced frame. Six different brace arrangements are considered for a five-story steel braced frame. Nonlinear static analyses are conducted to evaluate the lateral strength, ductility, and yielding mechanism of these study frames. In addition, nonlinear dynamic analyses have been carried out to assess the inter-story drift response and the occurrence of soft-story mechanisms in the braced frames. Analysis results highlighted the performance of staggered braced frames nearly at par with the conventional single stack arrangement. Axial force demand at the column bases are also remarkably reduced in case of staggered braces. Hence, to improve the performance of staggered braced frame a revised design method was implemented which resulted in improved lateral strength, ductility, and yield mechanism.