Inelastic behavior and seismic design of multistory chevron-braced frames with yielding beams

Chevron or inverted V-braced frames offer numerous architectural and structural advantages, but the current special concentrically braced frame (SCBF) seismic-design requirements in the American Institute of Steel Construction (AISC) Seismic Provisions for Structural Steel Buildings lead to deep, heavy chevron beams; as a result, few chevron SCBFs are built today. Recent research on single-story chevron SCBFs demonstrated that beam yielding can be advantageous at higher demand levels, and design for large, inelastic unbalanced brace-force demands may still result in acceptable seismic performance. However, this prior research did not consider the response of multistory frames. In particular, questions remain as to the potential for concentration of damage, the impacts of composite slabs, and the effects of different beam-to-column connections; these issues can only be investigated using multistory frames. A companion research program was conducted to investigate multistory systems with chevron SCBFs using experimental and computational simulation methods. In the first phase of the research, a three-story chevron SCBF designed to permit beam yielding was tested at the National Center for Research on Earthquake Engineering (NCREE) Laboratory in Taipei, Taiwan. The test results were then used to validate a nonlinear, continuum finite-element model. A limited parametric study was conducted to build upon and further the experiments, specifically to evaluate different beam strengths and stiffnesses. These results were combined to develop design recommendations for chevron SCBFs with yielding beams.