Investigation of the seismic response of three-story special concentrically braced frames

Special concentrically braced frames (SCBF) are stiff, strong and economical lateral-load resisting systems, which can sustain large inelastic deformation if properly detailed. Historically, experimental research on the seismic response of braced frame research has focused on the cyclic and monotonic responses of isolated components, such as braces or gusset plate connections. However, these components do not work in isolation, and recent research shows that accurate evaluation of their seismic performance requires consideration of the complete system. A collaborative research program with investigators from National Center for Research on Earthquake Engineering (NCREE) in Taiwan, and the Universities of Washington (UW), California, and Minnesota was undertaken to investigate the full system response of SCBFs. The research results presented herein focus on two three-story SCBFs that were tested at the NCREE laboratory. The specimens evaluated a new design approach for midspan gusset plate connections. The two specimens had HSS or wide-flange braces in combination with framing members and connections typical of those used in a three-story building in regions of high seismicity. Composite, concrete slabs were placed on each story. The tests were designed using a recently proposed design method to balance the desired yield mechanisms and form yield hierarchy. The results demonstrate that multi-story SCBFs exhibit good inelastic seismic performance with proper design detailing. Together with prior test results, the test specimens advanced design recommendations for SCBFs, which result in thinner, more compact corner gusset plate connections, a rational method of dimensioning mid-span gusset plates, and a balanced-design procedure for enhanced ductility.

► Describes cyclic testing and nonlinear analysis of 2 full-scale 3-story SCBFs.
► Develops improved midspan gusset plate connections for SCBFs.
► Demonstrates SCBF failure modes, yield mechanisms, and concentration of damage.
► Compares SCBF deformation capacity with wide flange and rectangular HSS braces.
► Nonlinear analysis results compared to experimental results.