Seismic Performance of Brace Middle‐Connection in Steel Concentrically Braced Frames with X‐Bracing

This paper presents the experimental investigation of two brace middle connections: 1) using a slotted tube knife‐plate connection (STKPC), and 2) a bolted sandwich plate connection (BSPC). The STKPC consists of a gusset plate slotted through the continuous brace and welded to discontinuous braces. The BSPC consists of two cover plates and four U‐shaped plates connecting the discontinuous braces using bolts. The two cover plates pass on either side of the continuous brace and are bolted to the U‐shaped plates. These connections are used to join the discontinuous braces in steel concentrically braced frames (CBFs) configured with X‐bracing. These connections were tested as part of a full‐scale CBF using quasi‐static testing. In both specimens, seismic energy dissipated through yielding and buckling of the braces. However, in the specimen with STKPC, axial deformation is concentrated in a single discontinuous brace, which led to local buckling at mid‐length and subsequent fracture. In contrast, the BSPC is able to better distribute axial deformation between the two discontinuous braces delaying local buckling. Moreover, the measured buckling capacity of braces when using the BSPC matches well the expected compressive resistance calculated using an effective length factor K = 0.45.