Inelastic Buckling Analysis of Steel X-Bracing with Bolted Single Shear Lap Connections

Abstract

Analytical models are proposed to predict the compressive resistance of discontinuous bracing members in steel X-braced frames when governed by flexure of the connecting plates at the mid-connections. The connections are bolted single shear splice connections commonly used for HSS bracing members. An incremental analysis procedure is developed to predict the axial load-deformation response of the brace-connection assembly including geometric and material nonlinearities. The buckling strength depends on the thickness of the connecting plates, the length of the connection, the clear distance between the continuous and discontinuous bracing members at the brace intersection, and the length of the discontinuous brace segments. The method is validated against test results from full-scale X-bracing specimens. It is also used to verify the design procedure proposed in the AISC Design Guide 24 for Hollow Structural Section Connections for a series of 17 X-braces covering a wide range of properties. The AISC design procedure generally over-predicts the buckling resistance. A new design procedure is proposed that better reflects the buckling response of discontinuous braces in X-bracing.