Experimental investigation on steel bracing members with bolted gusset plate connections

In concentrically braced frames, low-cycle fatigue failure may occur in the brace or bolted connection due to accumulated damage from multiple earthquakes. However, the current research on the hysteretic behavior and fatigue life of H-shaped bracing members with bolted gusset plate connections is lacking, and there is a notable omission regarding the impact of bolt slippage and plastic deformation within the connection. The objective of this study is to address the aforementioned limitation through pseudo-static tests of 8 steel bracing members with bolted gusset plate connections under different clearances, connection coefficients (akin to Ry used in brace design under AISC 341-16 Seismic Provisions), and loading patterns. Results showed that not all loading patterns were suitable for such tests due to bolt slippage. The strength capacity, energy dissipation capacity and deformability of specimens with five types of clearances displayed small variation in tests. It has been demonstrated that utilizing a connection coefficient (1.03) lower than the prescribed value (1.3) can still result in a favorable hysteretic performance. The effective length factor of the bracing member under double bolted gusset plate connections is estimated to be 0.79, which can provide valuable information for optimizing the brace design. Additionally, a method for predicting the fatigue life of test specimens is proposed. The fatigue performance and failure mode of the bracing members under bolted connections with clearances of 0t, -2t, -4t and -6t (where t represents the thickness of the gusset plate) are superior to those under welded connections.