Component-based model for bolted brace connections in conventional concentrically braced frames

Abstract

In low and moderate seismic regions, low-ductility concentrically braced frames (CBFs) are widely used as the seismic force-resisting system for steel structures. The capacity-based design method is not required for such systems, i.e. no individual component in the lateral load carrying path is explicitly designated to sustain plastic deformations under seismic loading. Such CBFs are referred to as conventional CBFs (CCBFs) in this paper. Prior studies have revealed that, in CCBFs, the brace-to-gusset connections are inherently weaker in tension than the adjoining braces and gusset plates. Therefore, the accurate numerical modelling of the brace connections is critical for the reliable seismic evaluation of CCBFs. However, few research publications address the inelastic bolted brace connection modelling necessary for the structural analyses of these braced frame systems. In this paper, an efficient inelastic numerical modelling method, comprising the component-based modelling concept, is proposed for bolted brace connections. The accuracy of the numerical model is validated through comparison with laboratory test results of full-scale I-shape brace connection specimens. Eight single-storey CCBFs with the symmetric diagonal bracing configuration were designed and modeled. The nonlinear static and dynamic analyses revealed that: 1) although the buckling of the middle column at small storey drifts resulted in substantial lateral strength deterioration, a secondary seismic mechanism provided stable resistance to prevent collapse; 2) when loaded in tension, the brace connections deformed more than the braces; 3) stronger brace connections resulted in higher structural lateral stiffness and triggered earlier buckling of the middle column; 4) stronger brace connections possessed higher frictional energy-dissipating capacity which reduced the maximum storey drift.