Response of partially-restrained bolted beam-to-column connections under cyclic loads

• Advanced FE models were validated in comparison with past tests on TSA joints.
• Solid models accounted for friction, prying and relative slippage of components.
• Detailed FE simulations faithfully reproduced the cyclic-reversal test protocol.
• Fiber-based models represented connection elements interaction, at a global scale.
• An alternative method for quick rotational stiffness estimates was proposed.

The structural response of steel moment resisting frames (MRFs) is greatly dependent on the behavior of beam-to-column joints, according to a properly detailed beam-bolts-plates-column structural chain, in light of capacity design principles. A modeling procedure for bolted top-and-seat angle components and connections for potential use in seismic MRFs is presented herein. Although these partially-restrained (PR) connection systems have been demonstrated to provide economic savings, they are not currently certified to be used for moment resistance in any major building specification jurisdiction. Examples of full-scale moment resisting connection systems, experimentally tested in past programs, have been numerically analyzed, focusing on top-and-seat angle components, which were observed to control the global response of the joint in terms of failure mechanisms, limiting the displacement ductility capacity and dissipation energy capabilities of the whole resisting system. Refined nonlinear solid FE models, accounting for the influence of friction, pretension of bolts, prying and relative slippage of components through highly nonlinear contact elements, have been developed to reproduce the cyclic-reversal test protocol. Simplified approaches, based on one-dimensional inelastic force-based fiber elements, combined with nonlinear links, to globally represent connection elements interaction, have been developed and validated by comparisons with experimental response.To propose an alternative and conservative method for quick rotational stiffness estimates of these PR bolted top-and-seat angle connections, a series of detailed parametric solid FE analyses have been performed and the effectiveness of this analytical preliminary-design-stage tool quantified in comparison with some of the most commonly known analytical approaches.