Analytical Investigation Of The Effect Of Partially Restrained Connections On Hybrid Moment Resisting Steel Frames

Hybrid steel moment-resting frames are a relatively new concept founded on a combination of ordinary, intermediate, and special moment frames within the same lateral force resisting system. The intent of hybrid frames is to improve seismic performance by attaining better control of the hinging sequence, thus maximizing energy dissipation while delaying loss of stiffness. This study focuses on the analytical investigation of a hybrid steel frame employing assorted connection patterns, including partially-restrained connections of varying strength and stiffness in combination with fully-restrained connections. The dynamic response of a hybrid frame with assorted connections was evaluated by comparing of the results of inelastic static and dynamic analyses conducted on both the hybrid frame and a traditional moment-resisting frame designed according to current specifications. Both frames were based on well documented and studied cases found in the literature (FEMA, 2000). The control frame was designed to reflect the most current American Institute of Steel Construction (AISC) specifications (ANSI/AISC 360, 2010). Its two archetypes respectively include the implementation of reduced beam sections (RBS) and bolted extended end-plates (EEP) steel moment connections as defined in ANSI/AISC 358-10 (ANSI/AISC 358, 2011; Engelhardt et al., 1998; Sumner et al., 2000). Partially-restrained steel connections of increasing strength, stiffness, and energy dissipating characteristics were incorporated in the hybrid frame to force the exterior bays to undergo inelastic deformations earlier than the subsequent interior bays, all the while keeping the central bay fully-restrained. This new connection pattern was developed using two partially-restrained EEP connections in combination with one fully-restrained EEP connection obtained from previous experimental research reports, see (Eatherton et al., 2013; Sumner et al., 2000). Nonlinear static pushover analyses and nonlinear time-history analyses, including incremental dynamic analyses, were conducted to compare the response of the hybrid frame to that of a traditional frame. It was concluded that these hybrid frames show promise for better control of the post-elastic behavior of lateral force resisting systems, offering benefits in terms of energy dissipation and delayed dynamic instability.