Testing protocol for short links in eccentrically braced frames

The inelastic rotation capacity of links in eccentrically braced frames (EBFs) is dependent on testing loading history or sequence. Current design rotations for links are based on experiments from the 1980s performed with somewhat arbitrary loading protocols. An AISC link loading protocol, derived from the standard moment frame loading protocol, has been used for link testing since 2002. This protocol results in lower link rotation capacities. Since no previous or current link protocols are based on EBF analyses, nonlinear time-history analyses were conducted to investigate cumulative rotation demands for links in EBFs. Results indicate the AISC link loading protocol is overly conservative, having 1.5 times the cumulative rotation demand and a much higher percentage of large cycles than is justifiable. A rational loading protocol for future link testing was developed based on cumulative and maximum link rotation demands observed from the time-history analyses. Experimental tests performed in a parallel study with this new protocol indicate that link design rotation capacities in the AISC Seismic Provisions are satisfactory.