Cyclic Load Tests of SFRM-Insulated Steel Gravity Frame Beam-Column Connection Assemblies

Abstract

Earthquake-induced damage to structural components and spray-applied fire-resistive material (SFRM) in steel gravity frame beam-column connection regions can impact connection performance during an ensuing fire. Bolted connections are particularly susceptible to failure at elevated temperatures due to a rapid loss in bolt capacity with increasing temperature, which occurs at an accelerated rate compared to the thermal degradation of structural steel. In order to characterize structural and SFRM damage over a range of seismic drift demands, two large-scale SFRM insulated beam-column connection assemblies utilizing single-plate and unstiffened seated connection designs, with composite floor slabs, were tested under combined gravity and lateral loading. SFRM cracking, debonding, and spalling were observed during both tests, exposing critical connection elements. In addition, the single-plate connection assembly, which was developed in accordance with U.S. national guidelines but contained design features based on empirical requirements that may lead to deficient performance during a seismic event, experienced multiple bolt shear failures at an interstory drift demand less than 3%. The tests demonstrate that structural and SFRM damage are credible threats during large-magnitude ground shaking, and suggest that demands on gravity connections during a postearthquake fire could be significantly greater than those assumed in a conventional design for fire safety.