Station Square revisited: distortional buckling collapse

Abstract

After failure of the roof of the new Save-on-Foods store at the Station Square development in Burnaby, British Columbia, Canada, the government of British Columbia established a commissioner inquiry to investigate the causes of collapse. Collapse was attributed to an undersized W610 × 113 beam in the cantilever-suspended span arrangement and inadequate buckling resistance of the beam-column assembly. The analysis of the lateral-torsional buckling resistance of the collapsed beam in the commissioner's report did not take into account two counteracting effects: the detrimental effect of the load applied above the shear centre and the beneficial effect of the lateral and torsional restraints provided by the open-web steel joists to the collapsed beam. A distortional buckling finite element program is used herein to determine the moment resistance at buckling of the collapsed beam. This program takes into account web distortion, height of load application, inelastic behaviour, and actual restraint conditions. The moment resistance so obtained is in good agreement with the moment applied to the beam at failure. Further analyses show that even with improved restraint details at the critical beam-column location, the beam was inadequate to support the factored loads. A W610 × 195 or even a W610 × 174 beam could be considered adequate. Key words: steel beams, Station Square, lateral-torsional buckling, cantilever-suspended span, web distortion, restraints.