Canadian Disproportionate Collapse Design Provisions and Recent Research Developments

Standard S850, published by the Canadian Standards Association and entitled Design and Assessment of Buildings Subjected to Blast Loads, is the only Canadian standard that contains explicit and detailed disproportionate collapse mitigation criteria for buildings. The standard is non-mandatory and may be invoked by a building owner to meet design objectives if blast loading is deemed to be a required consideration. While the scope of the standard encompasses design to limit damage under loads caused by an explosion, one component of the coverage is a set of provisions that aims to prevent the occurrence of post-blast disproportionate collapse. As a result, these provisions are not based on the so-called "threat independent" philosophy, as is typically the case for stand-alone disproportionate collapse guidelines; rather, the blast-damaged structure is assessed to determine how the building would be expected to be compromised, and this forms the basis for the initiation of the required disproportionate collapse analyses. The paper also provides a brief overview of some of the recent research developments in Canada related to designing to minimise the possibility of disproportionate collapse occurring in steel-framed buildings in the event of a column loss due to blast or another unanticipated localised trigger. Over 70 full-scale physical tests have been carried out on a variety of common types of shear connections, with or without the influence of a composite floor slab. In addition, high-fidelity finite element models have been developed that are able to simulate the behaviour of the tests accurately. Simplified methods are currently under development for characterising the essence of the behaviour of the various types of shear connections under this unique loading regime. These connection models will be appropriate for use in full-building analyses for disproportionate collapse assessments.