Investigations following structural failure of a roof in Canada

This paper discusses a complex, multi-parameter approach to questioning the capacity of the roof of an industrial facility in the Montreal area. The failure of a portion of the roof in March 2008 under heavier than usual snow loads triggered an investigation process that continues to this day. The roof was immediately repaired in order to allow the facility to continue its commercial activities. After the repair, an investigation of the snow loads on the roof was first conducted; this was followed by an assessment of the capacity of the roof joists and beams as designed and as built. An evaluation of the snow loads surrounding mechanical units on the roof was conducted. The building was erected in the 1960s and a significant number of changes took place following an expansion of the facility, including an addition with a roof higher than that of the existing building. The new elevated roof reduced the wind effects and created significant snow accumulation not only around the higher roof but also surrounding the mechanical units present almost everywhere. In the assessment of the joists, particular attention was paid to the welds between the web and the chords; these welds were at the origin of the failure of the roof as a whole. An evaluation of the mechanical equipment suspended from the joists was also carried out. An overall assessment of the structural system for earthquake resistance ultimately led to a seismic evaluation of the building, which is currently underway.