Project Manager:
Nabi Goudarzi, PhD, P.Eng.
Technical Experts Involved:
Nabi Goudarzi, PhD., P.Eng.
Yasser Korany, PhD, P.Eng, P.E., LEED AP
Incident Description
A 180 feet long by 60 feet wide wood-framed livestock shelter built in 2016 in Nova Scotia was damaged during a windstorm. The shelter was covered with a metal-plate-connected wood truss gable roof supported by a post and beam system on either end. The roof ridge was along the east-west direction and the posts were spaced at 12′ apart. The livestock shelter was reinforced with diagonal bracings at the east and west ends. The windstorm broke the west diagonal bracing and swayed the building a couple of feet to the north. After the windstorm, the building was jacked back into place and temporary diagonal shoring was installed to stabilize the shelter. Origin and Cause Inc. was retained to investigate the probable cause of the loss.
Investigation
During our investigation, we compared the structural design drawings to the as-built framing of the building and analyzed the failure mechanism under wind pressure. The maximum wind gust speed on the date of loss, as recorded by Environment and Climate Change Canada, was compared to the maximum design wind speed specified in the National Farm Building Code edition published in 1995 which was in effect at the time the shelter was constructed.
Cause of Loss
We determined that the probable cause of the excessive wind damage to the livestock shelter was substantial pre-existing construction deficiencies, mainly not installing the transverse knee braces between the posts and trusses, and inadequate fastening at the connection between the posts and the diagonal braces. Moreover, the wind gust pressure on the date of loss was 98 km/hr which was very close to the factored design wind speed of 101 km/hr. While strong wind triggered the failure, it merely exposed the absence of adequate resistance to horizontal forces from wind blowing in the north-south direction. Origin and Cause designed a clever system of intermediate lateral bracings to strengthen resistance to wind blowing in the north-south direction without compromising functionality.
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