UNBALANCED SNOW LOADS ON ARCHED ROOF - RESEARCH FOR THE NATIONAL BUILDING CODE OF CANADA

摘要

According to the 1995 National Building Code of Canada (NBCC), unbalanced loading ofarched roofs need only be considered for roofs with a rise (h) to span (b) ratio greater than 0.10. Recentbuilding collapses have indicated that significant unbalanced loads can still occur for rise/span (h/b)values less than 0.10. The purpose of this research project was to investigate the lower bound of archedroof geometry for consideration of unbalanced snow loading recommended in the NBCC. Finite AreaElement snow loading simulations were performed on roofs with five rise/span ratios using meteorologicaldata from: Vancouver, B.C.; Edmonton, Alberta; Toronto, Ontario; Montreal, Quebec; and St. Johns,Newfoundland. The sample roofs were rotated azimuthally in 15 degree increments to find the orientationproducing the greatest unbalanced loading for each city. Thirty-year return period design loads wereobtained using a Fisher Typpett Type I extreme value fit. These loads were then compared to the NBCCunbalanced snow loads, as detailed in Figures H-2(a) and H-2(b), to assess the appropriateness of the0.10 lower cutoff value for h/b. Revisions to the NBCC formula are proposed and a new lower cutoff of0.05 is recommended. These recommendations were accepted as a special amendment to the NationalBuilding Code of Canada in April, 2002.