What was lacking in the NBCC prior to the arena collapses in 1959?
Little info recorded in Canada on snow loading on arch-shaped structures.
NBCC 1953 to 1960 lacked…
provisions in selecting uniform and non-uniform snow loads on arch-structures
1965 NBCC changes and issues
snow load distributions used in USSR.
Not directly applicable in Canada. Often experience one side completely clear.
NBCC 1970 and 1975 changes
One-sided loading (1970 to 1975 the same)
Issues discovered after 1975 Code
Only considered flat, long-span arches.
Steeper, shorter-span arch structures more common in Canada.
1977 NBCC changes
Based on snow-load study in the Ottawa region:
- Provisions for uniform snow loads
- Slope reduction factors
- New distributions for nonuniform snow loads
- considering snow drift
1980 NBCC changes
provided modifications to the distribution of snow loads on arch structures
1985 NBCC changes
- increased the unit weight of snow by 1.9%
- simplifications to examine unbalanced loading on arches
- specified loading due to snow accumulation (formula)
- snow load factor due to tests in Canada
- wind exposure factor
1990 NBCC changes
- increase unit weight of snow (2.4 to 3.0)
- Lowering wind exposure factor (0.75 to 0.5) for exposed roofs north of tree line
- Revised design snow loading formula (separating snow and rain loads)
–> assumes snow would drift due to wind loads but not rain
