Snow Loads & Arch Roofs
Snow Loads & Arch Roofs
(OP)
I have some questions regarding snow loading around a arched roof.
We have a school we are working on which is essentially square in plan with a rectangular gymnasium in the middle of the square. The Gymnasium walls project a minimum of about 2.5 ft above the 1.5:12 sloping low roof (which runs all around the gym) and the gymnasium roof consists of glulam arch trusses (total depth of approx. 10 ft), wood framing and a corrugated steel roof deck.
I am trying to calculate the snow build up around the perimeter of this high arched gym roof as per NBCC (Cdn Code) and am a little unsure of the best way to do this.
Whenever you have two roofs separated by a step height, you get a snow build-up on the low roof, which is a function of the difference in elevation from the upper roof to the lower roof. Now, what about for arch roofs? If I take the top of the arch as the step height, then the snow build up load is very high, but if I use the low end of the arch the snow build up is much lower.
In addition, the tricky part is that this is a slippery metal roof, so sliding snow comes into effect as well on two sides of the arch. Would I consider the sliding snow from the unbalanced load case to all end up on the low roof, or do I use the basic snow load from half the upper arch? How would it spread out along the low roof after sliding?
PS - Go Flames Go!
We have a school we are working on which is essentially square in plan with a rectangular gymnasium in the middle of the square. The Gymnasium walls project a minimum of about 2.5 ft above the 1.5:12 sloping low roof (which runs all around the gym) and the gymnasium roof consists of glulam arch trusses (total depth of approx. 10 ft), wood framing and a corrugated steel roof deck.
I am trying to calculate the snow build up around the perimeter of this high arched gym roof as per NBCC (Cdn Code) and am a little unsure of the best way to do this.
Whenever you have two roofs separated by a step height, you get a snow build-up on the low roof, which is a function of the difference in elevation from the upper roof to the lower roof. Now, what about for arch roofs? If I take the top of the arch as the step height, then the snow build up load is very high, but if I use the low end of the arch the snow build up is much lower.
In addition, the tricky part is that this is a slippery metal roof, so sliding snow comes into effect as well on two sides of the arch. Would I consider the sliding snow from the unbalanced load case to all end up on the low roof, or do I use the basic snow load from half the upper arch? How would it spread out along the low roof after sliding?
PS - Go Flames Go!






RE: Snow Loads & Arch Roofs
RE: Snow Loads & Arch Roofs
Whats the diff. higher lower roof along the sides of the arch and the gable ends? Whats the span of the arch?
RE: Snow Loads & Arch Roofs
The sides the same thing only i would use the mid-height of the arch.
Unbalanced load, the figure in OBC is clear, however depending upon the exposure, ie north or south,
really need to know the geometeric configuration of the arch to comment further, length, width? and geometry of lower roof. Melt water from the arch if it has a southern exposure, were does it go? into the snow of the lower roof?
RE: Snow Loads & Arch Roofs
RE: Snow Loads & Arch Roofs
The arch is spanning approximately 50 ft. In addition, the walls supporting the arch trusses project about 2.5 feet above the low roof. The dimension from the peak of the arch to the low roof is about 10 feet. The plan dimensions of the arched roof are 74' (22.6 m) by 53.5' (16.30 m). The 74' dimension runs north south.
I ran the snow build up loads for the low roof at the gable ends (for Wpg, Ss = 1.7, Sr = 0.2), with l = 22.6, w = 16.3 for the following step heights
a) 11 ft -> So = 5.17 kpa (108psf)!! with 6.0m long drift
b) 2.5 ft -> So = 2.48 kpa (52psf)!! with 1.533m long drift.
Quite a big difference!
I'm thinking I should reduce l,w for the step height of 11 ft or use an average step height for the full w,l?
RE: Snow Loads & Arch Roofs