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ANSI A58.1 - 1972 Snow Loads

ANSI A58.1 - 1972 Snow Loads

ANSI A58.1 - 1972 Snow Loads

(OP)
I am trying to find out how flat roof snow loads were determined and what provisions were in place (if any) to account for unbalanced snow loading. I believe that the ground snow was set at 25 psf at least in the Chicago area. I cannot find any copies of this old code so any help would be appreciated.

RE: ANSI A58.1 - 1972 Snow Loads

If you are working on a building designed under the review of the Chicago Building Department they have there own codes which are not derivative from any other code.

You will need to find a library which has older Code books available. They don't change their building codes very often but they generate them by themselves.

Jim

RE: ANSI A58.1 - 1972 Snow Loads

(OP)
I am attempting to review the design loads used on an older building designed in 1976 which was using ANSI A58.1-1972. BTW the design loads in the Chicago building code still reference ANSI A58.1-1982 for wind and snow. Thanks.

RE: ANSI A58.1 - 1972 Snow Loads

There are provisions for unbalanced loading in the 1972 version.

RE: ANSI A58.1 - 1972 Snow Loads

(OP)
Is there any way you could forward me 1) how flat roof snow load was determined? (I think that for the Chicago area the ground snow load was listed at 20psf) 2) What were the unbalanced snow provisions for a hip roof? (e.g. 0 psf windward and 1.5Pf leedward?) Thanks.

RE: ANSI A58.1 - 1972 Snow Loads

(OP)
I have a partial copy of ANSI A58.1 -1982 that lists information for calculating flat roof snow and unbalanced conditions. Was ANSI A58.1 -1972 different?

RE: ANSI A58.1 - 1972 Snow Loads

The 1973 UBC, although not used in the Chicago area, mentions the use of unbalanced loading for snow loads and roof live loads. Apparently this provision also existed in the 1970 UBC as the paragraph is not alluded to as changed See Section 2301 and 2305(b).

Interesting to note though that in this code, by it's own definition of live load (Section 2301), snow was considered a live load, different than what we view it now - it's own separate load classification.

Mike McCann
MMC Engineering

RE: ANSI A58.1 - 1972 Snow Loads

I also noted in the 2305(a) that there is an exception to the alternate span loading requirement that may or may not apply in Chicago - "Alternate span loading need not be considered where the uniform roof live load is 20 psf or more and the provisions of Section 2305(c) are met." 2305(c) dealt specifically with snow loads, drifting, extra loads in valleys and slope reduction due to roof pitch.

Mike McCann
MMC Engineering

RE: ANSI A58.1 - 1972 Snow Loads

(OP)
That is exactly what I was looking for. Many thanks JAE!

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