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Snow Pg

Snow Pg

(OP)
Lots of roof collapses in the area lately.

So, I had a little time during lunch and decided to run outside and measure Pg. I used a 5 gallon bucket and a fish scale to measure the snow (I pushed the bucket into the snow and then collected the snow within the circle created by the bucket).

Weight of empty bucket = 1 lb 12oz
Weight of snow bucket 1 = 16 lb 6 oz
Weight of snow bucket 2 = 7 lb 0 oz
Total Weight = 23lb 6oz
Total Weight of snow (less 2 buckets) 19 lb 14 oz
Area of bucket = 84.5 in2
Pg = 33.9 psf
Density = 18.9pcf

Comparison:

Jurisdiction Required Pg = 50
Density = 20.5pcf

ASCE 7-10 Pg = 40 (however really close to 50)
Density = 19.2 pcf

I only took the measurements at one location.

RE: Snow Pg

Cool!

So roofs designed to ASCE 7-10, even without your local increase, should be OK.

DaveAtkins

RE: Snow Pg

(OP)
Dave,

I would say the roof of my house should be OK.

RE: Snow Pg

Houses in our area are designed by the local code which may or may not be the same as ASCE 7.

RE: Snow Pg

(OP)
jike, I think you missed the point.

RE: Snow Pg

I keep looking at Boston and wondering why they aren't using compactors to drive the density up for the snow storage. It could be nearly 60 pounds/cu-ft. Instead they melt it, which is a very large energy expenditure. 100 years ago compacted snow could have been used in ice-houses for summer cooling.

RE: Snow Pg

Some years ago there was a large 8" snowfall in San Antonio, Texas. Needless to say there were numerous collapses - mostly carports, small awnings and some metal buildings.

The estimated weight of the snow was about 13 psf (pretty wet). So that theoretically meant that all the Roof Live Load capacities in that area should have been 20 psf....all OK.

The problem seemed to be clogged roof drainage and ponding of water as the snow began to melt. Resulted in a warehouse collapse that we were hired to look at. Only problem with this one was that the owner had hired out some workers to start torching up the steel and moving it off the building pad to allow trucks to haul it off. The torches caught the paper products stored underneath on fire - which resulted in even more damage.

I recall seeing all the building columns (12" square concrete columns) still standing as the wide flange steel roof beams had no stiffeners and simply twisted off the columns and dropped - with the columns poking through the metal roof deck.

So many San Antonians were shocked by the snowfall that they ran out and bought all the camera film (and all the toilet paper for some reason) from the stores. Lots of photos of the Alamo with snow on it.

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RE: Snow Pg

I feel better now

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