Roof Top Unit Point Loads
Roof Top Unit Point Loads
(OP)
Some manufactures do not provide corner point loads for roof top units or sometimes this information is not available and only the total weight of the unit is known. When it is know that the center of gravity is not dead center what would be a good factor to increase the point loads by? For example 1000 lbs/4*1.35=337.50 lbs. Is 1.35 to conservative? Thanks!






RE: Roof Top Unit Point Loads
RE: Roof Top Unit Point Loads
Sometimes the 30% increase becomes outrageous that I don't factor it in if the plans reviewer will go along. I use 2/3 of the total weight on 1 side. I was told way back that the motor side would be about 2/3 of the weight of the unit. I use that as my worst case.
RE: Roof Top Unit Point Loads
RE: Roof Top Unit Point Loads
I agree with Ron. If 87.5 pounds makes a difference, there are other problems.
RE: Roof Top Unit Point Loads
RE: Roof Top Unit Point Loads
If you only have two rails, it's even simpler, it's just a simple beam reaction analysis.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Roof Top Unit Point Loads
Also, when you apply the 1.9 factor to the wind loads on the unit (ASCE7 6.5.15.1)- you will get some overturning that needs to be accounted for.
RE: Roof Top Unit Point Loads
RE: Roof Top Unit Point Loads
RE: Roof Top Unit Point Loads
RE: Roof Top Unit Point Loads
If you can justify that there is sufficient margin to make a slightly unconservative assumtion, then you are okay. If you cannot do so, then you need to get more info.
Like Ron said, you are not building a watch.
RE: Roof Top Unit Point Loads
So I agree with Ron.
Only if you are checking existing roof joists would I get this accurate, and I have been there before. If its new, use KCS joists and a conservative load, or if its a WF beam assume 1 kip and keep chugging. The MEP may change the damn thing 4 times before you go to 100% CDs anyway so I overestimate MEP loads, saves you a lot of work and hassle!