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Re: "DL" displacing LL?

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It would seem that the equipment is your LL unless you can see additional loads from workers and/or service tools required to work on the equipment (similar to snow load in the case of a roof).
What I would do is to check the structure for uniform LL and then check it for the actual equipment loading (plus any service personnel and/or service tool loadings) with uniform load only on the remainder of the structure excluding the footprint of the equipment.
Bill Cain, SE
Berkeley CA
-----Original Message-----
From: T.W.Allen(--nospam--at)
To: seaint(--nospam--at)
Sent: Fri, 20 Oct 2006 8:20 AM
Subject: "DL" displacing LL?

I’ve read the CBC 2001, the IBC 2003 (sorry, I don’t have a copy of 2006) and ASCE 7-05 and can’t come to a consensus to a quandary I have.
If I’m installing a piece of equipment to a floor (or a roof for that matter), can the uniform live load be displaced by that weight? For example, suppose I have an occupancy that dictates 50 PSF live load and I install a piece of equipment that is 5 feet square and weighs 1,250 lbs or 50 PSF. I don’t have to superimpose the 50 PSF load induced by the piece of equipment onto the 50 PSF uniform live load, do I? About the only place where I see that this would not be the case would be in the case of roof loads which consider snow loads. In other words, if I install a Roof Top Unit and that load is to be combined with a snow load, then I can see where those would be additive.
The UBC definition of DL appears to be more broad than in the IBC or ASCE 7.
Of course, maybe my problem is thinking that the equipment is DL in the first place which is more in tune with the UBC definition.
Opinions are appreciated.
T. William (Bill) Allen, S.E.
Consulting Structural Engineers
V (949) 248-8588 F(949) 209-2509

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