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RE: "DL" displacing LL?

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When equipment weight distributed over its footprint is less than the applied uniform live load, I typically assume that the equipment weight is included in the live load (even though technically the equipment is dead load, not live load).  When a piece of equipment exceeds the uniform live load, I sometimes will subtract the live load times the footprint area from the equipment weight and apply the remainder as a concentrated load. 
 
This is only for gravity design - the full equipment weight must be included in lateral seismic loads.
 
Bill Sherman
CH2M HILL / DEN
720-286-2792
 


From: refugio rochin [mailto:fugeeo(--nospam--at)gmail.com]
Sent: Friday, October 20, 2006 9:39 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: "DL" displacing LL?

Bill, I would use this as Live Load.  However, you may want to include it when you do seismic calculations as Dead.
We view these live loads before any equipment is put on the building.  So we don't expect to know where the live loads (or big equipment) are going to actually go.  If you know ahead of time, then you just have more information up front than most projects do.
My 2 cents.


On 10/20/06, Bill Allen <T.W.Allen(--nospam--at)cox.net> wrote:

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.

 

Regards,

 

T. William (Bill) Allen, S.E.

ALLEN DESIGNS

Consulting Structural Engineers
 
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