Paring Down Sesmic Loads
Paring Down Sesmic Loads
(OP)
At my current place of employment when there is a problem with the seismic loads they like to reduce the dead loads to "what is actual there".
Example:
We design a roof for a gravity dead load of 24psf.
Deck - 3 psf
Joist - 6 psf
Roofing - 10 psf
MEP - 5 psf
Then we design the weight for seismic using a dead load of 20 psf
Deck - 2 psf
Joist - 5 psf
Roofing - 8 psf
MEP - 5 psf
We use the logic that the second set of loads are more acurate becasue they more closely reflect what is really there. We then proceed to put the 24 psf dead load on our plans as what we design for, but have the seismic load really correspond to less.
I don't feel this is correct. Is this type of thing standard practice? Is there a code reference (IBC) that tells me this is or is not allowed?
Example:
We design a roof for a gravity dead load of 24psf.
Deck - 3 psf
Joist - 6 psf
Roofing - 10 psf
MEP - 5 psf
Then we design the weight for seismic using a dead load of 20 psf
Deck - 2 psf
Joist - 5 psf
Roofing - 8 psf
MEP - 5 psf
We use the logic that the second set of loads are more acurate becasue they more closely reflect what is really there. We then proceed to put the 24 psf dead load on our plans as what we design for, but have the seismic load really correspond to less.
I don't feel this is correct. Is this type of thing standard practice? Is there a code reference (IBC) that tells me this is or is not allowed?






RE: Paring Down Sesmic Loads
The one thing to worry about is re-roofing, new ceiling, new HVAC units etc.
Our local code enforcement buys off on it.
Is it right or more accurate - kind of an engineering judgement.
I beleive the code allows you to use actaul weights if you can define them. Most people pick conservative loads for gravity - I do. But when it comes to seismic - I often use actaul based on the assumption the really BIG one will never hit. Maybe not the greatest decision.
RE: Paring Down Sesmic Loads
RE: Paring Down Sesmic Loads