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How accurate to be with Dead Loads?
7

How accurate to be with Dead Loads?

How accurate to be with Dead Loads?

(OP)
Verbage in IBC code says we must consider everything when calculating dead loads.  How accurate must we get? Is it ok to say:
Beams: 5psf
Purlins: 2psf
Deck: 1psf
Sprinkler: 5psf
Other collateral: 5psf
Total: 18psf
Is this too simplified?

RE: How accurate to be with Dead Loads?

No. That looks pretty close to the way I do it. If this is a roof, don't forget insulation and roofing (particularly if it is a ballasted roof). Otherwise, I probably would round up to 20 psf and be on my way.

RE: How accurate to be with Dead Loads?

Beams and purlins about 3 each and deck 2 and sprinklers 3.  Roofing as it shakes out and MECS (mechanical, electrical, ceiling and sprinklers(already included)) varies from 5 to 15

All adjusted as reqd... the beam and sprinkler load you use may be on the upper end.

Dik

RE: How accurate to be with Dead Loads?

When I do house design I do 15 psf DL for all floor, deck and roof (just to safe me time). Then if we put gypcrete or veneer, I just add it to the DL. Or sometimes for the roof they want to use tile roof, then I just add the load on the top of 15psf I already have.  So my minimum DL is 15.

RE: How accurate to be with Dead Loads?

(OP)
Thank you everyone...this helps much.

RE: How accurate to be with Dead Loads?

If you have wind uplift, then you should remove the sprinkler and collateral loads from the resisting dead loads.

Also I was taught that the sprinklers are fixed to every 2nd purlin therefore you would have twice the load on each purlin as a maximum downward load. This would obviously even out for the beams.

RE: How accurate to be with Dead Loads?

csd72... unless you have a real massive sprinkler system, you'd be hard pressed to have a load of 3 psf...

Dik

RE: How accurate to be with Dead Loads?

   Do an accurate summing of a typical project or two. Then your estimated psf rules will have a basis in fact to compare to.

RE: How accurate to be with Dead Loads?

I carry the sig. figs to the tenths for each item.  Then I add 5 to 10% of the total (minimum around 5 psf) as miscellaneous dead load to round it to some nice even number.

RE: How accurate to be with Dead Loads?

(OP)
Good advice y'all...from Georgia

RE: How accurate to be with Dead Loads?

Be careful with the dead loads in ASCE 7. I have found some of them (e.g. CMU walls) to NOT be conservative.

RE: How accurate to be with Dead Loads?

But don't overestimate DL when using uplift combinations, or you'll be unconservative.  If you want to add for just-in-case, you can add LL to avoid this.

Be accurate and be realistic, since using loads significantly heavier than the customer needs will cost them money they didn't ask to spend.

RE: How accurate to be with Dead Loads?

I think it prudent to be accurate, especially for floor loads.  In the past I used 12 psf for residential floors, however, in todays market for hydronic heating systems, you add +/-2" of concrete topping, likewise, marble/stone flooring over topping slab and cantilevered floor joists where another +/- 1" stucco to the underside of the joists can actually push the DL to 25-30 psf.

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