Span tables for dead loads above 20 PSF.
DIYJester
| Posted in Building Code Questions on
Does anyone know where I can find span tables or equations to calculate dead loads in excess of 20 PSF?
Every table I’ve found including IRC, AF & PA show dead loads of only 10 or 20 PSF. I’m looking to see my options for a pour over a subfloor I’m designing for an addition. I do plan on having a Structural Engineer double check my math and stamp the drawings, I just would prefer not to pay them and extra $500-600 to pretend like it took them all day to do a set of calculations for the floor joist, girder, and columns.
Thanks for any help in advance!
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Michael, you don't purchase a stamp. You will be obtaining professional service for a small amount of engineering and that will be the cost you are charged after which plans are stamped. That stamp also is who now is liable for what is detailed. That's why there is a cost above what you feel an hour is worth. Liability insurance for professionals can run into tens of thousands which is what you pay for in a small job not someone overcharging for an hours work or two.
The calculations are quite simple for simple beams. Live plus dead loads total load
I still go back to my paper copy of 'from the ground up' as the online version is quite incomplete in this area, but the formulas must be on the web
Keith, it is my understanding the safety factors and actual loading are calculated differently for a live load vs a dead load. I have found plenty of tables for adding these values but all of the span tables only specify dead loads of 10-20 PSF and live loads of up to 48 PSF. My dead loads will be closer to 25 PSF for 2" of concrete if I used 150 lb/cu. ft. portland cement with no gypsum or fillers (heaviest scenario I would envision). I have not found enough correlation in the difference between the 10 PSF tables and the 20 PSF tables to create an equation that would allow me to work backwards for a larger dead load.
Here are the tables from IRC 2009 which is what our local codes require:
http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_5_par020.htm
Many good books to buy and this site has many online calculators
https://courses.cit.cornell.edu/arch264/text/contents.html
Keith for dead loads there is a factor to do with the longevity of a load verses live loads. Snow loads for example are not year round loads but may be there for months etc...
I still feel one phone call to your engineer and there shouldn't be much difference with the need to calc your 25 pound load.
If you follow the calcs, deflection becomes the dominating factor, you will be upsizing a beam for deflection before you do for weight alone. When roofs or floors fail in a modern building it is attachment points and almost never beam or joist failure
these formulas will give you something to show an engineer.
cannot locate this stuff on the web just don't have the patience
https://courses.cit.cornell.edu/arch264/calculators/example8.1/index.html
Here's the online calculator you need. The same site has dozens of calculators all to do with the book I posted.
snippet pic of page follows
I ran some numbers for kicks, doubling your joists works and going to 12" centers works easily.
Awesome, that's exactly what I was looking for! I figured I would have to go 12" OC, just wasn't sure if 2x10's or 2x12's would be able to handle the load alone or if I'd end up doubling them up.