ASCE 7-10 Third Printing- Section 2.4.3

[ENGINEER92]

I am designing a platform, on top of a building, to hold equipment and a walk way for people to work on the equipment. Section 2.4.3 of ASCE 7-10 says I use load combination D+L+.7Di. Do I really need to design my platform to hold my live load of 40 psf and ice weight, at td=2.23". I just find it hard to believe that if there is that much ice on my platform, people will go up there to work on the platform. Just wanted a second opinion, on if I was reading the code right.

 

[TehMightyEngineer]

I'd say yes, that much ice causes equipment to fail and/or requires removal rather than letting it melt. Thus, you could get a live load even with the ice load.

Plus, how much different does that really make to the cost of your structure?

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[briancpotter]

The only way out would be if your live load was actually a roof live load (and thus subject to item 2 instead of item 1). Otherwise, yes.

 

[ENGINEER92]

It does up my beam sizes bit. I am mainly concerned with having to cover plate the beams the platform will be sitting on.

I thought about classifying it as roof live load, but I cant justify it being a roof live load.

Thank you all for your responses.

 

[DETstru]

Is your design controlled by strength or deflection?
If it's deflection, I'd be fine with a very large deflection with both ice and live load. I can't imagine you'd have much damage caused by a platform deflecting substantially.

 

[EDub24]

If you consider it a live load then yes you have to include it. However, ASCE defines a roof live load as a load on a roof for workers for maintenance of equipment. Unless the workers need to attend the equipment every day you can use that angle to argue for the use of a roof live load. With that said if the invrease in beam size isn't ridiculous then I would be conservative and design it to include the wind amd ice load.

 

[P1ENG]

If your live load is from people only, you won't ever have 40 psf for maintenance live load; so reduce it if it is not code driven. If it is 40 psf then it likely includes non-permanent equipment, then you need to keep the 40 psf. So, to make it seem more probable, is there a chance that something that weighs near 40 psf is already up there (not permanently attached) and then the ice storm comes? I would say that would be a safe design assumption. You are right that people aren't likely going up there after a storm (unless it is one person that really needs to fix something) and that one person wouldn't equate to 40 psf. But when thinking about non-permanent equipment, it becomes more likely.

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant