Rooftop Unit Equipment Load

[cgstrucg]

Hello,

I have a question regarding catwalks at the rooftop. As per ASCE7-05, the uniform load is 40 psf and concentrated 300 lbs. Are these laods supposed to be applied together? I can't seem to find any text mentioning otherwise.

Thanks

 

[SlideRuleEra]

IMHO, yes, apply the loads simultaneously.

My reason has nothing to do with the document's text, just engineering judgement:

If the catwalk is designed so "closely" that adding exactly one, 300 lb. concentrated load (anywhere on the catwalk) to a 40 psf UDL makes the structure "unsafe", the design is unrealistically "precise".

http://www.SlideRuleEra.net

 

[cgstrucg]

That's true. Thank You for the input.

 

[jittles]

In ASCE 7-10, 4.4 explicitly states it is either uniform OR concentrated, whichever produces the worst effect.

 

[R Naples]

cgstrucg,

The Code does not require the UDL and the Concentrated loads to be applied concurrently. Essentially the UDS is for main carrying member design, and to provide sufficient mass in the building for the VFRS and the LFRS. The concentrated load often controls the grating design and the grating supports.

 

[JStephen]

Long ago, my brother worked for a pacemaker manufacturer.
The pacemakers had a lead on them that the surgeon trimmed to length when installing it.
So as long as it was plenty long, it didn't really matter how long.
But, it was a highly regulated industry, so it had to be just so-so on paper.
So their slogan was "Measure it with a micrometer, mark it with a piece of chalk, cut it with a hatchet."
So, if I calculate seismic loads to 10 decimal places, that's the thinking behind it.
On the loads there- yes, see 4.4 and also note that it defines how big a "concentrated" load is. Also, see the load combinations in Chapter 2.
OSHA has some load requirements for stairs and ladders, but I don't see anything specific for general walking surfaces.

 

[dhengr]

Cgstrucg:
The 300lb. concentrated load is sorta supposed to represent a 250lb. worker and 50lbs. of tools and equipment, per OSHA and others. Then, I wonder if you’ve ever seen two guys working close together on something, plus a few pieces of pipe or other bldg. material laying on the catwalk? I’m inclined to agree with SRE and also agree with jittles thinking, ‘which ever produces the worst loading.’