ASCE 7 Wind on Rooftop Equipment
ASCE 7 Wind on Rooftop Equipment
(OP)
I'm looking at the ASCE 7-05 wind loads on a large rooftop cooling tower. I just noticed for the first time the provision specified in Section 6.5.15.1. It requires that you calculate forces on the unit per Eq. 6-28, AND THEN MULTIPLY THAT FORCE BY 1.9!! There is no explaination in the commentary as to why. I think this is ridiculous! Does anyone know where this provision comes from, and what the logic is? I'm coming up with 43 psf for a paltry 90 mph wind load, which puts an unbelievable wind force of 35,000 lbs. on the cooling tower.






RE: ASCE 7 Wind on Rooftop Equipment
RE: ASCE 7 Wind on Rooftop Equipment
I wonder if the whole issue is a result of over-reliance on statistical models. For large firms that can devote many man-hours to meeting the constantly-changing code provisions some of the refinements might have some value, but for the small firms and sole-practitioners trying to get projects out the door some of the provisions have become quite onerous.
I guess my point is that if the gust around roof-top units can just about double the value of the applied load, then why the pretense of being able to refine the rest of the applied load so precisely using the various Rube Goldberg equations?
RE: ASCE 7 Wind on Rooftop Equipment
RE: ASCE 7 Wind on Rooftop Equipment
RE: ASCE 7 Wind on Rooftop Equipment
In design, the codes require that we measure with a micrometer....
In bidding, the contractor then marks it with a crayon.....
In construction, it gets cut with an axe......
I have so many code complaints I can't even keep up with them.
RE: ASCE 7 Wind on Rooftop Equipment
How this provision could have been added without any explaination in the commentary is beyond me. I'm seriously considering ignoring it. I can just see a bunch of academicians, who have never designed a real structure in their life, sitting around a committee table deciding for the rest of us how we should design. If it wasn't for codes and committees, most of them would have nothing to justify their existance. My favorite (most hated) is the professor at the University of Florida who came up with ACI 318 Appendix D.
RE: ASCE 7 Wind on Rooftop Equipment
As logical as the government most of the time.
RE: ASCE 7 Wind on Rooftop Equipment
RE: ASCE 7 Wind on Rooftop Equipment
RE: ASCE 7 Wind on Rooftop Equipment
RE: ASCE 7 Wind on Rooftop Equipment
RE: ASCE 7 Wind on Rooftop Equipment
RE: ASCE 7 Wind on Rooftop Equipment
Jed, how do you figure (no pun intended)? Zone 4 & 5 GCp from Figure 6-11A is +0.7, -0.8. My GCp is 2.12!
RE: ASCE 7 Wind on Rooftop Equipment
As far as the other comments, I'll agree with with the criticisms that the wind (and seismic) aections are tough to get through. It does get easier with repetition. Going into something different (like rooftop units) is the challenge.
About 10 years ago, I asked one of the committee members why they were refining the wind from UBC, when there was no evidence of problems with existing designs. No real answer, except they had better information that they couldn't ignore.
RE: ASCE 7 Wind on Rooftop Equipment