ASCE 7-05, 7.8 Roof Projections
ASCE 7-05, 7.8 Roof Projections
(OP)
ASCE 7-05, 7.8 Roof Projections, says, "If the side of a roof projection is less than 15 ft. (4.6 m) long, a drift load is not required to be applied on that side."
See attached... https://res.cloudinary.com/engineering-com/image/upload/v1480959017/tips/ASCE_7-05_7.8_Roof_Projections_wfubpp.pdf
I have a 450' x 330' roof with (30) Roof Top Units (RTU's) that are each 7'-4" x 14'-3" in plan dimension; 5'-0" high. The plan dimensions create a 16'-0" diagonal dimension, which, when viewed from a direction normal to the diagonal, would, thus, prompt the greater than 15'-0" requirement.
These RTU's are evenly and uniformly spaced 50', 75' or 100' o/c.
My typical practice would be to employ the conservative, safe route of applying the drift loads to each of these RTU's, even though each "side" is less than 15'-0". HOWEVER, I do NOT want to over-design and unnecessarily raise the cost. YET... Safety!
1. Would any of you consider the 15'-0" diagonal a justifiable "side"?
2. Is there a(n unpublished) concern for the multiple units which might induce the slightest turbulence or tunneling effects as implied by ASCE 7-05, 6.5.15.1 Rooftop Equipment, thereby justifying the snow drift application?
3. Would any of you ignore the drifts around the RTU's altogether?
Suggestions?
Thank you!
See attached... https://res.cloudinary.com/engineering-com/image/upload/v1480959017/tips/ASCE_7-05_7.8_Roof_Projections_wfubpp.pdf
I have a 450' x 330' roof with (30) Roof Top Units (RTU's) that are each 7'-4" x 14'-3" in plan dimension; 5'-0" high. The plan dimensions create a 16'-0" diagonal dimension, which, when viewed from a direction normal to the diagonal, would, thus, prompt the greater than 15'-0" requirement.
These RTU's are evenly and uniformly spaced 50', 75' or 100' o/c.
My typical practice would be to employ the conservative, safe route of applying the drift loads to each of these RTU's, even though each "side" is less than 15'-0". HOWEVER, I do NOT want to over-design and unnecessarily raise the cost. YET... Safety!
1. Would any of you consider the 15'-0" diagonal a justifiable "side"?
2. Is there a(n unpublished) concern for the multiple units which might induce the slightest turbulence or tunneling effects as implied by ASCE 7-05, 6.5.15.1 Rooftop Equipment, thereby justifying the snow drift application?
3. Would any of you ignore the drifts around the RTU's altogether?
Suggestions?
Thank you!






RE: ASCE 7-05, 7.8 Roof Projections
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: ASCE 7-05, 7.8 Roof Projections
I don't think taking the diagonal is what was intended here.
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RE: ASCE 7-05, 7.8 Roof Projections
Thank you for your replies.
What about Question 2?
2. Is there a(n unpublished) concern for the multiple units which might induce the slightest turbulence or tunneling effects as implied by ASCE 7-05, 6.5.15.1 Rooftop Equipment, thereby justifying the snow drift application?
Thanks again!
RE: ASCE 7-05, 7.8 Roof Projections
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RE: ASCE 7-05, 7.8 Roof Projections
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: ASCE 7-05, 7.8 Roof Projections
Check out Eng-Tips Forum's Policies here:
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