jefftsolar
Structural
- Sep 16, 2011
- 11
Good evening!
So as I'm learning how to design lattice frame structures such as ground racks for Solar PV Systems, there's a lot of confusion to designing to the 2012 IBC (or in my case, the 2014 Florida Building Code).
One thing that always gets me confused is the concept behind the ASD Load Combinations (as noted in section 1605.3.1 of the 2012 IBC). In the Florida Buiding Code, there's the ultimate wind speed and the nominal wind speed. I'm working on a ground rack design, and I've always been taught to calculate the wind pressures (via ASCE 7-10) based off the ultimate wind speed, and then multiply the pressures by 0.6 to get the ASD (nominal) wind pressures.
The dead load of the rack is approximately 4 PSF. I figured to calculate the design load by plugging in the ASD nominal wind pressure into W (which ends up getting factored by 0.6 again) and plug in 4 for D. This results in a much lower design pressure.
Some PE's I work with argue that W in the ASD Load Combination has to be based off the ultimate wind speed, but some PE's also argue that you never mix up the LRFD and ASD design theories, thus plugging in the ASD Nominal Wind Pressure for W to get factored again by 0.6.
I'm just looking for some guidance to make sure I do not miscalculate anything. What does everybody here think?
So as I'm learning how to design lattice frame structures such as ground racks for Solar PV Systems, there's a lot of confusion to designing to the 2012 IBC (or in my case, the 2014 Florida Building Code).
One thing that always gets me confused is the concept behind the ASD Load Combinations (as noted in section 1605.3.1 of the 2012 IBC). In the Florida Buiding Code, there's the ultimate wind speed and the nominal wind speed. I'm working on a ground rack design, and I've always been taught to calculate the wind pressures (via ASCE 7-10) based off the ultimate wind speed, and then multiply the pressures by 0.6 to get the ASD (nominal) wind pressures.
The dead load of the rack is approximately 4 PSF. I figured to calculate the design load by plugging in the ASD nominal wind pressure into W (which ends up getting factored by 0.6 again) and plug in 4 for D. This results in a much lower design pressure.
Some PE's I work with argue that W in the ASD Load Combination has to be based off the ultimate wind speed, but some PE's also argue that you never mix up the LRFD and ASD design theories, thus plugging in the ASD Nominal Wind Pressure for W to get factored again by 0.6.
I'm just looking for some guidance to make sure I do not miscalculate anything. What does everybody here think?
