Open Structure Wind Loading ASCE 7-16 1

[161km]

I'm designing a monosloped steel frame canopy supporting solar panels to be mounted on a parking deck. I believe it'd be best to design it based on ASCE 7-16 section 27.3.2, specifically with Figure 27.3-4 for wind directions (γ) = 0° & 180° and Figure 27.3-7 for γ = 90° & 270°.

However, the h/L value for my structure is ~0.074 with a 2° canopy slope (θ). Figures 27.3-4 through 27.3-7 all specify that they apply to structures with values 0.25 <= h/L <= 1.0, and I can't find a section that specifically deals with h/L values outside of this range.

There is a footnote (#5) in Figure 27.3-7 that states "For monoslope roofs with θ < 5°, Cn values shown apply also for cases where γ = 0° and 0.05 <= h/L <= 0.25. See Fig. 27.3-4 for other h/L values." (But Fig. 27.3-4 says nothing about different h/L values.)

So it seems like I can use this exception in Fig. 27.3-7 for γ = 0°, but it specifically doesn't mention it being applicable to γ = 180°. And there seems to be no such exception made for γ = 90° or 270°

I'm unclear if I can apply these figures to my structure or where else to look in the code for loading. Does anyone know how to approach this?

Thanks for any help!

 

[Aesur]

Can you post a sketch of your structure? I assume with an aspect ratio of 0.074, you are designing something either very close to the deck or a large canopy system covering a very large area. It is worth looking at Figure 29.4-7 as well, as it applies directly to solar panels, however they are typically closely mounted to the roof surface. Without knowing more about the configuration it's hard to advise based on the provided information.

 

[161km]

It is both close to the deck and covers a large area. The mean canopy height is 13.5' above the deck and the canopy is 183' long in axis of the slope (211' wide perpendicular to slope). We did look at Figure 29.4-7, but the panels are not directly attached to a flat roof. The bottom surface area of the panel will be exposed to wind.

Here is a model that I've put together for the structure. The solar panels are not shown in the model but will attach to the purlins shown in blue.

 

[SandwichEngine]

The MBMA manual has your back.

 

[Aesur]

@SandwichEngine - That is useful, I wasn't even aware of the MBMA table, will save for myself later.

One thing I have done a few times when designing solar on the top of a taller building or parking garage is look at the Kzt factor as if it's a cliff. This came about from a discussion years ago with the wind tunnel guys who did the SEAoC PV documents which are now the solar wind figures in ASCE7.

 

[161km]

Thank you both, this is very helpful!