Wind Load Calculations and Deflection

you need to hire an licensed engineer.

The testing company has an engineer on board. He is not familiar with wind load requirements and wants us to do the leg work to keep his cost down. That is the only reason I am asking, plus time is a consideration. Thanks for the advice though.

Mike

This is for Miamai dade county which is 146 mph and Exposure C if that helps you at all. The testing company does not have an engineer after all so you are right we are going to have to find a structural engineer who can do the calcs for us. Our problem is time. Thanks for responding.

Mike

Google wind load here's one that came up http://scholar.lib.vt.edu/theses/available/etd-62197-23325/unrestricted/figb2.pdf

As far as the accepted amount of deflection. Would be the amount the solar panel can endure repeatedly with out damage. The module of three panels needs to be able to retain the panels in and reduce the deflection to keep the flexing from damaging them. The panel manufacture should be able to help in how much flexing the panel can endure.

What are they being tested for?

Thank you for answering. these are being tested for Miami Dade wind zone which is 146 mph in Exposure C. Is that website a calculator where I could plug these figures in? Thanks again,

Mike

In the following CR4 Thread Calculating Wind Resistance, there are a full details.

OK...Assume for the moment we have a 60ft x 40 ft solar panel arranged on a framework structure inclined at 60 degrees from the horiz. With wind vel @ 110 mph, mid height of the panel at 25 ft from ground level, IF Category IV, Exposure C..... am I then looking at

.00256 x .98 x 1.0 x 12,100 x 1.1+ 33.9 psf

Advise.

By selecting Category IV and Exposure C:

Design Wind Force, F = q_z * G_h * C_f * A_f , lb. ......... where q_z = 0.00256 K_z(I V)²

F = 0.00256 *0.98* (1.0 x 110)² * (1.23)* (1.1) * (60x40/√2) = 69 702 lb

RCE is correct that you should look into a licensed PE as most cities/counties in high wind/high seismic areas require PE stamp for all designs. However, if you are only looking for a quick number for wind tunnel testing purposes and not for submittal of the structural design, ASCE 7-95 (ANSI A53.1) provides the following formula for (approximate) wind force: Qz = 0.00256 x Kz x Kzt x I x V x V where Kz is the velocity pressure coefficient (approx. 0.9), Kzt is the velocity pressure exposure coefficient, I is the importance factor, and Vsquared is the wind velocity - squared. Assuming your panels are not mounted in critical areas assume 1.0 for Kzt and 1.0 for I and you have Qz (in lbs/sq.ft) = 0.00256 x 0.9 x 146 x 146 = 49.1 PSF.

Deflection is up to the tolerance of your panels to not crack or fail during bending, or to the structural mounting you use. Assume maximum deflection of panel length divided by 360 (structural code) as starting point. Check your local library for copies of Uniform Building Code, ASCE 7-95, Internation Building Code, or BOCA for design requirements and see what code Miami/Dade requires the designs to be built to.

You may also want to consider the microfracturing due to cyclic flexure of the panels, which will reduce the product life and could cause a impact due to warranty period. this becomes an issue of how many times you can bend it a specific amont before it fails.

The Uniform Building Code or the Southern Building Code will give you all of the formulas for calculating both wind and seismic loads. For Miami-Dade you will probably need to supply dead load, live load, wind shear and moment, and seismic shear and moment. These calculations are easy to do with canned formulas in the codes if your equipment mounting can stand some "worst case" forces (wind acting full face on panels with no deflection). If you do the calculations yourself and they are correct, a local structural engineer can review and seal them for you. Miami-Dade will only accept sealed calculations.

You noted Miami Dade county's wind coefficient as 146 mph exposure C wind zone. Is there a good online resource to find a city's wind coefficient? thanks, lawrence