Design Wind Pressure 1

[greencircle]

Hello All,

While I am learning this & I am actually refreshing my basics. Using this old sample(2008) calculated by a PE, I am trying to understand and manually recalculate it.

Please see attached image & the circled design wind pressure calculation.
I have manually calculated the design wind pressure using the formula

Pz=0.00256 x Kz x G x VxV X Ir X Cd

=0.00256 X 0.8821 x 1.14 x 8100 x 1 x 1.1

=22.93 (lb/sq in)

Couple of difference I notice :
1. I have used 0.8821 for Kz (Per aashto, Kz for 18ft pole Table 3.8.4-1 ). Not sure why this PE is using 1.16

2. Per the Aashto formula, we should include a Cd value for the calculation of this design wind pressure. But, I also feel it should not (just like in sample calc attched). the Cd value should be multiplied per each member ( luminaire, pole, banner etc) because the Cd will be different for each element. Do you guys agree with my thinking?

3. Not sure about the units? Can some one please tell me how its ib/sq in?

Thanks

 

[woodman88]

1. & 2. This design is to simple to do a lot of calculations that will have little impact of the answer.

3. Pz equation gives a psf answer with the input as shown.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[PSEPK]

I don't have relevant codes available with me. However, my response is based on general engineering practice and the calculation image you have uploaded.

To start with, in order to compare your calculations with those in the image, you should first check 'which Design Code and Code Version (year)' has been used in the original calculations. You should have at least relevant part of that code with you to start the calculation check.

The formula you are using appears to be lightly different from that used in the original calculations. May be, you are using formula from the design code of a different year.

Now, coming to your questions:

1. You might be using a different code version possibly.

2. Might also be due to use of a different code or code provision.

3. The wind pressure calculation formula is a universal sort of relation, adopted in many codes, with some minor variation. It takes wind speed in miles/hour (MPH) units, and gives pressure in 'lb/sq ft' units. Same is done here, and the wind pressure is "27.42 lb/sq ft", (NOT lb/sq in). Here # denotes "lb" and the square shape with apostrophe(') sign (possibly missing in the image), indicating units of "sq ft".