ASCE 7-05 Wind Load- Needing a little beginner help/ explanation

[wtstreetglow]

Hi all,

And thanks in advance for any help you guys can shed on my question. I believe it is an elementary but hopefully I can explain it thoroughly.

So I am working on a carport structure. It has a gable roof with dimension of 30' perpendicular to ridge and 18' parallel to ridge.

I have attached the spreadsheet where I am trying to determine my loading. The only one I am struggling with is the wind loading (I am having issues understanding if I have things in the orientation, as in local/ global etc.)

If it is highlighted in yellow in my spreadsheet, that is what I am questioning in my mind.

The doubt has been created by statements 6.1.4.1 and 6.1.4.2 in the ASCE7-05 code. Where it is talking about a 10 psf min for loading in perpendicular plane of MWFRS or loading normal to a Cladding member.

The figures in the back (6-18, 6-19 etc.) always help you in achieving the pressure perpendicular to the surface that you are looking at.

So does that mean when you use figure 6-18 for the MWFRS pressures, they are in an axis perpendicular to the roof. And then you have to take the components of the pressure derived from 6-18 in order to ensure you are above the 10 psf minimum that is specified in statement 6.1.4.1?-- The 6.1.4.1 statement specifies in a plane normal to the projection of the roof.-- The last question I have about this is, does that then me you will have a wind component that is vertical and that both projections must be above the 10 psf minimum?i.e., both the vertical and lateral

I hope I explained this well enough, I have attached the spreadsheet if anyone versed in the subject would be kind enough to spend a few minutes looking at it for me in order to help me with an educational response.

Thank you all so much ahead of time!!

 

[Ron]

First of all, why are you using ASCE 7-05? Is that mandated by your local code? What Building Code are you using?

 

[Ron]

wtstreetglow....your post says you are working on a carport structure. Those are usually classified as open structures, not enclosed or partially enclosed. Can you provide a sketch of the structure? Does it have side walls/endwalls?

My reason for asking about ASCE 7-05 is that I believe your area has adopted the 2012 version of the International Building Code. That code references ASCE 7-10, not 7-05. They are somewhat different.

 

[wtstreetglow]

Ron,

I agree with you. 7-05 is probably not the addition I should be using (should be using the newer one)-- I have it also but haven't checked to see if the same statements are in it.

This is really an educational process for me at the moment. Not something I will have to turn to the cities building permit guys (they are just wanting a sketch of what were wanting to do, no calculations etc).

But for educational purposes for myself, I was hoping someone could help me with understanding how those minimums are to be applied.

I have attached a 3d image of what were wanting to build (from Chief Architect)

Thank you all again for your help ahead of time.

 

[Ron]

I would design this as an open structure, with the likely worst case being with wind perpendicular to the ridge. Check in each direction and take the worst case for design. Uplift parallel to the ridge might be a concern, but check both conditions as well as the oblique condition.

It is arguable and interpretive as to whether you should use MWFRS or C&C. Won't make much difference either way.

Since this is mostly an educational exercise for you, I agree that 7-05 is a better starting place than 7-10! Obviously if you are designing to code, you'll use 7-10, but not a bad idea to get your feet wet with 7-05 first.

Good luck.

 

[wtstreetglow]

I see. So the minimum 10 psf load specified for MWFRS in 6.1.4.1 of ASCE 7-05 is the lateral pressure to be applied to the roofs vertical projected area?

But the values given in the figures at the end of chapter 6 help the user in getting a pressure that is normal to the roof surface.

So I don't see how to compare the 2 since it's not apples to apples (I'm not seeing how to determine whether I need to design for the 10psf or for the pressure calculated using the ch. 6 figures).-- does the 10 psf just need to be composed into its vector components- 1 vector axial of the rafter direction and 1 normal to rafter direction. Then compare the normal component to the 10psf

Thank you for your help again.