Wind coefficients for overhangs...

[McEngr]

Can anyone give me confirmation on the following?

I gave my boss a proof in one of my texts that if you have an overhang on a building that matches the roof slope that you don't have to design the MWFRS with a C&C wind coefficient when design the MWFRS. He doesn't agree with me.

I've researched this topic, and while it's less conservative than his, I wish that he would at least take heed in what I'm telling him.

Can anyone else confirm for me that when you have a matching-roof-line outrigger/canopy/overhang, that you still design Main-Wind-Force-Resisting-System as that of the main portion of the roof?

Scottiesei, I know that you and I have discussed this before and we came to the conclusion that it can be partially-enclosed, but not necessarily a 2.20 coefficient from the C&C tables with theta between 7 and 27 degrees.

Thanks,

McEngr

 

[scottiesei]

Let me preface this by refering you to Figure 6-2 in the ACSE 7-02. It has a seperate column for overhangs with higher pressures. with that being said, also look at the FRC R802.2.9.1 which also has an extra column for overhangs.

I would look at it this way:

1. If I was designing the connection at the truss to the top plate or wall, I would include the higher pressure on the overhang due to the fact that the overhang may experience a local ized gust at that truss.

2. If I was designing an outlooker, again, I would use the higher value.

3. If I was designing bond course steel, I would not use the higer value. Chances are that the localized gust would not effect the entire length of the overhang down the building.

4. If I was designing footing sizes for uplift resitance, again I would not use the higher value. For the same reason as #3 in addition to the fact that they take %40 of the dead weight away for uplift.

So I guess it all depends on the circumstance to me.

But then after I type all of this, I read section 6.5.11.4.1 and am told what to do by someone apparently much smarter than I. :multiplespotting: :multiplespotting:

 

[McEngr]

Let me preface this by refering you to Figure 6-2 in the ACSE 7-02. It has a seperate column for overhangs with higher pressures. with that being said, also look at the FRC R802.2.9.1 which also has an extra column for overhangs.I would look at it this way:

1. If I was designing the connection at the truss to the top plate or wall, I would include the higher pressure on the overhang due to the fact that the overhang may experience a local ized gust at that truss.

2. If I was designing an outlooker, again, I would use the higher value.

3. If I was designing bond course steel, I would not use the higer value. Chances are that the localized gust would not effect the entire length of the overhang down the building.

4. If I was designing footing sizes for uplift resitance, again I would not use the higher value. For the same reason as #3 in addition to the fact that they take %40 of the dead weight away for uplift.

So I guess it all depends on the circumstance to me.

But then after I type all of this, I read section 6.5.11.4.1 and am told what to do by someone apparently much smarter than I. :multiplespotting: :multiplespotting:

Hi scottiesei, I'm at home so I don't have the luxury of looking up all the stuff that you've entailed. However, I'm desiging, in most cases, a 4-6 foot overhang that is supporting purlins. The main component supporting the purlins is a little W8x10. It will work regardless of the coefficient, I think you'd agree. However, when I'm desigining it for the MWFRS, my boss wants to ULTIMATELY use the higher value when reporting reactions to a foundation engineer. I refer to him my MBMA 2002 manual, which is supposed to be the Bible for metal-building-type structures and is very, very easy to follow: he's seen the references, but either outright disagrees or has forgotten what he agreed to a couple of months ago.

Nonetheless, I'll read and disect your notes 1-4 and comment if I think I agree/disagree. THANKS!

 

[scottiesei]

But then after I type all of this, I read section 6.5.11.4.1 and am told what to do by someone apparently much smarter than I. :multiplespotting: :multiplespotting:

I would read this ASCE 7 section first. I think it will answer your question.