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# ASCE 7-10 Wind loads on rooftop platform

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## ASCE 7-10 Wind loads on rooftop platform

(OP)
I am designing a platform to hold equipment on top of a building. I have already calculated my wind pressure. I am a bit confused on the force coefficient to use. I know to use Figure 29.5-1 for the force coefficient on the equipment, but unsure on what figure to use for the force coefficient on the platform itself. I am thinking I use the force coefficients in figure 29.5-2. The platform has four pipe columns, the beams are made out of wide flanges and channels and i have knee braces to stabilize the structure.

It would greatly appreciated any help on the correct way to calculate the wind force on the platform.

### RE: ASCE 7-10 Wind loads on rooftop platform

Which edition of ASCE 7?
It's possible that an uncommon geometry simply may not be covered by the standard. I suspect a platform above a building could have large uplift forces that aren't covered by the projected-area methods. Also note the section dealing with increased loading for rooftop equipment.

### RE: ASCE 7-10 Wind loads on rooftop platform

I will check tomorrow, but above a certain height, you have to increase thenpressyer, I believe as much as 30 percent.

Mike McCann, PE, SE (WA)

### RE: ASCE 7-10 Wind loads on rooftop platform

In these environs... the bigger problem is usually snow accumulation.

Dik

### RE: ASCE 7-10 Wind loads on rooftop platform

(OP)
I am using the ASCE 7-10 third printing. And my rooftop is about 100' in the air. And our live load governed over our snow load.

### RE: ASCE 7-10 Wind loads on rooftop platform

(OP)
Also, when I am applying my ice weight to my structure. Would the equipment on the platform have ice weight?

### RE: ASCE 7-10 Wind loads on rooftop platform

#### Quote:

I am a bit confused on the force coefficient to use. I know to use Figure 29.5-1 for the force coefficient on the equipment, but unsure on what figure to use for the force coefficient on the platform itself. I am thinking I use the force coefficients in figure 29.5-2. The platform has four pipe columns, the beams are made out of wide flanges and channels and i have knee braces to stabilize the structure.

Yes, getting Cf from 29.5-2 (and loading each individual member for wind) would be one acceptable approach.

Also keep in mind that there is a uplift case to consider with rooftop equipment/framing.

#### Quote:

Also, when I am applying my ice weight to my structure. Would the equipment on the platform have ice weight?

Unquestionably. (Unless it runs hot/warm.....and even then I'm not sure you should ignore the ice load because you can always lose power in a ice storm.)

### RE: ASCE 7-10 Wind loads on rooftop platform

(OP)
Thank you WARose for responding. Section 29.5.1 is for "Rooftop structures and equipment for buildings h<60ft" if my building is greater then 60ft does this section still apply?

### RE: ASCE 7-10 Wind loads on rooftop platform

#### Quote:

Section 29.5.1 is for "Rooftop structures and equipment for buildings h<60ft" if my building is greater then 60ft does this section still apply?

I didn't notice your height until after I posted. I think at that point, you can use Part 6 of Chapter 30 (C&C).

### RE: ASCE 7-10 Wind loads on rooftop platform

(OP)
Thank you that is helpful, I should of posted my height in my original post. When I am calculating my ice load of the equipment, do I use equation 10.4-1 to get my ice weight?

### RE: ASCE 7-10 Wind loads on rooftop platform

#### Quote:

When I am calculating my ice load of the equipment, do I use equation 10.4-1 to get my ice weight?

I think we are talking (then) more of a structure composed of flat surfaces. (I.e. then you would figure it by volume, ergo Eq. 10.4-2.)

To go back to the wind load for a second (while it is on my mind), I wanted to say: I went to a seminar on wind loading (based on ASCE 7-10) some years back and the guy giving it said that the wind load on rooftop structures with h ("reasonably") greater than 60' is just about what you get if you did it by that section anyway. At the time, I don't think they had the research to justify it in excess of that. Not sure if that has changed since. (I know that is not much of a source.....but I thought I'd mention it anyway.)

### RE: ASCE 7-10 Wind loads on rooftop platform

(OP)
Yeah, equation 10.4-2 makes a lot more sense.

So basically there just isn't enough research on rooftop equipment above 60ft get mentioned in asce 7-10. Just to double check, the uplift acts simultaneously with lateral wind force on the equipment?

### RE: ASCE 7-10 Wind loads on rooftop platform

(OP)
Also, since my platform deck is metal grating, does that mean I have to consider a ice weight on it?

### RE: ASCE 7-10 Wind loads on rooftop platform

#### Quote:

Just to double check, the uplift acts simultaneously with lateral wind force on the equipment?

That's what I've typically done. (In the proper combination with minimal Dead Load.)

#### Quote:

Also, since my platform deck is metal grating, does that mean I have to consider a ice weight on it?

Most definitely.

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