4 Replies Latest reply on Nov 3, 2011 2:08 PM by Legt Chevrollier

# Wind pressure analysis on curved roof

I want to make a pressure analysis of wind on my curved roof.

What I am confused of are the values of the pressure, which I get from the Solid works analysis. Take a look:

The maximum value I got is 101348 Pa and minimum one 101290 Pa.

I know that normal atmosferic pressure at sea level is 101325 Pa.

So by knowing this, how can I get my wind pressure load on the surface?

I know 1000 Pa = 1 kN/m2, so by that I can get a uniform load from the wind pressure. Fore example 101348 Pa = 101,348 kN/m2. But this is too high, and not the way to do it right?

Thanks.

• ###### Re: Wind pressure analysis on curved roof

Legt,

The pressure that the roof sees is 101348 - 101325 Pa or 23 Pa. , assuming that the pressure under the roof is atmospheric.

• ###### Re: Wind pressure analysis on curved roof

Thank you David.

So when I get a wind analysis like this, I only need to substract the normal atmosferic pressure at sea level (101325 Pa), from the highest value of the pressure I got in the Solidworks analysis. Right? In this example, like you said, the highest pressure is 23 Pa.

But on the other hand, when I substract the minimum pressure (I got from Solidworks analysis) with normal atmosferic pressure at sea level (101325 Pa): 101290 - 101325 Pa = -35 Pa     So this means I have suction, not only compression as a result of the wind load, right?

Then how can I apply this load to my grid (space frame) construction I already have in my structural engineering software (I am using RSTAB, although SAP 2000 could handle it too)?

• ###### Re: Wind pressure analysis on curved roof

Legt,

Because of the "airfoil" like shape of your roof you certainly could have a suction or negetive load on your structure.  Flow is computing the absolute pressure on the roof and ignoring the atmospheric pressure under the roof.  Perhaps a means of netting this out would be to shell the  structure in your model and place a "port" with a lid in a wall with a Boundary Condition that would be "environmental pressure".  Then the values that you would be extracting from Flow should be actual roof load less the atmospheric pressure.

• ###### Re: Wind pressure analysis on curved roof

Hi David.

I am not sure, I understood you this part:

"to shell the  structure in your model and place a "port" with a lid in a wall with a Boundary Condition that would be "environmental pressure"."

Can you be a bit more specific please?

Thank you.

About getting the actual wind pressure, rather then absolute pressure, I am trying to use this solution: making a new parameter that will automatically extract the noral atmosferic pressure (101 325 Pa) from my absolute pressure:

For now, I am having some problems with implementing that new parameter, as you can see in that topic.

But still, even in case I work out this, I still do not understand how would I then apply the results I got, to my grid (space frame construction) for that roof, I have in RSTAB or SAP2000?

Is this the way to do it:

http://imageshack.us/photo/my-images/513/14401185.jpg/

So I will take the maximum compression (positive pressure) and maximum suction (negative pressure) and make two load cases with these values.

Correct? Or not?