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

    Wind pressure analysis on curved roof

    Legt Chevrollier

      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:

       

      vray3d.jpg

       

      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?

       

      Any help please?

      Thanks.

        • Re: Wind pressure analysis on curved roof
          David Paulson

          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
              Legt Chevrollier

              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
                  David Paulson

                  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
                      Legt Chevrollier

                      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:

                      https://forum.solidworks.com/thread/49268

                      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?