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Drag Coefficient (Cd) values for I-beams, Channels, etc.

  1. Sep 7, 2011 #1
    Can anyone PLEASE help me in pointing me in the right direction? I need to obtain drag coefficient calues for I-beams. I found a site stating it was 2.7, but it says nothing about the orientation?? I basically need the Cd-value for flow parallel to the I-beam, from the top and from the side.

    Any help will be appreciated.

  2. jcsd
  3. Sep 7, 2011 #2
    I think you need to clarify your request. Your use of the word parallel and then "from the top and bottom" seems in conflict. The 2.7 number is likely for a flow perpendicular to the length and sounds pretty reasonable.
    Last edited: Sep 7, 2011
  4. Sep 8, 2011 #3


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    2.7 sounds really high. A very good parachute has a cd of about 2.2-2.5.
  5. Sep 8, 2011 #4
    What I meant was that I need 3 Cd values. (I attached a quick sketch of it.)

    [PLAIN]http://img32.imageshack.us/img32/6361/ibeam.jpg [Broken]

    Cd values are for:

    1 - Flow onto "web" area.
    2 - Flow onto flat "plate" area.
    3 - Flow parallel to the length of the I-beam.

    I would like to see the change in wind load according to change in orientation.
    Last edited by a moderator: May 5, 2017
  6. Sep 8, 2011 #5


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    I would use Cd1 and Cd2 as 1.6. For Cd3, I've never used it, but I assume it's value would be very low parallel to the web, and dwarfed by the drag factor on the end face, which would again be about 1.6.
  7. Sep 8, 2011 #6
    Wouldn't the value for Cd1 be a bit higher than Cd2?
  8. Sep 8, 2011 #7


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    Perhaps, but i've aways in both cases just used the projected area to calculate the wind force, using the drag factor for a 'flat' surface (Cd = 1.0 for a cylindrical face, Cd =1.6 for a flat face).
  9. Sep 8, 2011 #8
    Yes, but when the air hits the web side (as in Cd1) it will be restricted when trying to move around the web area because of the plates either side. This will definitely cause the Cd value to be higher.
  10. Sep 8, 2011 #9
    Last edited by a moderator: May 5, 2017
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