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Thread: Design of a Steel Beam with Hole in Web

  1. #1
    Lead Engineer Cake of Doom's Avatar
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    Design of a Steel Beam with Hole in Web

    Evening all,

    Being a Temporary Works specialist, it's not often I get to play around with structural design anymore but today we had an interesting (for us) problem come up. A company we design for wanted to cut holes in the webs of their beams to allow services to pass through. To save time my boss asked me to take a certain amount and he would take the rest. The holes are 240mm long by 90mm high, 840mm from the beam end and ~71mm from the top of the beam. The beams are 203x203x46kg/m.

    As per the current standard (and my preferred method) I went straight into checking stuff out using Vierendeel's methods as if it were a composite beam and the numbers indicated that local stiffener plates would not be required. When I saw my boss's design however, I was shocked! He'd used enough steel plate to build a house on and the sketch of the beam looked one of Frankenstein's creations. Turns out he'd treated it like a splice and said thats how he'd always done it.

    So my fellow interneters, What are your preferred methods for getting round these little things? Any "quick fixes" you've come across over the years?

    (Not the most interesting thread but it's all I got so nur!)

  2. #2
    Lead Engineer RWOLFEJR's Avatar
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    Hi Cake of Doom...
    Two sayings come to mind when I read this... make that three...

    1) A truss is a beam with the unnecessary parts of the web removed. (some professor at school)

    2) When in doubt... make it stout. (my dad)

    3) I wouldn't touch it with a ten foot pole. (ZZ Top)

    I couldn't quite follow you on the location and number of these holes? One hole 840mm from the end of one beam out of how many how long supported where and holding up what for who?

    I'll take saying number three please. (humor)

    Sorry but that's something that only somebody with all the information can answer.

    Good Luck,
    Bob

  3. #3
    Technical Fellow Kelly_Bramble's Avatar
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    Quote Originally Posted by RWOLFEJR View Post

    2) When in doubt... make it stout. (my dad)
    It is way easier to over design than to design it "just right".

  4. #4
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    ...and a 90mm high hole in a 203 UC with a flange thickness of what? would leave about 45mm of web. Not what I would call a beam anymore when about 60% of the web has gone missing. Ooops, just saw that the hole is vertical offset too. That leaves 41mm for a flange and some (any??) web.

    If you can't talk the client out of those holes, or at least make them smaller in height, then listen to your boss. .

  5. #5
    Lead Engineer Cake of Doom's Avatar
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    The client had already had them cut before seeking a design; which I didn't know at the time. Should have expected it though because its par for the course from this company.

    It was one hole per beam which they have sited on top of the bottom flange, even removing the bottom root radius leaving only the 11mm flange in that area. They rejected my bosses design as a bit over the top but once we had all the info for what they had done we told them to go to their Structural Engineer for a proper analysis. Was a fun exercise though.

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