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Thread: Beam deflection

  1. #1
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    Default Beam deflection

    Hi guys, got just of a bit of an academic question for the gurus here. I've got a metre length of 50 by 50 by 3 rhs (supported at each end and not restrained) that is to have a centre point load of 1000kgs. I need to know the deflection.
    I remember doing a bit of this 30 years ago, but I'm out of touch now. Something about second moment of area
    and bending moments I think. Any hellp welcome.
    Eric

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    God j remember doing those calcs using eulers questions..

    Be buggered if i could do it now! Sorry.

    Simon

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    About 76mm according to this site https://www.easycalculation.com/engi...ular-beams.php

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    Quote Originally Posted by grunto View Post
    Thanks grunto, that does seems pretty excessive, and I would imagine it would exceed Youngs modulus. Might have to get out the old text books.
    Eric.

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    Quote Originally Posted by Gestalt View Post
    that does seems pretty excessive, ...
    I dunno. I would expect 1000kg to deflect it by more. Just a stab in the dark tho.
    Chris

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    That calculator doesn't seem to give much info as far as the beam details go. I think it must be referring to a cantilevered beam , ie supported at one end and the load applied to the other. If this was the case I can well believe that deflection with 1000kgs at one end of a metre length.

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    Also this calculator should include the point of exceeding the modulus of elasticity. Deflection past this point is meaningless.

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    The diagram under the calculator indicates the beam spans two supports. It also implies the load is evenly distributed along the beam.
    Chris

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    Quote Originally Posted by jack620 View Post
    The diagram under the calculator indicates the beam spans two supports. It also implies the load is evenly distributed along the beam.
    Thanks Jack. My mistake. I didn't get past the input fields.
    Eric

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    Thanks for the Link, grunto, hope you don't mind, I've put it at the bottom of the forums in the Conversions and Calculations section, hopefully for all members to find easily.
    I know I'll be using it a fair bit
    Gesalt, if your wanting to suspend the 1,000 kg off the bar, it would need to be 100 X 50 X 8 to get a deflection of 6.34 mm, going by the calculator grunto supplied.
    Kryn
    To grow old is mandatory, growing up is optional.

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    Thanks Kryn, but there's something wrong in those calculations. I did some practical stuff this morning and suspended the load on the rhs beam (see pics) and got a deflection of around 5mm. This made more sense to me. In fact, this calculator confirms it:
    Beam deflection and stress calculator
    I can't really understand the example in the first calculator of a beam that is 20 inches long and 30 by 30 inches high and wide with 10 inch wall thickness. It's probably just me, but I don't get it.
    Anyway it looks like I'm OK to go with the 50 by 50 .
    I have to get the thing inside the house and stand it up on its footing (once it's sand blasted and painted).
    Eric
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    I have new found respect for RHS!
    Chris

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    Nice. Good to see it all went OK.

    What is it BTW? Looks like something from a refinery, like a cracking tower!

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

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    Quote Originally Posted by simonl View Post
    Nice. Good to see it all went OK.

    What is it BTW? Looks like something from a refinery, like a cracking tower!

    Simon
    It's going to be our new wood heater Simon. (have to have it installed before the cold sets in next year and there's still heaps to do).
    Eric

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    I tried solid works which has a very simple wizard for simple people. it only works on single parts but you can only add simple fixtures and forces. Because your beam is not fixed either end, i drew it with the vertical arms, so there would be no force holding the beam back from bending in. SW has a complex calculator too, but by doing tricks like this I've never had to learn how to use it.

    Three pictures, one shows stress, one shows displacement (~6mm) and one shows factor of safety. The red on the blue beam, is where the factor of safety is below 1.

    I used a force of 10,000N and a material of AISI 1010 steel, not sure if thats right for material. For a point source, I used the forced displaced over a 10mm wide strip across the middle.

    I can't even remember if i knew how to work these things out or not. You'll have to guess if i got it wrong or not but I've trusted a lot of weight on this before but I leave a FOS of 4 at least, 8 if i can afford it. The model is a pure square with 5mm outer radius but no account for the welded seam.
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