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Thread: Angle steel strength question

  1. #1
    Associate Engineer jeff_allen's Avatar
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    Angle steel strength question

    Hi, I don't have my genius engineer neighbor at hand any more so signed up to try to find an answer here. My german sucks too much to ask any of my fine german engineer locals.

    I am building a tiny house on a trailer and it will overhang width-wise, so I need to create some shelf-like braces/wings. They will be under the walls, so holding most of the 2600 kg weight of the house. I'm thinking of something like this, made of angles of steel (upside down L, basically, with longer arm as the overhang):
    ~20-22 brackets, 10-11 on a side, ~2 feet apart
    150 mm long (the overhang arm)
    ~75-90 mm tall (side bolted to the trailer frame)
    ~50 mm wide
    9-14 mm thick steel.
    There will be a heavy board across the braces to carry the walls.

    The photo shows some another tiny house builder made, as a rough example. (Look at the original ones he planned to use and weep!)
    He used cold rolled steel. Would that be better than slices of angle steel (hot rolled)?

    My main question is: how thick would this stuff have to be to handle the load, considering it will be in motion at least once?
    Does this look like a good design?
    Does the length of the vertical arm (trailer attached side) effect the overall strength at all/much?

    Thanks for any help!!
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    Last edited by jeff_allen; 11-13-2017 at 02:28 AM.

  2. #2
    Administrator Kelly Bramble's Avatar
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    Technically, the actual load and stress calculations are not as simple as you stated. The floor boards and adjoining structure will carry significant portions of the 2600 kg mass, therefore the angle brackets will not see all of the load.

    If one assumes that the angle brackets do see all of the loading then:

    2600 kg / 20 = 130 kg (287#) per angle bracket.

    Area Moment of Inertia using the highest stress number (smallest 75 x 150 x 9 mm) from https://www.engineersedge.com/materi...gyration-7.htm

    Iyy = 804812 mm^4

    Cold Roller Steel E = 200 Gpa

    Using beam deflection calculator at:

    https://www.engineersedge.com/beam_b...flection_8.htm

    I get approximately 6.6 n/mm^2 at the support.. and a deflection so small the calculator does report it..

    Your trailer can easily support a herd of well fed Americans...
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
    Associate Engineer jeff_allen's Avatar
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    Dankeschön, Kelly!
    I figured they more than strong enough, going by what I read half inch bolts could hold, but better safe than sorry. It's amazing how strong steel is. I did know that not all the weight would be on the two walls...was just stating the max house weight. Nice to know I could host a herd of large yankees in a pinch.
    Hi to the cute pooch!
    Jeff

  4. #4
    Associate Engineer jeff_allen's Avatar
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    Quote Originally Posted by hannah_richter View Post
    It actually looks good to me? Technically, cold rolled steel should be hard but it does depend on what grade of steel we're talking about here. Plus I read somewhere that it's actually softer than hot rolled steel. We had a similar project at work and we actually used cold drawn steel that was additionally boronized. If you want to, I can try to find out more about that and ask around? But I mean, what you have looks pretty good and secure already so good job.
    Those pics are from another guy. I ended up scrapping the metal idea for now and will widen the trailer with a 10x14 cm slab of solid wood, bolted to the trailer sides, instead.
    It is just faster, and I need to build this thing fast.
    Eventually, I may want to design some kind of clever hand-operated attachment brackets to hold the house to the trailer, if I need to. German regulations stipulate that for a house to be considered a load, and not an RV (which is tougher to comply with), it has to be easily removeable without tools.
    Funny that ratcheting straps are ok for securing loads, and are not considered a tool. They are indeed a tool, by any logical definition.
    I thought one could cut a hex nut shaped hole in part of a ratcheting device and use it to turn bolts.
    Nein, Herr TÜV Inspektor, that is not a tool!
    Or just use wing nuts.
    Last edited by jeff_allen; 11-22-2017 at 10:04 AM.

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