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Thread: trailer boards

  1. Black Locust Robinia pseudoacacia is what they use for fence posts and boat docks. No preservatives required.

  2. #17
    Join Date
    Jan 2019
    Location
    Fairbanks AK
    Posts
    1,566
    Quote Originally Posted by Tom Bender View Post
    Hi Scott
    Here's a question for your spare time.

    If the supports are 4 ft apart but I install a crosswise cleat underneath fastened to the boards, how does that help? My thought is that it helps a lot with point loads but not at all for a distributed load. Is that right?
    Well Tom, that math can go way above my paygrade in a hurry. But there is good news. One, I know or think I know the pragmatic answer, and two we have an actual engineer here who sometimes enjoys these problems. Michael, Michael B...I have to check my PM box.

    If I understand the question correctly you have metal floor supports every four feet down the length of your trailer. So when you are looking at new trailer boards they only have to span four feet from floor support to floor support, so when you look at beam tables for deflection your trailer boards acting as beams only have a span of four feet from floor support to floor support.

    The cleats you are talking about do not act as beams (right?) because they fasten the floorboards together from underneath, but do not bear on any of the trailer metal, so your cleat does not act as a beam shortening the span of the floor boards from cross piece to cross piece. Yes?

    In that case your cleat is acting as a stiffener. It will help with point load distribitiuon but not contribute materially to ultimate floor strength, you are exactly right if I understand the question correctly.

    As a similar example, I designed and built a wood shed for one of the guys from my church last summer. His budget was a number. His wife desires a particular indoor temperature for indoor wedded bliss, our local ground snow load is 55 pounds per square foot, etc, etc.

    I could have supported all the cordwood on four cinder blocks, but to support the snow load I needed six cinder blocks under each 8 foot section. It was cheaper to use six posts instead of heftier roof framing. The pic is the first of three side by side modules.

    At the near end of the pic you can see a 2x6 rafter. The rafters support 5 SPF purlins (Joe 2x4), you can see the end grain on them. Between the purlins is more SPF 2x4 blocking. I could have held the blocking in with finish nails. The blocking, like your cleats, adds nothing to the ultimate strength of the roof. If I read the table on the metal roofing correctly I didn't need the blocking to support the metal roofing with the snow on it - but if the snow load in spring slides part way off the roof and I end up with a big point load at the low end and bare metal at the high end the blocking will keep the purlins from twisting..... My blocking will act in compression, your cleats will likely be limited by the threaded fasteners you used.

    Be advised the SPF (Canadian grown) I see routinely up here is a tiny bit stronger than the SPFs (USA grown Spruce Pine Fir, SPF south) available away from Canada in the lower 48. IIRC the two groups have nine species in common with 2 Canada species pushing that average up and 2 common USA species pushing that average down. They are pretty similar overall.

    Sorry the pic is rotated. I'll go find Michael B and see what he is up to.
    Attached Images Attached Images

  3. #18
    Join Date
    Apr 2019
    Location
    Madison, Wisconsin
    Posts
    283
    Hi Scott,

    I got your PM; if I’m interpreting your description properly, you and Tom are correct that the crosswise cleats will help with point loads (minimum factor of 8 improvement for a cleat halfway between the supports that is parallel to the supports and attached to the underside of the floor boards) but will do pretty much nothing for evenly-distributed loads.

    If I’m misinterpreting, please let me know.

    Michael

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