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Thread: I build a trailer for my tiny house and I'm wondering about the frame integrity.

  1. #1
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    I build a trailer for my tiny house and I'm wondering about the frame integrity.

    I build a trailer for my tiny house. I've had 2-3 year welding experience and have built large objects before under supervisors with knowledge of structural engineering.
    This trailer I've built though was not under any guide or supervisor and I'm wondering about a critical connection.
    About the trailer:
    It's 34 ft trailer total length, bumper pull, triple axle 21K total weight including trailer.
    The steel is 6" x 2" x 5/16 thick there's also some 3/16 for less critical applications.
    The design is basically squares of channel with 5 cross beams between the main beams with large gussets in connections. The trailer seemed to be very sound before it was loaded. It passed inspection, but I don't know if they took into account that it would be holding ~12K pounds.
    The dilemma:
    When I ordered the steel the max length was 20 feet so I added the extra 8 feet to the end by welding the channel together, grinding the seams and welding two 2 foot lengths of 1/4 plate on both sides for each beam (2 per 5/16 channel). I welded along the entire perimeter of the plates getting good penetration.
    Question:
    Will drilling and adding 8 high strength bolts per connection increase the overall strength? Because the house is currently built but has not been moved. I'm sure it will hold the weight well when stationary but once it starts bumping up in down the road then I'm unsure. There's less than 1500 pounds on it the end of the trailer.
    If you need more information please ask. Thanks
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  2. #2
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    Re: I build a trailer for my tiny house and I'm wondering about the frame integrity.

    Welcome from NE GA , not exactly sure what your question is ? I have been welding and fabricating 25 + years and have built trailer,s in professional shops and noticed a few things that were done incorrectly . First thing NEVER rely on butt weld,s for tongue of trailer ! not to worry though this is a easy fix , just get a couple more pieces of channel and run them underneath the current ones , make sure they run the entire length of the tongue from outer sides of frame and taper them off so as to end about one foot from hitch . this will greatly strengthen and support the tongue . Next thing , i would weld in X braces at both empty box,s between the axles and box in this part of your frame . you could get a couple more pieces of 6'' channel for this , if you are at all unsure of your [welding capabilities ] this is were to get some experienced help ! Also if your trailer is not going to have perfectly distributed weight the area over the axles will probably need to be strengthen as well . Third thing every cross brace should have at least a 12'' x 12'' gusset on both sides for support . I hope this will help you out .

  3. #3
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    Re: I build a trailer for my tiny house and I'm wondering about the frame integrity.

    bumper pull, triple axle 21K total weight
    ???????

  4. #4
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    Re: I build a trailer for my tiny house and I'm wondering about the frame integrity.

    I agree that the tongue is a bit strange.

    You're in the unique situation of building the equivalent of a deckover trailer, where the frame, and tongue, are one-in-the-same.

    The frame should be one continuous piece. It really shouldn't be welded to the front crossmember, even though you've continued the shape with the extra piece between the crossmember, and frame side rail.

    Like this.....continuous.

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    Just a matter of notching the channel, and bending it to the desired angle.

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    Finish it out with a fishplate, and a cover plate on both flanges (upper and lower).

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    Some guys are comfortable with welding the notch, and calling it good. I'm not comfortable with that, but everybody has his/her preferences.

  5. #5
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    Re: I build a trailer for my tiny house and I'm wondering about the frame integrity.

    I personally don't see a problem in the axle area. Never heard of any x bracing in this area. Not saying it doesn't exist, I've just never seen it.

    The only thing a guy sometimes wants to do, is run a piece of channel across the frame between the hangers, welding it to the hangers, and the frame. This prevents the hangers from moving sideways when the trailer is turned sharply, or jackknifed. There's a lot of side force on axles/tires when a tandem, or triple, suspension goes thru a turn. Look underneath some trailers, and I'll bet you'll find this feature on a few of them.

    Ladder frames on trucks, and trailers, are twisty little boogers. It's almost impossible to engineer that out of them, and you wouldn't want to anyway...……...the whole thing needs to flex to some degree.

    The most important function of the crossmembers, aside from supporting your load, is to prevent the frame channel from tipping to one side or another. The crossmembers hold the channel perpendicular, where they are strongest. Same function as joist blocking in a house floor.....don't want the joists to tip.

    Once you add your house on top of that frame, the subfloor is gonna make it very rigid in the horizontal plane.

  6. #6
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    Re: I build a trailer for my tiny house and I'm wondering about the frame integrity.

    Looks good from here, though generally with that kind of weight it would need to be a fifth wheel or gooseneck.

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