[coily96]

I've recently heard when building a trailer that there can't be any vertical structural welds on the chassis/frame, is this correct or BS?

[pete_79]

BS.

Vertical welds on the sides of the drawbar do create a weak point though.

[coily96]

That may of been it, thanks

[buzbox]

Yep that's right. Should only make horizontal welds on the structual parts / chassis / frame of the trailer.

[pete_79]

I would only be concerned with welding on the drawbar, between the box and the hitch.



If you do want to weld on the sides of the drawbar do it on an angle or use fish plates like everyone does on their vehicle chassis.

Fish plate example;




Vertical welds on the rest of the box are fine in my opinion, there is a structure to take the load and reduce risk of failure.
Once the side panels are welded to the RHS frame this is effectively one big I-Beam 450mm high.
For example, I recon Lost's spring mounts are a great idea.


There's less chance of these plates failing then the mounting brackets that came with my springs.
My spring mounts are only fixed to the bottom surface of the RHS frame, there is a chance that over time this can fatigue and 'could' tear the bottom of the RHS. Lost's design would not fail in that way and the vertical welds would not cause any problems because of the side panels as noted above.

[just_cruizin]

Any weld across the draw bar should also be avoided, like the front of the box. There shoulder be a weld on the the front cross bar for the front of the box, should only be a weld on the under side along the drawbar. This is the highest stress point on the draw bar, attaching boxes onto the drawbar should also be done with care, you don't want to be drilling the top or bottom faces

[31zook]

just_cruizin wrote:

Any weld across the draw bar should also be avoided, like the front of the box. There shoulder be a weld on the the front cross bar for the front of the box, should only be a weld on the under side along the drawbar. This is the highest stress point on the draw bar, attaching boxes onto the drawbar should also be done with care, you don't want to be drilling the top or bottom faces

Its to do with the structural integrity (as you know engineer). The strength in RHS (when its held at either end with force applied in the center) comes from trying to strech and compress the top and bottom of RHS. The sides only transfer the force into the top and bottom of the RHS. Look at an I beam, they have thick top and bottoms but thinner webs, you can cut most of the guts out of them and still keep 99% of the strength. Hence, why your not allowed to weld/break the top and bottom steel.

[just_cruizin]

Second moment of area (moment of inertia)

[gardnep]

All my joints on the rhs frame have vertical and horizontal welds, as a matter of fact, the vertical ones appear the neatest. The gussets and rhs joining the drawbar also have vertical welds, is that a problem on a 1580 x 1010 frame?

[Coyote]

Lets just start with BS
The welding on any member is only as good as the preparation and finish, the only section that is remotely attached to fact is that vertical welds tend to have more undercut (only talking vertical up here, vertical down is only for sealing, has very limited penetration etc.)
it you are talking about the attachment point, then fully sealed (weld all round) is always the best option), in so far as the members themselves, it is a matter of good welding not limiting the position of the welding.

All welding should be checked for undercut, this is the main surface defect that affects the strength, it is all about notch sensitivity, jot just that the member has been thinned but how the stresses transmit in the member, hence undercut is always bad.
Weld all round also helps with stress transmittal, and is a key method of reducing the corrosion senility.