Hello. I am going to renovate a trailer where the beam at the rear needs to support 3 tons. What I am a bit uncertain about is the thickness I need for the square steel tube. The external dimensions have space for 100x100 mm. Is there someone skilled in this as I have a tendency to over-dimension things and in this case, I don't want to do that in order to keep the curb weight as low as possible?
What is the span of the beam and what does the load look like? Is it a point load, and if so, where, or a uniformly distributed load?
Span width just under two meters. It's an all-round trailer used for everything from pre-cut timber to pillars. You can usually load 4 tons on the trailer distributed over an area of 2x4 meters. Hence, an estimated 3-ton tolerance on the rear axle to be on the safe side. The somewhat unfortunate aspect of the trailer is that the wheel axle is located at the very back. This means that the weight is distributed between the pull and the very back of the trailer. It is over 20 years old, so the wheel axle has bent where the beam in the middle goes. It has a loading height of 40 cm, so you want to fix it before it bends further, causing damage that is much harder to repair. I'm considering a regular KKR pipe 8 mm 100x100.
With KKR 100x100/8 mm, the maximum deflection is approximately 4 mm when a 3-ton load is evenly distributed. Then you have good margins to 1/300 of the span, which is about 7 mm. That sounds like a reasonable compromise. Otherwise, there are more material-efficient solutions.
Thinking of something specific? The reason for KKR is because it's easier to obtain and above all, it's cheaper. Half the price compared to VKR. I also considered an HEB beam, but then it becomes difficult to find a feasible solution for the wheel axle that's adapted to run inside a 100x100 beam on the sides. After all, the old construction has held up for 20 years.J justusandersson said:
I understood that you preferred a square cross-section for practical reasons. I was thinking more about other readers when I wrote as I did. A rectangular profile (in height) can provide the same strength at a lower weight. For example, KKR 120x60/6 mm. Over such short distances, the price difference becomes negligible.
Yes, I know. But then it becomes quite a lot of extra work to adjust the wheel well itself that goes a bit into the tube. The reason it's made that way is probably to distribute the load against each wheel. It was originally an old feed cart that has been modified. Thanks to the wheels being positioned outside, it's ideal for carrying materials at the construction site, removal of brush, etc. You don't have to lift high. Thanks for the response.