HoSS Posted January 24, 2021 Share Posted January 24, 2021 I'm just designing the bed/floor of my camper box. I've agonised weather to do it in Alu beams or Steel, and come to steel as i feel it will handle the dynamic loads better (plus easier to weld and less prone to fracture) The next question is what grade. Obviously it does not want to be over-engineered, but also should not be too weak either. I found some calculators online and looked at flex for certain loads on single beams. I came up with using 30x50x3mm wall tube, that had a deflection of 0.7mm for 150kg on the end of a 1m overhang. But it would be nice to look at the whole structure. Its basically a ladder frame 3m long by 2m wide, supported along point on the chassis rails, the overhang to the outside no being more that about 600mm. Transverse beams every 450mm. I'll post a sketch up when i have a chance to draw it. Can anyone help in a scientific or experience way? Quote Link to comment Share on other sites More sharing options...
Badger110 Posted January 24, 2021 Share Posted January 24, 2021 Consideration for the floor material? This will have a factor on the strength of the frame or are you looking to gain the strength from the frame alone? Quote Link to comment Share on other sites More sharing options...
Ed Poore Posted January 24, 2021 Share Posted January 24, 2021 Is this bed going to be structural or is it sitting on a pre-existing chassis? I'm sure @simonr can do some structural analysis for you but I can offer a little experience with the bed of the 6x6 (104" x 66") so a little smaller than yours in both dimensions. Here's a convenient picture I had of the framework when I removed the floor to remove it from the chassis. It's welded aluminium C section approximately 4x2". It's light enough that I could probably pick it up and drag / move it around if I needed to by hand. When I brought the mill over from my parents farm and Dad was lifting it onto the bed with his digger he watched the bed closly and commeted that looked like it flexed, probably about 600kg of mill since I think it's about 800kg fully assembled, but it was a fairly concentrated load. But the 6x6 has taken something like 3-4t of hardcore on the back of it (albeit that was evenly spread out) so the bed is certainly man enough for it. Quote Link to comment Share on other sites More sharing options...
simonr Posted January 24, 2021 Share Posted January 24, 2021 I sent Hoss a PM - and I'm happy to oblige. I agree that Steel would be easier to fabricate & more likely to be structurally sound long term. Aluminium is great, but has a shorter fatigue life. In some circumstances, once you've built up the Ali to have the life expectancy you require, you loose much of the weight advantage. The down-side of steel is corrosion - but that can be largely prevented. Quote Link to comment Share on other sites More sharing options...
HoSS Posted January 24, 2021 Author Share Posted January 24, 2021 Floor material will be either camper floor composite, or my own wood-foam-wood. It will be sitting on mount points on the existing chassis, hard mount at rear points, then about 4 or 6 more spring pull-downs (a-la 3-point flex mounts). It just has to support the weight of the camper body and contents, the heaviest thing being 2x 60L water tanks, walls will be foam composite, at a guess max load 500kg I'm at a loss how to estimate dynamic forces, but 500kg at 1-2 g already becomes 1.5 tons.... Quote Link to comment Share on other sites More sharing options...
simonr Posted January 24, 2021 Share Posted January 24, 2021 As a rule of thumb, for vehicles, the bump loading is about double (as the vehicle body is mounted on the vehicles suspension). So double the static load. On top of that, you build in a factor of safety to cover bad welds & unexpected loads - the unforseen. Hopefully, the combination will be sufficient for anything you throw at it. Quote Link to comment Share on other sites More sharing options...
Badger110 Posted January 24, 2021 Share Posted January 24, 2021 Are you looking to build the entire structure from steel/alli or just the floor? Quote Link to comment Share on other sites More sharing options...
HoSS Posted January 25, 2021 Author Share Posted January 25, 2021 Just the bed/floor, the rest will be composite sheet (alu/foam/alu) bonded into alu profiles Quote Link to comment Share on other sites More sharing options...
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