load strength of aluminum

[02rangeredge]

I'm reinforcing my aluminum truck cap with 1/8in aluminum so I can haul my 2 kayaks (90lbs) and was just trying to lay out where on my truck cap I can safely put the feet of my rack towers

 

[UHAULER]

As close to the edges and as close to the front and back as possible would be my suggestion.

 

[02rangeredge]

As close to the edges and as close to the front and back as possible would be my suggestion.

that was my original plan but part of me says straddle the factory ribs of the cap for load dispersal

 

[rayra]

Depends on all sorts of dimensional criteria. You'd do better to use a tubular extrusion if you want load strength. If you are worried about tear-out / -thru, then the flat reinforcement would be ok.

 

[02rangeredge]

Depends on all sorts of dimensional criteria. You'd do better to use a tubular extrusion if you want load strength. If you are worried about tear-out / -thru, then the flat reinforcement would be ok.

what do you mean by tubular extrusion? a sort of exocage type of deal?

 

[rayra]

No I just mean using some square or rectangular tubing as your interior bracing for your external rack. Then you get both the tear-out prevention discussed in your other topic on the same setup and you get a bit of load-bearing capacity from the tubular metal.

your earlier topic on the rivnuts
http://forum.expeditionportal.com/threads/170245-Rivnut-weight-capacity

 

[NMC_EXP]

I'm with Raya - flat stock will bend under a load that would not affect square or round tubing. If the structure is fiberglass, that may be a problem.

If the reinforcement must conform to a curved surface, the tubing option is out.

 

[02rangeredge]

I'm with Raya - flat stock will bend under a load that would not affect square or round tubing. If the structure is fiberglass, that may be a problem.

If the reinforcement must conform to a curved surface, the tubing option is out.

it's an aluminium cap, the roof is thin, so very flexible to meet the reinforcement, original plan was 1x2 tubing, flat strap will only be short connecting braces crossing tube seems

 

[rayra]

These needs some photos of the cap or a same-product and some sort of explanation of your plan.
My suggestions are predicated on the idea that your cap skin is corrugated aluminum and the grooves run from the forward edge to the tailgate. Thus a rack or whatever is being attached on the roof ought to be sitting on some form of runner / rail, in continuous contact wtih the skin, to spread the weight as much as possible. And in the rivnut discussion my suggestion was some reinforcing flat stock (or large 'fender' washers) on the inner surface of the cap, so the thin cap skin would be sandwiched between outer and inner rails. Maximum support and maximum resistance to tear out, without having to put a larger more complicated support structure inside the cap or outside on the sides.

I suggest you contact the cap manufacturer and ask them what they think the max weight load that could be borne on top of the cap without permanently deforming it. They'll very likely tell you zero pounds, out of liability concerns.

 

[02rangeredge]

These needs some photos of the cap or a same-product and some sort of explanation of your plan.
My suggestions are predicated on the idea that your cap skin is corrugated aluminum and the grooves run from the forward edge to the tailgate. Thus a rack or whatever is being attached on the roof ought to be sitting on some form of runner / rail, in continuous contact wtih the skin, to spread the weight as much as possible. And in the rivnut discussion my suggestion was some reinforcing flat stock (or large 'fender' washers) on the inner surface of the cap, so the thin cap skin would be sandwiched between outer and inner rails. Maximum support and maximum resistance to tear out, without having to put a larger more complicated support structure inside the cap or outside on the sides.

I suggest you contact the cap manufacturer and ask them what they think the max weight load that could be borne on top of the cap without permanently deforming it. They'll very likely tell you zero pounds, out of liability concerns.

yeah, that basically describes the cap, I planned on doing the flat strap washer set up from the start but his post was more about will the aluminum tubing (1 x 2 x.125) end up bending under the 90-100lb load

and I would contact the cap manufacturer, but the cap is unmarked- I got it free off of craiglist since at the time it was shy a window

but thanks for the feedback, I'd upload pictures but the links aren't working

 

[javajoe79]

The rack on my work truck is 1/8 wall 1" square aluminum tube. It has had a canoe and 2 kayaks on it. I think the actual structure of your capper is what you need to worry about. Does it have support ribs at each end built into the corners? Either way attaching the rack to the vertical part of each corner may be your best bet. Or to the sides, where the ribs are

 

[02rangeredge]

The rack on my work truck is 1/8 wall 1" square aluminum tube. It has had a canoe and 2 kayaks on it. I think the actual structure of your capper is what you need to worry about. Does it have support ribs at each end built into the corners? Either way attaching the rack to the vertical part of each corner may be your best bet. Or to the sides, where the ribs are

thanks, thats exactly what I was hoping to hear about- first hand experiences, I'll look at it- that reinforcement will be easy enough after the fact if I question its integrity and test it with a few boats on short drives