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general truss design question

general truss design question

general truss design question

OK ... here is a dumb one.

I need a temporary slide.

I need to get 96 pieces of metal roofing ... 16" wide x 38 ft long ... to a roof. The edge of the roof is about 18 ft off the round.

The metal is super flexible ... if it bends, it is garbage ... If you hold one end straight up, the other will fall over.

It is not heavy ... about 40 lbs per piece.

So, I am thinking of a cart ... 40 ft long ... can slide them out of the crate and onto it. Then I can use it like a wheelbarrow ... move it over (about 50 ft) to the building ... then lift one end (I have a man lift on site) ... finally sliding up and onto the roof.

OK ... sound like work but I have put every nail into this shop so far .. even got the trusses up myself ....

Anyway, my question ...

If I make a cart out of say PVC pipe ...the side (about 2 ft high) would need to be like a floor truss to make it stiff.

Without going through hours of calculations ... is there a best arrangement for the memembers.

Attached is an image shown a couple of layouts .... there are many many ways to go ... is one "stronger" (less flexible) than another?

Just looking for some practical advice.

You can see videos of my build on my facebook page: Link

Thanks ....

RE: general truss design question

Interesting challenge

Don't do your second one - it's not a proper truss, the middle bay is a Vierendell truss that relies on moment connections at the uprights either side

Without doing any numbers or anything, I doubt it matters that much what you do out of the other options as it's probably fine
Your connections will be the critical components most likely anyway - unsure how that will be done in PVC tube
Try get the centrelines to all neatly align at a point to prevent accidental eccentricities as that will compound connection difficulties

I would do Option #1 though if I had to pick
1/ Simple to build (equilateral triangles, lay out continuous top/bottom rail and then cut the same pieces over and over)
2/ Your weight will be applied as a distributed load to the top chord, may as well keep that span short between the truss notes
3/ The diagonals framing down to the support points at the corners is nice (I'm imagining that you just have wheels at the ends of these things?)

RE: general truss design question

Thanks ...

There is obviously a lot more options

In the long run, it is such a small load that it may not matter but I may as well build it as strong as possible.

When you are working by yourself, there is just no easy way. Even getting a crane and lifting the crate onto the roof would not help. I would still need to lift them out of the crate ... which is super hard to do (I lifted a couple out ... used a 16 ft spread bar so I didn't bend them).

Thanks so much for the advice!


RE: general truss design question

why a truss ? why not a simple plywood web (between the two chords) ?
why PVC piping ? unless it is readily available and cheap ? why not wood stringers, maybe cover with a PVC layer for reduced friction

what's the cheapest and nastiest way to "git her dun". No one is paying you to do this, the cost is if it breaks and effs up some sheeting.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RE: general truss design question

I agree ...

I actually got up thinking about this (again ... and again ...)

I was thinking I have some left over 2 x 4's that are 16 ft long.

Maybe split them into 2 x 2's and the webs into 1 x 2's

Or even use some left over osb split into 2" strips for the web pieces.

I don't want a solid web just because of weight.

I used 21 ft TIJ's (wood I generic name I think) for the floor trusses. I moved them by hand and got them up but I could not imagine moving 4 of them at once (two on each side to make a 40 ft slide).

I even thought a ladder would work ... but I can's find anyone with a 40 ft one ... and I don't want to spend $1000 on one for one use.

I keep thinking "cheap and easy to build"

Even if I make it out of wood or OSB or ??? ... same question, what is the best layout for the web.

Thanks ...

RE: general truss design question

"same question, what is the best layout for the web." I don't think it's worth worrying about. your configurations (except for #2) are pretty equivalent. Do something that'll get the job done. If you plan to reuse this, then maybe take some care over it; if it's a one-off, then quick and cheap.

you say each piece of sheeting is very flexible ... what if you just clamp some sheets together ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RE: general truss design question

They really should not touch each other ... they are painted and will be scratched. They come packed face to face so only the raised seams will touch the panel and that part has a plastic cover.

Even if I took up a few, I would have to man handle them on the roof to spread them out.

They shop them on edge ... 30 to a crate ... and even then tell you to use a spreader bar to lift them.

Here is a good short video on my facebock page. I think this was the second load I got (first came in all damaged) .... it show how they are shipped and what they look like.

One set is being held by a small spreader bar and lift I rigged up just to pull a few and check them.


RE: general truss design question

Tough problem. Maybe make a few friends.

RE: general truss design question

Interesting ....

I actually have a vacuum pump.

My panels are flat so no issues with a suction cup sticking.

The problem is I still would need to get them over to the center of the roof. My man lift will only go over a few feet.

Moving the slide along gets them lined up where they need to go.

I wish I had a crew (friends) but even then, you need to get these up 18 ft without bending them. You would need staging and have people at different levels.


RE: general truss design question

The problem is I still would need to get them over to the center of the roof. My man lift will only go over a few feet.
Zip line / pulleys, use the man lift to do the work.

RE: general truss design question

I am going to let the man lift do the work ... it will lift the end of the cart up to the roof. With one end still on the ground, I can slide them right up onto the roof.

The original question was, what is the best way to make the slide/cart.

I am thinking two flat trusses like floor trusses.

I am trying to figure out the best way to arrange the web design to make it as strong as possible.

Thanks ....

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