Truss style Gantry

[D.C.]

As I understand it a truss works efficently because as force is transmitted through it one part is in compression and another in tension which leads to a stable shape. A triangle is a stable shape but a square isn't. When you diagonally brace a square you are in effect creating two triangles that form a compound truss which is why diagonal bracing works so effectively.

In the arrangement I posted, the struts should be able to cope with forces in any direction encountered by a cnc machine a lot more effectively than a design based on one or two beams that are fixed to a thick plate either end, or so I thought.

I've just had a quick look around the web for stage collapses and I can't find any where the investigation blamed a failure of the truss system for the accident, do you have any links to demonstrate what you mean?

For example if you read

Indiana State Fair stage collapse - Wikipedia, the free encyclopedia

The failure ... was due to the inadequate capacity of the lateral load resisting system, which was comprised of guy lines connected to concrete "Jersey barrier" ballast. The concrete barriers used as anchors for the guy lines were not fixed in place; they resisted loading only by friction with the ground and through their own weight—about 4,200 pounds (1,900 kg).^[6] Just before the collapse, wind loading caused several of the barriers to slide or pivot from their original positions, allowing the top of the truss structure to lean toward the crowd. The subsequent bending forces within the support columns were too large, and the structure collapsed under its own weight.^[6] Measurements indicated that the total weight was 70,000 pounds (32,000 kg).

[Musht]

I can't find any where the investigation blamed a failure of the truss system for the accident, do you have any links to demonstrate what you mean?

****The subsequent bending forces within the support columns were too large, ****and the structure collapsed under its own weight.^[6] Measurements indicated that the total weight was 70,000 pounds (32,000 kg).

Toronto the week before, there has been a few others.

The legs on self raising stage roof systems are truss on end, even with thin wall its very strong in compression, but tilted off axis , its a thin tube getting bent.

The saving is in weight, early lighting truss was steel antenna tri truss, its a lot of weight to manhandle and to hoist.

Mebbe 2D truss shape , as used by Steeldeck staging

Middlesex University steeldeck 8x4 by Rory - 3D Warehouse

again its used to reduce weight for a given strength, if weight is less of a concern apart from moving the mass of the gantry and possibly damping resonance?

[D.C.]

Toronto the week before, there has been a few others.

If you look at pictures of the Toronto collapse it is very clearly a scaffold structure that has collapsed and no report has been released so far, let alone one claiming truss beam failure. Just because stages collapse and truss systems are often to hang lights above a stage doesn't mean that all truss designs are fundamentaly flawed.

Anyway, given that the thread is about a cnc gantry built from multiple 4mm thick pieces of steel box section I doubt very much that any force is going to be generated that will come close to causing structural failure, death and destruction just so long as an invading column of tanks don't decide to take a short cut through my garage. :)

I was more interested in a comparison with the usual designs of gantry, like for example a couple pieces of alu extrusion bolted together or the unsupported L shape, bolted to plate supports at either end.

[Musht]

If you look at pictures of the Toronto collapse it is very clearly a scaffold structure that has collapsed and no report has been released so far, let alone one claiming truss beam failure. Just because stages collapse and truss systems are often to hang lights above a stage doesn't mean that all truss designs are fundamentaly flawed.

Sorry , where did you draw that i said all truss designs are fundamentally flawed?

As said not a rigger, not playing one on T.V. not playing one on the internet, haven`t said anything about the inherent safety or otherwise of trussing, of which many miles are hung above peoples heads very safely every day and night of the week.

Eaxmple of stage collapses, of which there has been multiple incidents in last 5 years, was used as an example of how aluminium truss or indeed steel tubular scaffolding will NOT:

"deal well with forces in all sorts of directions"

It is immensley strong for it`s weight but will fold up like a wet newspaper if forces are applied in the wrong direction.

Sorry you couldn`t read to end of the post before having to reply

" cnc gantry built from multiple 4mm thick pieces of steel box section"

a link was provided to a 3d model of a staging system that uses steel box section with triangulated reinforcement, more similar to your requirement than 3D alloy truss.

"comparison with the usual designs of gantry"

Cause you missed it last time:

"weight is less of a concern apart from moving the mass of the gantry and possibly damping resonance?"

Not questions can answer afraid.