Anchored Structure Analysis

[wderrick]

Hello Fellow Engineers,

I'm getting log jammed by the safety department on a project and I'm hoping someone can help me do analysis to prove the project is safe (or, in fact dangerous )

Imagine your typical structural base. In this case it is a two legged structure made of steel tubing. The two legs are tied together with cross beams. each base consists of a welded on base plate anchor bolted into the ground, and gusseted on the two sides perpendicular to that of the tied legs. If I know everything about this structures dimensions, center of mass, material seletion ect.... what are the propper steps to determining how much side load these legs can withstand before we got ourselves a safety hazard.


I really do not know where to start... typically I would try to isolate a component and treat it as a cantilever ... but with two anchored GUSSETED tubes TIED together... it makes the structure more complex...

Help!!!

thankyou to anyone who responds!

PS... I decided to give your imaginations a break and attach a picture of the structureRH Queue Table.PDF

[PinkertonD]

I hate to say it but that is a pretty common structure approach, and the basic calculations are also straightforward.

You need to be more specific with the Load. Is it a point load at the top? Distributed load all down one edge or something else?

What are the legs supporting? A load? Any twisting component?

If this is a safety concern issue, and I mean you no disrespect, but it sounds like you are out of your depth a little. Given that safety seems to be the main concern then you should (must) get a Structural Engineer to do the calculations. Using results from the faceless Internet folk, (myself included) is a nuts idea when thirty people lay dead under a failed structure.

[wderrick]

I agree of course. Obliviously this is a verry common structural approach. Which is why I was hoping someone might be like oh sure I can get you started on a good approach for estimating that...

honestly I am more/less just curious to hear what people say and learn whatever I can. This is an inhouse structure for manufacturing... It will be much cheaper to just make this thing beafffffy as heck than get a structural engineer to look at it. I appreciate your caution though.

The Load is located on that horizontal tube. It will be distributed evenly all along that tube. This structure is located right next to a fork path (a verrryyy low-traffic path). hence the safety concern

[PinkertonD]

This structure is located right next to a fork path (a verrryyy low-traffic path). hence the safety concern

OK, well that in itself is enough for me. And - "beefy" means nothing in the Engineering world. It would be very dangerous to assume it would be strong enough to withstand a forklift hit. It only takes one hit and it may be years (or days = "ooops - that wasn't here yesterday") before that happens, but happen it will. It will be irresponsible to hope it was strong enough.

It is not "caution," it IS Engineering experience. I spent five years of my working life in Failure Analysis and you would be terrified to see what did fail from what people thought could never fail. Ever hear of the unsinkable Titanic?

I shall pass on any further comment other than to say, "Structural Engineer."

Please show these replies to your "I'm getting log jammed by the safety department," I am impressed with their wisdom.

[wderrick]

I am here simply for mathematical engineering advice. If anyone would be gracious enought to give advice on this I would be more than grateful. I do know basic structural analysis. and would be treating the analysis as a sort of cantilever like this http://www.engineersedge.com/beam_be...m_bending9.htm ... where Im stuck is the fact that the two legs are tied together... and the shape of the cross section at base of gussets... it makes finding section properties tricky! I plan on analyzing the location directly above the gussets, at the base of the gussets, and also analyzing the anchor bolts.

[jboggs]

If I were you I would analyze it as if the additional strengthening structure wasn't there at all. That way you know you can trust your answer. And I'll also say this, if fork truck impacts are your concern, you need additional protection. The most successful method I have seen consists of round pipes anchored in epoxy in cored holes in the concrete.

[Cake of Doom]

If I were you I would analyze it as if the additional strengthening structure wasn't there at all. That way you know you can trust your answer. And I'll also say this, if fork truck impacts are your concern, you need additional protection. The most successful method I have seen consists of round pipes anchored in epoxy in cored holes in the concrete.

Emphasis mine. You can throw all the gear in the world at it but a frame is still a frame and should be treated as such. The factors of safety should be enough to 'beef' it up; if you're not happy, increase the factors. 'Eyeing in' sections before you have justified them can lead to all sorts of troubles, especially when it's a type of work you are not used to.

As for the protection from impact issue, I'm with the other folks. This is where you need an experienced Engineer to get involved.

[RWOLFEJR]

I second that... error to the safe side.
Also could consider a curb to protect this if it could apply...?

The other thing that you need to look hard at is your anchors. I would imagine that could potentially be your weakest link anyway. Won't matter what your tube will handle if you're not tied down well or anchored in mush.

[wderrick]

The most successful method I have seen consists of round pipes anchored in epoxy in cored holes in the concrete.

these steel tubes are welded to the structure? or do you lay the tubes into the ground tapped and then screw into them?


I didn't really mean to focus on the fork lift... especially not on a momentum impact. The path will be curbed to protect that to the best it can... there are some things that you just cant design for... Although I do find it almost strange that it is a subject of such uncertainty. Almost any plant manager safety manager ect. will tell you that the most dangerous aspect of their plant is the forklifts running around, and yet, there seams to be such a widespread fear of how to design for structural certainty against such a common safety concern? I feel that something like this should be common knowledge for anyone who calls themselves an engineer of any the degrees relating to structure (civil, structural, mechanical, and maybe manufacturing after all we are engineers arn't we? or has engineering stooped to the level of a few book smart individuals swimming in a sea of glorified managers? thoughts? anyone?

[Cake of Doom]

Have you ever seen an impact analysis from a heavy, loaded vehicle on a structural element? It's scary custard.

there are some things that you just cant design for

That's were professional judgement and experience take over.

I feel that something like this should be common knowledge for anyone who calls themselves an engineer of any the degrees relating to structure (civil, structural, mechanical, and maybe manufacturing after all we are engineers arn't we?

If all problems were as simple as they seemed, we'd all be out of a job.

[jboggs]

I'm with the other guys. You have two potential failure points here. One is the frame. The other is the anchors. By far the most common frame failure in industrial environments is in the anchors. I suggested round pipes anchored in the concrete, and you come back and ask if they are welded to the frame. No! By welding them to the frame you transfer the impact forces through the frame to the frame's anchors. The whole purpose was to absorb the force before it contacts the frame. And I'm not talking about bolt-type anchors. I'm talking core drilling a 10" hole into the concrete, placing an 8" pipe stand in it, and surrounding it with impact absorbing epoxy.

[RWOLFEJR]

We do like Mr. Boggs suggests at several spots but with an exception at our truck doorways. Where trucks back under our crane in the building we have about 6-1/2" or 7" sleeves about 3 feet in the ground to accept 6" tubes full of concrete. We do this slip fit to make it easier to replace them after their tagged. Happens too often at these spots and at about two and a half feet from the door opening the trucks usually stop before they ram them home... :(