Lifting Certification for Existing Structure

[murphy89]

Hi, I've read through some of the existing threads for lifting but don't see anything that I think applies to my situation.

I've been asked by a client to provide a lifting certification (he thinks that's what they need) for a small steel framed structure that houses a bunch of electrical equipment. The structure itself was not designed by an engineer and has tabs welded to the top of it to hook the crane to and has been lifted via these tabs in the past. The client says they are looking for whatever they need to make the crane operators comfortable to lift this thing.

My questions are:
1) Since the frame itself wasn't designed by an engineer, should I check all the members and connections of it? (fun twist, the framing is actually totally covered in and no longer visible. All we have is a hand sketch showing the framing sizes and overall dimensions)
2) I think that to achieve a full lifting certification the lifting components between the crane hook and the tabs welded to the structure need to be certified. Is that true? If that is the case then I will recommend that to the client but it would not be in our scope.
3) Do the tabs welded to the structure need to be load tested? I'm unclear on that requirement.

I imagine that my task will be to check the tabs and welds to the structure for the various failure modes and the deliverable will be a stamped letter stating that the welded tabs are able to support the full load of the structure with the required factor of safety. Is that what others would do?

Thanks for any guidance!

 

[milkshakelake]

I've done this kind of thing before.

1) Yes, you need to check all the members and connections of it. If your scope of work is only for lifting, then you have to make sure that you're not certifying the structure itself under normal dead and live load (i.e. normal structural design). You're certifying the structure under lifting conditions with no live load, and it has to be clear on your notes that there is to be no live load.

If all you have is a hand sketch, I'd be very wary. Anyway, you put your pinned supports at the top instead of the bottom. If there's a possibility that it's being shipped on a truck sideways, check that too. The ones I designed had full lateral design so I didn't check lateral swaying of the structure while being lifted, but that's something you need to check. It should at least have bracing or moment connections.

2) I certified the lifting tabs and their connection to the structure only. Not the crane hook itself or its attachments. That's out of your scope, unless you want to include that, but I'd leave it to a crane engineer. For me, it's too far outside my knowledge.

3) Not when I did it. If it passes calculations, it should work. Anyway, how would you test it? By lifting it up with a crane? They're doing the work at that point anyway.

I imagine that my task will be to check the tabs and welds to the structure for the various failure modes and the deliverable will be a stamped letter stating that the welded tabs are able to support the full load of the structure with the required factor of safety.

That depends on your scope of work. I generally certified the whole structure for lifting. If you simply don't have the resources to do that (like the welding/connection info behind the sheetrock, and more info beyond a hand sketch), then I'd only certify the tabs. But that might not be what the client wants.

 

[WinelandV]

1) Yes, you'll need to check the whole thing.

2) Whatever rigging is used should be certified by manufacturer (Crosby, etc), but your client's client/engineer may want a sealed rigging plan. Regardless, whatever rigging is used should also conform to the assumption that you're going to make for your analysis. Do all 4 slings go directly to the crane hook? A single spreader bar? 3 spreader bars?

3) I don't think they HAVE to be load tested, as they are a permanent part of the structure, and thus not under a "Below the Hook Lifting Device".

Please note that is a "v" (as in Violin) not a "y".

 

[SWComposites]

Is this a one time lift, or is it going to be lifted multiple times?
Where is it being lifted and what are the potential safety issues?
And why do they need a “certification”?

 

[murphy89]

Thanks! Your response is really helpful. I am just coming up with my scope now so I'm not stuck absolutely having to certify the whole structure, but I will see if the client can either a) take off what's covering it so I can get all the info I need for the structure itself or b) tell them that I can only certify the lifting tabs themselves as the rest of the structure isn't visible.

 

[LuK13]

A long time ago I used to do some lifting and shipping design work for modular plant equipment. They came in two flavors, skid mounted equipment (which sounds like your case here), and equipment that had temporary shipping and lifting steel that was bolted on and reusable for the next job.

You should look into ASME B30.20 and ASME BTH-1. We would only perform certifying load tests on the reusable shipping and lifting frames, but the skids are "below the hook" so we would check the skid frames and lifting lugs with the same factors of safety. We would produce a set of lifting and shipping drawings showing the center of gravity, how the lift/transport was supposed to be set up, and the design criteria used. Those drawings and/or a written lifting plan are probably what your client needs.

Key thing to keep in mind is how are they actually going to rig the lift. I ended up taking over a shipping frame that was designed assuming the best case lifting scenario, 3 spreader bars to keep the lifting cable at each lug vertical. It was discovered that the ports were in fact skipping the spreader bars and running 4 diagonal cables back to the hook, introducing a lot of axial force into the frames. After some conversations we determined that the best rigging we could hope for was one spreader bar, so I had to do some redesign to account for the axial force along the short dimension as we could only eliminate the axial force along the long dimension with better enforcement of our lifting plan.