Jib crane on post in pre-eng building

[canwesteng]

I'm looking at tossing a jib crane on an HSS post in a pre eng building. The post is unconventionally beefy for a pre eng building, and additionally there's been an addition built onto the long end of the building, essentially reducing my wind load in one direction, so I'm not concerned about the barcing capacity. What I am concerned about is getting the kick into the roof bracing - probably not prudent to rely on the torsional bracing to the purlins for this is it?

This can't be too clear, but a sketch is worth a million words.

 

[spieng89]

Are the roof members cold form purlins? If so it may be tough to use the roof framing for bracing in the orthogonal direction of the roof beams you are showing framing into the column. May need to add new beams in that direction.

Another item to watch for is deflections. Are you positive the jib crane will be a one arm member or will it have a stabilizing beam and two connections back to supporting column. Many manufacturers limit differential deflections between connections to 1/16"

 

[canwesteng]

The client wants a one arm jib. Capacity will only be ~500 or 1000 pounds, and the post is 6x6, so I can't imagine the deflection of the post is going to control.

 

[DrZoidberWoop]

Most of your decision making is going to be based on what you intend to do with the crane. If you have to be OSHA compliant and it's going to be making many heavy lifts by various employees, you're going to have to put in much more effort than if it's for your home workshop or something.

The load is going to distribute itself into the stiffest elements. I don't know your structure at all, but I'd hesitate to attribute significant point loads to a roof purlin.

 

[canwesteng]

It's for a client's shop. OSHA doesn't apply here but obviously I need to design something structurally sound, regardless of application.

 

[Ron247]

If this is PEMB with cold-formed roof purlins, I do not see how you can use the lower flange braces that are connected to the purlins for load transfer. That is not what they are designed for. You loading appears to be out of plane with the frame. Also, I do not know the dimensions of your project but I would not consider a 6x6 to be "unconventionally beefy". PEMBs rarely supply "extra beef" unless the Client pays for it for some reason.

One way or another, you are torquing the PEMB frame.

 

[canwesteng]

30'x100' bays. Hard to see how this post is loaded up to capacity from gravity loads, and hard to imagine it is stiff enough to attract wind loads.

 

[KootK]

I'm torn.

- load is pretty small.

- just doesn't sit right with me, especially for something with a dynamic load.

Best option I could think of below.

 

[MIStructE_IRE]

Can you do a completely independent vertical cantilever instead?

 

[dhengr]

Canwesteng:
You claim this is an extra beefy column, and that there was an addition put on the end of the bldg. In that case, it is likely a wind column which was part of the gable end framing, and it might already have some extra lateral load transferring abilities at the roof and the fl. slab. You might want to check that out. Otherwise, I generally agree with Koot’s take on the solution to the problem for lighter crane loads, if all else checks out.

 

[Ron247]

For 30' bays, the roof purlins are usually continuous over the frames. They tend to lap them about 2.0' to 2.5' on each side of the frame. Hard to make simple span ones work for 30' bays. Are the roof purlins actually joined at the frame?

Interior columns are usually designed as pin-pin in both directions although they most likely do not act fully pinned. If there is one set of stiffeners in the middle of the column, then it was probably pin-pin.

 

[canwesteng]

Kootk,

Not a bad idea, I was thinking of 30' beam from portal to portal with some bracing as a fall back but this is a little lighter.

dhengr,

There is not a solid load path for taking lateral load on this post. It would to be moment connected at the roof (unlikely), and it sits on a 2'x2' pile cap, the only lateral resisting system of the pile cap being bearing against a 4" slab on grade.

Ron,

Single stiffener above the post. Looks pin pin to me, with the connection designed to restrict rotation at the support to prevent buckling. Purlins are lapped.

 

[KootK]

Not a bad idea...

I'll just go ahead and assume that you meant to say "bloody brilliant idea...".

I was thinking of 30' beam from portal to portal with some bracing as a fall back but this is a little lighter.

Whatever this, it sounds like the way to go to me.

 

[CANPRO]

canwesteng, apologies for the somewhat incoherent sketch, but maybe something like this could work - install a new post adjacent to the existing to take the lateral loads direct to the slab/purlins. You could use the kootk channel across a few purlins and attach the post to it with vertical slots.