Construction lift crane operating wind speed

[WARose]

I have a heavy lift crane that will be operating on a project of mine. I have been asked to look at it to determine a safe operating wind speed. (The manufacturer refuses to provide it and OSHA regs do not (as far as I can tell) dictate it either unless you are lifting personnel. I am not lifting any people.....just load.)

Aside from my calculations on stability......does anyone know of a limiting reg by any government organization? Thanks.

 

[KootK]

Yuck. I'm not sure I'd be willing to take responsibility for this as I think that it's manufacturer specific. But life must go on.

This is nothing more than the result of some random Googling hoping to help a friend in need: Link. Perhaps it can be a useful benchmark.

 

[CANPRO]

Weird the crane manufacturer wouldn’t provide that number, they must know what the limiting wind speed is for their cranes.

Do you have the crane specifications? Checking the stability of the crane manually is a good check, but not that accurate unless you’re given the centre of gravity for the entire crane...lots of moving parts and it’s hard to nail that down with any precision.

When I haven’t been able to get all the info I need from the crane specs, I move on to the code to which it was certified, which should be stated in the specs. ASME B30.5 might be a good start if you have nothing else to go on.

As a general reference, “Cranes and Derricks” by Howard Shapiro is a great book.

 

[WARose]

Thanks everyone. 30 mph is what I have been checking it for (good find Kootk). That's a number I've heard a lot over the years but I didn't want to throw the number out there and have anyone's reply influenced by it.

I'm probably going to wind up specifying that as a max. on the drawings.

 

[JStephen]

Wouldn't a major part of the wind load on the crane be from wind load on the suspended load? I'm thinking of something like the Big Blue failure. And in that case, I can see why the manufacturer couldn't specify a wind speed. But, in that case, they need to specify a maximum lateral load or something of the sort. And probably, yes, a maximum wind speed to have the boom up.

 

[WillPESE]

Not sure why you are willing to take liability for that. The crane manufacturer must provide it. If not, just seek another manufacturer.

 

[CANPRO]

How much control do you have over this lift plan? I’ve done this type of work before and there is a lot to consider and a lot that can go wrong. Things like boom configuration (multiple ways of getting same boom length for a telescoping boom) can have a major impact on stability. I’m sure you’re already on top of this, but I would be extremely specific about the items considered in your limiting wind speed.

 

[WARose]

How much control do you have over this lift plan?

Basically to be sure they don't wreck my slab that they are running on. I'm not responsible to keep the thing upright (and I had better be clear on this point on the drawings).......I just need to be sure they aren't going to go for a ride because of my support.

So I'm going to have to put a lot of criteria on the drawings.

 

[GC_Hopi]

DOT usually have recommended construction wind speeds e.g. for FDOT they are construction active wind speed is 30 mph and construction inactive wind speed is 90 mph.

 

[racookpe1978]

No. I disagree with the "reason" for those limits.

See, you're looking at the "extra load" on the slab at the four support legs, caused by wind pressure on the crane, the boom, the load, and the rigging cables.

A crane company will be limiting its wind loads based on the extra load on its crane structure and boom and lines caused by unknown loads of unknown shapes and unknown wind load factors (drag coefficients) at unknown angles to the wind with unknown gusts.

The actual limit is the movement of the load as it is picked up and put down: The riggers CANNOT safely move a load if they cannot control its motion (twisting, going side-by-side, swaying, etc.) The crane should have a wind anemometer on its tip. Our company's standard rigging limit is 25 mph - but ANY rigger or field engineer can and must stop the lift if the load threatens to become unmanageable. (If you need more than one rigger on a tagline, the wind is too fast to lift that load.) Which are independent of crane boom heights.

 

[CANPRO]

Agree with racookpe that the crane operator and riggers have ultimate responsibility when it comes to crane stability. You can a plan a lift to death, but site conditions vary and they have to make the final call on the ground.

So you’re determining the limiting wind speed that your slab can handle, not necessarily the crane? If that’s the case, I wouldn’t base this on a limiting wind speed, I would base it on either track pressure or outrigger loads that have been supplied by the crane company (or maybe work backwards and set the reaction limits). That’s run on the mill type info - if they can’t give you a ground pressure/outrigger load based on the lift, then they aren’t qualified to do this kind of work.

I think you’re stepping into a very grey area by setting a limiting wind speed for your slab. Too many variables out of your control that effect the reactions on your slab.

 

[WARose]

I think you’re stepping into a very grey area by setting a limiting wind speed for your slab. Too many variables out of your control that effect the reactions on your slab.

Trust me: the wind speed is not my highest priority. There are a lot of other scenarios that are far more concerning (at least as long as the wind speeds are relatively low).

 

[CANPRO]

Fair enough, I understand the wind speed is probably minor in the grand scheme of things...my bigger point is that if you’re only concerned about the slab supporting the crane, I’d give them a limiting reaction between the crane and the slab and let them (contractor/crane supplier) be responsible for respecting that limit. Anything beyond that and it sounds like you’re taking responsibility for things you can’t control.

 

[WARose]

Agreed, but first I have to be sure that the likely reactions will work on that thing. (Short of them having a race or flipping one.) I'm good at CYA notes.

 

[CANPRO]

Gotta love a well written CYA note...I feel like this should have been a core course in university. I can picture this drawing being 90% CYA notes and 10% title block. Good luck!

 

[JStructsteel]

I would say the best CYA in the world wont protect you 100% if something happens, and your name is on or around 'wind calcs on a crane to check a slab'

 

[WinelandV]

WARose,

What kind of crane are you dealing with? (tread/crawler, large truck, etc)

Is it actually the manufacturer who is refusijng to give the max wind speed for operation, or is a middle man who is renting the crane out?

For a heavy lift (say, 100 tons at 60ish feet, more weight at less distance), even if you're technically w/in whatever the wind operating range is, it may be almost impossible to set the load in the correct spot. When I was doing heavy lift plans, we never worried about wind for max tread pressure on the crane mat, as any semi-significant wind would cancel the lift.

As far as your situation, I would go back to the manufacturer and ask for their max pressure (or point load, if it's an outrigger style), and design some kind of strengthening for your slab (shores, additional steel/wood mats to span to hard points, etc.).

 

[WARose]

What kind of crane are you dealing with? (tread/crawler, large truck, etc)

crawler

Is it actually the manufacturer who is refusijng to give the max wind speed for operation,....

The manufacturer.

When I was doing heavy lift plans, we never worried about wind for max tread pressure on the crane mat, as any semi-significant wind would cancel the lift.

Seems to me like it would add to it (if it hit in the right direction). But it really isn't that big of a deal (by my calcs). Just wanted to be complete here.

 

[CANPRO]

WARose, I was thinking about this more last night (damn you eng-tips for keeping me up!!) - not knowing your familiarity with crane loads and reactions I wanted to mention a couple other things. Your max contact pressure may not be a result of your final lift, it could be during offloading the load from transport, or if swinging the load in place you could swing past your critical angle (for crawler cranes, likely as you swing past the toes of the tracks). Another condition to consider is the no-load/full-counterweight condition with the boom all the way in (this condition can actually cause some cranes to tip over backwards).

 

[racookpe1978]

Seems to me like it would add to it (if it hit in the right direction). But it really isn't that big of a deal (by my calcs).

No. The opposite. The lift will be cancelled entirely (NO load on the hook!) BECAUSE the wind is too high (above 20-25 mph) to control the load safely in midair, and to place the load accurately when it is coming down.