40T Bridge Crane

[SteelPE]

I have been approached to submit a proposal for the design of a building with a 40 ton bridge crane. I have designed a few buildings with bridge cranes before but nothing of this size (stopping at about 15 tons). The things I know will be needed:

-Crane will be on a separate column system that will be tied back to the main building columns (no brackets)
-Separate column system will have bracing parallel to the runway girders. Bracing will be in plane with the runway girders.
-I have preliminary loads from the Whiting Crane Handbook (should be good enough to get use going)

The building is going to have a system of concentric braced frames for the LFRS. My question is in relation to the diaphragm. We usually allow for the roof diaphragm to distribute the lateral loads from the crane to the building’s LFRS. However, above 5 tons we begin to introduce a system of horizontal bracing to distribute these loads. Is this type of system (a horizontal truss to distribute the lateral loads) still recommended for a crane of this size?

My old mentor designed a building similar to this one 20 years ago. We are trying to go through his archive to see if we can dig out his old plans. I also have yet to dig out the AISC DG 7 which might cover what I am asking. Just trying to get opinions of others in the community.

 

[JedClampett]

I've done 20 ton bridges, but it was with a PEMB. Lother's "Design in Structural Steel" uses horizontal bracing like you said. I guess I'd trust that more than a bunch of puddle welds or button punches for real lateral loads.

 

[SteelPE]

Jed, not really even considering using the deck. Just want to make sure I am not suppose to be doing something else (say moment frames at every crane line). If I do, I need to make sure I capture that in my proposal.

 

[canwesteng]

In my experience bracing would be preferred to some system of moment frames. Otherwise what you are proposing sounds correct to me.

 

[DaveAtkins]

For 20 ton and larger bridge cranes, I recommend a moment frame at every grid line, perpendicular to the direction of crane travel, and braced frames for the crane AND the building, parallel to the direction of travel.

Then, you could use the steel deck as a diaphragm, and eliminate the roof bracing. Or include the roof bracing if you don't like using the deck.

DaveAtkins

 

[mtu1972]

Agree with DaveAtkins. Did several buildings with heavy cranes in paper mills. Rigid frames with stepped columns perpendicular to crane runway and braced frames parallel. Also always used roof bracing. There are good references in ASCE Design Guide 7.

gjc

 

[FLCraneBuilder]

Agree with replies & general direction offered
Suggest clear definition of this in plans & specs to:

building designer/provider
foundation designer /provider
runway system designer/provider

The building to withstand the crane's lateral loads
The runway system to include longitudinal bracing that will transfer the longitudinal loads to the foundation
The foundations to be designed to resist these loads

Notes of caution.
1) Whiting loads may be a bit high depending on type of 40 ton crane. there are 40 ton cranes out there that weigh 1/2 of what whiting cranes weighed back in the day
Then again , if this was say a Class E recycling crane, Whiting loads will be low. I've seen 15 ton trolleys that weigh 2000 lbs and I've seen them weigh 40,000 lbs. The building design process should include a step where actual crane loads are implemented into the design.
2) I feel that these larger capacity cranes should include end of travel limit switches that will all but eliminate the horizontal forces (unless switch fails or there is a power outage under full load at full speed. This does not eliminate the need to design for these forces - it just reduces the likelihood
3) On one of the projects we built, there were 4 - 50 ton cranes in a somewhat common PEMB. we designed & built runways based on the four cranes bumper to bumper. The building designer neglected to consider all 4 cranes and there was a lot of reinforcement added after shipping the building. In essence, our longitudinal bracing was designed for 200 ton crane capacity

 

[thaidavid40]

I suggest that you also work through the recommendations found in AIST-TR13. It can be a world of help with mill buildings which have heavy cranes.
Dave

Thaidavid