Jib Crane Analysis

[joeHSE]

Checking my first jib crane setup. Single four-wheel trolley with a hoist rated for 1-ton. Should I apply tractive and side thrust forces along with the vertical load or are those forces (tractive and side thrust) more applicable to heavier bridge crane setups?

 

[BAretired]

I don't think so, but you should consider an impact factor of 1.1 to 1.2.

BA

 

[DaveAtkins]

Did the jib crane manufacturer give you design loads?

DaveAtkins

 

[ToadJones]

should have no tractive or side thrust on jib. You can have a horizontal load factor from picking off center from the centerline of the jib arm.
You'll have hoist load and dead load factors. The design is similar to a monorail. You'll also have local flange checks for the wheels on the trolley riding on the beam flanges.
Be aware also that CMAA does not cover patented track systems which are usually proprietary and cover in ANSI MH27.1.
Jibs can be kind of a gray area....CMAA to my knowledge does not cover jibs in CMAA No. 74, which is for under running trolley hoists, but many of the design requirements will be similar.

 

[JAE]

If the manual hoist is pulled along toward the end of the jib, you could get longitudinal impact thrust when the hoist hits the end stop.

 

[joeHSE]

I figured as the load was moved along the length of the rail or began swinging perpendicular to the rail then tractive and/or thrust forces would be generated (albeit small ones).

BA: got the impact factors.

Dave: Nope. I was given the configuration, trolley and hoist dimensions specs and ratings...no forces.

Toad: Flanges checked out.

JAE: I'll check that.

Attached is an ISO. Trolley rides on the bootm flange of the top beam(W8x21). Col is W12x65. Bottom beam (W12x65) mounts to a frame with a four bolt pattern in the two locations you can sort of see there. As I add side thrust the column and bottom beam will be in torsion. W-shapes usually don't do well with torsion.
And the bloody thing is already built...hence my questioning the need to apply side thrust.

 

[DaveAtkins]

Bridge cranes cause side thrust because the rails can be slightly out of alignment, and as a result, the wheels push the rails sideways.

But a monorail hoist does not cause side thrust because it does not span between two rails.

DaveAtkins

 

[ToadJones]

Side thrust can also be the result of simply accelerating and braking the trolley on a bridge crane; especially with a heavy load....just another reason that monorails dont have this problem

 

[MikeHalloran]

Jib cranes constructed like that are usually hinged to a wall.
The unspecified 'frame' under the mounting bolts seems a potential problem, whether the frame supports a platform, or comprises in part a vehicle.

One could conjecture, e.g., lifting a load that didn't happen to be in the structure's strongest plane, by the simple expedient of pulling the hoist chain over to the load, and engaging the hoist.
... which in turn could apply a substantial out of plane load, and a torque to the column, which would not be relieved until the load left the ground.



Mike Halloran
Pembroke Pines, FL, USA

 

[weab]

Like Toad says CMAA74 does not specifically cover jibs. It covers "under running trolley hoists". By your sketch, I would say that it does apply in this case. It specifies all the factors that you need. It's a very good reference, and I'd use it.