Bridge Cranes & AISE Technical Report No. 13

[n8engr]

I am working on a project to upgrade an existing crane rail system to a higher capacity.

The question I have is regarding the Longitudinal or Tractive force load. AISE states it is equal to 20 percent of the maximum load on driving wheels. Let's say for example my tractive force load is 0.2*45k wheel load=9k. Is that 9k load applied at each wheel or distributed amongst them.

This existing crane has two trucks with two wheels on each truck for a total of four wheels on each side. Right now I am using the tractive force load = 9k per wheel or 36k per side. Should it only be 9k/4 wheels=2.25k per wheel?
Thanks for the help...

 

[Ltwine]

It is not necessary correct, but I used to use individual wheel load to calculate traction & thrust. Conservative, but safe.

Note most crane has one driving axile, but some has two. Check with your crane supplier and asking for specific design considerations.

 

[FLCraneBuilder]

We use AISC as our point of reference for this - Page 5-30 (9th edition) states that longitudinal load shall be not less than 10% of maximum wheel loads. Our interpretation of this is that means the SUM of the wheel loads.


For example, a 20 ton capacity crane with 2 wheel end trucks will impart the exact same acceleration & deceleration forces into the runway as a 4 wheel end truck (assuming the cranes weigh exactly the same)

Note that if a future crane is planned - one would add the forces of that crane into the total.


Note also, we use wheel load W/O impact.

I normally stay with the 10% unless there is a known variable that would increase it.
IE
The crane will be used in such a fashion that the operator will end up hitting the end stops repeatedly,
OR
In the case of an outdoor crane, wind load might increase longitudinal load (perhaps dramaticaly if a big crane.
OR
If its a very fast accelerating / Decelerating crane in a production environment, this could increase the forces. This is a rare occasion though, load swing on a standard hoist would be very problematic.

Most all cranes these days use VFD controlled motors which provides programable acceration & delceration rates. Hence, hitting the end stops might be the most important factor under "normal" circumstances. Or a power failure wich causes the brakes to Lock up and crane comes skidding to a stop.

BTW - does anyone know how to spell check these posts ?

 

[Ltwine]

Crane stop comes many forms, depends on type of crane involved. The critical one is bumper stop for bridge crane on elevalated runways. Not difficult to check, but difficult to achieve desirable stiffness without stiffen the runway beams/girders. It's a whole package - runway + stop, also need to know what type of bumper is on the crane that deliver the impact.

 

[CTW]

9 kips total. I guess it could be distributed among the wheels on each side, but it's generally taken as a total force on the runway.

 

[ToadJones]

I use table 3.2 for determining what percentage to use....say 20%.
Then, I use the max wheel load w/o impact to determine the tractive force.
I also take into account that the tractive force not ony adds a longitudinal force in the girder but also a moment as the tractive force is applied at the rail height.