Lateral Bracing for Crane Beam 1

[Watermelon]

When providing lateral bracing for a crane beam (under-riding hoist), which is best?

1. a channel welded to the compression (top) flange with legs down, or

2. horizontal bracing at appropriate points.

 

[RockEngineer]

Part of the answer depends on what type of crane you are talking about, monorail or bridge crane with underrunning hoist.

On bridge cranes for the runway girder and the bridge girder there are usually very few places to tie to so a channel is welded to the top of the beam. This does two things. For the runway girder the common practice is to take out all the horizontal loads in the top flange rather than go through all the calculations for torsion applying the load at the top of the rail. For more information see Engineering Journal Second Quarter 1998, "Design of Crane Runway Beam with Channel Cap" and Engineering Journal 4th Quarter 1982 "Tips for Avoiding Crane Runway Problems". A good design reference for runway girders is AISC Design Guide 7 "Industrial Buildings". Part 2 of Design Guide 7 is Industrial Buildings With Cranes and gives lots of good information and design requirements for the runway girders and building.

On the bridge girder there are several trains of thought. One is to do a single beam with or without a channel cap. Adding the channel cap can often give you a lighter beam because of reduced allowables in a plain S or WF section due to the compression flange buckling. Weight can be critical. A single beam is easy construction but can have some problems in the connection of the beam to the end trucks to prevent skeewing.

The other thought is to have your main beam without a cap designed to support all your hoist loads and have a second light weight follower beam with a lattice work connecting the top flange of the main beam to the follower beam. Having two beams gives a more rigid connection to the end trucks and prevents skewing. The draw back is more weight and more labor in putting the lattice between the two girders. Which item you choose depends on money, weight restrictions, speed and capacity of your crane.

If you are talking about a monorail, I have not seen monorails built with channel caps. The monorails are usually designed to be supported at the required brace points. For monorail design see the previous thread from today on monorail design.