Discontinuous Crane Runway Beam

[Althalus]

I've known for years that we don't design a bridge crane runway beam to be continuous over supports. But I can't seem to find any reference that says why. Anyone know of a good one?

 

[canwesteng]

If the columns settle or deflect they will stress the crane beam. True of any continuous beams, but in most cases we aren't running over them repeatedly with heavy suspended loads.

 

[Brad805]

I think another reason is the effect on the beam size when you add negative moments. You could end up needing a channel cap on both the top and bottom flange.

 

[Ron247]

Thermal expansion is another reason, that pesky PL/AE thing. Kind of plays havoc on bolts and column spacings.

 

[Ron247]

AISC Design guide 7 "allows but discourages continuous" I think. The number of computer iterations could be a nightmare especially if you have inconsistent bay spacings added with thermal added with different combos of loading (vertical & horizontal)

 

[HTURKAK]

But I can't seem to find any reference that says why. Anyone know of a good one?

There are two reasons;
- In case of differential settlement of the supports , the original design moment values in the section could be only wishful figures. ( as pointed out by Canwesteng,)
- to minimize the impact of dynamic loads . It is a recommended practice to use simply supported beams for supporting dynamic loads.