Skew steel bridge with no cross-beams

[TLycan]

I am Reviewing an Existing steel bridge. the Bridge is very skew, average Span = 40meters, main girder depth = 2.00meters and you can say NO cross-girders.

My questions are:
1-is there is any specs about the analysis/design of such bridge with No cross-beams
2-I run the normal grillage analysis and the girders were safe, but am I missing any other strains because of the "no X-girders issue"
3-if, we assume No lateral torsional buckling, No wind , No seismic, why do I need the cross-frames for?

thanks for your assistance in advance

 

[graybeach]

A composite concrete deck would act like crossframes. You have composite deck, right? Otherwise, how are the compression flanges supported? How did you model the deck? Do you see large forces in the deck due to differential deflection between adjacent girders? Does the existing deck show signs of distress?

How can you assume no lateral torsional buckling and no wind?

 

[TLycan]

Graybeach

Yes I have a Composite deck. I modeled the deck as a shell/plate element with a very weak properties in case of dead load, i.e. wet concrete and with the right properties in case of superimposed dead and live load.

What I mean by there is no lateral torsional buckling and no wind, is according to NSBA/AASHTO, the function of the cross frames is following:
1-prevent lateral torsional buckling
2-transfer wind/ lateral loading to support
3-reduce the differential deflection between different girders at the same location
4-reduce flange lateral bending and torsion in case of Skew/and curved bridges, knowing that part of the flange lateral bending or torsion that exist in the skew bridges result from the action of cross-frames trying to reduce differential deflection.

So if 1& 2 is some how prevented, are points 3 & 4 will make a problem to me.

Moreover, I don't remember seeing any skew bridge with No cross-frames and neither I remember that the AASHTO addressing the possibility of such situation

 

[graybeach]

Crossframes on a highly skewed bridge can actually be a hindrance because they provide a shorter path for forces to get to a bearing. Sometimes this results in lift off at the acute corners. I would think the girders were somehow braced while the deck was being poured. Once the deck cured, perhaps the bracing was removed by design.

I can't speak to whether they are absolutely required at your location if calculations show that they are not needed. Here in the states, the governing DOT would have an opinion. I have always found them necessary at the bearings to transfer seismic loads to the substructure.