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Cross Frame Fatigue Check in MDX

Cross Frame Fatigue Check in MDX

Cross Frame Fatigue Check in MDX

I am designing a skewed plate girder bridge with continuous cross frames (not staggered) in MDX using a the Plate & Eccentric Beam System Analysis. I am working on the design of the intermediate K shape cross frames and the sizes of the angle members are getting pretty big, L5x5x3/4, due to the check for fatigue stress. I turned off the fatigue check and changed the member sizes to L4x4x1/2 and they are good for strength.

I think the problem is is the fatigue category for the gusset plate to angle member weld. I selected Category E because the thickness of the connected members is less than 1 inch. I know there are a lot of bridges out there with cross frames composed of members much smaller than 5x5 angles that don't have a bunch of cracked welds. Has anyone else ran into a similar problem? I am contemplating ignoring fatigue for the intermediate cross frames.

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