Bridge Diaphragms

[PhredCutter]

Designing skewed, steel bridges using MDX. The diaphragm connection loads seem absurdly high. MDX assumes the diaphragm connection to the girder is fully fixed. So, as loads travel transverse to the bridge, the diaphragms transfer the loads. The LRFD version of AASHTO requires this for cases where the diaphragms are primary members: curved, severe skew, ect. I understand that I can remove or reduce the section properties of the diaphragms, but this would effectively remove the ability of the diaphrams to transfer loads. Does anyone else have methods to design the primary member diaphragms?

 

[graybeach]

This is a good question. I ran into this designing diaphragms for a highly skewed curved girder bridge. In my case, the diaphragms were needed to transfer seismic loads to the piers, but their presence caused a shorter load path for the vertical loads resultants in, as you say, absurdly high forces in the diaphragm members.

I took the brute force option and designed the diaphragms for the calculated loads. In hindsight, I wish I would have tried to stagger the diaphragms.