Through Truss Sway Bracing

=>My question is should the deck have any diagonal bracing? My town has =>several bridges, but they're all tall deck type steel trestles. None of =>these have diagonals parallel to the ground plane.

Older deck type grider bridges did have sway bracing tieing the two girder together. They also had vertical sway bracing. Through trusses should have swaybracing tieing the cross beams together, and the longitudinal stringers that supported the track were usually placed above these cross beams. Depends in part on how deep those cross beams were. There's also sway bracing at the top tieing the two trusses together, with cross beams (ties) as well. The purpose of all this was/is to prevent twisting of the bridge, expecially in double rack designs, which experience off-center loading when only one train rolls across them. Modern bridges tend to have less bracing, partly because calculation of loads is better, partly because modern steel is stronger, and partly because they are welded rather than riveted.

If you google "truss bridge design" you will get more hits than you can look at in a reasonable time. Warning: bridge design can become a hobby in itself. :-)

Wolf Kirchmeir ................................. If you didn't want to go to Chicago, why did you get on this train? (Garrison Keillor)

Short answer: yes.

The stringers (beams parallel to the rails) may be braced together with diagonal angles from top flange to top flange, or "X" angles flange to flange.

Then there will be longitudinal bracing from the panel points in "X"'s beneath the floor system. These might be rods in older trusses; newer trusses use angles, or "T" sections.

The reason for this bracing is to transfer wind loads and locomotive nosing forces to the bridge seats.

C.H. "Chas" Hague, PE SE