|Jeff Lewis posted|
A gentlemen who works as an inspector for a Class 1 asked if I would post an image for him because he prefers anonymity.
Overhead canted truss out of Downtown Omaha, Ne.
It transverses the UP yard below. No date given.Andy Why: I would like to ask a structural engineer what's the purpose of a canted/skewed truss versus a more conventional design. Seems like you would create asymmetric loads on the girders.
Bob Mason: Andy Why that's kinda true. There's a sharp skew btwn the two track grades and you do see more skewed bridges when the track speed is lower. The loading is actually equal when you look at the two members individually. But looking at the truss as a whole you get a differential deflection. At higher speeds you see very few skewed bridges and almost no skewed trusses. The timing of the deflection between the two truss members(or girder) can impart a wobble to the higher rail cars. The right member will deflect down before the left member does which can accelerate the car sway. Newer bridges are much more rigid in some instances and deflection often less than an inch. But the preference is to not skew them.
|Dennis DeBruler commented on Andy's comment|
The skewed trusses allows them to be shorter because piers can easily be built among the UP+Missouri Pacific tracks.