[Joe McGarry]

I'm wondering if anyone knows of a protoype railroad bridge built on a grade. I'm sure no engineer, but it seems that the downslope bridge abutment would have to carry most of the load. I have a spot on a 2% grade that would be a good place for a bridge. Have not seen any examples on a real RR. Be glad for some feedback on this.

Thanks

Joe

 

[chuck n]

I think that it is quite common. I'm sure that most railroads built in mountains have bridges with grades. Several that come to mind are the Lobato trestle on the Cumbres and Toltec. That is a long grade up to the summit and I doubt very much that they would level it out for a bridge. The South Ramp of the Gottard in Switzerland has many bridges and pictures in books seem to show a slope to them. I also think that the cog railroad that connects the RhB and SBB at Andermatt, Switzerland has some bridges with relatively steep grades.


Chuck N

 

[Semper Vaporo]

Granted the drawing is quite exagerated, but to make the point...

Build your bridge as in "A" and yes, there will be a horizontal component that will cause it to slide toward the lower side and some sort of support will be needed to counteract that force.

Build your bridge as in "B" and NO, there is NO horiontal component, nor more weight on the lower pier than the higher one. There is NO sideways force if the bottom of the bridge at the support points is parallel to the Earths surface.

 

[Joe McGarry]

Question answered!! Thanks for the info guys.

Joe Mc

 

[neals645]

I'm no engineer but it seems to me that the above would be true for a stationary train but not for one in motion.

For a train going up the grade the loco drivers will apply force to the rails pushing the rail down the grade with a force equal to the force of the driver pulling the train up the grade. On the downhill trip the brakes, if used, will transfer some of the train's momentum to the rail and therefore to the bridge.

Not sure whether these forces are significant enough to require the downhill support to be stronger.

Neal

 

[CCSII]

Posted By neals645 on 09/29/2008 10:52 AM
I'm no engineer but it seems to me that the above would be true for a stationary train but not for one in motion.

For a train going up the grade the loco drivers will apply force to the rails pushing the rail down the grade with a force equal to the force of the driver pulling the train up the grade. On the downhill trip the brakes, if used, will transfer some of the train's momentum to the rail and therefore to the bridge.

Not sure whether these forces are significant enough to require the downhill support to be stronger.

Neal

Also true of a 0% grade with this change - a train going across the bridge will apply force to the rails pushing the rail across the supports with a force equal to the force of the driver pulling the train across the bridge but in the opposite diection.

 

[aceinspp]

Actually the rail never really moves on 0 grade unless under abnormal circumstances. That's why rails are anchored. Later RJD

 

[Semper Vaporo]

The rail would most definitely move if not anchored somehow. Spikes hold the rail to the ties, the ties IN the ballast and the ballast on the ground and gravity holds them together to create the friction that keeps the rail from moving.

Co-worker of mine, many years ago said he had run off the road the night before. He could not get the car to move so he wedged some plywood under the car to drive up on and get a better footing for getting out of the ditch. His wife was behind trying to push. The plywood shot out from under the back of the car and broke BOTH of her ankles!