Trestle bent question

[jim81147]

In the real world , how would the railroad handle this situation? On the trestle I am building now , I have all the full length bents done and now I am getting ready to do the ones that go up and down the incline . Lets say that my cross ties on the bents are 10 feet apart but with the incline/decline the position of the next bent would require the bottom cross brace at 6 feet instead of 10 to sit firmly on the foundation ( I am doing this one on a foundation of some sort ) would the railroad build a bent that was custom fit to the terrain or would they build the foundation up to keep all the cross braces even and symmetrical ? I hope I explained that clearly .

 

[RBMNfan]

I believe they tried to keep the cross braces horizontal. Every old picture seems to have level track. They placed a beam flat on top of the rock or concrete and the bents sit on that. That beam is usually the lowest part of the trestle visible. The base is unseen.
I hope I answered your question.

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[OldGuyHO]

How modelers usually do it is build the bridge and then build the canyon to fit it.

 

[D&J RailRoad]

Go to this link then scroll down to post 668. That is the start of how I installed a trestle on a section of my layout.

http://www.modelrailroadforums.com/...4509-The-D-amp-J-Railroad-From-Scratch/page17

 

[Red Oak & Western]

This may help -

 

[Lynnb]

How modelers usually do it is build the bridge and then build the canyon to fit it.

This was the point I was too late to make in your layout topic.

 

[jim81147]

Not to late Lynn , this part of the canyon is yet to be built .

Thanks guys for the input . Kevin , your pictures are worth a thousand words !!

 

[Selector]

The trestle designers knew the elevation or the sub-roadbed and they knew the ties on the stringers atop the caps would have to meet the rail tops on groomed and ballasted tracks on either end of the bridge deck. From there, it was all about specs. What was the length of the bent sections before a cap was to be placed across it? They worked down from the stringers to that first level, with cross-bracing and girts factored in for strength, and then they added another layer of bents below the first where they could. If the terrain didn't permit a full second layer, they would build what they needed in the way of mud sills and then placed bents of an appropriate length above them. Cross-bracing and sway-bracing wasn't strictly even, but it was the desired practice 99% of the time. I have seen, and constructed, scale trestles where the sway-bracing was simply cut to fit the length between bents.

 

[cv_acr]

Keep in mind that unless the trestle is only like 10' tall and using pile bents, there are horizontal and diagonal side and internal bracing tying the bents together, as in the diagram posted above.

So the cross-braces on the bents will tend to be at a more or less fixed height (measured *down* from the top) along the length of the bridge, and the length extended downwards as required. If your brace is 10' from the top, then the bridge will grow until it's over 20' tall and establish the level of the next fixed brace, and then continue downwards again. The image really does the best job of explaining this.