Question about bridges


O

Orange Irish

Member
Is there a difference in settings under which a Warren Truss or a plate girder bridge would be used? Are there specific settings that one would be used instead of the other? I have several of each and wonder if I could be more prototypical in where I use them...ie - over a river/lake as opposed to over another set of rails or roadway.

Another question I have is about deck bridges. Under what circumstances are they used over another type of bridge?
 
Deck bridges are preferred over through bridges, fewer clearance restrictions. Through bridges are preferred over deck bridges where the clearance under the track is limited. Girders are preferred to trusses for maintenance and cost. Girders are preferred for shorter spans, trusses for longer spans.

If the river or road is 25 ft below the tracks it would probably be a deck girder If the river or road is only 15 ft below the tracks, it would be a through girder.
 
Generally plate girder bridges are used for the shorter spans, trusses for longer ones. How long a plate girder can be, and how deep the girders have to be, depends on the load it needs to carry. A ratio of 1:12 (depth versus length) is about right.

The Warren truss is just one among many types of truss bridge, but it's the most common modern type.
 
Thanks guys. I plan on building a layout that includes 45 inches of fully elevated track - 3 inches above a river/lake. If my math is correct that equals 326 scale feet long and 22 feet high - not high enough for a deck bridge. Is that long enough that a truss bridge would typically be preferred over a plate girder?
 
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