Bridge over the tippy

[Jim Davis]

The bridge over the Tippecanoe River.

JD

[Gene Remaly]

Looks like this photo was shot during one of the times the lake was lowered 10-12 feet for repair work on the dam

[Pete Pedigo]

That is a very unusual bridge design.   I am not sure to even call it.   A Girder/truss combination of some type.  But I have never seen girders on top of a truss structure of that configuration.  Maybe Bob Wheeler can identify the type.

Pete

[Jim Osborne]

I think that's a standard Pratt truss. The girders aren't anything special - the trusses are loaded only at the joints, so there needs to be a beam/girder grid to carry the tracks between the joints. You just don't normally notice them because it's hidden down at the base of the truss.

The top-loaded truss was probably used because of the high banks. A conventional bottom-loaded truss would have towered over the area, and there was obviously sufficient clearance underneath for a top-loaded truss.

[Jim Wolfe]

Thanks for posting the photos Jim. I have never seen a closeup of the South end as you have it in the 2nd. photo.  All of the stone and foundation were removed just a few years ago.

[Pete Pedigo]

I realilze the girders are only bearing at the pier points or end of the girders.  Making the piers taller to the bottom of the girders would be a lot more preferable than the steel truss to keep maintained. 

[Robert Wheeler]

Pete & All:

To qualify the comments below I am a roadway engineer and not a structural (bridge)engineer.

I agree, I’ve never seen one like this anywhere or even in my bridge picture books. Usually the truss is under the track and doubles as the floor beam.
It looks like a truss bridge that they forgot to turn over to make it a ”deck” truss instead of a “thru” type.

A SWAG  is that they designed a Thru Curved Chord Pratt Truss beyond “the point of no return” in the design. To save 1880-1901 design costs they decided to moved the floor beams to the “top”, made the top chord straight and put the curve in the bottom chord.