Dan Robirds Wrote:
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> WOW!
>
> What caught my eye was the picture of the bridge
> in the link. Typically, early truss bridges were
> of the Howe truss design where wood timbers were
> used for spans and posts. Iron vertical rods held
> it together. The wood beams were primarily in
> compression while the iron rods were in tension.
>
> Look at this bridge! It has wood beams forming the
> top and angled end chords and stringers like a
> Howe truss. It also appears to be a "pony" design,
> the trusses being shorter than the equipment going
> over it (versus a through truss). The rest is a
> "pin connected" design with iron flat bars and
> rods tying it all together and connecting at
> several pins. The I beams and U channel braces
> look out of place making me question if they were
> original or part of a later replacement or
> strengthening?
>
> I don't think I've ever seen such a truss bridge
> as this combining wood and iron in such a unique
> arrangement, at least for rail service.
>
> Pin connected truss bridges had the advantage in
> that they could be built at a factory, easily
> assembled in the field from a kit, and if
> necessary disassembled and used again elsewhere.
> They fell out of favor circa 1900 since a failure
> or damage to a single component could lead to
> catastrophic failure. I-beams riveted together at
> each joint in the truss were far less prone to
> failure, plus could be both in compression and
> tension. But there are still plenty still around
> and still in service. I occasionally still run
> trains over a steel pin connected truss that was
> relocated decades ago to it's present location by
> the NP.
DSPP bridges were fairly unique , they generally didn't just bang in a trestle with wood supports, they built them to last with stone piers and caps , quite fancy.
