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Local Flavor



Engineering, like every other design profession, develops styles. I’ve been noticing – on the interminable bus rides to Pittsfield- that Massachusetts seems to have a lot of bowstring pony truss bridges. Local roads tend to have a lot of short-span bridges which today are almost always built as concrete girders, but during the road-building frenzy between 1900 and 1930, that was not yet a realistic option.

A bowstring truss is a truss with an arched top chord and a straight lower chord; a pony truss bridge is one where the road deck is aligned with the bottom chords but the trusses are too short to allow the top chords to be connected above the roadway. In modern design, trusses aren’t used for short spans because they’re more expensive than girders; pony trusses aren’t used because the unbraced top chords have to be heavier than through truss top chords, where the tops are connected above the road.

But they’re kind of purty.

Bridgey.



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