Simple Engineering of 19th Century Bridge Stands Test of Time

ch16-2bridge-interiorI’d read that the Jediah Hill covered bridge, named for my 4x great-grandfather who built it in 1850, was constructed in a queen-post truss design. My curiosity about all things related to my ancestors’ doings being insatiable, I set out to learn more:

A queen-post bridge has two uprights, placed about one-third of the way from each end of the truss. They are connected across the top by a beam and use a diagonal brace between the outer edges. The central square between the two verticals was either unbraced on shorter spans, or had diagonal braces from the bottom of each queen post to the center of the upper cord.

The queen posts create tension that prevents the sagging of the tie beam, which is the bottom of the truss. The truss for the wall is in the shape of a rhombus, and when used as a roof support, takes on the shape of a triangle (see below).

These photos clearly show the queen-post truss used on the walls of the bridge.

Queen-post trusses can better support a wider structure than king-post trusses, which have just one center support.












Brent Gregory, a resident of Mount Healthy, took the first three photos in this post during the renovations to the Jediah Hill covered bridge in the late 1970s and early 1980s.





















The fourth photo is the most recent, and shows the bridge as it is today, without windows.






Thanks to Doug at Vermont Timber Works for providing information and the graphic of a queen post truss design for me to use in my upcoming book, Pride of the Valley.

Queen Post Truss

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