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Simple Engineering of 19th Century Bridge Stands Test of Time | Tracy Lawson Author
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 about that design: 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