Bow Bridge

by Don Friedman on August 17, 2015

The construction is done and getting press. The work went well from start to finish, even if it did take four years from when we first got involved.

This blog, of course, is a place to discuss the engineering details that tend to be overlooked while people are staring at beautiful architecture. In this case, our biggest challenge was repairing the tension-rod girders that span side-to-side across the bridge and support the wood deck. These girders consist of a vaguely T-shaped cast-iron section at the top and wrought-iron tie rods at the bottom. Depending on your preference, you can analyze these girders as tied arches or as beams with the cast iron carrying compression and the wrought iron carrying tension. At Bow Bridge, the ends of the wrought iron rods had rusted at a number of the girders, leaving the cast iron to work alone. Our repair detail re-tied the rods, thereby restoring the full strength of the girders. In the first picture below, the red rectangle highlights one of our new connections. (Click on the picture top enlarge it.) The girder to the right of the one marked has had work completed and the new connection has been painted; the girder to the left of the one marked did not require any work. The wood plank on top of the cast-iron is a nailer to allow attachment of the wood deck.


The second picture below gives a sense of the work site, with six of our repairs visible on the left end of the girders.



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