A new entry in the National Register of Historic Places may be a spot you regularly pick up dog poop! That's right, Balch Gulch Bridge-spanning the gulch between NW 29th and NW 31st, where many pick up Forest Park's Lower Macleay Trail-was officially designated by the National Park Service in September. Bridge heads likely already know that the steel structure makes use of a load-bearing framework of triangles fastened with flexible pin connections.
Bridges, which are exposed to water and salt, are some of the most vulnerable. About one third of bridges in the United States need to be repaired or replaced, which could cost nearly $400 billion over the next decade. There are plenty of ways engineers cope with rust, from coating the rebar with epoxy to pouring extra concrete to buy some time before seeping water reaches the rebar.