With its rivers, hills and valleys, Southwestern Pennsylvania has more bridges per square foot and per capita than any other city in the world. In fact, the only kind of bridge we don't have here in Southwestern Pennsylvania is a drawbridge. . . Bridge basics Bridges are a tough structure to master. The tricky part is to make them strong and lightweight enough to span a distance without bending or buckling, yet flexible enough to handle traffic, wind, and temperature changes without shattering. For over 200 years, Pittsburgh bridges have met those challenges with a succession of progressively modern bridge designs.
Bridges are a great way to study structure because all of the structural elements are in plain view.
The next time you're caught in a traffic jam, take a moment to figure out the science and mathematics of such engineering feats. The simplest kind of bridge is a simple beam spanning two points. When gravity acts on a beam, it bends . A beam can be stiffened against bending by making it larger and stronger, as in the Veterans Bridge across the Allegheny, or more commonly to make the beam into a huge truss, which uses the lightweight triangle to resist bending. Traffic on truss bridges can drive over the truss or literally through the truss.