Hard Cases, Edge Cases, and Attacks

Engineers often test a finished bridge by loading it. In a proof load test, which is commonly run after construction to check the design assumptions, they drive test trucks loaded with concrete blocks or water tanks onto the deck. Each truck is parked in several positions in turn. A related test, the diagnostic load test, can check limits such as the maximum deflection, or bending, at the middle of a span.

The engineers do not test the bridge only with the cars that usually cross it. Ordinary traffic would show that the bridge carries ordinary traffic, which nobody doubted