Chapter 15, Problem 91GP

A highway overpass was observed to resonate as one full loop $\left(\frac{1}{2}\lambda \right)$ when a small earthquake shook the ground vertically at 3.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground as shown in fig. 15–41. What resonant frequency would you now expect for the overpass? It is noted that earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good? Explain.