Answer
Yes, the modifications are helpful.
Work Step by Step
The new support forces the bridge to have a node at the midpoint. Looking at the middle picture in Figure 11-41b, we see that the new fundamental frequency corresponds to the first overtone of the original structure. Assuming that the wave speed in the bridge span stays the same, the new resonant frequency is 2(3.0 Hz) = 6.0 Hz.
Since earthquakes “rarely do significant shaking above 5 or 6 Hz,” the new support would help to minimize oscillations during an earthquake.
