Rensselaer Republican, Volume 15, Number 45, Rensselaer, Jasper County, 19 July 1883 — BRIDGES AND RHYTHMIC VIBRATION. [ARTICLE]

BRIDGES AND RHYTHMIC VIBRATION.

• Measured -vibrations are more trying to any kind of bridges, and particularly to the suspension bridges, than irregular agitation. Music alone would not strain a bridge enough to injure it materially; but a regiment of troops keep- • ing step to music when crossing a suspension bridge would subject it to a very severe strain. Consequently it is customary to stop the music before troops reach the bridge, and let the men break step, and march more or less irregularly. The reason of all this is obvious. The structure will naturally suffer least strain when at rest. When in uniform

motion the bridge acquires a momentum equal to its entire suspended weight multiplied by the velocity of the motion. It is manifest that, in the case of a heavy structure, a uniform downward vibration, be it ever so small, would develop a momentum of many tons in the direction of a breaking strain. The same disturbing forces acting irregularly, so as to counteract one another, would be far less trying to the strhoture,