Vibration Test Machines

The EERC use special machines called "Rotating Eccentric Mass Exciters" to put a small vibration force into a structure. This picture shows one being used in a tower.

The exciters are bolted down to the structure. A backwards and forwards force is generated by weights that spin round in opposite directions. The size of the force can be changed by adding or taking away weights. The speed at which the weights spin can also be varied. The frequency of the force can be changed by varying the speed of the spinning weights.

The exciters generate a very small force, so you cannot see any movement at all in the structure being tested. However, the small vibrations are measured using very sensitive electronic instruments. These exciters have been used by the EERC to vibrate dams and intake towers.