Experimental determination of the dynamic properties of a bridge substructure

As part of an investigation of the dynamic properties of bridge substructures, a series of steady-state vibration tests were undertaken on a multispan continuous deck bridge at several stages during construction. In this paper the method of testing is outlined and the measured natural frequencies and derived values of equivalent viscous damping are presented. The results confirm that the bridge does behave in a manner reasonably consistent with the design assumptions. At the small values of vibration amplitude generated, an equivalent viscous damping of the order of 4 per cent of critical was determined for the completed bridge.