Dynamic testing of a highway bridge

Artificial excitation of large civil structures requires bulky equipment in the field. In most cases, this becomes a logistical problem. Ambient excitation would be preferred if the resultant modal data were of comparablequality. Ambient excitation in this paper refers to vehicle traffic since the civil structures under consideration are highway or rail bridges. The modal test described in this paper was designed to compare mode shapes obtained by impact excitation and a controlled ambient excitation. A method of extracting valid modal frequencies and mode shapes from cross spectral data is then presented.