Dynamic testing and system identification of a multi-span highway bridge

A simple and effective procedure for conducting the free vibration test on highway bridges is presented. The impulsive force in each direction is gene rated by a loaded truck that either stops suddenly or falls down from a rig id block. The feasibility of the procedure is demonstrated in identificatio n of the dynamic properties, i.e. the vibration frequencies, mode shapes, a nd damping ratios, of a three-span box-girder concrete bridge using the Ibr ahim Time-Domain (ITD) technique. Up to 14 modes have been identified for t he present case, For the purpose of verification, ambient vibration tests w ere also carried out, with the data processed by the random decrement (Rand omdec) technique to yield the free vibration response, followed by the ITD technique. The dynamic properties identified from the two types of test cor relate very well with each other, indicating the validity of each procedure described herein. Although many more modes can be identified from the free vibration test because of the higher quality of data produced, the easines s and general applicability of the ambient vibration test can still be appr eciated. A comparison of the experimental results with those by the finite element method indicated a lesser degree of correlation, implying that the finite element model adopted in design requires further refinement, say, th rough a more realistic evaluation of the boundary conditions, geometric and material properties of the bridge. Copyright (C) 1999 John Wiley & Sons Lt d.