Comparison of forced and ambient vibration measurements on a bridge

This paper presents the methods and results of the processing of response only data collected from the Z24 bridge in Switzerland. Two sets of data were analysed: (1) data from drop weight forced vibration measurements, where the excitation force was not measured, and (2) data from ambient vibration measurements. it was found that the spectral estimates from the forced vibration measurements were of higher quality and therefore led to more consistent and reliable estimated modal parameters, even for this fairly crude method of forced vibration testing. It is possible that the results from ambient vibration testing could have been improved if longer data acquisition times were utilised.