Modal testing for a multispan continuous segmental prestressed concrete bridge

Continuous segmental prestressed concrete bridges have been used extensively all over the world since the late 1960's. In this case the authors are investigating one such bridge in the state of Illinois. The bridge has developed extensive cracks on the webs of the segments. Yet, it is very difficult to assess the safety of this bridge. One of the possible ways of coming up with some quantification involves the estimation of the structural dynamic properties, such as modal frequencies and mode shapes. This approach is especially useful if a previous baseline has already been established for that structure. Such a baseline does exist for the structure. This paper is a summary of the ongoing of experimental investigations and Finite Element simulations that have been conducted on the bridge. In particular, three experimental modes have been identified using both forced vibration and ambient vibration excitation at two different seasons of the year and the results have been compared to results that were obtained by CTL twelve years ago.