Experimental Investigation of Dynamic Behaviour of Prestressed Concrete Bridge Girders

This paper presents observations of an experimental study of the dynamic behaviour of prestressed concrete bridge girders. In practice, it is often necessary to monitor the condition of bridges for maintenance to ensure safety conditions. Given the fact that bridges are larger, and complex in nature and their operating environment is hostile, non-destructive, modal parameter-based techniques outperform the conventional damage detection and health monitoring techniques. However, a prerequisite of baseline data of undamaged structure has been one of the major drawbacks hindering the modal parameter-based technique from effective use. Thus, in this study, the modal frequency and damping behaviour of newly cast prestressed concrete girders are investigated. Experiments and subsequent analysis revealed that the effect of magnitude of the prestress force on natural frequencies of standard prestressed bridge girders is minimal, as opposed to some of the literature suggested. Hence, the natural frequencies of standard pre-stressed concrete girders can be determined through a linear elastic beam theory with an equivalent moment of the area of the composite section. The damping behaviour of prestressed girders could be modelled by a viscous type of damping in undamaged conditions. The observed damping was varying between 0.4% and 0.8%. Well-approximated analytical prediction of damping could be possible using a damping prediction formula for reinforced concrete beams.