Dynamic Assessment of Horizontally Curved Reinforced Concrete Box-Girder Bridges

The dynamic characteristics of a reinforced concrete box-girder viaduct have been quantified through on-site dynamic testing. The results have been compared with the results of another set of tests carried out on the same bridge, 25 years ago. Both investigations, i.e., the old and the new ones, included ambient vibration testing as well as operational modal analysis. In the modal tests carried out previously, simple equipment utilizing a few uniaxial accelerometers had been employed repeatedly and the natural frequencies of the bridge had been extracted by simple peak-picking technique from the frequency response functions (FRF), while in the modal tests conducted recently more advanced triaxial accelerometers were used in a rather fine measurement grid and the dynamic characteristics of the bridge were determined by means of commonly used frequency domain decomposition (FDD) and enhanced frequency domain decomposition (EFDD) modal identification techniques. The paper highlights the actual dominant modes and the corresponding mode shapes and focuses on the changes in the natural frequencies and damping characteristics of the viaduct after 25 years. Supporting finite-element models of the bridge have been constructed and updated in accordance with the results of the modal tests. Through a parametric study, the effects of changes in influential variables such as the radius of curvature, the material properties of members (time dependent properties of concrete), the effective member sectional properties, and the shear stiffness of the elastomeric bridge bearings have also been investigated. Finally, a discussion has been provided to address the minimum sensor placement for possible permanent monitoring of such a bridge with sufficient accuracy. (C) 2019 American Society of Civil Engineers.