In order to extend the Swiss railway grid in the 1960s and 70s, many railway bridges were constructed for which pot bearings were taken for the supports. It is essential that the long-term behavior of these pot bearings is examined, as their life expectancy is, in most cases, much more limited than that of the associated superstructure. In this study, the operational condition of the pot bearings from a prestressed concrete girder bridge was investigated through in situ measurements and by evaluating the accumulated sliding path due to traffic loads and temperature impacts. It was found that long-term effects in relation to the traffic loads affect minimally the fatigue behavior of the bearings. Within extensive laboratory test series, the influence of parameters such as the lubrication condition, rotation angle, pressure acting on the elastomer pad and temperature on the restoring moments of the pot bearings was studied. Results of this study indicate not only that the condition of the pot bearings has deteriorated, but also that they were still in reasonable working condition after 32 years of service. (C) 2007 Elsevier Ltd. All rights reserved.

Large scale tests with progressive damage on a prestressed concrete highway bridge have been performed to investigate the sensitivity of several damage detection, localization, and quantification methods based on modal parameters. To investigate the quality of modal parameters, the data set of one damage step was analyzed by several output-only identification techniques. Although the bridge was severely cracked, natural frequencies as well as mode shapes display only minor changes. However, the relative changes of mode shapes are larger than those observed for natural frequencies. A novel damage indicator, called mode shape area index, based on changes of mode shapes, has been developed and found as the most sensitive damage detection approach. Damage detection or localization via changes of the flexibility matrix performed better than natural frequencies or mode shapes alone. The application of the direct stiffness calculation and a sensitivity-based model update technique showed results having a high level of ambiguity about the location and quantification of damage also at the highest damage level. Evaluating the information collected in this study the test results indicate that an early stage damage identification in prestressed concrete bridges is hardly possible because of the nearly complete recovery of stiffness after closing of cracks in prestressed concrete and the effect of environmental parameters on modal data.