Dynamic Properties of the Painter Street Overpass at Different Levels of Vibration

摘要

This paper describes the results from a series of ambient vibration studies conducted on the Painter Street Overpass in Rio Dell, California. Painter Street is a two-span, skewed reinforced concrete bridge with two single piers near the middle and monolithic abutments, typical of bridge overpasses in California. Strong motion instruments were installed on the bridge in 1977, and since then it has recorded the motions from more than ten significant earthquakes. Because of the valuable amount of strong motion data available, the aim of the ambient vibration tests was to determine the dynamic characteristics of the bridge at low levels of vibration and to compare these with those measured during the strong motion events. In this paper, a description of the recorded strong motion events is presented first, then the ambient vibration tests are described and the results are compared with those obtained from analyses of selected strong motion records. The magnitude of the events investigated ranges from ML=4.4 to ML=6.9, which produced accelerations of up to 0.54g at the free field site, 1.3g at the abutments, and 0.86g on the deck. The results of this study indicate that the overall dynamic properties of the bridge are very sensitive to the level of ground shaking and that soil-structure interaction is very important for this type structural system. Although the superstructure exhibited a nearly elastic response, the motions at the abutments and base of piers were significantly different for each event.