Dynamic characteristics of a long span seismic isolated bridge
ruben boroschek2003, Engineering Structures
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Abstract
The central zone of Chile is located in a high seismic risk area with occurrence of magnitude 7 earthquakes every 10 years and magnitude 8 events every 90 years. This paper deals with the mechanical and dynamic characteristics of a 383 m long seismic isolated bridge located in that area. The tests carried out on rubber components, isolators and the bridge structure are presented. Some simple structural models that show good correlation with measured response are also addressed. A strong motion permanent network installed on the bridge allowed the recording of ambient-traffic vibrations as well as seismic motions. Seismic records show the beneficial effect of the isolation in the horizontal direction, but important amplification occurs in the vertical direction for relatively high frequency components.
Key takeaways
- The bridge consists of a single continuous 383 m superstructure supported on 36 high-damping rubber bearings that rest on two abutments and seven piers.
- At the piers, the transverse distortion is controlled by the isolators and superstructure stiffness.
- A strong amplification is observed for vertical maximum acceleration from superstructure to piers ((a14 + a8) / (2 * a5)), with an average value of 7.5 for ambient vibration and 2.5 for seismic, a characteristic also observed in other isolated structures [11,12].
- The motion between the base and the top of pier and the average of superstructure (d8+d14)/2 are nearly identical indicating no special amplification, although maximum acceleration amplification is observed due to the frequency content of these records.
- Superstructure masses were lumped on the deck over each pier and abutments while pier masses were lumped on piers top.
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