Full-Scale Bridge Tests Examine Isolation Bearing Properties/Performance
General view of the seismically isolated full-scale bridge.
Testing has begun on two full-scale bridges designed and built specifically to determine the performance of seismic isolation technology over time and over a wide spectrum of temperatures and other environmental conditions. Initial tests took place at a dedicated site in Ashford, New York, during the first week of November, 2010. The tests will be repeated weekly over the next five years and will be run remotely from the Structural Engineering and Earthquake Simulation Laboratory (SEESL) and NEES Equipment Site at the University at Buffalo.
Close up of an elastomeric bearing on a multi-axis
Two 72-foot long adjacent single lane girder bridges have been constructed six feet from each other and supported on elastomeric bearings. The girders were donated by Hubbell Galvanizing from New York Mills, New York, The superstructure consists of ten concrete box girder beams that are post-tensioned in the longitudinal direction, whereas the uniform behavior of the superstructure is achieved through transverse post-tensioning of the girders. Each deck has been filled with 9 inches of gravel to account for the permanent loads applied on the bridge’s superstructure.
Two adjacent single span bridges.
Actuator with fast retraction rate is used to subject the two bridges in free vibration.
Full-scale seismic isolated bridge test set up in Ashford, New York.
Eight elastomeric low-damping bearings of circular cross-section have been donated for the test by Dynamic Isolation Systems from McCarran, Nevada, an MCEER Industry Partner. The design displacement of the bearings has been set to four inches given that the target period of the isolated bridge is 2.0 seconds and the total weight per bearing is 100 kips. Two different elastomeric compounds have been selected, resulting in two groups of bearings with different stiffness properties, assigned to each of the two bridges. Prior to installation, the bearings were tested at SEESL to obtain their initial mechanical properties.
A hydraulic actuator spans the 8-foot gap between the two bridges and can slowly push them apart at the design displacement, and upon release, the two spans are subjected to free vibration.
Several sensors including accelerometers, displacement transducers, and a multi-axis load cell under each elastomeric bearing, digital cameras and a weather station are in place to collect information on the structural behavior of the system and the change of properties of the isolation bearings due to time and environmental conditions (temperature, humidity, frost, etc.).
This project will contribute to a better understanding of the effect of temperature, environmental conditions and wear on the mechanical properties of isolation bearings, and provide a more realistic determination of bounding values of isolator properties for analysis and design based on better estimated Property Modification Factors (λ-factors). Given that the bridges can incorporate different seismic isolation systems, this bridge field station can provide insight into the long term efficacy of these systems under a variety of environmental conditions.
The project is led by MCEER Director Andre Filiatrault and Professors George Lee and Michael Constantinou. Other team members are Myrto Anagnostopoulou, SEESL Structural and Test Engineer, Mark Pitman, SEESL Technical Services Manager, and Ricardo Ecker Lay, Ph.D. Candidate, all of the Department of the Civil, Structural and Environmental Engineering, University at Buffalo, and Doug Stryker and Andrew Dailey from Calspan Corp.