Pollino and Bruneau 2010
Utilizing controlled rocking, where bridge steel truss piers are allowed to uplift and rock on their foundation, allows for seismic protection. The rocking motion is controlled within allowable limits by displacement-based steel yielding devices or fluid viscous dampers. Prior research has shown that the system can provide a restoring force allowing re-centering and protect existing members of the pier and foundation.
System Concept
An experimental study was conducted on a scaled model of a generic prototype bridge steel truss pier for a typical two-lane highway bridge. Shaking table test were conducted in the Structural Engineering and Earthquake Simulation Laboratory at the University of Buffalo.
A controlled rocking system is allows pier uplift from the base. The passive energy dissipation devices are located at the base and control behavior response. The specimen contained three sets of steel yielding devices and a set of fluid viscous dampers. It was subjected to past recorded ground motions and compared to previous analytical design predictions.
Experimental Study, Results and Discussion
The specimen was a 1:5 scale four-legged bridge pier. Base excitation consisted of ground motion histories including the Newhall record from the 94’ Northridge EQ and a synthetically generated record. The ground motions were implemented using a shaking table.
It was found in a few instances the analytical prediction of displacement was underestimated by 30-50% of the observed experimental values. Some of the experimental tests also showed significant deviation in the force response when compared to the analytical analysis. It is noted that large axial forces in the pier legs were developed and may require strengthening.
Reference
Pollino, M., & Bruneau, M. (2010). "Seismic Testing of a Bridge Steel Truss Pier Designed for Controlled Rocking." Journal of Structural Engineering, 136(12), 1523-1532.