Large-Scale Validation of Seismic Performance of Bridge Columns

Professor José I. Restrepo
Professor Stephen Mahin, UCB
Professor Ian Buckle, Univ. of Nevada, Reno

A full-scale, circular reinforced concrete bridge pier designed in accordance to Caltrans' Seismic Design Criteria and Bridge Design Specifications guidelines has been tested under seismic excitation on the NEES-UCSD Large High Performance Outdoor Shake Table. The 4-ft (1.2-m) diameter cantilever pier spanned 24 ft (7.2-m) above the footing. A massive 261-ton (2,322-kN) reinforced concrete block supported by the pier generated gravity and lateral inertial forces.

The specimen was tested under historical ground motions, starting with low-intensity shaking and bringing the column progressively near collapse. Under the design earthquake the pier underwent a displacement ductility of 4.3, with only superficial concrete spalling and minor signs of incipient longitudinal bar buckling in the plastic-hinge region at the base. Under higher-intensity ground motions the system reached a displacement ductility of 7.6, preserving its vertical and shear force bearing capacity. Failure involved buckling and subsequent fracture of longitudinal bars, after yielding of the hoops; the concrete core suffered only superficial crushing in proximity of the buckled and fractured bars.

This test has proved that current design practices provide a safe and resilient structure: not only the system performed as desired under the design earthquake, but it was able to sustain a much larger displacement demand before reaching collapse.

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