Shake table test response of large-scale bridge columns supported on rocking shallow foundations

This paper presents the results of a series of large-scale shake table tests of bridge columns supported on rocking foundations. The tests took place at the NEES@UCSD facility in May 2013. Two one-third scale specimens of bridge piers were built and tested; one was aligned with the uniaxial direction of shaking and the other was placed on a skew configuration. They were placed inside a large confining soil box with 3.4 m height of well compacted clean sand at 90% relative density which weighed 2.5 MN. The columns were designed to remain elastic and support a weight of 235 kN each. Three series of tests were performed; (a) one with no underground water, (b) a second with the water level 1.2 m below the footings, and (c) a third with the water level 0.6 m below the footing. The test protocol included up to six historical near fault ground motions of increasing intensity which resulted in drift ratios of the columns up to 13.8%. The specimens sustained drift ratios up to 6.9%, corresponding to the level of demand expected for the Maximum Considered Earthquake, with small residual drifts and no structural damage. Key experimental responses are presented.