Monotonic and Cyclic Pushover Testing of Isolated Piles of the Whirokino Trestle

Abstract

In New Zealand, over 60% of State Highway bridges were designed and built during eras with low seismic provisions and most of these bridges are supported by pile foundations. An improved understanding of the in-service performance of these bridge foundations is a key aspect of seismic resilience. However, there is limited data on the performance of these foundations in the field. A unique opportunity to study bridge foundations from this period has been presented during the replacement and demolition of the Whirokino Trestle in Foxton, New Zealand. A field-testing program involving static cyclic tests was developed in order to characterize the lateral behavior of isolated pile foundations that are embedded in loose to medium dense sands. These results highlighted the significant influence of loading, plain round bars, and soil nonlinearity and gapping on the seismic response of older bridge piles. Even with the use of plain round bars and with widely spaced transverse reinforcement in these piles, there was no loss of strength observed at large displacements and through multiple cycles of loading, suggesting a better than expected performance of these older pile foundations.