9. Reliability Analysis of Existing Bridge Foundations for Reuse

Reuse of bridge foundations often requires determining the capacity of in-situ driven piles and drilled shafts. These piles have a proven history of load carrying capacity, but often lack test data from which the capacity can be obtained. It is possible to estimate the pile capacity with empirical calculations based on pile geometry and soil properties, but these produce highly uncertain results due to the variable nature of soil and impacts from the installation method. As a result, the LRFD code requires lower resistance factors be used for these calculations than would be required for piles with test data. Estimation of pile capacity using empirical calculations often produces over conservative results due to these low resistance factors. Since the piles have been in service for the lifespan of the original bridge, they have proven that as a system they have more capacity than the total dead and live loads previously applied. The amount of load applied to each pile, however, is uncertain due to variability of the loading and uncertainties of how the load is distributed to the individual piles. This research proposes reliability based methodology to determine the capacity of driven piles or drilled shafts accounting for these uncertainties.