There are 22 bridges with hollow-core pile foundations in Washington State. Sudden, catastrophic failure has been observed in tested piles of this configuration at displacement ductilities of four or less. To investigate the behavior of these piles and predict their in-service strength, a series of detailed nonlinear 3-D finite element (FE) analyses were performed. In addition, simplified 2-D nonlinear Winkler beam models were developed to evaluate their ability to predict failure.
The modeling techniques were calibrated through simulation of experimental test specimens, and shown to be capable of capturing the behavior of prestressed hollow core concrete piles. Compared with experiments, load capacity and displacement ductilities at yield and failure were reasonably well-predicted.
Results from the FE analysis of an in situ hollow pile illustrated that confining pressure supplied by the soil does not provide significant additional strength to cover concrete. Also, the subgrade plastic hinge was found to vary from 2.88 to 3.0 pile diameters and it was located, on average, 610 mm (24 in.) below ground level, depending on the soil type.
The Winkler beam models were found to provide conservative approximations to the load-displacement response of the 3-D FE models. The simplified analyses under-predicted load capacity and displacement ductility capacity by roughly 30 percent.
A typical connection between a pile and cross beam was also considered to evaluate its behavior and mode of failure. The response was shown to be nearly bilinear, and the moment strength was shown to be sensitive to the axial load on the pile.