Compression Tests of Very Large Reinforced Concrete Pile Caps and Comparison with Predicted Strength

An experimental program consisting of four full-scale specimens was conducted to assess the structural behavior of very large rein-forced concrete (RC) pile caps supported on steel pipe piles. The tested specimens replicated the geometry, reinforcement details and placement, material properties, as well as support and loading conditions typical of in-service 1980s vintage pile caps. Prior to testing, three-dimensional (3-D) strut-and-tie models were devel-oped to predict the strength of the specimens and expected failure modes. During tests, widespread reinforcement yielding was observed in all specimens. One specimen failed in one-way shear, two specimens failed in two-way shear, and one specimen did not reach failure before reaching the load capacity of the test setup. Based on the experimental results, the strut-and-tie capacity predic-tions were highly conservative for all specimens and would have required retrofit of the pile caps to carry the expected column axial loads associated with a potential vertical expansion of the building. The high degree of conservatism is attributed to neglecting the beneficial effects of active confinement in the 3-D structure, espe-cially at the pile locations, that underestimates the available bond strength, thereby minimizing the available tension ties.