Quasi-Static Cyclic Testing of Elevated RC Pile-Cap Foundation for Bridge Structures

In current practices, the elastic design principle for the seismic design of pile foundations is an overly conservative strategy. In this regard, cyclic lateral loading tests were conducted to investigate the seismic failure mechanism and ductile behaviors of elevated RC pile-cap foundations. Two six-pile specimens with different aboveground heights were constructed and embedded in a single layer of cohesionless soil. Hysteretic characteristics and observed damages of the pile groups were presented, together with the corresponding soil pressure and pile curvature responses. From the test results, the sequence and positions of the pile plastic hinges were established. Ultimate limit states of the pile groups were determined according to test data, as well as numerical analysis results. Test results revealed a ductile flexural failure mode for both specimens. Plastic hinges were detected first at the top of outer piles, then underground at a depth of 4–6 times the section width. A displacement ductility capacity of 3.5 was observed for the elevated pile-cap foundation. Test results also indicated a linear relation between the displacement ductility factor and the cap rotation, which was important for determining the displacement at the top of piers.