Parametric Pushover Analysis on Elevated RC Pile-Cap Foundations for Bridges in Cohesionless Soils

Abstract

For bridges under seismic excitations, current design practices recommend to comply with the capacity protection principle for pile foundations. However, in cases, such as elevated (or scoured) RC pile-cap foundation typologies that are partially embedded, the piles may suffer large deflections under lateral loads, which make it difficult for them to remain in the elastic state. In this regard, the present study makes an in-depth analysis on the ductile behavior of elevated RC pile-cap foundations to explore potentials for seismic ductile design. A beam-on-nonlinear-Winkler-foundation model with or without the consideration of bond-slip effect at pile head/cap connections is built in accordance with quasi-static testing of a 2 × 3 elevated RC pile-cap foundation, and validated in various aspects, including the global force-displacement relationship, the failure mechanism, and the location of plastic hinges. The validation results indicate that the bond-slip effect is generally unremarkable and can be neglected for the modeling of studied elevated pile-cap foundations (EPFs). Two limit states and the corresponding ductility factors, named easy-to-repair and ultimate displacement ductility factors, are proposed for EPFs. Parametric pushover analyses are then performed to investigate the impact of structural and geotechnical parameters on the ductile behavior of real-scale 2 × 3 elevated RC pile-cap foundations embedded in homogeneous and multilayered cohesionless soils. The numerical results show considerable ductile capacities (with an average quantified as 2.77 and 4.05 for the easy-to-repair and ultimate displacement ductility factors, respectively) for elevated RC pile-cap foundations. Additionally, a mathematical relationship between displacement and curvature ductility factors is established for future ductility-based design practices.