AUTC project number: S18140
The use of reinforced concrete filled steel pipe piles is common in the state of Alaska, as well as across the nation. In many of the Alaska Department of Transportation projects, it is a preferred support system for bridges for several reasons: (1) The steel pipes serve as the formwork for the pile-columns, (2) The steel pipes can be used in driven (for smaller diameter to thickness ratios) or drilled foundation applications (larger diameter to thickness ratios), (3) The steel pipes provide high levels of confinement, thus providing the ability of sustaining large deformations, which is important for good seismic performance, (4) The system results in less environmental impact than conventional substructure elements requiring larger cofferdams, and (5) Construction is simplified because the steel tubes serve as “piles” below the soil surface, and as “columns” above the ground level. In Alaska, the preferred system utilizes longitudinal reinforcement in addition to the tube section, which is always circular. A research project on reinforced concrete filled pipe piles concluding in May of 2013 had the following objectives: (1) Develop recommendations for strain limits for use in seismic design at key design limit states as a function of diameter/thickness (D/t) ratio and material properties, (2) Develop an equation (via computation) for the plastic hinge length of “below ground hinges”, (3) Quantify the impact of reinforcing steel on performance and confirm that strain compatibility can be used for prediction of the force-displacement response. These three objectives have been studied through the use of large scale experimental testing, and the analysis of pile members. In addition, work in the project provided recommendations for equations to estimate equivalent viscous damping, which are required for implementation in a direct displacement-based design approach. This proposal builds upon the work previously conducted through the following proposed tasks: (1) Large scale testing of reinforced concrete filled pipe piles in soil media, and (2) FEA and fiber-based soil-structure (SSI) analysis. The specific goals of this proposed research project are to examine the impact that the relative soil-pile stiffness has on: (1) Pipe pile strain limit states, (2) Plastic hinge length and integration of curvature for deformations, (3) Proposed analysis methods, and (4) Damping.