Flexural test of precast high-strength reinforced concrete pile prestressed with unbonded bars arranged at the center of the cross-section

In this study, a prestressed reinforced concrete pile that uses high-strength material to increase the pile's flexural capacity was developed. The main structural characteristics of the developed pile include (1) the neutral axis is constantly near the centroidal axis of the pile, even if the longitudinal reinforcement yields due to a flexural moment, because the pile has a high axial compressive force that is induced by prestressed steel bars, and hence, the concrete in the compression region can contribute to increasing the flexural strength of the pile; and (2) the flexural strength of the pile increases because the high-strength concrete is confined by high-strength spirals and carbon-fiber sheets in combination with concrete infilling, and, together, these modifications provide a sufficiently high lateral-confinement pressure. The results of bending tests demonstrate that the proposed prestressed reinforced concrete pile with carbon-fiber sheets and concrete infilling had a much higher flexural capacity than a conventional precast concrete pile. In addition, an analytical approach is presented that can be used to obtain the relationship between the bending moment and the curvature of the proposed pile. Even if concrete bridge systems are constructed on strata that can experience soil liquefaction, such as very soft soil, bridge foundations that use the proposed piles could remain undamaged under the design seismic action.