Obtaining ductile performance from precast, prestressed concrete piles

A parametric study of the inelastic seismic response of precast, prestressed concrete piles was conducted to determine whether piles with only light transverse reinforcement could act as ductile structural elements. A nonlinear, inelastic finite-element program written specifically for this project was used to validate results for both laboratory and in-place testing. The study examined single piles using several types of pile-cap connections, the addition of mild-steel reinforcement, varying levels of axial load, and a range of soil stiffness. The piles were modeled with 1% transverse reinforcement, which is less than 1/3 of that required by ACI 318. The results indicated that modest levels of transverse reinforcement will allow for ductile response. Assuming that the pile-cap connection is detailed to allow and support the formation of a plastic hinge, with subsequent redistribution of moment down the shaft to form a secondary subgrade hinge in the pile shaft, the pile configurations analyzed provided a minimum displacement ductility of 2. The addition of mild-steel longitudinal reinforcement did not enhance ductility, though it did increase flexural strength. The optimum pile-cap connection to maximize ductility is embedment of the pile head into the cap. Rotation capacity is maximized by embedment of the prestressing tendons and any mild-steel longitudinal reinforcement present into the pile cap.