Structural behavior of double-CFT-pile foundations under cyclic loads

Abstract

This paper presents experimental and analytical studies on the structural behavior of double-pile foundations under cyclic loads. Three large-scale pile foundation specimens with vertical or battered concrete filled steel tube (CFT) piles plainly embedded into concrete caps were tested. The effects of embedment depths, inclination angles and unequal heights of the CFT piles on the failure modes, strength, lateral stiffness, ductility and energy dissipation capacity were evaluated. The experimental and analytical results indicate the pile diameter embedment is adequate for forming the plastic hinge at the ends of both vertical and battered CFT piles. However, block shear failure and pry-out of the concrete caps inhibited the complete development of the plastic hinges at CFT pile ends. The use of battered piles significantly increases the loading capacity, lateral stiffness and energy dissipation capacity of pile foundations, but decays the deformation capacity and ductility of pile foundations. The unequal heights of battered CFT piles increase the shear and axial loads carried by the short pile, resulting in the potential premature failure of the short pile. The total lateral loading capacity of the pile foundation is not significantly affected by the unequal heights; however, the deformation capacity of the foundation decreases with increase of the unequal height ratios.