Improved design method for bent pile structures (cast-in-drilled-hole shafts) based on nonlinear characteristics

A fundamental study of bent pile structures subjected to combined loads in multi-layered soil is conducted using in situ load tests and a load transfer approach. The emphasis is on quantifying an improved design method developed by considering the pile's plastic hinge and the column-pile interaction. An analytical model is developed that takes into account the nonlinear behaviour of materials for different soil-pile conditions. A framework for determining an optimized column-pile diameter ratio on basis of theoretical analysis is proposed through the relation between the column-pile diameter ratio and lateral crack load ratio. Based on the measured results, an optimized limit depth for a minimum steel reinforcement ratio is defined as the relationship between the bending moments and the crack moments of the concrete pile. An optimized limit depth for a minimum steel reinforcement ratio proportionally decreases as pile length increases, and beyond that the limit depth converges at a constant value (≃0.3).