TY - JOUR
T1 - Pile groups under vertical and inclined eccentric loads
T2 - Elastoplastic modelling for performance based design
AU - Franza, Andrea
AU - Sheil, Brian
PY - 2021/7
Y1 - 2021/7
N2 - This paper presents a numerical study of 3×3 pile groups embedded in clay under vertical and inclined eccentric loads. Simplified modelling, based on elastic beams embedded in a soil continuum, is used to explore the soil-pile-cap response. This simple model allows rigorous treatment of the 3D foundation geometry and local soil plasticity, demonstrated through validation with 3D finite element analysis. The numerical results reveal that complex roto-translational displacements of the pile group are induced by eccentric or inclined loads, with highly nonlinear relationships when soil plasticity is considered. Interestingly, vertical eccentric loads mobilise the lateral soil resistance at large cap displacements. Thus, while existing t-z type models are shown to be adequate for serviceability predictions, they could provide overly-conservative estimates of the ultimate load capacity. Also, foundation internal forces can exceed allowable bending moments of reinforced concrete piles under multi-directional loads. For performance based design of pile groups under inclined eccentric actions, engineers should estimate the impact of soil yielding on both displacements and rotations of the cap, to satisfy limit state requirements. Dimensionless charts are presented, which describe the reduction in vertical capacity, for a prescribed cap displacement, as a function of load eccentricity and inclination.
AB - This paper presents a numerical study of 3×3 pile groups embedded in clay under vertical and inclined eccentric loads. Simplified modelling, based on elastic beams embedded in a soil continuum, is used to explore the soil-pile-cap response. This simple model allows rigorous treatment of the 3D foundation geometry and local soil plasticity, demonstrated through validation with 3D finite element analysis. The numerical results reveal that complex roto-translational displacements of the pile group are induced by eccentric or inclined loads, with highly nonlinear relationships when soil plasticity is considered. Interestingly, vertical eccentric loads mobilise the lateral soil resistance at large cap displacements. Thus, while existing t-z type models are shown to be adequate for serviceability predictions, they could provide overly-conservative estimates of the ultimate load capacity. Also, foundation internal forces can exceed allowable bending moments of reinforced concrete piles under multi-directional loads. For performance based design of pile groups under inclined eccentric actions, engineers should estimate the impact of soil yielding on both displacements and rotations of the cap, to satisfy limit state requirements. Dimensionless charts are presented, which describe the reduction in vertical capacity, for a prescribed cap displacement, as a function of load eccentricity and inclination.
KW - Displacements
KW - Eccentric inclined loads
KW - Elasticity
KW - Piles
KW - Soil/structure interaction
UR - http://www.scopus.com/inward/record.url?scp=85103774793&partnerID=8YFLogxK
U2 - 10.1016/j.compgeo.2021.104092
DO - 10.1016/j.compgeo.2021.104092
M3 - Journal article
SN - 0266-352X
VL - 135
JO - Computers and Geotechnics
JF - Computers and Geotechnics
M1 - 104092
ER -