Bearing capacity of pile groups under vertical eccentric load
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Abstract
The paper deals with the problem of the bearing capacity of pile groups under vertical eccentric load. Widespread practice is to consider the achievement of the axial capacity on the outermost pile as the ultimate limit state of the pile group. However, this approach neglects the ductility of the foundation system and may be thereby overconservative. With the aim of proposing an alternative and more rational approach, a novel formulation for interaction diagrams based on theorems of limit analysis is presented and discussed. The methodology is applicable to the general case of groups of unevenly distributed, dissimilar piles. Piles’ connections to the pile cap are modeled as either hinges or rigid-plastic internal fixities. An application example to a slender structure is also provided, showing that the proposed approach can lead to significant advantages over the traditional design.
Keywords
Bearing capacity Eccentric loading Limit analysis Pile groupsList of symbols
- α
Adhesion factor
- αM
Inclination of the applied moment vector
- γb,γs
Partial resistance factors for pile base and shaft capacity
- γst
Partial factor for shaft capacity in tension
- γsu
Partial factor for undrained shear strength
- δ
Coefficient depending on number of piles
- δθ
Increment of rotation
- δWi,δWk
Increments of work done by internal forces
- δEi,δEk
Increments of work done by external forces
- η
Efficiency of a pile group
- ξ3
Correlation factor to derive characteristic value
- ξj
Coordinate of the j-th pile in the reference system (ξ, η)
- σVL
Total overburden stress at depth L
- Ab
Base area of the block containing the piles
- As
Side area of the block containing the piles
- B
Distance between two external piles of a row
- c
Abscissa of the center of the row
- d
Pile diameter
- L
Pile length
- M
External moment vector
- M0
Moment capacity of the pile group under zero axial loading
- Mu,Mui, Muk
Moment capacities of the pile group
- Mux,Muy
Moment capacities along x- and y-axes in the 3D domain
- m
Number of alignments of piles parallel to external moment vector M
- myc,myt
Dimensionless yielding bending moments
- Myc,Myt
Yielding bending moments
- Nc
Bearing capacity factor
- Nu
Axial capacity of the single pile in compression
- Nuj
Axial capacity in compression of the j-th pile
- n
Number of piles in a row
- p
Number of piles in a group
- pk
Unit base resistance
- Pk
Characteristic value of pile base resistance
- Q
External axial capacity
- Qi,Qj
Axial loads on piles i an j
- Q0
Axial capacity of the pile group
- Qu,Qui, Quk
Axial capacity of the pile group
- Sk
Characteristic value of pile shaft resistance
- Su
Axial capacity of the single pile in uplift
- Suj
Axial capacity in uplift of the j-th pile
- s
Pile spacing
- sk
Unit shaft resistance
- su
Soil undrained shear strength
- xj
Abscissa of the j-th pile
- yj
Ordinate of the j-th pile
Notes
Acknowledgements
This research has been developed under the auspices of research projects ReLUIS 2014-2017, granted by Italian Emergency Management Agency.
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