Transcript Folie 1 - Ram Cadds

Piled Raft Foundations
Dr.-Ing. Holger Heidkamp – SOFiSTiK AG
Piled Raft Foundations
 KPP-directive (KPP-Richtlinie, Germany)
[Richtlinie für den Entwurf, die Bemessung und den Bau von
Kombinierten Pfahl-Plattengründungen (KPP), 2000]
[Directive for Design and Construction of Piled Raft Foundations (KPP),
2000]
 Requirements for the design
„Prerequisite … is a realistic incorporation of the various interactions
between structure, supporting elements and subsoil.“
„These requirements demand for a analysis models that account for
these interactions in a reliable and realistic way …“
17.07.2015 / 2
Geotechnical Engineering
Piled Raft Foundations
 Various interactions
1) pile-soil interaction
2) pile-pile interaction
3) raft-soil interaction
4) pile-raft interaction
17.07.2015 / 3
Geotechnical Engineering
Piled Raft Foundations
 Computation strategies (I):
 Empirical.
 Equivalent subsidiary models (monopile/ raft foundation).
 Analytical (theory of elasticity, analytical solutions).
 Numerical analysis schemes (II):
 FEM/ FDM:
 Discretization of subsoil as nonlinear 3D continuum, embedded
structure; piles as 3D continuum, too.
 Drawback: High cost regarding modeling/ computation/ postprocessing.
 ???
17.07.2015 / 4
Geotechnical Engineering
Extended Piles –
Extension of the Elastic Halfspace
17.07.2015 / 5
Geotechnical Engineering
Extended Piles – principle (I)
 Idealization: Subsoil = elastic halfspace.
 DOF at halfspace surface.
 Coupling of DOF via
(analytical) halfspace theory.
 Incorporates shear transfer!
17.07.2015 / 6
Geotechnical Engineering
Elastic
Halfspace
(analytical)
Extended Piles – principle (II)
 Extension for pile elements:
 DOF inside the halfspace
(pile nodes).
 Additional load transfer at
the interior points.
 Coupling of DOF via
analytical half space theory.
17.07.2015 / 7
Geotechnical Engineering
Extended Piles – principle (III)
 Extension for pile elements:
 Load transfer along pile
elements (nodes).
 Full coupling of interior DOF
(pile) and DOF at the halfspace
surface (raft).
 Interaction
17.07.2015 / 8
Geotechnical Engineering
Extended Piles – Modeling
 Bore profiles
 Subsoil stiffness properties
 Subsoil strength properties
 Structural modeling
 piles -> beam elements
 raft -> shell elements
 Pile resistance
 From strength properties:
 max[skin friction]
 max[pile foot pressure]
17.07.2015 / 9
Geotechnical Engineering
stiffness
Extended Piles – Processing
 Halfspace analysis
 External flex/stiffness matrix
 Soil-structure interaction
 Support/ bedding of structure via
halfspace stiffness
 Optional nonlinear effects:
 Reduced pile resistance.
 Maximum soil pressure (below raft).
 Uplift of raft (no tension transfer).
 Halfspace postprocessing
 Stress calculation inside the halfspace
17.07.2015 / 10
Geotechnical Engineering
Extended Piles – Benchmarks
 Monopile
„The adopted analysis scheme must be able to
simulate the characteristic load carrying behavior of a
monopile, identified in section 6.3. This requires
qualitative and quantitative correct account of the
shearing mechanism at the pile skin and compressive
action at the pile foot.“
 KPP-System 3x3/ 5x5
Investigation of the combined load carrying action
and mechanisms of interaction.
17.07.2015 / 11
Geotechnical Engineering
Extended Piles – Benchmarks
 KPP-System 3x3
17.07.2015 / 12
Reference solution:
Geotechnical Engineering
Extended Piles – Benchmarks
 KPP-System 5x5
17.07.2015 / 13
Reference solution:
Geotechnical Engineering
Questions?… please contact
www.ramcadds.in
Ram Caddsys Pvt Ltd
#10/2, 50th Street,7th Avenue, Ashok Nagar,
Chennai - 600 083, India.
Ph: 044 23717641, 24743955 / 3966
Fax: 044 24896097
Email: [email protected]
17.07.2015 / 14
Geotechnical Engineering