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Design Analysis for Pile Foundation in Liquefied Ground DFI Seminar, April 3, 2009. Project Funded by PEER Po-Lam - EarthMechanics Pedro Arduino UW Peter Mackenzie-Helnwein UW Ahmed Elgamaal UCSD Greg Fenves UT/UCB. Presentation Outline Overview.

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design analysis for pile foundation in liquefied ground dfi seminar april 3 2009

Design Analysis forPile Foundation in Liquefied GroundDFI Seminar, April 3, 2009

Project Funded by PEER

Po-Lam - EarthMechanics

Pedro Arduino UW

Peter Mackenzie-Helnwein UW

Ahmed Elgamaal UCSD

Greg Fenves UT/UCB

presentation outline overview
Presentation Outline Overview

Kinematic load case from ground deformation/displacement.

Focus on the three layer liquefaction

lateral spread problem and its impact

on pile performance

design issues related to kinematic pile loading due to ground deformation or displacement
Design Issues Related to Kinematic Pile Loading due to Ground Deformation or Displacement

Two Generic Soil Conditions Encountered for Liquefaction Design Problems

slide4
Elements for Designing the Pile Foundation Against the Kinematic Ground Displacement Loading Problem
  • Define the amplitude of ground displacement, including accounting for pile pinning effects.
  • Define the ground displacement profile
  • Conduct soil-pile interaction analysis
  • Assess the pile performance
analysis approaches for the kinematic pile loading problem
Analysis Approaches For the Kinematic Pile Loading Problem

Beam on Winkler Spring

Models

Fixed-Fixed Beam Models

Finite Element Models

comments regarding the finite element approaches
Comments Regarding the Finite Element Approaches
  • Finite element model potentially be most powerful and be more rigorous, but they are impractical as a design tool. Furthermore, from experience they tend to be misused, leading to mistakes.
  • Best to be used as research tool for developing guidances to designers.
comments regarding the fixed fixed beam model
Comments Regarding the Fixed-Fixed Beam Model
  • The fixed-fixed beam equation model is the simplest, but requires gross assumptions and tends to be overly conservative.
  • Best to be used as preliminary screening tool, recognizing that the approach is conservative.
  • Further discussions to be provided.
comments regarding the beam on winkler spring model
Comments Regarding the Beam On Winkler Spring Model
  • Beam on Winkler spring model, probably is the most widely used approach favored by designers. Some softwares are available and designers are familiar with them.
  • We found significant problems with the approach as there are shortcomings in conventional way to define the ground displacement profile and also difficulty in defining p-y curves.
  • Further discussions to be provided.
presentation of a peer opensees research project
Presentation of a PEER OPENSEES Research Project
  • Description of the research concept and results to-date.
  • Development of steps for simplified step-by-step procedure that can easily be implemented to-date for designing a wide range of kinematic pile loading problems.
  • Calibration of prior listed widely used analysis solutions from beam on Winkler spring and fixed-fixed beam model.
  • Outline future research program for further improvements.
new approach beam solid contact element
New approach: Beam-Solid Contact Element

Pile: beam elements

Soil: solid elements

Pile-Soil Interface:

Beam-Solid

Contact Element

slide12
3-D Finite Element Pushover Solutions of a 3-Layer Liquefied Lateral Spreading Ground Soil-Pile Interaction Problem

Single 3-D linear elastic pile

3 layer soil with liquefied

middle layer

Linear elastic soil model, Es at non-liq.

Free-field shear beam displacement

profile on side boundaries (common

assumptions by Geotechs)

Near field soil displacement is

automatically reinforced by the pile

(pile curvature is continuous to

the 4th order). An important issue!!

Amplitude of displacement increased

monotonically in pushover solution

Es

Es

The FE Mesh was designed for the basic

Single Solitary Pile Loading Problem where

The Liquefied Layer is Sufficiently Deep

And away from the Basic Inertia Load Case.

paramatric finite element solutions
Paramatric Finite Element Solutions

24-In Prestressed

Concrete Piles

54-Inch Prestressed

Concrete Piles

(Coronado Bay Bridge

Dumbarton Bridge

Antioch Bridge)

2.5-m Diameter Steel Piles

(SFOBB East Span,

New Carquinez, and

New Benicia Bridge)

parametric study
Parametric Study

Scope and Schedule Constraint Project to Basic Problem Understanding

  • Pile diameters
  • D1=2.50 m, D2=54in., and D3=24in.
  • Soft Layer Thicknesses
  • T1=1D, T2 = 2D, and T4=4D.
  • Piles stiffness, EI
  • (scale factors for base EI values
  • “E-3”=0.125, “E-2”=0.25, “E-1”=0.50, “E0”=1.0, “E1”=2.0, “E2”=4.0, and “E3”=8.0.
  • Total cases = 84 cases
development of simplified solution approach
Development of Simplified Solution Approach

Design Needs:

Location of max. moment

Equation to solve for max.

moment, or curvature

Equation to solve for max.

shear

Definition of Embedment Depth, Lem

identification of the liq soil pile interaction parameter
Es modulus of elasticity of stiff soil layer

EI stiffness of pile

T thickness of liquefiable layer

D outer diameter of pile

Identification of the Liq. Soil-Pile Interaction Parameter
comparison of proposed solution to beam on p y curve solutions
Comparison of Proposed Solution to Beam on P-Y Curve Solutions

24-Inch Concrete Pile

Solution in blue from

conventional API (Reese’s

P-y curves) yielding

38,570 kN-m/ m disp.

vs. 7,180 kN-m from study,

or 5.4 times correct sol.

Solution in red (softened

p-y from Vesic’s) yielded

11,000 kN-m as

compared to 7,180 kN-m,

or 1.5 Times correct sol.

Due to conservatism in

infinite curvature implicit

in shear beam displacement

function (implicit in free-field)

which ignores pile EI

reinforcing effects

comparison of proposed solution to beam on p y curve solutions1
Comparison of Proposed Solution to Beam on P-Y Curve Solutions

2.5-m (10-ft) pile

Solution in red (softened

p-y from Vesic’s yielded

208,000 kN-m as

compared to 138,000 kN-m,

or 1.5 times correct sol.

Due to conservatism in

infinite curvature implicit

in shear beam displacement

function (implicit in free-field)

which ignores pile EI

reinforcing effects. Such curvature reinforcing effect has

never been addressed by past

Researches!

conclusions
Conclusions
  • Complex 3-D finite element analyses were conducted by expert analysts with careful checking.
  • Resultant solutions were used for development of simplified solution charts to support practical design needs.
  • Comparisons have been made to conventional widely used analysis approaches (fixed-fixed beam and beam on Winkler spring models).
  • Comparison showed some problems with conventional approaches, that they tend to be overly conservative.
  • Reasons on potential errors have been identified.
  • Use of proposed method leads to more rational design decisions (e.g. big diameter piles be beneficial for soft or liquefied soil sites).
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