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

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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


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

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


Laterally loaded piles comparison with lpile

Laterally Loaded Piles(comparison with LPILE)

3x Magnification


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

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


Typical solutions for a 24 inch 0 61 m pile in 0 61 m thick liquefied soil for reference ei and e s

Typical Solutions for a 24-Inch 0.61-m Pile, in 0.61-m Thick Liquefied Soil for Reference EI and Es


Characteristic results of parametric study maxm and location

Characteristic Results of Parametric studymaxM and location


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


Embedment depth l em versus characteristic parameter

Embedment Depth, Lem versus Characteristic Parameter 


Dimensionless moment as function of

Dimensionless Moment as Function of 

Curvature = Moment/EI


Dimensionless shear as function

Dimensionless Shear as Function 


Comparison of proposed solutions to fixed fixed beam equation

Comparison of Proposed Solutions to Fixed-Fixed Beam Equation


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!


Aspects of reinforcing effects of piles on ground curvature

Aspects of Reinforcing Effects of Piles on Ground Curvature


Aspects of reinforcing effects of piles on ground curvature1

Aspects of Reinforcing Effects of Piles on Ground Curvature


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).


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

THANK YOU!


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