three dimensional lateral load analysis of pile foundation by roger hart ppt

8/10/2019 Three Dimensional Lateral Load Analysis of Pile Foundation by Roger Hart PPT

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ThreeDimensional(FLAC3D)

LateralAnalysis

for

Seismic

Loading

ofPileFoundations

RogerHartandVarun

ItascaConsultingGroup,Inc.

Minneapolis,Minnesota,USA

16October2012

1. A brief introduction to FLAC3D What is the

applicability ofFLAC3D for dynamic SSI analysis of

pile foundations?

2. A recommended procedure for seismic analysis of

soil-pile interaction in liquefying soils.

3. Lateral load test calibration of pile-soil couplingspring properties for a FLAC3D simulation of

lateral/seismic loading of a pile foundation

Topics


2/42

FLAC3D is a general-purpose code that can simulate a full range of

nonlinear static & dynamic problems, with coupled fluid flow, heat transfer

and structural interaction. Any geometry can be represented, and the

boundary conditions are quite general.

FLAC3D simulates the behavior of nonlinear continua by the generalized

finite difference method (arbitrary element shapes), also known as the

finite volume method.

FLAC3D solves the full dynamic equations of motion even for quasi-static

problems. This has advantages for problems that involve physical

instability, such as collapse, as will be explained later. To model the

static response of a system, damping is used (dynamic relaxation) to

absorb kinetic energy.

FLAC3D contains an embedded language, FISH, that gives the user access

to all internal variables and allows custom-written functions.

What isFLAC3D?

FLAC3D

1. Large-strain or small-strain calculation mode.

2. Many built-in constitutive models that are representative

of geologic, or similar, materials; optional user-written

models.

3. Interface elements to simulate distinct planes of weakness.

4. Groundwater and consolidation (fully coupled) models with automatic phreatic

surface calculation.

5. Structural element models for rock/soil-structure interaction cables, piles,

beams, liners, shotcrete, soil reinforcement, etc.

6. Optional dynamic analysis capability; full groundwater coupling.

7. Optional viscoelastic and viscoplastic (creep) models.

8. Optional thermal model, with coupling to solid & fluid.

is best suited to model continuous

materials (containing, perhaps, a fewdiscontinuities) that exhibit nonlinear

behavior. In particular, it features:


3/42

Basis ofFLAC3DFLAC3D uses an explicit, dynamic solution scheme to solve the

full dynamic equations of motion even for quasi-static problems.

This has advantages for problems that involve physical instability,

such as collapse.

To model the static response of a system, a relaxation scheme

is used in which damping absorbs kinetic energy. This approach

can model collapse problems in a more realistic and efficient

manner than other schemes, e.g., matrix-solution methods.

FLAC3D treats interactions between separate objects (e.g., zones

or structural elements) as boundary conditions; there is noconcept of a joint element. The Distinct Element Method

(DEM) is used for interactions.

Difficulties faced in numerical simulations in geomechanics

1. Physical instability

2. Path dependence

3. Implementation of strongly nonlinear constitutive models for

example, strain-softening models or models that exhibit volumetric

collapse.

These difficulties are addressed by using an explicit, dynamic solution

scheme. This approach is not new or unique, but it has been used withsuccess to test, calibrate and apply constitutive models on many ill-

behaved physical systems for more than 30 years.

Why use an Explicit, Dynamic Solution scheme?


4/42

The consequence of this scheme is that each element appears to be

physically isolated from its neighbors during one time step;

Thus

The calculation cycle

Forces are fixed

duringthis

calculation

Strainrates are

fixed duringthiscalculation

(forallmass-points)

(forallelements)

Hence the implementation of nonlinear constitutive laws is

quite straightforward:

The input strain is fixed, and there are no influences from otherelements, during the step. No incremental stress/strain matrix is

needed the constitutive relations are used directly. Plastic

behavior requires no iteration (or return algorithm) during the step.

p

min

C

xt

The explicit scheme

uses a time step so

small that information

cannot propagate

between neighbors in

one step.

Thus, each element is isolated

during one step, enabling


5/42

ConstitutiveModelsforFLACandFLAC3DBuiltinModels UserdefinedModels*

Elasticitymodels:

Isotropic

Transverselyisotropic

Orthotropic

Plasticitymodels:

DruckerPrager

MohrCoulomb

Ubiquitousjoint

Strainhardening/softening

Bilinearstrainhardening/softening/ubiquitousjoint

Doubleyield

ModifiedCamclay

HoekBrown

Cysoil frictionhardening,withellipticalcap

Chsoil simplifiedCysoil (alternativetoDuncanChang)

DynamicLiquefactionmodels:

Finn(Martinetal.,1975)model

Bryne,1991model

Creepmodels:

Viscoelastic

Burgerssubstanceviscoelastic

Twocomponentpowerlaw

Referencecreepformulation(WIPP)Burgercreep/MohrCoulombviscoplastic

Twocomponentpowerlaw/MohrCoulombviscoplastic

WIPPcreep/DruckerPrager viscoplastic

Crushedsalt

*partiallistofmodelscreatedby

(ordevelopedfor)codeusers

Elasticitymodels:

HyperbolicelasticDuncanChang,1980

Plasticitymodels:

NorSand

Jardine etal.,1986

ManzariDafalias,1997

Kleine etal.,2006

Concretehydration

vonWolffersdorff hypoplastic

DynamicLiquefactionmodels:

UBCSAND

UBCTOT

Wang,1990

Rothetal.,2001

Andrianopoulos,2005

Creepmodels:

Minkley viscoplastic

Heincrushedsalt

Salzer creep

Lubby2creep

Why useFLAC3D for dynamic

analysis?

FLAC3D simulates the full, nonlinear response of a system

(soil, rock, structures, fluid) to excitation from an external

(e.g., seismic) source or internal (e.g. vibration or blasting)

sources.

Therefore it can reproduce the evolution of permanent

movements due to yield and the progressive development of

pore pressures (and their effect on yield).


6/42

Step1:

Estimate

representative

soil

and

structure

properties

Considereffectivestressanalysis

Includemodulusreductionanddampingratiocurves

Selectrepresentationofliquefaction

Step2: Determineappropriatedynamicloading

Performandcheckdeconvolution analysis

Evaluateseismicmotioncharacteristics

Step3: ConstructFLAC3Dmodel

Ensureaccuratecalculationofwavepropagation

Calculatestaticequilibriumstate

Checkstability

Step4: Performseismicsimulations

applydynamicloadingandboundaryconditions

undamped elasticandMohrCoulombseismic

simulationstocheckmodelconditions

dampedMohrCoulombseismicsimulations

liquefactionseismicsimulations

Recommended Steps in a Seismic Analysis of

Soil-Pile Interaction in Liquefying Soils

Step1: Estimaterepresentative soilandstructureproperties










Checkstability










7/42

Deformation Properties

for an Effective Stress Analysis

Materi al moi st un it wt . s at . uni t wt . po rosi ty dry un it wt . d ry dens . V s V p G K

(pcf) (pcf) (pcf) (slugs/ft3) (ft/sec) (ft/sec) (psf) (psf)

Soil 1 126 132 0.35 110.0 3.421 856 2138 2.510E+06 1.230E+07

.

.

.

Strength Properties

for an Effective Stress Analysis

Mater ia l d ra ined cohes ion dra ined f ri ct ion (N1)60 c1 c2 res idua l s t rength

(psf) (degrees) (psf)

Soil 1 0 30 10 0.4892 8.176E-01 400

e.g., Finn-Byrne model

To simulate liquefaction:

.

.

.


8/42

Dynamic simulations with fully-coupled pore fluid

In order to include water in the groundwater mode (CONFIG fluid) in FLAC3D then

the water modulus must be selected carefully. The behavior of the model depends on

the following ratio

43

/WF

K nR

K G

Where is the water bulk modulus, n is the porosity and K& G are the drained

elastic bulk and shear moduli.W

K

There is a temptation to decrease the water modulus, in order to increase the time step

(and reduce the simulation time). There are two cases to consider:

1. Using the correct water modulus ( for pure water), if then it may

be decreased such that without affecting the results significantly.

2. If using the correct fluid modulus, thenthat value should be used.

As an example, is considered representative of saturated sandy soils

(Chaney, 1978).

74.1 10 ps f 20FR

20FR

20FR

In the case of models with a large range of elastic moduli, the fluid modulus can be made

to depend on localvalues of moduli, provided that the above conditions are respected.

64.1 10wK psf

Soils exhibit stiffness degradation and energy dissipation when subjected to dynamic

cycling loading. Hysteresis occurs for all levels of cyclic strain, resulting in an

increasing level of damping with cyclic amplitude. Damping is rate-independent.

Volume strain is induced by shear strain; in particular, volume-strain accumulates with

cycles of shear strain.

Nonlinear characteristics of soils (Martin and Seed, 1979)

Soil characteristics under dynamic loading

How do we represent this behavior in a nonlinear numerical solution method?


9/42

Elastic/plastic modelsThe built-in models in FLAC3D consist of various elastic/perfectly-

plastic relations. There is only hysteresis for cyclic excursions that

involve yielding.

strain

stress(Note that even this crude model produces

continuous damping and modulus relations, for

excursions above yield)

There may be volume

changes during yield but

normally they are dilatant

(not such as to cause

liquefaction)

Material Models and DampingIdeally, a comprehensive model for soil would account for all the

physical effects that occur during cyclic loading, such as energy

dissipation, volume changes and stiffness degradation.

An ideal model does not exist, so we need to compromise, and

account for some important aspects (such as damping and

cyclic volume changes) separately.

Additional hysteresis damping can be included in an elastic/plasticmodel using either:

Rayleigh damping

Hysteretic damping


10/42

Rayleighdamping

RayleighdampingmaybeusedinFLAC3Dasanapproximationtohysteretic

(frequencyindependent)damping.Twoviscouselementsareusedtomakeup

thedampingmatrix:

Themassproportionaltermislikeadashpotconnectingeachgridpointto

ground. Thestiffnessproportionaltermislikeadashpotconnectedacross

eachzone(respondingtostrainrate).

Althoughbothdashpotsarefrequencydependent,anapproximately

frequencyindependentresponsecanbeobtainedoveralimitedfrequency

range,bytheappropriatechoiceofcoefficients.

Rayleighdamping cont.

frequency

ratioofdampingtocritical

combined

stiffnessproportionalonly

massproportionalonly

Note3:1frequencyrangeoverwhich

combineddampingisalmostconstant

Combinedcurvereaches

minimumat:


11/42

Rayleighdamping cont.

ThedrawbackswithRayleighdampingarethat:

1. Thecenterfrequencymustbechosen fromsometimes

conflictingdata(e.g.,thesiteresonanceortheearthquakeaverage

frequency)

2. Thestiffnessproportionaltermcausesthetimesteptobereduced

asthedampingratio(lambda),atthehighestnaturalfrequency,is

increased:

HystereticDampinginFLAC3DFLAC3Dprovidesanoptionalhystereticdampingfunctionfordynamic

simulations.Thedampingisindependentofthematerialmodels,andconsists

ofastraindependentmultiplieronthetangentshearmodulus.

0

0.2

0.4

0.6

0.8

1

1.2

0.0001 0.001 0.01 0.1 1 10

Cyclic strain %

Modulusreductionfactor

Ifthesecantmodulusisgivenbya

degradationcurve,thenthetangent

moduluscanbederived:

secant modulus

tangent modulus

shear stress

shear strain

s

t

M

M

FromSeed&Idriss (1970)

d

dM

Md

d

M

M

s

st

s

)(

oG/

Go = smallstrain

shearmodulus


12/42

Givenaparticularmodulusdegradationfunction,theresultingtangent

modulusisusedtomultiplytheapparentshearmodulus(Go)providedbythe

constitutivemodel:t

G M G

Theapparentstrainisthe

deviatoricstrainaccumulated

sincethepreviousreversal

point.Suchreversalpointsare

keptinastacksothat

embeddedcycleswithina

maincyclemaybefollowed.

FLAC (Version 4.00)

LEGEND

12-Feb-03 15:39

step 3700

HISTORY PLOT

Y-axis :

Ave. SXY ( 1, 1)

X-axis :

X displacement( 1, 2)

-40 -20 0 20 40

(10 )-05

-2.000

-1.000

0.000

1.000

2.000

(10 )+04

JOB TITLE :

Itasca Consulting Group, Inc.

Minneapolis, Minnesota USA

Thus,energyisdissipatedforminiloopsaswellasthemain

hysteresisloop.

elasticmodelwithhystereticdamping

Thehystereticdampingformulationhasthreeadvantages.

1. StandardG/Gmax degradationcurvesusedinequivalentlinearanalysesmaybeuseddirectlyinFLAC&FLAC3D,toperformfully

nonlinearsimulationswiththesamematerialresponse.

2. Thedampingdoesnotaffectthetimestep(incontrasttoRayleigh

damping,whichmayprofoundlyreducethetimestep).

3. Thedampingmaybeusedwithanymaterialmodel,andwithanyof

theotherdampingschemes(optionally)active.

Onedisadvantageisthatpublisheddegradationcurvesseemtobe

inconsistent i.e.,ahystereticmodelthatconformstotheG/Gmax curve

doesnotnecessarilyconformtotheassociateddampingcurve

0

0.2

0.4

0.6

0.8

1

1.2

0.0001 0.001 0.01 0.1 1 10

Seed data

FLAC - Sig3 fit

0

10

20

30

40

50

60

0.0001 0.001 0.01 0.1 1 10

Seed data

FLAC - Sig3 fit

GoodfittoSeed&Idris dataforG/Gmax (sigmoidal 3parameterfunction)

noteinconsistentdampingresult.


13/42

Estimate material damping parameters

for the FLAC3D modelSHAKEcan be used to estimate material damping input to represent the inelastic

cyclic behavior of the soils specified as Mohr-Coulomb material in a FLAC3D

model. Damping parameters can be estimated for both Rayleigh damping and

hysteretic damping. An equivalent-linear analysis is performed with SHAKE

using the shear wave speeds, densities, and modulus reduction and damping ratio

curves for the different soil layers and the target earthquake motion specified for

the site.

Strain-compatible values for the shear modulus reduction factors and damping

ratios are determined from the SHAKE analysis. Average modulus reduction

factors and damping ratios are estimated for each of the layers, and are input

parameters forRayleigh damping applied in FLAC3D.

The expected range of cyclic shear strains for the given site conditions is needed

in order to specify a best-fit range for the modulus reduction and damping ratio

curves used with hysteretic damping in FLAC3D. This can be estimated fromthe range of the equivalent uniform cyclic shear strains determined from the

SHAKEanalysis.

72ft

0

SHAKEanalysis

57.4ft

36ft

1122 ft/secsC

630 /secs

C ft

610 /secs

C ft

113pcf

125 pcf

107 pcf

0

0.2

0.4

0.6

0.8

1

1.2

0.0001 0.001 0.01 0.1 1 10

strain - %


0

5

10

15

20

25

30

0.0001 0.001 0.01 0.1 1 10

strain %

Dampingratio

Range of (equivalent uniform)

cyclic shear strains ~ 0.04%

5 10 15 20 25 30 35

-2.500

-2.000

-1.500

-1.000

-0.500

0.000

0.500

1.000

1.500

2.000

(10 )-01

ModulusReductionCurve

DampingRatioCurve

Average strain compatible

shear moduli and damping

ratios for each layer:

85.0/ max GG

80.0/ max GG

90.0/ max GG

%0.2rD

%0.4rD

%5.2rD


14/42

Select damping ratio and

modulus reduction

parameters corresponding to

equivalent uniform strain

(typically 50-65% of

maximum strain) -20 -15 -10 -5 0 5 10 15 20

(10 )-04

-2.000

-1.000

0.000

1.000

2.000

3.000

(10 )03Selection of parameters for

Rayleigh damping

0

0.2

0.4

0.6

0.8

1

1.2

0.0001 0.001 0.01 0.1 1 10

strain - %


0

5

10

15

20

25

30

0.0001 0.001 0.01 0.1 1 10

strain %

Dampingratio

shear strain vs

shear stress for soil

with Rayleigh

damping:

G/Gmax = 0.8

Dratio = 4% andfreq. = 1.0 Hz

Select hysteretic

damping curve to

approximately fitmodulus reduction and

damping ratio curves

over expected strain

range

Selection of parameters

for hysteretic damping

-20 -15 -10 -5 0 5 10 15 20

(10 )-04

-2.000

-1.000

0.000

1.000

2.000

(10 )03

shear strain vs

shear stress for

soil with default

hysteretic

damping model:

L1 = -3.156L2 = 1.904


15/42


16/42

(Byrne,P.M.,Naesgaard,E.,andSeidKarbasi,M.,2007)

CyclicSimpleShearTest

CyclicStressRatio(CSR)

SchematicshowingbasicprincipalsofRothetalmodel

iD =

i

LN/5.0

Roth et al Model

Roth, W.H., Bureau, G., Brodt, G., (1991) Pleasant Valley Dam: An Approach

to Quantifying the Effect of Foundation Liquefaction, 17th International

Congress on Large Dams, Vienna, 11991223.


17/42

Finn-Byrne Model

Forsimpleshearloading(dryconditions):

1

1

0.4exp

B B

v vCC

1.25

1 1 608.7C N

Volumetricstrainincreases

withlevelofcyclicshearstrain

Forgiven ,rateofaccumulation

decreaseswiththenumberofcycles

Volumetricstrainincreaseswhen

SPT decreases

Amplitudeofcyclicshearstrain

1

B

v

C

Numberofcycles

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

x10 2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1 60( )N

Byrne, P. M. (1991) A Cyclic ShearVolume Coupling and PorePressure Model for Sand, in

Proceedings : Second International Conference on Recent Advances in Geotechnical Earthquake

Engineering and Soil Dynamics (St. Louis, Missouri, March 1991), Paper No. 1.24, 4755, 1991

Wharf Deck and Pile PropertiesDeck (shell structural elements)

elastic modulus, Poissons ratio,

thickness, unit weight (mass density)

Pile (pile structural elements)

elastic modulus, Poissons ratio,

radius

Pile/SoilInterface(defaultbehavior)

shearstiffness,cohesion,friction,

normalstiffness,cohesion,friction,

perimeter


18/42

Step1:

Estimate

representative

soil

and

structure

properties










Checkstability









Mejia&

Dawson(seeproceedingsofthe4th International

FLACSymposium

paper0410)presentaverycleardescriptionofthewaysinwhichseismicinput

maybeappliedtoamodel.(Thefiguresinthissectionarereproducedfromtheir

paper,withpermission).

Therearetwomainoptions

1. Rigidbase(velocityoraccelerationhistoryapplieddirectly)

2. Flexible base(velocityhistoryconvertedtoappliedstresshistory)

Ifthetargetmotionisprovidedforanylocationexceptforthebaseofthe

model,thendeconvolutionisnecessary,todevelopatimehistorytobe

appliedatthemodelbasesuchthatthesimulationwouldreproducethe

targetmotionatthespecifiedlocation,underfreefieldconditions(e.g.,no

structures).

NormallytheprogramSHAKEisusedfordeconvolution.SHAKEisan

equivalentlinearprogram,andisthusunabletofollownonlinearity

directly;itadjuststhesecantshearmodulusanddampingofeachlayer

iterativelytoobtaintheapproximateeffectofnonlinearity,averagedover

thewholetimehistory.

SeismicInput


19/42

EarthquakeDeconvolution

Seismicinput

SHAKEworksinthefrequencydomain,

usingthe

sum

of

the

upward

and

downwardpropagatingwaves.Ateach

interfacebetweenlayers,thereisan

analyticalsolutionforthereflected&

transmittedportionsofeachwave.By

solvingtheresultingsystemofequations,

transmissionbetweenanytwolocations

(e.g.,betweenbase&surface)maybe

computed.

SHAKEinput&outputisavailableeither

1. attheboundarybetweentwolayers termedwithinmotion,whichisa

superpositionofupwardanddownwardpropagatingwaves;or

2. atanotionalfreesurfaceofthesamedepthastherequestedlayer

boundary themotionthatwouldoccuratanoutcropfreesurface.

Thus,theoutcropmotionissimplytwicetheupwardpropagatingwave.

(AfterMejia&Dawson,2006)


20/42

ForarigidFLAC3Dmodelbase,thefollowingexampleillustratestheprocedure.

Notethatthewithinmotion(at60m)istheactualmotionatthat

depth thesumofupwardanddownwardpropagatingwaves.


TheuseofSHAKEtocomputetherequiredinputmotionfortherigidbaseofaFLAC3Dmodelleadstoagoodmatchbetweenthetargetsurface

motionandthesurfacemotioncomputedbyFLAC3D,foramodelthat

exhibitsalowlevelofnonlinearity.(Theinputmotionalreadycontainsthe

effectofallthelayersabovethebase,becauseitcontainsthedownward

propagatingwave).

AdifferentapproachmustbetakenifFLAC3Distomodelmorerealistic

systems,suchas

1. sitesthatexhibitstrongnonlinearity;or

2. theeffectofasurfaceorembeddedstructure.

Inthefirstcase,therealnonlinearresponseisnotaccountedforbySHAKEinitsestimateofthebasemotion.

Inthesecondcase,secondarywavesfromthestructurewillbereflected

fromtherigidbase,causingartificialresonanceeffects.


21/42

Formostsitesencounteredinpractice(exceptthosewheretheexistenceofaverystiffbedrock

justifiesarigidbase)aflexiblebasetotheFLAC3Dmodelshouldbeused.Inthiscase,thequiet

baseconditionisselected,andtheupwardpropagatingwaveonlyfromSHAKEusedtocompute

theinputstresshistory.(Thisisderivedastheoutcropvelocityhistory,convertedtoastress

historybyusingtheformula ).S

C v


Note that

FLAC3Dchoosesitstimestepfornumericalstabilitybasedonthepwavespeed

where

Thus,small,stiffzones(elements)determinethetimestep.

Zonesizesshouldbechosensmallenoughtoresolvethesmallestwavelength:e.g.,

( / )sC f

minP

xt

C

43

P

K GC

min /10x

Evaluate Seismic Motion Characteristicsdeterminefrequencycontentofinputmotion

determinecutofffrequencyforreasonablemodelsize andruntimes

checkresidualdrift(Isbaselinecorrectionneeded?)


22/42

Effect of zone size

High frequencies should be avoided in input waveforms,

to reduce the minimum wavelength (try filtering).

time time

min /10x min /10x

Checkfrequencycontentofinputrecord

FLAC (Version 4.00)

LEGEND

7-Mar-04 23:32

s te p 0

TablePlot

Table 1

5 10 15 20 25 30 35

-2.500

-2.000

-1.500

-1.000

-0.500

0.000

0.500

1.000

1.500

2.000

(10 )-01

JOBTITLE : AccelerationRecord


Minneapolis,Minnesota USA

FLAC (Version 4.00)

LEGEND

7-Mar-04 23:32

s te p 0

TablePlot

Table 2

5 10 15 20 25

0.200

0.400

0.600

0.800

1.000

(10 )-04

JOBTITLE : Power Spectrum (power versus frequency)


Minneapolis,Minnesota USA

Inputaccelerationrecord

Powerspectrum(fromFFT.FIS)

time

frequency


23/42

Step1:

Estimate

representative

soil

and

structure

properties










Checkstability









2D Extrusion ToolConstruction View


24/42

2D Extrusion ToolExtrusionView

FLAC3D Grid


25/42

FLAC3D Gridwith Wharf and Piles

Pile Elements connected to

Shell Element

shell element

pile element


26/42

Initial Pore Pressure Distribution

6000 (psf)

5000

4000

3000

2000

1000

0

Factor of Safety*

*based upon the strength reduction method


27/42

Step1:

Estimate

representative

soil

and

structure

properties










Checkstability









Steps to apply dynamic boundary conditions

for the FLAC3D model

1. Apply free-field boundaries along the sides of the model afterall

other grid conditions are set.

2. Apply quiet boundaries along the bottom of the model.

3. Apply compliant boundary at base by converting input wave into a

shear stress wave where and Cs are properties of

the material at the model base and is the deconvoluted velocity.

4. Monitor velocities at selected locations during test runs to check that

the applied input wave at the base is appropriate.

sss vC 2

sv


28/42

Dynamic Boundary Conditions

Free-Field Lateral Boundaries

Quiet Base Boundary

Input Velocity at Base

Time (seconds x 10)

0.75

0.60

0.45

0.30

0.15

0.0

-0.15

-0.30

-0.45

-0.60

-0.75

Velocity

(ft/sec)sv


29/42

Perform undamped elastic and Mohr-Coulomb

seismic simulations to check model conditions:

- monitor maximum elastic shear strains that develop

- monitor frequencies for natural response of materials

- check that applied dynamic loading is correct

- check lateral dynamic boundary conditions

- check use of quiet boundaries along model base

- check distance of boundaries from region of interest

Velocity at Base and Crest

Time (seconds x 10)

0.75

0.60

0.45

0.30

0.15

0.0

-0.15

-0.30

-0.45

-0.60

-0.75

Velocity

(ft/sec)sv

0.90

-0.90

x-velocity at base

x-velocity at crest


30/42

Excess Pore Pressure Distribution at 20 sec(with Finn-Byrne material)

2400 (psf)

2000

1600

1200

800

400

0

Excess Pore Pressure Histories(with Finn-Byrne material)

1100

1000

900

800

700

600

500

400

300

200

100

0

Pressure

(psf)

Time(secondsx10)


31/42

PileDisplacementVectors at 20 sec

(with Finn-Byrne material)

max. displacement (at 20 sec.) = 3.65 ft.

PileMomentsat 20 sec

(with Finn-Byrne material)

1200

1000

800

600

400

200

0

200

400

600

PileMoments(kft)


32/42

General Comments1. This model is composed of 156,000 hexahedral zones,

400 pile elements and 6480 shell elements.

2. A dynamic simulation for 10 seconds of seismic

loading requires approximately 1 day to complete on

an Intel four-core i7 (2.67GHz) computer. (FLAC3D is

multi-threaded, so faster runtimes can be expected on

computers with more cores.)

LateralLoadingofASinglePile

NumericalLoadTests


33/42

LateralLoadingofSinglePile

PileDesign:Responseofasinglepiletolateralloading

DevelopcasespecificpycurvesaccountingfortheeffectofSoillayering

Rotationfixityconditionathead

Pilebendingstiffness

Pilecrosssection

GroundSlope

AxialloadInteractionwithotherloadsnearby

FLAC3DModel

ConcretePile:0.6m(2ft)diameterand6m

(16.4ft)long

Axialloadof100kN (22500lbs)

Embeddedinsoilwith=35andc=1kPa(42

psf)

Freetorotateatthetop


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SoilPileInterface

Interfaceneededbetweensoilandpile

elementstocapture

Notensionatpilesoilinterface(developmentof

gapbehindthepileindirectionoppositeto

loading)

Slipatpilesoilinterface

Properties:Normalstiffness,Shearstiffness,

Shearstrength(CohesionandFrictionangle),TensilestrengthandDilationangle

InterfaceElement


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GuidelinesforInterfaceProperties

Stiffness:

Notveryimportantasweareinterestedonlyinslipandseparation

Usevaluesstiffenoughnottoaffectresultsbutnottoostifftopenalizetimesteptoomuch.

Cohesionandfriction:About2/3timesthatofsoilunlessbetterdataavailablefromtesting

min

4

3, 10maxn s

K G

k kz

FLAC3DGrid


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Step1:StressInitialization(PileWeight)

Units:Pa

Step2:VerticalLoading

Units:Pa


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Step3:LateralLoading

YieldingZones

Step3:LateralLoading(final)


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Pycurves(Freehead)

Pycurves(Noheadrotation)


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Slopingground(upslope)

Slopingground(downslope)


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Pycurves(upslope)

Pycurves(downslope)


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General Comments

1.This model is composed of 3276 hexahedral

zones

2.A dynamic simulation for 0.8 inches of lateral

movement at head requires approximately 30

minutes to complete on an Intel four-core i7

(2.67GHz) computer.

Final Comments

1. Know the limitations and capabilities of the numericalanalysis program you are planning to use. Does thecode have sufficient capabilities to simulate theimportant conditions of the problem?

2. Start as simple as possible. It is better to add complexity as necessary.

3. Check and calibrate the model (with other solutionmethods, or in-situ data, if possible) throughout themodel simulation.


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Thank You for Attending !!

Questions ??

For more detailsWeb:www.itascainternational.com

Email:[email protected]

three dimensional lateral load analysis of pile foundation by roger hart ppt

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