geo tech examples

8/10/2019 Geo Tech Examples

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Geotechnical Examples using

OpenSees

Pedro ArduinoUniversity of Washington, Seattle

OpenSees Days 2014,Beyond the Basics, Friday September 26, 2014U.C. Berkeley, CA


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Outline! Take advantage of tcl scripting!!

" OpenSees Wiki Geotechnical Examples" Useful links

! Take advantage of pre- and post- processors" GID, just one possible alternative #

! Some recent research projects completedusing OpenSees" Dynamic analysis of piles"

Analysis of complete bridge system" 3D analysis of piles" 3D Analysis of bridge abutment


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Take advantage of tcl scripting!!! tclcan be used to develop scripts for

geotechnical applications.

! Possible applications:" Laterally Loaded Pile Foundation (similar to lpile)" One-Dimensional Consolidation

"

Total Stress Site Response Analysis of a LayeredSoil Column- (similar to shake)

" Effective Stress Site Response Analysis of a layered

Soil Column"

Dynamic Effective Stress Analysis of a Slope" Excavation Supported by Cantelever Sheet Pile Wall

" Other .


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OpenSeesWiki Geotechnical

Exampleshttp://opensees.berkeley.edu/wiki/index.php/Examples


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Other useful tclscripts @

! http://opensees.berkeley.edu/

! http://sokocalo.engr.ucdavis.edu/~jeremic

! http://cyclic.ucsd.edu/opensees/

! http://www.ce.washington.edu/~geotech/opensees/PEER/davis_meeting/

! http://opensees.berkeley.edu/wiki/index.php/Examples


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Pseudo-Static Pile Pushover Analysis

The pile is modeled using the dispBeamColumnelement with an elastic fiber section for linear elasticconstitutive behavior.

This example describes how to run a pushoveranalysis of a pile in OpenSees.

The pile and spring nodes are tied together using theequalDOFcommand.

The soil is represented byp-y, t-z, and Q-zsprings

using the PySimple1, TzSimple1, and QzSimple1uniaxial materials withzeroLength elements.

The model is created in 3D. Pile nodes have 6 DOF,

and the soil nodes have 3 DOF.


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Pseudo-Static Pile Pushover Analysisresults of pushover analysis for a fixed-head pile


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1D Consolidation

A column of soil is modeled in 2D using the9_4_QuadUPelement. This element has nine nodes.The nodes in the corners of the element have anadditional degree-of-freedom for pore pressure.

This example describes how to run a total 1D soilconsolidation analysis in OpenSees.

The surcharge load is applied as a constanttimeseries inside of aplainload pattern. Atransientanalysis is conducted due to the time-dependent nature of consolidation.


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1D Consolidationexcess pore pressure: double drainage single drainage

other results: vertical effective stress vertical settlement


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Total Stress Site Response Analysis

A layered soil profile is modeled in 2D using nodes

with 2 DOF.

This example describes how to run a total stresssite response analysis in OpenSees.

The plane strain formulation of the 4-nodequadrilateral element quadis used for the soil.

Soil constitutive models include:PressureDependMultiYieldPressureIndependMultiYield

Periodic boundary conditions are enforced in horiz.direction using the equalDOFcommand

A compliant base is considered using a viscousdashpot modeled using azeroLength element and theviscousuniaxial material.


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Total Stress Site Response Analysis

Input motion

surface response spectra

comparison with other analytical methods

surface acceleration

surface response spectra


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Effective Stress Site Response Analysis

The approach is similar to the total stress analysis. Alayered soil profile is modeled in 2D with periodic

displacement boundary conditions enforced using theequalDOFcommand and a compliant base is consideredusing a viscous dashpot modeled using azeroLengthelement and the viscousuniaxial material.

This example describes how to run an effective stresssite response analysis in OpenSees.

The 9_4_QuadUPelement is used to model the soil.This element considers the interaction between thepore fluid and the solid soil skeleton, allowing forphenomena such as liquefaction to be modeled.

The PressureDependMultiYield02 constitutive modelis used for the soil.


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Effective Stress Site Response Analysis

summary of soil behavior at three depths within the soil profile


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3D Effective Stress Site Response Analysisdisplacement of soil column during analysis with contours of excess

pore pressure ratio


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Dynamic Analysis of 2D Slope

Model problem:

This example presents a 2D effective stress analysis of a slope subject to an earthquakeground motion.

The elements and constitutive models match those used in the site response analysisexamples.

The free-field soil response is applied to the model using free-field columns which are muchmore massive than the adjacent soil.

Finite element mesh:


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Dynamic Analysis of 2D Slopeexcess pore pressure ratio

shear stress-strain

lateral displacement

excess pore pressure ratio

contours near slope


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Dynamic Analysis of 2D Slopedisplacement of full mesh during analysis showing propagation of shear

stress waves


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Dynamic Analysis of 2D Slopedisplacement near the slope with contours of excess pore pressure ratio

(red is ru= 1.0)


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Excavation AnalysisThis example presents a simulated excavation supported by asheet pile wall using OpenSees.

The InitialStateAnalysis feature is used to create the gravitationalstate of stress in the model without accompanying displacements.

The plane strain formulation of the quadelement is used for thesoil with the PressureDependMultiYield nDMaterial for constitutivebehavior.

The sheet pile wall is modeled using the dispBeamColumnelementwith an elastic fiber section for linear elastic constitutive behavior.

Soil elements to the right of the wall are progressively removed tosimulate an excavation.

The soil-wall interface is modeled using the BeamContact2Delement.


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Excavation Analysisshear and moment in the wall wall-soil contact forces

vertical stress contours shear stress contours


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Excavation Analysis

Nodal displacement magnitude during the excavation analysis


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Excavation Analysis

shear and moment in the wall during the excavation analysis


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! Difficult to create tclscripts for complexboundary value geotechnical problems."

complex foundation configurations

" embankments

" wharves

" bridges

" 3-D analysis

! Need to use pre- and post processors tocreate meshes and visualize results

!

GID, just one possible alternative #

Take advantage of pre- and post-

processors


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GiD Problem Type for 2D AnalysisCreate geometry and select problemType

Assign boundary conditions


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GiD Problem TypeAssign materials to the geometry

Generate mesh and OpenSees input file


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Some research projects completed

using OpenSees"Dynamic analysis of piles

"Analysis of complete bridgesystem

"3D analysis of piles

"3D analysis of bridge abutment


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Dynamic Analysis of Piles in OpenSees


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SPSI modeling in OpenSees


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Two-column Bent

Northridge motion, amax= 0.25g

Northridge motion, amax= 0.74g


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Two-span bridge


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Two-span bridge

Bent-S Bent-L Bent-M


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SPSI of a complete bridge system

Five-span bridge

pile group foundation

abutment

liquefiable soil / various layers

lateral spreading

earthquake intensities

uncertainties


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Five-span bridge

Approach embankments

Variable thickness of liquefiable soil



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Bearing pad spring Pile cap passiveearth pressure

spring

abutmentreaction spring

PressureIndependent Multi

Yield material

clay

Pressure DependentMulti Yield material

liquefiable soil

py(liquefiable)

py spring

(dry sand)

py (stiff clay)

Nonlinear fiberbeam column

Mackie &Stojadinovic

(2003) CL



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OpenSees model

Bridge Idealization



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Northridge motion (0.25g)

time time

Soil Strain Profile during shaking



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Loma Prieta (1.19g)

time time


Soil Strain Profile during shaking


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Erzincan, Turkey 1992 (amax= 0.70g)

displacement

ru

90 cm20 cm


Max. pile demand


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3D Pile Analysis

Solid-Solid Model Beam-Solid Model


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3D Pile Analysis

Axially Loaded Piles$ Evaluation of pile forces and accumulation of side resistance

Self-weight forces

Zero friction under self-weight

Applied force at pile head

Force at pile toe

Full friction mobilization

Sticking interface behavior

Qtotal

Qtoe

Qtotal = Qtoe+ Qside

Qside= !B"fcdz

fc

fc = !h(z) tan "


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3D Pile Analysis

Laterally Loaded Piles (solid-beam contact element)

! Perform numerical load test ! Compare results

3x Magnification


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3D Pile Analysis

Lateral Spreading Effects

The soil is modeled with brick elements and a Drucker-Pragerconstitutive model to capture pressure-dependent strengthThe pile is modeled with beam-column elementsBeam-solid contact elements are used to model the soil-pile interfaceLateral spreading is modeled by applying a free-field displacement profile to theboundary of the model


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The beam-solid contact elements enable the use of standard beam-column elementsfor the pile

This allows for simple recovery of the shear force and bending momentdemands placed upon the pileAdditionally, the surface traction acting on the pile-soil interface can berecovered and resolved into the forces applied by the soil to the pile

3D Pile Analysis



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A rigid pile kinematic is used to evenly activate the soil response with depth and to obtainp-ycurves which are free from the influence of pile kinematics, reflecting only the

response of the soil.

Work with 3D FE models has shown that use of a general pile deformation createsp-ycurves which are influenced by the selected pile kinematics

Computational process

3D Pile Analysis



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3D Pile Analysis


The presence of the weaker liquefied layereffectively reduces the available resistanceof the adjacent portions of the unliquefied

soil

This is manifested in a reduction in theultimate lateral resistance of the p-y curvesnear the liquefied layer

The initial stiffness of the unliquefied soil isalso reduced, but the effect is more local tothe liquefied interface

Homogenous soil profile

Liquefied soil profile


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Shear diagrams Bending Moment diagrams

Location and value of maxV and maxM changeswith soil displacement

3D Pile AnalysisLateral Spreading Effects


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Recent Improvements at UW

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Efficient solid element formulations would greatly benefit the performance of anysimulation

How can we obtain more efficient finite element formulations?

Can this be done?

The integration of a typical 4-node quadrilateral element involves 4 integrationspoints. If this could be reduced to only a single integration point, thats 4 timesless work. In 3D, it would be 8 times less work.

! Reduced integration

! There are issues which must be overcome in order to use single pointintegration. The stiffness matrix becomes rank deficient, leading to

spurious modes

! Stabilization techniques can be used to overcome the rank deficiency

!A single-point integration element with assumed strain hourglass stabilization hasbeen implemented in OpenSees % SSPquad


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Stabilized Single-Point Quad

Element

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Execution time: Quad element = 330 sec SSPquad element = 146 sec

Site response analysis test problem

The single-point element is less computationally demanding than thecorresponding full integration element.


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Modeling Tools and

Improvements

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The SSPquadelement has been extended for use in the analysis of fluid saturatedporous media. This new element has also been implemented in OpenSees %SSPquadUP

The SSPquadUPelement uses a mixed pressure-displacement formulationcommonly known as the u-p approach.

A staggered time integration scheme is used to introduce unconditional stability inthe temporal solution and to symmetrize the coupled system.

Near the incompressible-impermeable limit, this element does not satisfy the inf-sup condition, and stability of the pressure field solution cannot be guaranteed. Aconsistent stabilizing term is added to the system.

Liquefaction and lateral spreading involve saturated soil. When saturated, soilbehavior can be described as a two-phase medium.

Finite element formulations have been developed to consider this aspect of soilbehavior (Zienkiewicz and Shiomi 1984, Prevost)


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Recent Improvements

Stabilized u-p Quad Element

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unstabilized SSPquadUP stabilized SSPquadUP9 node quad element

The effectiveness of the pressure field stabilization near the incompressible limit canbe demonstrated by comparing the pore pressure distribution for stabilized andunstabilized cases.


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Recent Improvements

Stabilized u-p Quad Element

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Surface response spectra

A site response analysis is conducted to gauge the robustness and efficiencyof the SSPquadUP element.


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Other Applications: Piles in

Sloping Ground, Bridge bent

analysis


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ApplicationNumerical Analysis of Mataquito River bridge

1D Modeling Approach


Prototype



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Bridge deck spring

ApplicationNumerical Analysis of Mataquito River bridgeModeling the abutment and grouped shaft foundation


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3D Applied Kinematic Model

ApplicationNumerical Analysis of Mataquito River bridge3D Applied Kinematic Model


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A li i


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ApplicationNumerical Analysis of Mataquito River bridgeDeformation of shafts with contact forces acting on their surfaces


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Application3D Parametric Study


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Liquefiable Layer Thickness

LiquefiableLayer Depth

EmbankmentWidth

1 m

3 m1 m 6 m

3 m

6 m

4 m

8 m

16 m



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Photo by Catalina Prussing

Representative Case History

Llacoln Bridge Concepcin Chile! Across Bo-Bo river - Length : 2160 m! Completed in 2000! Simply supported precast pre-stressed concrete

girder! Column bent with inverted-T cap beam

! Two seismic bars between each adjacent girder

February 27, 2010 Maule earthquake! Moment Magnitude 8.8!

Duration more than 2 minutes! Depth 35 Km! 105 Km North-East of Concepcin


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Bridge Damage Lateral Spreading

! Unseated span due to lateralspreading

Concepcin

San Pedro de la Paz

Source: FHWA-HRT-11-030


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Source: Mitchell, Denis et al (2012)

Source: FHWA-HRT-11-030

Source: Olsen, Michael J. et al (2012)


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UnseatedSpan

!

Relativemovement ofcolumns withrespect to their

bases

Source: Olsen, Michael J. et al (2012)

~ 0 cm

- Increasing from 1.26 cm

to 11.96 cm- Opposite to lateral

spreading direction

- ~ 11 cm

- In thedirection oflateralspreading

- ~ 16 cm

- In thedirection oflateralspreading


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3-D Finite Element Model


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Llacoln Bridge Structural Details


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70.0m

25.0

5m


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Bridge deck spring


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Columns and Piles Sections

Concrete and Steel Uniaxial Material Constitutive Models

Elastic bending stiffness


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Kinematic Loading


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Results Pile Pinning and 3-D Geometrical

Effects

Pile and Column Response

Pier without deck spring

Pier with deck spring

Contour of piles displacements:

Foundation cap depth


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Results Structural Demands

Mmax= 3000 kN.m

Mmax= 4200 kN.m

Mmax= 8900 kN.m

Mmax

= 7100 kN.m

Mmax= 4100 kN.m

Mmax= 3000 kN.m

Relativemovement of

columns head toits base

Free field

displacement = 30.5cm

Effects of foundationcap on the shear

diagram

Columns reached

maximummoment capacity


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Thank You! Questions?

Universidad Nacional deCo doba

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