Computer Simulation for Civil Structural Civil-Structural Applications ...

Computer Computer Simulation for Civil Structural Civil-Structural

Applications using ANSYS

Peter R Barrett P EPeter R. Barrett, P.E.Hsin-Hua Tsuei, Ph.D.

November 10 2004

© 2004 CAE Associates

November 10, 2004

Computer Aided Engineering Associates, Inc. 2

ANSYS / CivilFEM / CFX Agenda

• Who we are?• What software we Represent?• Nonlinear Structural Analysis • CivilFEM Pre- / Post-processing• Computational Fluid Dynamics (CFD)


Who is Computer Aided Engineering Associates

• Engineering Consulting Firm• ANSYS Channel Partner (ASD since 1983)

– Value Added Reseller• Engineering Seminars• Custom Software Development

Conveyor Belt at Olympic Canoe Kayak Slalom Center


CAEA - ANSYS Services

Customer Training

Technical Support

Software Sales


Who we are?

• CAEA is a 25 year old consulting company that provides solutions to complex Structural, Thermal and Fluid analysis problems.

• CAEA is a value-added re-seller for ANSYS, ANSYS/LS-DYNA, ANSYS/CFX and associated software now including CivilFEM

• CAEA is a world leader in Finite Element Training providing exclusive ANSYS training for:

— General Electric Aircraft Engines, Power Generation, R&D— United Technologies (Pratt & Whitney, Sikoirsky, Otis Elevator,

Hamilton Sundstrand, and Carrier)— IBM Research Center


Nicholas M. Veikos, Ph.D., PresidentPeter R. Barrett, M.S.C.E., P.E., Vice President

Michael Bak, Ph.D., Project Mgr.Kenneth R. Brown, Ph.D., Sr. Project Engr.Patrick Cunningham, M.S.M.E., Project Mgr.

Dan Fridline, Ph.D., Project Mgr.Steven Hale, M.S.M.E., Project Mgr.

Stan Kelley, M.S.M.E., P.E.,Applications Engr.James Kosloski, M.S.M.E., Project Mgr.Lawrence L. Durocher, Ph.D., DirectorHsin-Hua Tsuei, Ph.D., CFD Manager

CAEAI Technical Staff


Engineering Consulting Firm – Sample Projects

Large concrete dams require detailed analyses to evaluate their strength and stability. CAEA has evaluated the safety of large concrete dams subjected to flood and earthquake loading conditions. 3d cracked-base analyses are performed in an automated sequence, which updates the uplift loading as a function of crack growth. CAEA has worked with clients that have required analyses to be performed to meet either FERC or the Corps of Engineers licensing criteria.



• Nuclear Transportation Cask Analysis— Drop Events— Thermal-Stress Analysis— The analyses were reviewed by the NRC and

approved without any follow-up required.



• Subcontractor for NIST’s World Trade Center 1,2 & 7 collapse evaluations

• Under solicitation number SB1341-03-R-0044, a purchase order has been awarded to Simpson Gumpertz & Heger Inc. (SGH) of Waltham, Massachusetts, to determine the response of structural components and systems to the fire environment in the World Trade Center towers and to identify probable structural collapse mechanisms. SGH is partnering with Computer Aided Engineering Associates (CAEA), anengineering consulting company specializing in advanced engineering analysis services. CAEA specializes in thermal-stress analysis and has extensive experience in applied mechanics, dynamics, contact mechanics and finite element code development.

• Under solicitation number SB1341-03-R-0028, a purchase order has been awarded to Gilsanz Murray Steficek LLP (GMS) of New York City and its team composed of Dr. John Fisher of Lehigh University, Pennsylvania, and Computer Aided Engineering Associates Inc., of Woodbury, Connecticut.

• See wtc.nist.gov for details


ANSYS Channel Partner (used to be ASD)

• ANSYS Reseller since 1983• Technical Support

— Hotline Phone / Email Support• Software & Engineering

• Customized Training— Group & Individual Training

• Software Development— Analysis Templates— Macros— Custom GUI’s— Solution Sequences— User Elements


What software we Represent?

• ANSYS— Multi-physics— Structural— Heat Transfer

• Civil/FEM• ANSYS LS-DYNA

— Explicit Dynamics• ICEM-CFD

— Pre- / Post-Processing• CFX• SAP-ANSYS Translator


Structural Analysis Capabilities

• Linear Stress Analysis• Contact• Plasticity• Large Deflection – P-Delta Effects• Full Element Library

— Beams— Shells— Plates— Solids— Pipes— Springs— Etc.


ANSYS/Structural features cont.

• Dynamic Analysis:— Modal Analysis

• Axial symmetry, Cyclical symmetry and prestressed structures— Seismic Analysis:

—Spectral (simple and multiple)—PSD (Handom vibrations)—Accelorograms (Linear and non linear transient analysis)

— Harmonic Analysis:—Foundations—Harmonic loads (Wind, wave,etc)

— Linear and non linear transient analysis :—Explosions—Impacts—Traffic—Etc.


ANSYS/Structural Features

— Special/Advanced and non linear finite elements:• Non linear reinforced concrete element Cables, membranes,

springs and contact elements• Plastic beam elements and 3D non symmetric beam elements• Piping elements• Prestressed element (anchorages,etc)

— Beams and shells elements with soil foundation stiffness— Elements Birth and Death capability with a simultaneous change

in the material properties. Simulation of construction process (tunnels, dams, bridges, installations, etc)


ANSYS/Thermal Features

• Thermal— Steady-state

• Conduction• Convection• Radiation

— Phase change— Transient

• Conduction• Convection• Radiation

Thermal Study of a Concrete Dam


ANSYS – The Program

• ANSYS can be run in either interactive or batch modes.

/solu

ksel,s,loc,x,0

DK,all, ,0,,1,UX,ROTY,ROTZ

allsel

!

DK,2001,all,0,,0,

acel,,386.4

!bfunif,temp,1000

bfe,all,temp,1,1200,

sfa,all,2,pres,2

tref,70

nlgeom,on

nsubst,10,100,10

outres,all,all

solve

/POST1

plns,s,eqv


ANSYS – GUI Layout

Output Window

Icon Toolbar Menu

Abbreviation Toolbar Menu

Utility Menu

Graphics AreaMain Menu

Input Line

Current SettingsUser Prompt Info

Model Control Toolbar


ANSYS Commands

• ANSYS is a command driven program— All GUI menu picks generate and submit a command or series

of commands to the program.— All commands are stored in the log file.

— Commands can also be manually typed in the input box.

— Or read in from a script/macro file


ANSYS Main Menu

• Expandable tree structure format.

• Contains the main functions required for an analysis organized in a top down fashion.— Preprocessing— Solution— Postprocessing

• Work down through the menus in the general order that steps should be performed in an analysis.


Scripting in ANSYS

• ANSYS has a powerful built-in scripting language called APDL

— APDL stands for ANSYS Parametric Design Language,— It is a scripting language that you can use to automate common

tasks or even build your model in terms of parameters (variables).

— APDL also encompasses a wide range of other features such as:

• Repeating a command• Macros• If-then-else branching• Do-loops• Scalar, vector and matrix operations.


• Parametric models are setup as input files or macros— They allow for rapid design modifications

• Changes in dimensions, material properties, mesh density, etc.

— Recommended procedure:• Create a first pass at a model using parameters for design variables• Copy the jobname.log file to another file name to be used as your

parametric input file.• Modify the design parameters in the input file• Read the input file into ANSYS to solve the new analysis with the

design changes

Parametric Modeling with Input Files

Example: Parametric Plate Model

length = 20

width = 5

thick = 0.25

/prep7

rect,0,length,0,width

r,1,thick…


Workbench Environment


Example of LS-DYNA Blast Analyses

• Example Analysis• Material Properties• Loading Input• Reference


Example Analysis – FEA Model

• Mode Includes:— TNT loading— Nonlinear Concrete Material Law— Failure @ tensile Stress of 450 psi— Contact After Failure


Example Analysis – Loading

• Area of Blast Impact (Elements with 2) – Center of charge is 30ft above


Example Analysis – Results

• Compressive Stress @ time = .03 sec



• Tensile Stress @ time = .4 sec



• Vertical Displacement @ time = 1 sec


RE: Concrete Damage under BLAST Loading

• The damage formulation in Mat 16 Pseudo-TENSOR can be used to model concrete damage under blast loading:

• >If you want, i.e. reduced or zero strength in damaged elements, add erosion to remove the zero-strength elements that are highly deformed and controlling the time step.

• >In LS-DYNA, version 971, will add two erosion criteria that should help, i.e. a maximum pressure and minimum principal strain,


$ LSDYNA Model for Concrete

$

*MAT_PSEUDO_TENSOR

……..

*EOS_TABULATED_COMPACTION

……..

*MAT_ADD_EROSION

………

RE: Concrete Damage Material Input




ANSYS/LS-DYNA Applications

• Modeling structural elements — reinforced concrete beams — reinforced concrete shear walls — steel beams — cables — masonry

• Nonlinear Material Models for Steel, Concrete, Soil and Soil-structure Interaction

• TNT input for blast Simulation• Representation of Energy Dissipation and Isolation

devices— Modelling techniques such as Damping

• Detailed pre- and post-processing


LS-Dyna Application Examples

• Application of 3D Finite Element Modeling in Pavement Analysis and Design

— Samir N. Shoukry Gergis W. William West Virginia University • Application of DYNA3D to Non-Linear Soil Structure Interaction

(SSI)Analysis of Retaining Wall Structures— Stefan Stojko NNC Limited

• Non-Linear Analysis of a Reinforced Concrete Structure under SeismicLoading

— Dr. Neil Kirk Mr. Andrew Rushton Mr. Jeremy Sargent WS Atkins Science & Technology

• Seismic and Soil Mechanics Applications Using LS-DYNA — Jeremy M. TandyBrian D. Walker Ove Arup & Partners

• Simulation of the Refloat Operation for a Large Marine Structure Using Offshore-DYNA

— M.D. KempP.P. JacobR.D. JonesB.N. MakerD.J. Wynne Reverse Engineering


CivilFEM for ANSYS

• OEM Agreement ANSYS, Inc. - INGECIBER S.A.— Ingeciber is the world-wide responsible of the distribution and

development of the solution ANSYS + CivilFEM— Combined products (ANSYS/Structural + CivilFEM) specifically

for the the Civil Engineering sector.— Independent commercialization.

• Objective:— ANSYS + CivilFEM becoming the world-wide leading solution

for the Civil Engineering sector with medium and high end needs.


CivilFEMfor

ANSYSINGECIBER, s.a.

forANSYS

CivilFEM for ANSYS® ®

CivilFEM is the best customization for the construction and Civil Engineering fields of the powerful Finite element software “ANSYS”.

The combination of both programs fully integrated into one product enables the user to simulate and analyze projects of high complexity and technologically more advance.

ANSYS+CivilFEM allows to solve with only one software a wide range of reinforced concrete structures, steel structures, prestressed concrete, geotechnical applications, bridges, dams, foundations, etc.


CivilFEMfor


forANSYS

CivilFEM INTROCivilFEM using ANSYS pre, post and solving capabilities, adds more than 250 new features and specific utilities for the Civil engineering field. CivilFEM can be purchased as “add-on” to any ANSYS product or as a “Bundle” product as ANSYS/Structural Opt.I, II or III.

ANSYS

PREPROCESSOR

SOLUTION

POSTPROCESSOR

PREPROCESSOR

ADITIONAL OR COMPLEMENTARY ANALYSIS

POSTPROCESSOR

CivilFEM INTRO

+Specific Modules

ANSYS CivilFEM (Features added to Ansys by CivilFEM)

ANSYS + CivilFEM “BUNDLE”(Bundle product)


CivilFEMfor


forANSYS

CivilFEM Product LineANSYS+CivilFEM (Unlimited) Bundle Products

Specialized Modules

Geotech

Bridges and Civil Non Linearities

Advanced Prestressed Concrete

Custom

Ansys/Multiphisics+CivilFEM INTRO Unlimited

Ansys/Mechanical+CivilFEM INTRO Unlimited

Ansys/Structural +CivilFEM INTRO Unlimited

Ansys/Professional +CivilFEM INTRO Unlimited

Ansys/Structural OPT I+CivilFEM Intro OPT I(32,000 nodes/elements)

Ansys/Structural OPT II+CivilFEM Intro OPT II(8,000 nodes/elements)

Ansys/Structural OPT III+CivilFEM Intro OPT III(2,000 nodes/elements)


SAP2000 to ANSYS Translator

• The model translator is written in a combination of Tcl/Tk and ANSYS APDL commands.

• This allows the program to work seamlessly within the ANSYS Graphical User Interface.

• The translator utilizes a wizard style format requiring minimal user interaction.

• Translation status indicators allow user to track progress.

• Summary report with translation tables will be added for final product.


Model Translation

• ANSYS keypoints, lines and areas represent all elements in the SAP model

— The SAP joint coordinate file is changed to a sequential Keypointlisting. Each Keypoint has a corresponding alphanumeric array character that can be used to cross-reference to the SAP model. This allows for a one-to-one correspondence with the SAP model.

— Each beam element in SAP is defined as a Line in ANSYS. Meshing is initially performed with a large element size such that each line will be meshed with a single element. This will allow for a one-to-one correspondence with the SAP model. Mesh refinement is possible by refining the lines

— Each shell element in SAP is defined as an Area in ANSYS. Meshing will initially be performed with a large element size such that each area will be meshed with a single element. Mesh refinement is possible on individual areas.


Translator Features Frame Sections Properties

• SAP “FRAME SECTION PROPERTIES…” tables are parsed and used to create beam section definitions in ANSYS.

• Both section properties and real constants are created to allow switching between BEAM44, BEAM24 and BEAM188/189elements.

• Section properties are defined using the parameters found in the SAP file (no fillets, tapers, etc. considered).

• Real constant properties are defined using the AISC values of Area, I22, I33, etc. found in SAP file.

y

z

SAP ANSYS


Translator Features: Frame Example

• Sample SAP model consisting of a 2x2x2 frame structure.

• Two frame sections defined:

— C10x20— W18x35

• Local joint axes and local frame axes defined.

• Dead (gravity) load applied.


Translator Features Frame Example

• Translation of Frame Sections and Frame Local Axes


Translator Features: Frame Example Results

• Reaction Forces:

Vertical Reaction Force (kip)Joint/Node SAP ANSYS 1 1.767 1.7664 4 3.130 3.1277 7 1.914 1.9130 10 2.802 2.8007 13 4.485 4.4892 16 3.051 3.0502 19 1.953 1.9502 22 3.120 3.1219 25 1.919 1.9158


What are Nonlinear Structural Analyses ?

• Material Nonlinearities (Plasticity, Creep) • P-Delta & large deflection effects• Pre- / Post-tensioned Concrete • Post-buckling Response • Collapse Sequences


Equations for Solution

• The general equation of motion is given by:

• Different analysis types solve different forms of this equation.— Linear static analysis: Derivatives with respect to time are zero, [K] is constant

— Nonlinear static analysis: [K] is a function of load— Modal analysis: F(t) is set to zero, and [C] is usually ignored.

— Harmonic analysis: F(t) and u(t) are both assumed to be harmonic in nature, i.e, Φsin(ωt), where Φ is the amplitude and ω is the frequency in radians/sec.

— Transient dynamic analysis: The above form is maintained.

[ ]{ } [ ]{ } [ ]{ } ( ){ }tFuKuCuM =++ &&&

[ ]{ } { }FuK =

[ ]{ } [ ]{ } 0=+ uKuM &&


Nonlinear Analysis Methods

• To solve a nonlinear analysis ANSYS uses the Newton-Raphson algorithm:

— Applies the load gradually, in increments.— Also performs equilibrium iterations at each load increment

to drive the incremental solution to equilibrium.

— Solves the equation: • is the tangent stiffness matrix• is the displacement increment• is the external load vector• is the internal force vector

— Iterations continue until (difference between external and internal loads) is within a

tolerance.

— Some nonlinear analyses have trouble converging. Advanced analysis techniques are available in such cases (covered in the Structural Nonlinearities training course).

1

23 4

equilibriumiterations


Nonlinear Analysis Example

Example Floor Buckling Simulation:


Linear vs. Nonlinear Analysis

• The Bad News— Are more complicated to set up, run and post-process.— An iterative solution is required. — No guarantee that a converged solution will be obtained. — The problem could take orders of magnitude longer to run

compared to a static analysis.• The Good News

— Allow for a more general response and much more accurate results.

— Current Software is much better at automating the process— Computers are CHEAP and fast enough to solve very complex

analyses today that were not possible even 2 or 3 years ago.


Example Nonlinear Behavior

Geometric Nonlinearities: • Large deflections• Large rotation• Stress stiffening

– Cables– Membranes

—Membrane when taut pick up bending stiffness

– Spinning structures



• Example of nonlinear geometry – a thin rectangular plate with a pressure loading.

— One-quarter of plate is modeled using symmetry.— Plate is 20” x 20” x 0.1” thick.


NonlinearLinear


Comparison of linear and nonlinear analysis results:


Plate Under Uniform Pressure

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Vertical Displacement

Tota

l For

ce

Large Deflection

Linear analysis


Force-deflection results plotted for linear and nonlinear analyses:


Simple Column Buckling under Temperature


Material Nonlinearity

• Robust implicit material integration algorithm• Consistent tangent stiffness matrix• Plane stress algorithm for plane stress and shell elements• The temperature dependent data table is applicable to all

material models


Material Modeling

• Examples of linear and nonlinear stress-strain curves:

• Example of nonlinear creep behavior:

t

ε

SecondaryTertiary

Primary

Rupture

( ) ( ) ( ) ( )Tftfffcr 4321 εσε =&

Strain

Stress

Elastic modulus(EX)

Strain

Stress


Combination of isotropic and kinematic hardening

Chaboche nonlinear kinematic hardening

Multilinear kinematic hardening

Bilinear kinematic hardening

Isotropic hardening

ANSYSMaterial


• Plasticity

Combination of creep and bilinear kinematic

hardening plasticity

Combination of creep and isotropic hardening

plasticity

Rate-dependent plasticity

Creep

Anand’s model

ANSYSMaterialRate-independentRate-dependent/Creep


Nonlinear Material Behavior

• Material Nonlinearities — Plasticity— Hyperelasticity— Viscoelasticity— Creep

t

ε

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

-0.5 0 0.5 1 1.5 2 2.5ε

σ

Yield Point σy

Elastic Plastic

Unloading


Loaded Springback

Material Nonlinear Behavior

An example of material nonlinear – plasticity of clip.


Force vs. displacement

0

0.02

0.04

0.06

0.08

0.1

0.12

0 0.005 0.01 0.015 0.02 0.025 0.03

Displacement

Forc

e

Force vs. Displacement

Plastic Strain

Force - Deflection

Material Nonlinear Behavior

FEA predicts permanent set in “plastic” part.


Concrete

Drucker-Prager

Cast Iron Plasticity

ANSYSMaterial model


• Other Material ModelsUniaxial Tension & Compression Data

-6.00E+08

-5.00E+08

-4.00E+08

-3.00E+08

-2.00E+08

-1.00E+08

0.00E+00

1.00E+08

2.00E+08

3.00E+08

4.00E+08

-0.0250

-0.0200

-0.0150

-0.0100

-0.0050

0.0000

0.0050

0.0100

Strain

Stre

ss (P

a)

Uniaxial TensionUniaxial Compression

Opposite Biaxial Loading

-60000

-40000

-20000

0

20000

40000

60000

-0.0060

-0.0040

-0.0020

0.0000

0.0020

0.0040

0.0060

0.0080

Strain

Load

(N)

Experimental - Strain X ANSYS Output - Strain X

Experimental - Strain Y ANSYS Output - Strain Y

Cast Iron Model compared with Experimental Results


Strain Measures

Engineering vs. True Stress-Strain• If presented with engineering stress-strain data, one can convert these

values to true stress-strain with the following approximations:— Up until twice the strain at which yielding occurs:

— Up until the point at which necking occurs:

— Note that, only for stress conversion, the following is assumed:

• Material is incompressible (acceptable approximation for large strains)• Stress distribution across cross-section of specimen is assumed to be

uniform.

engσσ = engεε =

( )engeng εσσ += 1 ( )engεε += 1ln


Mises Yield Criterion

• A common yield criterion is the von Mises yield criterion (also known as the octahedral shear stress or distortion energy criterion). The von Mises equivalent stress is defined as:

• In tensor form, this can be expressed as

where s is the deviatoric stress, defined as the stress tensor plus thehydrostatic stress

( ) ( ) ( ) ( )[ ]222222 621

xzyzxyxzzyyxo τττσσσσσσσ +++−+−+−=

ss :23

=oσ

( )zyxp

p

σσσ ++−=

+=

31

Iσs


Ratcheting & Shakedown

Time

0 2 4 6 8 10

Plas

tic s

train

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

Plastic strain

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Stre

ss (M

Pa)

-1500

-1000

-500

0

500

1000

1500

2000

Time

0 2 4 6 8 10

Plas

tic s

train

0.000

0.002

0.004

0.006

0.008

Plastic strain

0.000 0.002 0.004 0.006 0.008

Stre

ss (M

Pa)

-1500

-1000

-500

0

500

1000

1500

2000

Ratchetting

Shakedown

LoadingControlled StressUnsymmetry

t

σ

RatchettingTB,CHAB,1TBDATA,1,980,224000,400

ShakedownTB,CHAB,1,,2TBDATA,1,980,224000,400,20000


ANSYS Procedure for Concrete

• Up to six sets of temperature-dependent constants may be specified.— A value of “-1” for constants 3 or 4 removes cracking or crushing

behavior, respectively. — Command input shown on left.

Constant Symbol Meaning1 βt Shear transfer coefficients for an open

crack. (defaults to 1e-6)2 βc Shear transfer coefficients for a closed

crack. (defaults to 1e-6)3 ft Uniaxial tensile cracking stress.4 fc Uniaxial crushing stress (positive).5 fcb Biaxial crushing stress (positive).6 σa

h Ambient hydrostatic stress state for use with constants 7 and 8. (default is 0.0)

7 f1 Biaxial crushing stress (positive) under the ambient hydrostatic stress state (constant 6).

8 f2 Uniaxial crushing stress (positive) under the ambient hydrostatic stress state (constant 6).

9 Tc Stiffness multiplier for cracked tensile condition, used if KEYOPT(7) = 1 (defaults to 0.6).

TB,CONC,1,1,9, TBTEMP,0TBDATA,1,ShrCf-OpTBDATA,2,ShrCf-ClTBDATA,3,UnTensStTBDATA,4,UnCompStTBDATA,5,BiCompStTBDATA,6,HydroPrsTBDATA,7,BiCompStTBDATA,8,UnTensStTBDATA,9,TenCrFac



• If rebars are present, their orientation can be displayed via the GUI:

— Utility Menu > PlotCtrls > Device Options > Vector mode [ON]— Utility Menu > PlotCtrls > Style > Size and Shape > Display of

element shapes based on real constant descriptions [ON]— Utility Menu > Plot > Elements

Or via commands:— /DEV,VECTOR,1— /ESHAPE,1— EPLOT

The rebar orientationare shown in red.



• After solution, cracks can be plotted:—Main Menu > General Postproc > Plot Results

> -Concrete Plot- Crack/Crush …or via command:— PLCRACK

Other items such as thestatus (unfailed, crush,open crack, closedcrack), crack orientationangles, and rebarsolution, can also beobtained.In the plot on right, notethat crack orientationand plane are plottedper integration point.


General Creep Equation

• Below is a summary of implicit creep laws available in ANSYS:

ImplicitCreep Equation Description Type TBOPT valueStrain Hardening Primary 1Time Hardening Primary 2Generalized Exponential Primary 3Generalized Graham Primary 4Generalized Blackburn Primary 5Modified Time Hardening Primary 6Modified Strain Hardening Primary 7Generalized Garofalo (Hyperbolic sine) Secondary 8Exponential Form Secondary 9Norton Secondary 10Time Hardening Both 11Rational Polynomial Both 12Generalized Time Hardening Primary 13User Creep 100

( )L& ,,, ttttttcr Tf ∆+∆+∆+= εσε

t

ε

Secondary

Tertiary

Primary

Rupture


Element Birth and Death

Definition of Birth and Death:• Element birth and death allows the user to (re)activate or

deactivate specific elements during the course of an analysis.— Elements can be “born” in a later time during the load history.

This means that the elements are initially deactivated but are later reactivated in the analysis.

— Elements can be “killed” during the load history. This means that the elements cease to provide any significant structural response.

• These changes (activation status) occur at the beginning of a load step and are maintained throughout that load step.

— Element birth and death is a changing status nonlinearity (similar to contact status). They provide a stepped, not ramped,change in the element status (a ‘sudden’ change in status).


ANSYS Elements

• ANSYS has a library of over 150 different elements to choose from.— Each element may have several different configuration options

(KEYOPTIONS)• The 18X series elements are the newest elements in ANSYS and

therefore employ the latest technology and have the most features.Classification Elements

Structural Point MASS212-D LINK13-D LINK8 , LINK10, LINK11, LINK1802-D BEAM3, BEAM23, BEAM543-D BEAM4, BEAM24, BEAM44, BEAM188, BEAM1892-D PLANE2, PLANE25, PLANE42, PLANE82, PLANE83,

PLANE145, PLANE146, PLANE182, PLANE1833-D SOLID45, SOLID64, SOLID65, SOLID92, SOLID95, SOLID147,

SOLID148, SOLID185, SOLID186, SOLID1872-D SHELL51, SHELL61, SHELL208, SHELL2093-D SHELL28, SHELL41, SHELL43, SHELL63, SHELL93,

SHELL143, SHELL150, SHELL181Structural Pipe PIPE16, PIPE17, PIPE18, PIPE20, PIPE59, PIPE60Structural Interface INTER192, INTER193, INTER194, INTER195Structural Multipoint Constraint Elements MPC184Structural Layered Composite

SOLID46, SHELL91, SHELL99, SOLID191

Explicit Dynamics LINK160, BEAM161, PLANE162, SHELL163, SOLID164, COMBI165, MASS166, LINK167, SOLID168

Hyperelastic Solid HYPER56, HYPER58, HYPER74, HYPER84, HYPER86, HYPER158

Visco Solid VISCO88, VISCO89, VISCO106, VISCO107, VISCO108

Structural Line

Structural Beam

Structural Solid

Structural Shell

Classification ElementsThermal Point MASS71Thermal Line LINK31, LINK32, LINK33, LINK34

2-D PLANE35, PLANE55, PLANE75, PLANE77, PLANE783-D SOLID70, SOLID87, SOLID90

Thermal Shell SHELL57, SHELL131, SHELL132Thermal Electric PLANE67, LINK68, SOLID69, SHELL157Fluid FLUID29, FLUID30, FLUID38, FLUID79, FLUID80, FLUID81,

FLUID116, FLUID129, FLUID130, FLUID136, FLUID138, FLUID139, FLUID141, FLUID142

Magnetic Electric PLANE53, SOLID96, SOLID97, INTER115, SOLID117, HF118, HF119, HF120, PLANE121, SOLID122, SOLID123, SOLID127, SOLID128

Electric Circuit SOURC36, CIRCU94, CIRCU124, CIRCU125Electromechanical TRANS109, TRANS126Coupled-Field SOLID5, PLANE13, SOLID62, SOLID98, ROM144, PLANE223,

SOLID226, SOLID227Contact CONTAC12, CONTAC26, CONTAC48, CONTAC49, CONTAC52,

TARGE169, TARGE170, CONTA171, CONTA172, CONTA173, CONTA174, CONTA175, CONTA178

Combination COMBIN7, COMBIN14, COMBIN37, COMBIN39, COMBIN40, PRETS179

Matrix MATRIX27, MATRIX50Infinite INFIN9, INFIN47, INFIN110, INFIN111Surface SURF151, SURF152, SURF153, SURF154Meshing MESH200

Thermal Solid


Truss Elements

• Truss elements have pin joint connections and only allow tension and compression loads, no bending.

— Truss elements available in ANSYS are:

• LINK1 – 2-D element• LINK8, LINK180 – 3-D element• LINK10 – Tension only or

compression only element.• (Nonlinear)• All Elements can have

geometric and material nonlinearities


Capabilities: Element Technologies

• Beam Elements— Analysis features and element technologies are extensive

• Finite strain, large rotation, consistent stiffness terms, etc.— ANSYS

• Supports multi-material beam analysis—Composite beams (e.g. reinforced concrete)

• Handles both open and closed cell cross sections • 3-D visualization of the cross section


Capabilities: Element Technologies

• Beam Sections

•Built-up (multi material).

•Variety of tools for custom cross sections.

•Visualization.

•FEM based section analysis for inertias, shear center, shear stress due to torsion and transverse shears.

•Tapered Cross Sections.

Section Analysis:

ANSYS section treatment is very user friendly, general and accurate.

Visualization of a beam element(Helicopter rotor blade cross section)


ANSYS: Nonlinear, Capabilities: Element Technologies

• Shell Element Composite Support


ANSYS: Nonlinear, Capabilities: Special Treatments

• Pretension Element— An automated way to specify

bolt pretension— Useful for any mechanical

fasteners• Bolts• Rivets

— Replaces trial-and-error techniques

— Uses pretension element PRETS179

• Similar topology to a contact element

• Automated generation capability Stresses Due to Specified

Pretension in Bolt


General Contact

• ANSYS contact element types and features.— Note: 17X series elements are the newest, most feature rich contact

elements

CONTAC12 CONTAC52 CONTA178 CONTAC26 CONTAC48 CONTAC49 CONTA175 CONTA171,172 TARGET169

CONTA173,174 TARGET170

Point-to-Point Y Y YPoint-to-Surface Y Y Y YSurface-to-Surface Y Y Y Y Y2-D Y Y Y Y Y Y3-D Y Y Y Y YSliding small small small large large large large large largeCylindrical Gap Y YPure Lagrange Multiplier Y Y Y Y

Augmented Lagrange Multiplier

Y Y Y Y Y Y

Lagrange Multiplier on Normal and Penalty on Tangent

Y Y Y Y

Internal Multipoint Constraint (MPC)

Y Y Y

Contact Stiffness user- defined user- defined semi- automatic user- defined user- defined user- defined semi- automatic semi- automatic semi- automaticAuto-meshing Tools EINTF EINTF EINTF None GCGEN GCGEN ESURF ESURF ESURFLower-Order Y Y Y Y Y Y Y Y YHigher- Order Y Y (2-D only) Y YRigid-Flexible Y Y Y Y Y Y Y Y YFlexible- Flexible Y Y Y Y Y Y Y YThermal Contact Y Y Y YElectric Contact Y YMagnetic Contact Y Y

Node-to-Node Node-to-Surface Surface-to-Surface


Capabilities Overview: Assembly Contact

• Beam-Solid Assembly — MPC is well suited for Beam-Solid assembly

CERIG type MPC

Pilot node

Solid elements

Beam elements

Contact elements


Capabilities Overview: Assembly Contact

• Beam-Shell Assembly — MPC is well suited for Beam-Shell assembly

Shell elements

Beam elements

Pilot node

Contact elements

RBE3 type MPC


Nonlinear Analysis Solution Sequences

• Static Analysis:— Incremental Analysis Sequences— Automated Time-stepping— Automated Convergence Solution tools— Post-Buckling Analysis Methods (Riks Method)

• Dynamic Analysis:— Nonlinear transient analysis :

—Explosions—Impacts—Traffic—Etc.

— Solution Tools— Damping Response


• There are five categories of loads:

DOF Constraints Specified DOF values, such as displacements in a stress analysis or temperatures in a thermal analysis.

Concentrated Loads Point loads, such as forces or heat flow rates.Surface Loads Loads distributed over a surface, such as

pressures or convections.Body Loads Volumetric or field loads, such as temperatures

(causing thermal expansion) or internal heat generation.

Inertia Loads Loads due to structural mass or inertia, such as gravity and rotational velocity.

Define Loads


Tabular Loading in Commands

• Examples:— SF, all, HFLUX, %tabname%— SF, all, PRES, %tabname%— F, all, FZ, %tabname%— SFA, all, 1, CONV, %tabname1%,%tabname2%

• Structural Analysis: Allowable Primary Variables— Disp., Force, Pressure TIME, X, Y, Z

• Heat Transfer Analysis: Allowable Primary Variables — Temp D TIME, X, Y, Z— Heat Flow F TIME, X, Y, Z, TEMP— Film Coefficient SF TIME, X, Y, Z, TEMP, VELOCITY— Bulk Temperature SF TIME, X, Y, Z— Heat Flux SF TIME, X, Y, Z, TEMP— Heat Generation BF TIME, X, Y, Z, TEMP


Solvers

• Sparse solver:— Default choice for most problems— Superior to PCG for ill-conditioned matrices (number of iterations to

convergence in file.PCS over 1,000)— If unsymmetric matrices (contact with friction) are present.— Uses parallel processing (for all major platforms in 6.0 and later)

• PCG solver:— Works best with fine meshes, 3D models and solid elements –

SOLID185,186,187,95,92, and 45s— Superior to sparse solver if convergence is fast (number of iterations

to convergence in file.PCS in hundreds)• Frontal solver:

— Only for small problems (< 50,000 DOF)• Original direct solver in ANSYS• Still the default for substructure (superelement) generation,

however, for 7.0 users now have the option to specify Sparse.


Buckling Analysis

• Analysis techniques for pre-buckling and collapse load analysis include:

— Linear Eigenvalue Buckling— Nonlinear Buckling Analysis

F

u

Idealized Load Path

Imperfect Structure’s Load Path

Pre-buckling

Linear Eigenvalue Buckling

Nonlinear Buckling

[[Ke] + λ[Kσ(σ0)]]{∆u} = {0}

The above relation represents a classic eigenvalue problem.


Background on Nonlinear Buckling

Summary of Three Nonlinear Buckling Techniques:• Load control, displacement control, and arc-length method are

summarized below. These are three techniques used in the solution of nonlinear static buckling problems.

• There is an additional method, which one can solve buckling problems via dynamics.

Loading Solution Method Pre-Buckling Post-Buckling RestrictionLoad Control Newton-Raphson

MethodYes No Response must have a one-to-one

relationship with respect to force.Displacement Control

Newton-Raphson Method

Yes Yes Response must have a one-to-one relationship with respect to displacement. Sometimes, imposed displacements are not possible (they may not characterize loading conditions well)

Either Arc-Length Method

Yes Yes The arc-length constraint must be satisfied. May not handle responses which are not smooth. For proportional loading only.


• In ANSYS damping is defined as

For Dynamic ANSYS: Damping

]C[C]K[]K)[(]M[]C[NEL

1kk

NMAT

1jjjc ξ

==

++β+β+β+α= ∑∑[C]α[M]β βc [Κ]βj[Ck] [Cξ]

structure damping matrixconstant mass matrix multiplier (ALPHAD)structure mass matrixconstant stiffness matrix multiplier (BETAD)variable stiffness matrix multiplier (DMPRAT)structure stiffness matrixconstant stiffness matrix multiplier for material j (MP,DAMP)element damping matrix (element real constants)frequency-dependent damping matrix (DMPRAT and MP,DAMP)


Modeling Piping Systems with Piping Commands

• Detailed On-line Help with step-by-step procedures:

• The procedure for building a piping model with ANSYS is automated.

• Piping Commands include: PUNIT, PDRAG, BRANCH, RUN, BEND, MITER, REDUCE, VALVE, BELLOW, FLANGE, PSPRNG, PGAP, /PSPEC, PINSUL, and PCORRO.


Piping Analysis using ANSYS


Analysis Results

• Use the ANSYS Postprocessors:— POST1, the General Postprocessor, to review a single set

of results over the entire model.— POST26, the Time-History Postprocessor, to review

results at selected points in the model over time. Mainly used for transient and nonlinear analyses.


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