This document summarizes an upcoming one week workshop on OpenSees at IIT Gandhinagar. OpenSees is open source software used to simulate the seismic response of structural and geotechnical systems. It was developed at PEER and is used for research in performance-based earthquake engineering. The workshop will cover modeling techniques in OpenSees including elements, materials, and solution algorithms. It will also discuss running analyses, registering for OpenSees, and downloading the software.

1. Welcome all for -
One week Workshop on OpenSees at IIT
Gandhinagar
By
Dhanaji S. Chavan,
Assistant Professor, Department of Civil Engg.,
TKIET, Warananagar (Maharashtra)
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2. OpenSees: Open
System for Earthquake
Engineering
Simulation
a software
simulate the seismic
response of structural
and geotechnical
system
What is OpenSees ?
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3. Developed as the computational platform for
research in performance-based earthquake
engineering at the “ Pacific Earthquake
Engineering Resesrch Center”
is also the simulation component for the
NEESit since 2004
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4.  Advanced capabilities for modeling and analyzing the
nonlinear response of systems using a wide range of :
i. Material models
ii. Elements
iii. Solution algorithms
 Parallel computing to allow scalable simulations on
high-end computers or for parameter studies
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5.  Modeling:
 Beam-column elements
 Continuum elements
 Wide range of uniaxial materials and section models for
beam-columns.
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6.  Analysis:
 nonlinear analysis requires a wide range of algorithms
and solution methods
 Provides
 nonlinear static and dynamic methods
 Equation solvers
 Methods for handling constraints
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7.  Registration: link is
 http://opensees.berkeley.edu/community/ucp.php?mod
e=register
 downloading : link is
 http://opensees.berkeley.edu/OpenSees/user/download
.php
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8.  Extract OpenSees.exe file and place it wherever you
wish.
 While Installing Tcl/Tk, make the following change
on the third screen:
 C:/Tcl to C:/Program Files/Tcl
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9.  Three ways to run OpenSees code :
i. Interactive:
 direct input of commands at the prompt
ii. Execute Input File at OpenSees prompt:
 most commonly used
iii. Batch mode:
 Through MS-DOS prompt
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10.  What is the deflection of the free end of a 3 m
cantilever beam subjected to a point load of 100 kN?
(The modulus of elasticity, E =2*1005 kN/m2)
How to do coding for this problem in OpenSees?????
3m
100kN
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11. wipe
model basic -ndm 2 -ndf 3
 wipe :
clears the previous coding present in OpenSees memory, if any
 model basic :
key word to start the definition of model
 ndm :
defines number of dimensions of the problem
 ndf :
defines the degrees of freedom at a node in a model
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12.  ndm: number of dimensions
we have to specify whether problem is 2-dimensional or 3-
dimensional.
How to determine whether problem is 2-D or 3-D:
If to specify the geometry of the problem only two coordinates x and
y are required , it is 2-D problem
If to specify the geometry of the problem three coordinates x,y and
z are required , it is 3-D problem
In present case ndm is 2
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13.  We have to specify degree of freedom at a node
What is degree of freedom?
 The number unknowns ,to be determined, at a node is called
as degree of freedom
 In present case: three unknowns are there at each node
i. translation in x direction
ii. Translation in y direction
iii. Rotation
 In present case dof is 3
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14. node 1 0 0
node 2 3 0
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Command to
define node
Node
number
X coordinate of
node
Y coordinate of
node

15. In finite element method we discretize the given
domain(geometry) into certain number of finite
elements.
 in our case 3 m long beam is the domain
 in present case let’s use only one element for sake of
simplicity.
The ends of an element in finite element method are
called as nodes
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1 2
(0,0) (3,0)

16.  If we assume origin at node 1, the coordinates for node
1 and 2 are as under:
 1(0,0) & 2(3,0)
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17. fix 1 1 1 1
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Command to
define fixity
Node
number
Constrain x-translation
Constrain y-translation
Constrain rotation 

18.  In our case boundary condition is : node 1 is fixed i.e.
 No translation in x direction
 No translation in y direction
 No rotation
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19. element elasticBeamColumn 1 1 2 0.25 2.1e5 0.0052 1
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20.  Which finite element to use to model the behavior of
beam? Why?
 OpenSees has wide range of elements in its library
 Is it fine if we use any element from it?
 Or we have to choose certain element only
 How to decide which element to use ?
…………..Needs some thinking…@ FEM…????????
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21. 1-d element :
 Used for geometries for which one of the dimensions is
quite larger than rest two.
 E.g. beam : in case of beam its length is considerably larger
than its breadth and depth. i.e. x >>> y, z
 In FEM such geometry is represented by just a line. When the
element is created by connecting two nodes, software comes
to know about only one out of 3 dimensions. Remaining two
dimensions i.e. cross sectional area must be defined as
additional input data & assigned to respective element.
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22. 2-d element:
 Two dimensions are quite larger than third one
 E.g. metal plate: length & width are considerably larger
than thickness. i.e. x, y >>> z
 The third dimension i.e. thickness has to be provided as
additional input in coding by user & assigned to
respective element.
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23. 3-d element:
 All three dimensions are comparable
 E.g. brick: x~y~z
 No additional dimension to be defined. While
meshing itself all three dimensions are included.
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24.  In our case, we understood that we have to use 1-d
element.
 Which 1-d element should we use?
 Should we use spring element?
 Or bar/truss element?
 Or beam element
Think……………….?????????????
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25. In present case,
 Shear force &
 Bending moment
will be developed in the cantilever beam.
 We have to choose 1-d finite element in such a way that
it will take both shear force & bending moment
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26.  We can not use spring or bar element because
 Spring element models axial load only
 Bar elements model axial load and axial stress
 However beam element takes axial, shear & bending
stresses. Hence….
 In script………
element elasticBeamColumn 1 1 2 0.25 2.1e5 0.0052 1
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27. Different materials behave differently when subjected
to load.
 This behavior is represented by stress-strain curves. e.g.
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

Elastic Spring


Mild Steel

28. Any software
analysis goes
through…..
Preprocessing
Solving
system of
equations
Post
processing
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29.  Solver takes the data generated in preprocessing,
process(solve) it using specific algorithms and give an
output as a result of analysis.
 Solver is brain of any software
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30. Types of solvers
• Direct solvers:(based on Gauss elimination/ LU
decomposition)
• Iterative solvers:
• error is minimized & solution is converged through
iterative calculations
• User has to set convergence tolerance
• Three types of tolerances: displacement , load, work
• Method used for convergence: Newton Raphson,
modified Newton raphson etc.
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