Introduction of OpenSees
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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.
Introduction of OpenSees
- 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) 1Dhanaji S. Chavan
- 2. OpenSees: Open System for Earthquake Engineering Simulation a software simulate the seismic response of structural and geotechnical system What is OpenSees ? 2Dhanaji S. Chavan
- 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 3Dhanaji S. Chavan
- 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 4Dhanaji S. Chavan
- 5. Modeling: Beam-column elements Continuum elements Wide range of uniaxial materials and section models for beam-columns. 5Dhanaji S. Chavan
- 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 6Dhanaji S. Chavan
- 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 7Dhanaji S. Chavan
- 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 8Dhanaji S. Chavan
- 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 9Dhanaji S. Chavan
- 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 10Dhanaji S. Chavan
- 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 11Dhanaji S. Chavan
- 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 12Dhanaji S. Chavan
- 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 13Dhanaji S. Chavan
- 14. node 1 0 0 node 2 3 0 14Dhanaji S. Chavan 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 15Dhanaji S. Chavan 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) 16Dhanaji S. Chavan
- 17. fix 1 1 1 1 17Dhanaji S. Chavan 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 18Dhanaji S. Chavan
- 19. element elasticBeamColumn 1 1 2 0.25 2.1e5 0.0052 1 19Dhanaji S. Chavan
- 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…???????? 20Dhanaji S. Chavan
- 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. 21Dhanaji S. Chavan
- 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. 22Dhanaji S. Chavan
- 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. 23Dhanaji S. Chavan
- 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……………….????????????? 24Dhanaji S. Chavan
- 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 25Dhanaji S. Chavan
- 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 26Dhanaji S. Chavan
- 27. Different materials behave differently when subjected to load. This behavior is represented by stress-strain curves. e.g. 27Dhanaji S. Chavan Elastic Spring Mild Steel
- 28. Any software analysis goes through….. Preprocessing Solving system of equations Post processing 28Dhanaji S. Chavan
- 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 29Dhanaji S. Chavan
- 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. 30Dhanaji S. Chavan