Introduction to OpenSees

Context for Simulation in Earthquake Engineering

• Research and practice is moving towards Performance-Based Seismic Engineering, which depends on high-fidelity models and simulation to assess performance.
• Simulation models capture knowledge from tests to leverage investment in limited experimentation.
• Community-based, open-source software for simulation promotes innovation in research and advanced applications for practice.
• NEES infrastructure is supporting OpenSees to provide simulation capability and integration with NEESit services for NEES research.

What is OpenSees?

• A software framework for simulation applications in earthquake engineering using finite element methods. OpenSees is not a code.
• A communication mechanism for exchanging and building upon research accomplishments.
• As open-source software, it has the potential for a community code for earthquake engineering.

Simulation Framework

Computation

• • Algorithms
  • Solvers
  • Parallel/distributed computing

Information Technology

• • Software framework
  • Databases
  • Visualization
  • Internet/grid computation

Models

• • Simulation models
  • Performance models
  • Limit state models
  • Material
  • component
  • system models

OpenSees Approach to Simulation

Basic approach

Modular software design for implementing and integrating modeling, numerical methods, and IT for scalable, robust simulation

Focus on capabilities needed for performance-based engineering

Programmable interfaces

Most users

a “code” for nonlinear analysis

Fully scriptable.

Generally

a software framework for developing simulation applications

Remember OpenSees is a Software Framework

• A framework is NOT an executable.
• A framework IS a set of cooperating software components for building applications in a specific domain.
• The OpenSees framework is written primarily in the objectoriented language C++; though other languages namely C and Fortran are also used.
• The abstract classes in the OpenSees framework define the interface. The concrete subclasses that exist the implementations. Other classes can be provided to extend the capabilities of the framework
• Most users, however, will use OpenSees.exe which is, indeed, an executable.

Basics of Object-Oriented Programming

• In object-oriented programming, the program is seen as a collection of objects. Each object is capable of receiving messages, processing data, and sending messages to other objects.
• Each object is of a particular type or Class. The class defines the data and methods of an object.
• 3 basic relationships between classes
  • IS-A (Truss is an Element)
  • KNOWS-A (Truss knows a Node)
  • HAS-A (Truss has a Material)