OpenSees provides a rich set of highly capable modules that support the nonlinear static and dynamic analysis of complex structural systems. Its advanced, object-oriented, open-source format makes it ideally suited for hybrid simulation, where some portions of a structure are modeled numerically, while others are physically tested. Many of the advanced hybrid simulation applications being considered as part of NSF’s George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) and elsewhere require high performance analysis capabilities. Next-generation hybrid simulation techniques require an analysis framework able not only to carry out complex structural computations quickly, but also one that is able to operate transparently within a complex, real time computing and control environment. As such, OpenSees provides an ideal computing framework, and its capabilities will substantially advance the development of hybrid simulation as an effective tool for use by the earthquake engineering community.

The goal of this project is to develop, implement and demonstrate concepts for utilizing OpenSees where a structure is partitioned for the sake of hybrid simulation into multiple subassemblies. One or more of these subassemblies would represent regions of the structure to be physically tested, while other subassemblies would represent regions to be numerically simulated. The modular, object oriented format and information exchange protocols adopted by OpenSees allows its advanced algorithms for solution of the equations of motion and state-determination to be integrated into the real-time Matlab/Simulink control environment commonly used for hybrid simulation.

This project will have a tremendous impact on the range of simulations that can be contemplated using the hybrid simulation approach. It will thereby be of substantial benefit to PEER researchers as well as those involved in hybrid simulation and in the overall NSF NEES program. The project will also significantly expand the capabilities of OpenSees by contributing to its capabilities to analyze partitioned structures and to operate in a real-time operating environment.

1. Develop an overall plan for incorporating OpenSees into a hybrid simulation environment,
2. Implement OpenSees in a real-time computing and control environment (Matlab/Simulink RT software utilizing MTS digital controllers and shared memory (SCRAM-net) communication procedures),
3. Use existing capabilities in OpenSees, as well as new capabilities being developed by others:
   • To allow regions of the overall structure to be partitioned into experimentally and numerically simulated domains;
   • To implement advanced procedures for integration of the equations of motion needed to carryout hybrid simulation, such as mixed implicit-explicit or operation splitting algorithms, and
   • To improve speed and convergence of numerical simulations.
4. Develop the ability to include OpenSees models of the laboratory reaction wall and loading fixtures into control algorithms, or in as assessment of set-up suitability and overall system stability.
5. Incorporate features for simulating the entire structure system using OpenSees. Such analyses might be done prior to a hybrid simulation to assess the behavior of the structure being tested, or to assess the stability and accuracy of the control system. It might be done after a hybrid simulation to help develop and calibrate analytical models for the type of structure being tested.
6. Demonstrate and validate the approach through a series of simple but representative experiments.

This project has just started. As such, the student involved has spent most of his effort in becoming familiar with the equipment and software-operating environment. Items listed in the previous section will be accomplished during the coming year.

It is assumed that concurrent work by researchers at PEER institutions and other NEES shared-used equipment sites will enhance general OpenSees capabilities. These separate efforts include a significant efforts at UC Berkeley to formulate real-time concepts for implementing hybrid simulation to partitioned structures, implementing communication strategies utilizing shared use memory, and developing features within OpenSees for partitioning, substructuring, parallel processing and so on. This project will collaborate as appropriate with investigators undertaking these other efforts and take advantage of the ensuing results where possible.

Work will be conducted to further expand and demonstrate the capabilities of OpenSees to conduct hybrid simulations.

It is anticipated that the results of this project would be widely adopted in laboratories utilizing the hybrid simulation technique.

A operating version of OpenSees capable of carrying out partitioned hybrid simulations will be developed, implemented and assessed through a series of tests.