Why OpenSees is suggested for analysis of structures in research activities? Wouldn’t it have been better to choose an experimental topic? In other words, which approach brings us closer to success more quickly and effectively: numerical analysis or experimental work? If we accept numerical analysis, is OpenSees the best nonlinear structural analysis software?
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The answers to the questions above largely depend on our understanding of several important topics. In this text, we’ll briefly review where we currently stand, what we aim to accomplish with OpenSees, and why we have chosen OpenSees for our work.
The ultimate goal: performance-based structural design
Have you thought about the ultimate endpoint of using OpenSees in nonlinear structural analysis? OpenSees House is working to support you so that your journey doesn’t end at the modelling step. In the short term, our goal is help you gain knowledge, develop skills, and publish one or more high-quality papers. However, your success can be more impactful and enduring—provided you take a long-term view. For further insights on this, explore our content on code-based or prescriptive structural design.
Why Numerical Analysis of Structures?
When choosing a topic to investigate structural behavior, we often face a crossroads: should we take the experimental path or pursue numerical analysis methods? There’s a longstanding notion that experimental data and findings drive the core of scientific advancement. This perspective is somewhat valid in empirical fields like physics, chemistry, and biology. However, in engineering disciplines, our focus shifts toward predicting the behavior of a system that is ultimately designed and built by humans.
In other words, if we were to build and test each structure in a lab before actual construction, what would be the purpose of design methods? “Design” involves estimating the actual forces applied to a structure, along with estimating the structure’s capacity, and ensuring a proper balance between these two aspects. In this process, it is the word “estimate” that ensures the structure can be designed with minimal cost and without the need for a lab prototype.
As we can see, at least in structural engineering, numerical and mathematical methods ultimately play the crucial role in estimating forces and capacities. In other words, the value of experimental methods and results lies in validating and calibrating numerical methods; on their own, they cannot serve as the basis for structural design.
Why Finite Element Analysis?
Once we recognize the importance of numerical methods in structural analysis, another question arises, challenging the suitability of the finite element method (FEM) as a numerical analysis tool. There are various numerical methods for structural analysis, but those that align effectively with the capabilities of computers and programming techniques include the following:
- The Finite Element Method (FEM)
- The Finite Difference Method (FDM)
- The Boundary Element Method (BEM)
- The Discrete Element Method (DEM)
- Mesh-Free Methods
- Adaptive Mesh Refinement
Explaining the features and capabilities of these methods is beyond the scope of this article. However, what has been proven effective, at least in the world of structural engineering, is the maximal efficiency of the Finite Element Method (FEM). In future content on this site, we will delve deeper into the FEM, which is the method used in OpenSees as well as in most of its major competitors.
Why Nonlinear Structural Analysis
What’s lacking in conventional finite element software used for common engineering projects that would make us turn to OpenSees? Essentially, OpenSees views analysis as an inherently nonlinear process, rather than a linear process with nonlinear adjustments, as seen in some other software. This foundational approach makes it more specialized and effective for nonlinear analysis than many of its competitors. More details on this topic are provided in our article on nonlinear structural analysis.
Performance-based structural design with OpenSees
The current major application of OpenSees is researching the structural behavior and providing data for developing prescriptive design requirements. However, as mentioned above, performance-based evaluation and design of the structures is the ultimate goal of employing OpenSees models. That is, realistic and nonlinear analysis of structural behavior is essential for modern structural design methods. These emerging methods, known as performance-based design, are gradually being adopted by engineering communities. Performance-based design requires not only complex and precise structural analyses but also advanced methods for estimating the performance measures interested by stakeholders and policy makers. OpenSees offers capabilities in all these areas that are, to a great extent, unique and unrivaled. We provide further details on this in our article on performance-based structural design (coming soon).
Why choose a framework rather than ready-made software?
Another significant difference between OpenSees and its competitors is the freedom it gives users to implement any desired modeling and analysis approach. OpenSees provides only a collection of primary tools, meaning that users need to identify, assemble, and test the appropriate tools for their specific goals. While this flexibility allows OpenSees to support a wide range of applications, it also comes with substantial challenges and complexities.
The primary challenge lies in having the scientific expertise to correctly select and apply the tools. Another major concern is overcoming unresolved issues that may arise from a new combination of tools. Additionally, the lack of a graphical user interface (GUI) and reliance on text-based input can lead to errors more easily. In other articles on the OpenSees House site, we’ve discussed further important points regarding the benefits and challenges of OpenSees lacking a ready-made GUI.