IDEA StatiCa Quick Tip: How to perform Stiffness Analysis to improve global model accuracy
VIDEO: IDEA StatiCa Quick Tip - how to perform Stiffness Analysis in IDEA StatiCa!
When performing a global analysis of a steel structure, engineers typically assume connections are either fully rigid or pinned. While this simplifies the analysis, real-world connections exhibit some flexibility. By accurately determining the stiffness of a joint, engineers can take advantage of this flexibility in some cases, and optimize their designs for weight, utilization, and cost!
This blog post summarizes key insights from our video tutorial on stiffness analysis in IDEA StatiCa and how it can improve global model accuracy.
How connection stiffness affects structural behavior
IMAGE: In global structural analysis, connections are often assumed to be either fully pinned or fully rigid.
However, accounting for their actual flexibility can improve accuracy and create opportunities for optimization. By incorporating stiffness analysis in IDEA StatiCa, engineers can refine their models, reduce material usage, and lower costs!
In traditional structural analysis, engineers classify connections as either rigid or pinned based on engineering judgment.
This assumption influences the way forces and moments are distributed throughout the structure. However, many connections fall between these extremes—they are semi-rigid and have a degree of flexibility.
By understanding and quantifying this flexibility, engineers can refine their global model and achieve more accurate results. This can lead to more efficient designs, reducing over-conservatism and optimizing material usage.
What is Stiffness Analysis?
Stiffness analysis in IDEA StatiCa allows engineers to evaluate the rotational stiffness of a connection and assign it a stiffness classification: rigid, semi-rigid, or pinned.
The software provides a moment-rotation diagram that helps engineers determine how the connection behaves under loading. This information can be used to refine the global model assumptions, leading to better structural performance predictions.
How it’s done in IDEA StatiCa
Export from global FEA, design the connection
In our demo, we start the process with exporting the structural model from the global analysis FEA software (like SAP2000, or FEM Design) to IDEA StatiCa Checkbot, where connections can be analyzed. Then we design the connection, which can be done either manually, or by using predefined templates from the connection library.
Perform the Stiffness Analysis and review the results
Once the connection is set up, select the connection and switch Analysis type to ‘Stiffness analysis’. The analysis considers different load cases, including moment and shear force combinations.
IDEA StatiCa generates a moment-rotation curve and classifies the connection as rigid, semi-rigid, or pinned!
IMAGE: Stiffness Analysis results in IDEA StatiCa: Stiffness values, moment-rotation curve and classifies the connection as rigid, semi-rigid, or pinned
Re-run the global analysis with the stiffness values for the connections
IMAGE: Re-running the global analysis with the rotational stiffness value calculated in IDEA StatiCa will affect the global analysis results
The initial rotational stiffness value can then be fed back into the FEA software, and the global analysis is re-run to observe how stiffness affects displacements, moments, and force distribution.
Comparing the results between rigid, pinned, and semi-rigid models can reveal significant differences in structural behavior.
Based on this, engineers can fine-tune their designs based on realistic stiffness values, rather than relying on simplified assumptions!
IMAGE: Validate stiffness analysis with the Member application. Compare moment diagrams to see how connection flexibility affects the global structure.
Bonus tip:
The Member app!
The Member application in IDEA StatiCa can be a valuable tool for stiffness analysis. By opening the analyzed frame structure in the Member app, you can further assess how connection flexibility affects overall behavior. This allows you to compare internal forces, moments, and deformations with your global analysis results, providing additional validation of your model.
Beyond stiffness analysis the Member application also helps evaluate stability-sensitive members, including checks for buckling, lateral-torsional buckling, and nonlinear behavior with imperfections.
If your project involves slender structures or stability-critical components, this tool can enhance your analysis workflow!
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Additional considerations
Engineers must also consider when to use Initial versus Secant rotational stiffness, how bracing affects stiffness, and which Eurocode guidelines apply to stiffness classification.
Additionally, interpreting the moment-rotation diagram correctly is also crucial, as is setting up load cases properly to ensure meaningful results.
Further learning and training
Stiffness analysis is a crucial aspect of structural design that can significantly improve model accuracy. If you’d like to explore this topic further, check out the IDEA StatiCa Support Center, where you’ll find webinars, technical articles, and training courses related to Stiffness Analysis!
Also check out our Training Calendar for upcoming courses! For company-specific training or support, feel free to reach out to our team.
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