Designing Castellated Beams Using IDEA StatiCa Member

Introduction

Castellated beams are not incredibly common in South Africa—at least not from what I’ve seen in practice—but when I do come across them, I’m always struck by their intriguing, almost quirky geometry. There’s a certain beauty in their design: the repeating cut-outs create a rhythm that feels both mechanical and artistic. Honestly, it always surprises me that some creative architect hasn’t thrown in a few LED strips inside the web openings just to highlight that geometry at night. But I digress—this article isn’t about aesthetics or illumination; it’s about design.

Despite their somewhat niche appearance, castellated beams offer some serious engineering advantages, and understanding these is key to appreciating their growing potential in both industrial and architectural applications.

According to Baker Steel Trading, castellated beams come with a robust list of advantages:

• Quick, efficient and easy assembly – avoiding a requirement for additional fasteners.
• Better strength and stability – their crenellated design makes castellated beams more resistant to bending and deformation.
• Improved load-bearing capacity – this is enabled by the interlocking design so they are ideal for heavy duty applications.
• Significant cost savings – their ease of assembly and the reduced need for additional fasteners means castellated beams are often cheaper than other types of beams.

But for all their advantages, the design of castellated beams is not straightforward. The web’s geometry varies along the longitudinal axis due to the cut-outs, creating zones of reduced shear resistance and potential stress concentrations—particularly around sharp corners or poorly detailed openings. Unlike solid-web beams, these variations must be accounted for carefully during analysis and design.

While many engineers are already familiar with IDEA StatiCa Connection, fewer are aware of the powerful features packed into IDEA StatiCa Member. One standout feature is the ability to analyze and design open cross-sections subjected to torsion, which is especially relevant when dealing with castellated beams due to their web discontinuities and asymmetric stiffness.

To demonstrate this, I’ll walk you through how to model, analyze, and refine a castellated beam in IDEA StatiCa Member using South African references. Specifically, I’ll be referencing Table 2.17 of the SAISC Red Book, which provides properties and dimensions for castellated I-sections with parallel flanges.

Modelling a Castellated Beam in IDEA StatiCa

Starting in IDEA StatiCa Member, I created a new project and selected the “AM1” option under Analyzed Members. From there, I opened the cross-section editor and chose the I-section type. Using the Red Book as a reference, I input the dimensions of the castellated beam. I also applied a naming convention, using “CI” to indicate a Castellated I-beam, followed by the standard designation.

With the basic geometry in place, the next step is to model the web openings. This is where the magic happens. I used the Opening operation, setting the related plate ID to the web. I then specified the shape, spacing, and size of the cut-outs based on the Red Book values. If you’re unsure about exact spacing or pattern alignment, I recommend drafting it out in AutoCAD first. That can help you fine-tune the dimensions and eliminate guesswork when transferring it into IDEA StatiCa.

Assigning Loads

After completing the geometry, I moved on to loading. For this example, I applied a 10kN/m uniformly distributed load to simulate a typical bending scenario, along with a small torsional moment to highlight how the software handles open-section torsion. As you assign the loads, the software provides immediate visual feedback. If the graphical representation doesn’t update, it usually means something went wrong in your input—so that’s a useful early warning.

Analyzing the Castellated Beam

With the loads applied, I initiated the analysis by clicking on Calculate. IDEA StatiCa automatically runs a materially non-linear analysis, or MNA, by default. The stress results give us the first glimpse of how the castellated beam behaves under loading. As expected, there are stress concentrations around the web openings, though they remain small under the initial load combination.

The beam is far from failure in this state, so I increased both the line load and the torsional moment to push the model closer to its limits. This revealed how significantly the torsion affects the results, showing that even modest torsional loading can become a critical factor in castellated beam performance.

Designing the Castellated Beam

At this stage, I began testing reinforcement strategies to improve the beam’s behavior. The first idea was to use transverse stiffeners. These are placed at intervals along the beam to provide extra support to the web, particularly around the openings. In IDEA StatiCa, you can add these using the Transversal Stiffener operation. After inputting the relevant data and re-running the analysis, I saw a minor improvement—about a 0.3% reduction in plastic strain. Unfortunately, this gain was minimal, and not enough to justify the added material and fabrication effort.

The second approach was to stiffen the top flange using a longitudinal plate that runs the entire length of the beam. This is done using the Longitudinal Stiffener operation in IDEA StatiCa. Admittedly, this step takes some getting used to. The UI requires precise inputs, and alignment can be a little tricky at first. But once the stiffener is properly added, the results speak for themselves.

The beam passed the analysis comfortably, and plastic strain dropped to around 2.6%. That might be slightly on the high side depending on the code you’re working with, but it’s definitely within acceptable limits for many practical designs. And now that the primary reinforcement is in place, smaller tweaks can be made to fine-tune the model as needed.

Of course, strength is only part of the story. Deflection is often the governing design criterion, especially in longer spans or when serviceability is paramount. In this case, the analysis showed a deflection of about 73.7mm. Given that the allowable deflection was roughly 35.75mm, this result was more than double the limit, indicating that more work was needed.

This could mean increasing the overall depth of the section, modifying the flange plate, or reducing the number or size of openings. The important takeaway is that IDEA StatiCa makes these kinds of investigations fast and visual. You don’t have to guess—you simulate, analyze, and decide based on data.

IDEA StatiCa also provides a built-in report generator under the Report tab. While not as detailed as the ones produced by IDEA StatiCa Connection, the Member reports still give you the essentials: geometry, loading, stress diagrams, and pass/fail summaries. You can customize and export these for documentation, presentations, or team review.

Conclusion

In summary, designing castellated beams using IDEA StatiCa Member opens up a range of possibilities. The software allows you to accurately model irregular geometries, simulate complex loading scenarios, and test reinforcement strategies in a way that removes much of the guesswork from the design process. Castellated beams offer a blend of efficiency, strength, and economy—but only if designed correctly. With the capabilities of IDEA StatiCa Member, engineers can approach these designs with confidence, precision, and creativity.