Conventional code-based methods for wind load calculations often have limitations when applied to non-standard scenarios. For example, asymmetric building layouts, which are far more common than neat, rectangular ones, pose challenges.

In SANS 10160-3, there’s no straightforward way to determine design pressure magnitudes across zones, nor clear guidance on defining the zones themselves. Even simple geometries like silos involve complex wind pressure distributions that are difficult to calculate, distribute, and convert into structural loads.

This is where Robot Structural Analysis (RSA) stands out, especially with its Wind Loading Tool. Leveraging Computational Fluid Dynamics (CFD) as its foundation, the tool significantly simplifies generating wind loads for even the most complex structures. While not flawless, a validation study conducted by Autodesk has shown encouraging results.

However, this article focuses on the Wind Profile tab in RSA—a critical feature for simulating boundary layer wind flows tailored to different terrain categories, as specified in local wind loading codes.

When accessing the Wind Profile in RSA, the graph plots Terrain Height against the Velocity Factor:

• Terrain Height: The height above the terrain.
• Velocity Factor: A coefficient relating wind speed at a specific location to the design wind speed used in calculations. This factor accounts for terrain roughness, height above ground, and local obstructions.

For those familiar with SANS 10160-3:2019, these terrain categories and their corresponding Velocity Factors are outlined on page 15.

Similarly, Eurocode 1 Part 1-4 defines five terrain categories (instead of four) on page 20.

SANS 10160-3:2019 defines the Terrain Roughness Factor, Cr(z), as the variation in wind speed due to height above terrain and ground roughness. The standard provides a graph relating height above terrain level to Cr(z) for each terrain category, alongside a convenient table of values.

Comparing the definitions of the Velocity Factor (from the RSA validation study) and Cr(z) (from SANS 10160-3:2019), they appear conceptually equivalent. This means the Cr(z) graphs from the code can be replicated and used directly in RSA.

So, what will this look like in RSA? Below you will note the Wind Profile plotted in RSA for Category A.

Ok, that isn’t quite right. The problem is that the Wind Profile Editor only allows for 0.1 increments and the Height selector isn’t very user friendly.

To accurately incorporate SANS 10160-3:2019 terrain categories into RSA, follow these steps:

1. Plot the Graph: In RSA, create a Wind Profile matching the number of points provided in the standard’s table. The default editor allows for 0.1 increments, which can be adjusted manually later.
2. Save and Edit the Profile:
   • Save your Wind Profile with a unique name.
   • Navigate to C:/Users/<User>/AppData/Roaming/Autodesk/Robot Structural Analysis 20xx/CfgUser/Wind Profiles.
   • Open the saved profile in Notepad and edit the values to match those from SANS 10160-3:2019.
3. Reload and Select: Return to RSA, adjust the Wind Profile height to that of the table (100m in SANS 10160-3:2019), and select your edited terrain category (e.g., Category A) from the dropdown.

You can now easily create all four terrain categories and use them as a part of your Wind Simulation.

By creating profiles for all four terrain categories, RSA users can more accurately align results with local standards, achieving more accurate designs.

Wind loading on structures often presents complex challenges, especially when dealing with unconventional geometries or local standards like SANS 10160-3. However, tools like Robot Structural Analysis (RSA) streamline these complexities with its Wind Loading feature, backed by Computational Fluid Dynamics (CFD).

By customizing wind profiles in RSA to align with local codes, engineers can achieve more precise simulations and efficient designs. This approach enhances both the accuracy and practicality of structural analysis in modern engineering projects.

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