Working with Castellated Beam

A castellated beam is created by slicing an I-beam longitudinally along its web in a specific pattern. The goal is to separate and then rejoin the beam with a deeper web. These beams are categorized based on the shape of the openings in the web section, with common shapes including hexagonal, circular (also known as cellular), octagonal, and diamond.

Additionally, castellated beams are useful in situations with height limitations. The openings in the beam web allow for easy passage of piping. However, these benefits come with trade-offs. The web openings introduce additional failure mechanisms, necessitating checks such as Vierendeel, horizontal shear, vertical shear and web post shear buckling. Furthermore, the section properties used in finite element analysis differ from those of conventional solid beams.

Inserting a Castellated Beam

To insert a castellated steel beam:

1. Pick the Steel Beam command on the Modeling > Frame ribbon tab.

2. Insert a linear or curved frame member as usual.

3. On the Frame Properties window, switch to Castellated tab.

4. You can select a Hexagonal or Circular Opening.

The code design formulations are given for circular (cellular) and hexagonal openings, thus rectangular openings are not supported.

5. Place the openings by specifying their Count or clear Spacing. You can also specify Start Offset and End Offset.

6. Also specify the dimensions of the web openings using the Width, Height or Diameter fields.

Important:

While inserting the castellated steel frame member, choose a hot-rolled profile or built-up profile that will have the final profile depth.

If the final profile will have 460 mm depth after slicing and welding, then choose, for example, a W18x46 hot-rolled profile, instead of the original profile before the cut.

7. You may want to infill some of the openings, in this case specify the number of openings to be infilled in respective order. For example, if you want to infill second, third and fifth opening you can enter 2, 3, 5 in the Closed Holes field. This does not have any effect on analysis or design. It can be used for detailing purposes.

Design of Non-Composite Castellated Beams

Due to the presence of the significant number of web openings, castellated and cellular beams cannot be treated as solid-web members or members with web openings. These structural members are highly indeterminate elements, which do not lend themselves to a simple method of analysis. The following limit states should be investigated when designing castellated or cellular beams:

1. Compactness and local buckling
   
2. Overall beam flexural strength
   
3. Vierendeel bending of tees
   
4. Web post buckling
   
5. Axial tension/compression
   
6. Horizontal shear
   
7. Vertical shear
   
8. Lateral-torsional buckling
   

The first step in designing both castellated and cellular beams is to calculate the overall bending moment and shear force at each opening and web post caused by external loads. These forces will be referred to as global forces. The global forces will be used to compute localized forces in the top and bottom tees, the web posts, and the gross section. The components (tees and web posts) of the beams will then be examined for failure under the localized forces.

Important

ProtaStructure 2025 performs castellated beam checks according to AISC360 and Turkish Steel Design Code. ProtaStructure currently supports only the non-composite castellated beams. 

[Reference: AISC Design Guide 31 – Castellated and Cellular Beam Design]

Analysis results shown for a model including castellated non-composite castellated beams

Castellated Steel Beam Design UI and Detailed Report in ProtaStructure

Detailing

The web openings are automatically communicated to ProtaSteel for detailing. Openings are defined by cut object, so you can modify them easily if needed.

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