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Cellular and castellated beam design

Design of cellular and castellated steel beams and columns, with web openings for long spans, lighter steel and services running through the beams.

3D structural model of the B1 Mall terrace steel frame in Dubai, with cellular beams and columns that have round openings along their webs

Wrenze Steel designs cellular and castellated steel beams for contractors, fabricators and consultants in Dubai, across the UAE and in the GCC. Both are steel sections with a row of openings along the web. They are deeper and stiffer than the section they are made from, for the same weight of steel, so they span further, deflect less and let services pass through the beam instead of below it.

Cellular and castellated beams explained

A castellated beam is made by cutting the web of an I-section along a zigzag line, shifting the two halves and welding them back together. The result is a deeper beam with hexagonal openings. A cellular beam is made the same way with a curved cutting line, which gives round openings. Round openings spread the stresses more smoothly around each hole and suit round ducts, so cellular beams are the more common choice in modern buildings.

What we design

  • Cellular beams: roof and floor beams with round web openings, as primary beams, secondary beams and rafters
  • Castellated beams: beams with hexagonal openings for roofs, platforms and frames
  • Columns with web openings: cellular columns for exposed frames, as on the B1 Mall terrace
  • Composite cellular beams: cellular beams acting with a concrete slab on metal deck, through our composite steel design service
  • Opening layouts: spacing, size and position of openings, with filled or stiffened openings where forces are high
  • Connections: beam-to-column and splice connections that suit the opening pattern

What the design checks

A beam with web openings has more ways to fail than a plain beam, so each part is checked:

  • Bending and shear at each opening. The section is weakest where the web is cut, so the top and bottom tees are checked for bending, shear and their combined effect.
  • Web posts. The web between two openings is checked for buckling and for the shear passed along the beam.
  • Lateral-torsional buckling. Long, deep beams are checked for buckling with their real restraints from the roof or floor.
  • Deflection and vibration. Including the extra deflection caused by the openings, and floor vibration for offices and walkways.
  • Welds. The welded seam along the web, where the two halves are joined.
  • Supports and point loads. Openings near supports and under heavy loads are filled or stiffened where needed.

Codes and design guides

We design to AISC 360 with AISC Design Guide 31, or to Eurocode 3 with the SCI guidance on beams with large web openings, following the project specification. The frame is analysed as a 3D model, and the openings are checked one by one with our own spreadsheets and hand checks. The approved design then goes to shop drawings and detailing, where the opening pattern is set out for cutting.

Where they fit best

  • Long-span roofs for warehouses, sports halls and showrooms
  • Car parks and office floors where services must run through the beam depth
  • Malls, terraces and exposed frames where the steel is part of the look
  • Mezzanines and platforms that need long spans with light steel

Cellular steel project

On the B1 Mall terrace in Dubai, Wrenze Steel carried out the structural design for CBD Projects. The frame uses cellular sections throughout, beams and columns, with the stability coming from rigid beam-to-column connections, which keeps the dining terrace open and gives the exposed steel a light look.

Cellular and castellated beams are part of our structural steel design work. Their joints are covered by steel connection design, long-span roofs by warehouse and PEB design, and composite floors by composite steel design.

Contact our engineers

For cellular and castellated beam design, contact our engineers.

Cellular & castellated beams: questions

What is the difference between cellular and castellated beams?

Both are made by cutting the web of a steel section along a profiled line, moving the two halves apart and welding them back together, so the beam is deeper than the section it came from. A castellated beam has hexagonal openings. A cellular beam has round openings, which spread the stresses more smoothly and suit round ducts.

When are cellular or castellated beams a good choice?

They suit long spans with light to moderate loads: roofs, car parks, offices, malls, terraces and sports halls. The deeper section gives more stiffness for the same weight, and services can run through the openings, which saves ceiling depth. For short spans or heavy point loads, a plain rolled beam is often simpler.

Which design guides do you follow?

We design beams with web openings to AISC Design Guide 31 or the SCI guidance (P355) used with Eurocode 3, following the project specification. Each opening and each web post between openings is checked, not only the beam as a whole.

Can openings be filled or stiffened where loads are high?

Yes. Near supports and under point loads, the shear in the web is highest. We can fill openings with plate, add ring or plate stiffeners around them, or keep those zones solid, and we show this clearly on the drawings for the fabricator.

Can you design columns with web openings too?

Yes. On the B1 Mall terrace in Dubai the columns and the beams both had cellular webs. Columns with openings are checked for axial load, bending and local buckling around the openings, and their connections are designed to suit the opening pattern.