Join slab to beam

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Note

5/7/2025: Created with the help of Copilot

Intro

  • Join slabs and beams properly in order that the quantities generated from the model are suitable for use.
  • For HKSMM, slabs should be modelled over beams, i.e. slabs should cut beams in Revit term. This in fact is Revit's default mode.
  • Slabs and beams can appear to be joined / overlapped on plans and in sections but are not geometrically joined. Like the following:

  • To switch the join order, select any model element to show the Modify menu.
  • Select Join at Geometry panel > Switch Join Order > relevant slab > relevant beam:

 

  • The switch order can only rectify the problem after modelling.
  • Better still, model it correctly in the first instance.

🎯 Why Beam–Slab Joins Go Wrong

Understand how these issues happen and how to catch and correct them.

  • Geometry Almost Touches, But Doesn’t: Small misalignments leave elements technically unjoined.
  • Sketched by Level, Not Geometry: Slabs snapped to levels or reference planes instead of actual beam faces.
  • Copy/Paste Without Rejoining: Duplicated elements don’t retain join data.
  • Linework Overrides or Coarse Detail: Visual tools mask missing joins in views.
  • Lack of Awareness: Teams may assume visual contact equals geometric join.

✅ Beam–Slab Join QA Checklist

🧱 Geometry Placement

  • ✔️ Use beam faces to sketch slabs directly.
  • ✔️ Snap slab boundaries to actual beam geometry, not just to levels or reference planes.
  • ✔️ Use the Align tool for precision when needed.
  • ✔️ Visually check in 3D or section cuts to ensure actual contact.
  • ✔️ Don’t rely on 2D guesswork.

🛠 Join Workflow Practices

  • ✔️ Model slabs after beams, then join them.
  • ✔️ Always use Join Geometry explicitly.
  • ✔️ Rejoin elements after edits to beam/slab placement.
  • ✔️ Don’t assume visual contact means joined—confirm using automated tool.
  • ✔️ Confirm joins using automated tool.

🧙‍♂️ Visual Deceptions

  • ✔️ Avoid Linework overrides that hide gaps and make unjoined elements appear cleanly cut in views.
  • ✔️ Use Fine detail in review views. Coarse and Medium may mask join gaps.
  • ✔️ Run a visual audit by resetting overrides in key views.

🔁 Modeling Efficiency

  • ✔️ Rejoin geometry after copy-paste or grouping, Join conditions are not preserved by default when duplicating elements.
  • ✔️ Use automated tool to check.

📚 Team Awareness & Training

  • ✔️ Train modelers on the purpose and impact of join geometry.
  • ✔️ Include checklist in onboarding and BIM standards.

Automated checking tools

  • pyRevit scripts have been written to :
    • list unjoined slabs and beams,
    • join them, and
    • switch to slab over beam mode,
    • for all beams and slab in close proximity.
  • Individual manual adjustments are required for exceptional items.
  • Some adjustments cannot be reversed if the model is saved.
  • The model should be inspected to see whether the adjustments are correct before saving the model for further use.

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