Clash Detection in BIM
Automated clash detection workflows for identifying spatial conflicts between building systems in BIM coordination.
Definition & Context
Clash detection is the automated process of finding spatial conflicts between discipline models (architectural, structural, MEP) in a federated BIM. Tools such as Navisworks Manage, Solibri, BIMcollab Zoom, and Revizto run rule-based tests that report intersecting geometry.
Clashes are classified as hard clashes (solid geometry overlapping — a duct through a beam), soft/clearance clashes (violations of required access or insulation space), and workflow (4D) clashes (time/sequence conflicts). Issues are grouped, assigned, and tracked to closure using the open BCF (BIM Collaboration Format).
Why It Matters
Detecting conflicts in the model — before they become expensive rework in the field — is one of BIM's clearest ROI drivers. Structured clash management keeps coordination meetings focused on real, prioritised issues rather than thousands of raw hits.
Best Practices
- Set up clash rules per discipline pair (e.g. Mechanical vs Structure) rather than testing everything against everything.
- Group and filter results to remove duplicates and noise before assigning issues.
- Use BCF to round-trip issues between coordination and authoring tools so nothing is lost.
- Assign clearance tolerances so touching-but-acceptable elements are not flagged.
Common Pitfalls
- Running one giant 'everything vs everything' test that buries real clashes in noise.
- Treating raw clash count as a KPI instead of resolved, verified issues.
- Coordinating against out-of-date model versions.
- Ignoring soft/clearance clashes that block maintenance access.
Standard Engineering Workflow for Clash Detection in BIM
2. Geometric Alignment & Profile Design
Lay out horizontal tangents and spiral transitions following AASHTO / Eurocode minimum curve radii, coupled with vertical slope crest/sag parabolic curves.
Common Failure Scenarios & Troubleshooting
| Failure / Geometric Issue | Root Cause & Mitigation Strategy |
|---|---|
| Surface triangulation bridges across steep ravines incorrectly | Add linear Breaklines along tops/toes of slopes or specify 'Maximum Triangle Length' under Surface Build Properties. |
| Horizontal curve radius triggers AASHTO violation flags | Adjust minimum transition spiral length or increase curve radius to meet minimum design speed superelevation criteria. |
| Coordinates offset by several meters after CAD/GIS import | Verify projection datum and false easting/northing parameters in MAPCSASSIGN before importing geospatial shapefiles. |
Industry Standards & Compliance Codes
- Eurocode 7 (Geotechnical Design - EN 1997)
- ISO 19650 (BIM for Civil Infrastructure)