Clash Detection

Clash detection is the automated process of identifying spatial conflicts between BIM model elements. Three types of clashes are typically identified: (1) Hard clashes — solid elements physically overlapping (a beam passing through a column, a duct intersecting a slab). (2) Soft clashes — elements that don't intersect but violate clearance requirements (a duct closer than 50 mm to a beam, blocking maintenance access). (3) 4D clashes — temporal conflicts where elements would be in the same place at the same time during construction (a duct installed before the slab is structurally adequate). Tools: Autodesk Navisworks Manage, Solibri Model Checker, BIMcollab, Trimble Connect.

Clash detection workflow: (1) Federate models — combine architectural, structural, MEP, and other discipline models into a single coordinated model. (2) Run clash detection — software identifies all hard, soft, and 4D clashes per defined rules. (3) Categorise — by severity (critical, major, minor) and discipline (structural-MEP, MEP-MEP, architectural-MEP). (4) Resolve — design teams modify their respective models to eliminate clashes. (5) Re-run — verify clashes are resolved. (6) Document — clash report for project record. Modern Indian projects routinely run clash detection at LOD 300+ models, with major federations performed at design milestones (50%, 75%, 90% design).

Real-world impact: clash detection finds 1,000-10,000+ clashes in a typical mid-rise office tower at LOD 300. Without resolution, each clash potentially requires field rework. Cost per field rework is 5-50× the cost of resolution at design stage. For a typical Mumbai high-rise: design-stage clash resolution costs ₹4-8 lakh; equivalent field rework would cost ₹2-4 cr. The most-overlooked aspect of clash detection: post-resolution verification. Many projects run initial clash detection but skip the verification step after resolution; clashes that were 'thought to be resolved' often re-emerge during construction. Verified clash-detection workflow with iterative federation is essential for genuine value.