Perhaps you have gotten that pesky message before saying "Lines cannot intersect each other, The highlighted lines currently intersect" when trying to place a slab on a wall in Revit (or maybe any other such message) when placing objects??? then you just saw a clash being detected. So... what is it really about?
What is a clash?
A clash occurs when elements of different models occupy the same space. A clash may be geometric (for example, pipes passing through walls), schedule based (when different aspects of work that are supposed to be sequential are scheduled to occur together or in reverse), or changes/updates not made to drawings.
But is there no way to check for clashes without BIM?
There is... but it is very tedious. It involves overlaying of drawing to see if there are any conflicts. With BIM though, this process is vastly improved as BIM brings automation to clash detection.
So what does clash detection serve to achieve?
Clash detection helps in effective identification, inspection and reporting of interferences in a project model. It is used for checking completed/ongoing work and reduces the risk of human error during model inspections. Clash detection is necessary because several models (structural, MEP, etc) are integrated into one main BIM model. With clash detection, mistakes which normally would have been discovered on the site (with high cost implications when corrected at that stage) can now be seen in the office even before anyone sets foot on the site. BIM even makes clash detection possible for objects within objects (a steel rod completely immersed inside a concrete wall)
There are 3 main types of clashes that clash detection seeks out:
- Hard Clash: when two objects pass through each other. Most BIM modelling software eliminate the likelihood for this using clash detection rules based on embedded object data (like the image above)
- Soft Clash: work to detect clashes which occur when objects encroach into geometric tolerances for other objects (for example, a building being modelled too close to a high tension wire).
- 4D/Workflow Clash: clash resolves scheduling clashes and abnormalities as well as delivery clashes (for example, work crews arriving when there is no equipment on site)
So what BIM software is available for Clash Detection?
There are 2 types of clash detection software
- BIM modelling design software: Clash detection within this is limited as it can only work on models created by the software (proprietary models.) For example, when you try to place a slab on a set of walls that do not make contact with each other in Revit, the software notifies you of a clash.
- BIM Integration tools that perform clash detection: is used to detect clashes between different non-proprietary software (software from different companies). Alterations, though, have to be carried out in the software in which the clashing part of the model is created. For example, After integrating all the models into a BIM modelling software like Revit, and carrying out clash detection with Navisworks, a mistake made by the Structural Engineer using Orion will involve having the structural Engineer make the changes in Orion before reintegrating into Revit. Examples of this type of Clash detection software include Navisworks and Solibri.
Is clash detection really that important?
Estimates of savings due to clash detection in the industry is about $17,000 per detected clash.
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