Last edited 23 Jul 2016

Clash avoidance

Building Information Modelling (BIM) is a very broad term that describes the process of creating a digital model of a built asset.

Building information models are likely to comprise a series of federated models prepared by different design teams, including model files, documents and structured data files containing non geometric information about the facility, floors, spaces, systems and components. Together these create a digital replica of the built asset that starts by representing design intent, but by handover, reflects what has actually been built and installed.

One of the benefits of adopting BIM is the potential for better avoidance of clashes, that is, it can help ensure there is spatial co-ordination between the different components that make up the asset.

For example, avoiding situations on site such as the route for pipework running through a steel beam (sometimes described as a 'hard clash'), which can be very difficult, disruptive and costly to rectify. Clashes can also occur as a result of construction tolerances, too little space to install or maintain a component of the building, the installation of insulation, proximity clashes, health and safety requirements, or from too many workers being programmed to carry out works in the same space at the same time. These are sometimes described as 'soft clashes'.

Clashes can be a particular issue where multiple disciplines are working on different aspects of the same project. Whilst in theory, BIM should reduce clashes by bringing together the entire design team to work on one collaborative, co-ordinated building model, BIM Level 2, allows disciplines to work on separate 'federated' models that are only brought together to create a single, complete model of the building at key stages. The building information model may also be broken down into volumes to allow more than one person to work on project models simultaneously, or to ensure that file sizes are manageable. This increases the likelihood of poor spatial co-ordination.

Clash avoidance and clash detection must therefore be carried out as an integral part of the entire design and construction process, from defining standard methods and procedures and establishing a BIM volume strategy, through specialist design and the creation of a virtual construction model and should continue during the construction phase itself as models are updated with as-constructed information. This requires that models are updated quickly so that the impact of changes on subsequent works can be checked.

Procedures for co-ordination and clash detection should be required from suppliers by the employer's information requirements (EIR) which form part of the contract documents for the project, and suppliers should respond to this in their BIM execution plan. During the design and construction process, interface managers within each design team should assess design decisions and clashes to see if they can resolve them internally, and where this cannot be done, separate models may be combined for review by the lead designer.

Clash detection software can identify clashes between different discipline's BIM data and generate clash reports. However, this should not be relied upon as a fail-safe check, and should not be used to justify poor design co-ordination processes.

Where there is poor interoperability between the building information produced by different teams, clash renditions can be performed on native format models using an agreed viewing tool.

[edit] Find out more

[edit] Related articles on Designing Buildings Wiki