Fundamental uses of BIM, or BIM dimensions, refer to the levels of information in a given BIM information model.
Consider the following:
- 1D – one-dimensional information, maybe in the form of text descriptions, specification documents, or contractual correspondences.
- 2D – two-dimensional; here drawings come into place. The graphical information about the facility is added here – lengths and widths (floor plans), or lengths and heights (elevations) + details. (Note: 1D and 2D are not BIM – what is BIM then?)
- 3D – involves three-dimensional modelling of geometrical and graphical information.
- 4D – The three-dimensional geometrical and graphical model is linked to a construction schedule, and a time dimension is introduced. This involves the simulation of the whole construction process; the 3D elements, objects and components in the model are displayed on a construction time frame.
- 5D – when cost information is added to the 4D model, this results to 5D BIM. Here, model information is used to aid in cost analysis, construction estimation, and quantity take-off.
- 6D – In this dimension, specialised third-party software or plugins embedded in the BIM authoring software are used to perform environmental sustainability and energy efficiency simulations and analysis on the BIM model. It is required that information on the environmental performance of materials, embodied energy, and energy consumption data is incorporated in the model to make these simulations and analyses possible.
- Analysing the energy performance right from the design stage provides the designer with the most suitable technical solutions to be adopted to ensure lower energy consumption, greater internal air quality, and comfort, which are key sustainability measures.
- 7D – This dimension represents the use of BIM in the planning and management of maintenance operations throughout the building’s life cycle (facilities management). The asset information model is developed to capture the as-built information, with important facility management information such as component manufacturer names, warranty information, operational notes and manuals, product codes, technical specifications, and other related information included.
- This will help the facility managers plan for the proper operation and maintenance of the building. When a certain building component needs replacement, all the information concerning it is there in the model, including the manufacturer contacts if the manager needs to procure another component from them.
A brief on the developments in construction IT: Traditional paper-based processes involved 2D drawings and text-based specifications that were not linked together. With advances in IT, these drawings could be created on a computer using software such as AutoCAD (this practice is called computer-aided drafting).
Software for measuring quantities from these PDF drawings (plans, elevations) was developed. The practice is called computer-aided estimating.
BIM developed from advancements in 3D CAD that made the model dynamic. Floor plans, elevations, sections, details, and 3D views became interlinked, meaning an update on one would be reflected on all the other views. Further, the introduction of text and non-graphical metadata fueled the development of all the other dimensions as discussed.
3D: Model-based Design Coordination and Clash Detection
We saw earlier that a 3D model contains intelligent BIM objects, building components, and elements that build up the information model. These objects and virtual components contain information on the length, width, and height; surface materials and finishes.
In 3D BIM, we expect the architectural, structural, MEP, and civil infrastructure models to be collated together to form the federated 3D information model. These are created using BIM authoring software such as Revit, Tekla Structure, or ArchiCAD.
To perform model-based clash detection and resolution, model review software is used.
Clash detection software is used to coordinate field conflicts by comparing 3D models (architectural, structural, MEP and civil) of building systems. The goal here is to eliminate significant conflicts before any work on-site.
- Geometry-based clash detection detects when two or more objects interfere. e.g., HVAC conduits interfering with a structural beam.
- Rule-based clash detection detects when certain coded rules are not met in the design, such as a column placed on a slab without a footing, or if a space is large enough as it should be according to building regulations or space requirements from the owner.
How it helps the QS: reduce and eliminate field conflicts; reduce RFIs; increase site productivity; and reduce change orders and cost overruns.
4D: Model-based Planning and Control
Model-based project scheduling is done by linking the 3D model parts to tasks in the construction schedule, using a 4D scheduling software, such as Vico Office, Synchro or Navisworks.
This approach makes it possible to visualise the whole construction process or just some phases of it and see how the timing of tasks affects the workflow, including resolving time-based clashes and verifying the planned sequence of works visually.
It is useful in the following:
- Phase planning – to plan occupancy in renovation projects or to show construction sequence and space requirements on the building site. Also, used to communicate how the job would be run on site, including design, phasing, site access requirements etc.
- Site utilisation planning – information models are used to visualise permanent and temporary facilities on-site during the multiple phases of the construction process. The model can also be linked to the 4D schedule to convey space and sequencing requirements on site, including information or labour, material and equipment requirements and planned deliveries.
This allows for identification of potential and critical space and time conflicts; evaluation of site layout for safety concerns; and selection of a feasible construction scheme.
5D: Model-based Estimating and Quantity Take-off
5D is where the quantity surveyor plays a very central role. It involves the use of the developed model to extract quantities of materials and associated costs for estimating purposes.
Model authors need to satisfy the level of development required to support cost estimation for this to be possible.
The process involves the generation of quantity take-offs from the models and linking these to a cost database to compute a cost estimate. BIM cost metadata can be exported to QS software such as Cost X, where the QS now manipulates the model to extract building quantities, add item descriptions from their database, and come up with a bill of quantities.
Provide more accurate cost information to the owner during the early decision-making phase of the design and throughout the lifecycle, including changes in construction; reduced time on quantity take-offs and cost estimations; allow estimators to focus on more value-adding activities in estimating, such as identifying construction assemblies, generating pricing, and factoring in risks, which are essential for high-quality estimates; the visual process is highly effective; easier exploration of different design options and concepts within the owner’s budget; and quickly determining the costs of specific objects.
The ability to define the specific design modelling procedures that yield accurate quantity take-off information; the ability to identify quantities for an appropriate estimating level upfront; and the ability to manipulate models to acquire quantities usable for estimation.