The increasing sophistication of digital systems has revolutionised the way that professionals in the fields of architecture, engineering, and construction (AEC) are able to plan, deliver and manage buildings or infrastructure projects. Computer aided design (CAD) is now an indispensable tool in the design process, but building information modelling (BIM) allows for a broader management process across the project life cycle, with the generation of and access to a wider array of data associated with the structure being built.
Virtual design and construction (VDC) is another process that utilizes an integrated multidisciplinary approach to create performance models for design and production projects. There is an overlap, as well as some confusion between CAD, BIM and VDC and how each technique can be used to achieve certain results. Many AEC teams will use a combination of the tools and processes made available by these disciplines in a holistic approach to building and infrastructure design and management.
What is BIM?
BIM stands for building information modelling. This is a digital process that involves the generation and management of information related to places. Despite the name, the usefulness of BIM is not restricted to traditional buildings such as commercial, public and domestic premises.
It can be used in the design, construction, and management processes of other physical structures, including:
BIM can also be used in larger conglomerations of buildings and facilities, like:
- Data centers
- Business parks
Definitions can vary depending on who you ask, but the US National Building Information Model Standard Project Committee offers the following:
“Building information modelling (BIM) is a digital representation of physical and functional characteristics of a facility. BIM is a shared knowledge resource for information about a facility, forming a reliable basis for decisions during its life-cycle; defined as existing from earliest conception to demolition.”
Where traditional design methods were previously limited to 2D technical drawings and schematics, CAD was able to make this process fully 3D. By some definitions, BIM goes even further, with time acting as the fourth “dimension” and cost as the fifth. BIM files can be information-rich models that pass from the design team to contractors and construction engineers, and then to the owners or caretakers of the facility. Each professional can add their own layer of expertise to the shared model, creating a dynamic ‘smart object’ or parametric model that changes in different ways when any one input is updated.
What is VDC?
VDC stands for virtual design and construction and is another process related to architecture, engineering and construction projects.
It is perhaps even more difficult to define precisely than BIM, but a working paper from Stanford University’s Centre for Integrated Facility Engineering offers the following:
“Virtual design and construction (VDC) is the use of integrated multidisciplinary performance models of design-construction projects to support explicit and public business objectives.”
The process is virtual in that it makes use of computer modelling, but the same could be said for both CAD and BIM systems. BIM can also provide a multidisciplinary model of a project to support business objectives. There is certainly a blurring of boundaries between them, but VDC is perhaps a narrower part of the process within the wider BIM umbrella.
Where BIM collates varied information concerning a building or structure from conception to demolition, VDC is more concerned with the design and construction phase of the project. VDC still goes much further than CAD, however, and can also be described as “5D” modelling, with time and cost built into modelling. This also allows the models to act as performance models as well as design models in the sense that they can both predict and measure many different aspects of project performance as it progresses.
Applications for VDC
VDC is so broad that it covers an entire construction lifecycle. It applies direct ties between virtual design and construction, meaning it more readily ensures the physical construction of a project is tied to and reflective of its digital doppelganger. Much of VDC involves the transition from digital, to physical, and back to digital again.
Some VDC services cover:
- 3D Modelling
- Model verification
- Point Cloud Modelling
The VDC application in relation to BIM is that team members model, build, scan, and then verify everything back to the model.
If you have ever delved into the world of BIM and VDC systems, you will probably be aware of the concept of level of development or LOD. If not, this is (again) a concept with various definitions, but the key idea is that levels of development should define the content and reliability of BIM elements at different stages of the project.
The American Institute of Architects (AIA) introduced one LOD standard in 2009 and the Associated General Contractors of America (AGC) expanded the definition. BIMForum, the current US chapter of buildingSMART, has published ‘Level of Development Specification’ standards that show the level of detail and development that should be present at each stage of the process.
In the 2017 draft specification guide, for example, it says:
“LOD 100 elements are not geometric presentations. They may be symbols or other generic representations of information that can be derived from other model elements. Any information derived from LOD 100 elements must be considered approximate.”
By the time you have read up to the section on LOD 350, it says that elements should be “enhanced beyond LOD 300 by the addition of information regarding interfaces with other building systems”.
An example is that a masonry wall element would include jamb conditions, bond beams, grouted cells, dowel locations and joints. In other words, all the information that would enable the model user to coordinate the wall element with other systems in the structure.
LOD 400 elements, meanwhile, are “modelled in sufficient detail and accuracy for fabrication of the represented component”. Upon reaching this stage, a contractor should be able to take the model and build the structure from it.
VDC models can be used to take the project through all LOD stages, but VDC is not all about physical schematics. As already noted, it allows AEC professionals to model those extra dimensions of time and money, while facilitating the possibility of predicting and measuring elements of performance.
This means that owners and funders can virtually simulate projects from the ground up, getting not only a realistic view of the buildings and structures but also the costs, time and workforce requirements involved. This allows for efficient fine-tuning before the building process begins.