What is BIM?
For many architecture firms it has become standard practice to construct digital models of their work. While a few firms are using programs such as Trimble Sketchup and Rhinoceros for this application, most architecture firms have switched into Autodesk Revit, a BIM (Building Information Modeling) tool. As defined by the US National Building Information Model Standard Project Committee, “Building Information Modeling (BIM) is a digital representation of physical and functional characteristics of a facility. A BIM is a shared knowledge resource for information about a facility forming a reliable basis for decisions during its life-cycle.”
To put it plainly, BIM is a form of 3D parametric modeling using software that assigns properties and functional characteristics to all modeled elements. This differs from other modeling programs such as Sketchup and Rhino in that each element in a BIM model is more than a group of simple geometric shapes and planes. Each element, for instance a wall, has knowledge embedded into it such as exterior and interior layers, stud thickness, product type etc. Notes, comments and warranty information can also be added to each modeled item. What you end up with is an all-in-one 3-dimensional representation of a future project that functions like a project manual.
Because each modeled element has its own identity and unique set of properties, it becomes easier to locate, schedule and quantify any item of interest. Revit models can provide construction professionals with square footages, volume, area, count and linear quantity data. Furthermore, the 3D model can assist with visualization and understanding how various project elements are intended to come together, which can help clarify unclear areas in the drawings. In order to get the most out of BIM, it is important to have a detailed, well organized model.
Typically, a construction company will negotiate with an architect to send over some form of the model. Most architects are not willing to share Revit models (.rvt), but they may be willing to export a .dwf or .nwc, which can then be used by construction professionals for higher level analysis in other programs.
BIM Programs & Functionalities
Design Review is a free program that allows you to view an architect’s model in 3D. For viewing, the model would have to be exported from Revit as a .dwf, .dwfx or .fbx file in order to open in Design Review. This program mostly assists with project visualization. You can orbit around the model, isolate items of interests, take sections, save views, create markups, etc. Cost : $0
Revit is primarily used by architecture firms for 3D modeling and 2D construction document generation. It combines modeling capabilities with all of the visualization elements of Design
Review but also allows for detailed quantification, crude scheduling, and schematic level cost estimates. A Revit file is a .rvt project file. Revit also comes with “Revit structure” or “Revit MEP” software, which can allow you to create structural and mechanical models separately of the architectural model, thus reducing file size. Cost : $1,200-$2,000
Navisworks Manage is a higher level analysis tool used primarily by construction professionals. It has all of the visualization capabilities of both Design Review and Revit, but to these it adds the ability to create animations or project walkthroughs. Navisworks also allows for Visual Scheduling and Clash Detection. As of 2014, detailed Cost Estimating and 2D drawing integration have been added to the software. Generally, a Navisworks project file is .nwf file. Cost : $8,000
Both Navisworks and Revit have an internal renderer built in, which allows for the creation of photorealistic views of the project spaces.
What does this mean for ease of construction?
As part of Rafn’s study of BIM capabilities and modeling programs, trial versions of the programs above were used during the preconstruction phase of a mixed use project. With the help of GGLO, Rafn received the digital model of the AMLI Wallingford project (seen above) which was used for higher level analysis.
Estimating/Quantification:
Revit can be used to create schedules of model elements. These schedules can include columns for areas, lineal footages, volumes and any other custom quantification criteria. The schedules can be exported into excel spreadsheets for further editing/integration with existing spreadsheets. For the Wallingford project, Revit proved particularly useful in quantifying windows, doors, showers, vanities, etc. Windows in particular were difficult for subcontractors to catch in this project as some windows were not shown in the plans or in the elevations. Revit allowed us to create a window schedule based on window type & location in a matter of minutes!