What is BIM, anyway? What most people in the construction world mean when they use this term these days is “building information modeling.” But like so many other labels, what BIM actually is depends very much on who is using it.
If it seems to you that BIM is just glorified 3-D CAD, you could be right—when it comes to some users. But when used as a workflow management and decision support tool, BIM offers a whole new way of doing business and the potential for remarkable productivity gains.
The fact is that BIM is simply a way of applying powerful computer technology to a database of information about a wide variety of building- and construction-related elements. Flexibility is the very thing that gives BIM so much potential and at the same time allows any individual user to do as much, or as little, with this tool as desired.
Various forms of BIM software are available from many different providers. But at its heart, any BIM program is simply an object-based parametric graphical database of building elements. That means each object—a wall segment, for example—can have dimensional data and information about its materials and their associated properties. Rather than being shown on a drawing as just a centerline from one point to another, in BIM a wall segment is an object whose length, height, thickness, location, orientation, and material composition are included in the model. Being able to associate these other characteristics with a building element is what gives BIM its “parametric” aspect. This is always an expandable area; for example, today users are exploring ways users to incorporate sustainability characteristics into BIM model.
Each object in a BIM model is related to other objects in very specific ways, such as a wall segment's location relative to the structure and its connections to other elements. Its material properties can be part of the data, and construction details can be modeled in as well.
A project modeled in BIM can incorporate a fourth dimension—time—thus adding the construction process to the model. As a 4-D visualization tool, it enhances communication among those planning construction. Anyone with the necessary hardware and software to access the model can not only walk through the 3-D model, but also see the changes that will occur as construction progresses.
Adding start, finish, and duration times to elements in a BIM model allows the review of project scheduling and construction sequencing much like time-lapse photography.
Including nonstructural elements further expands what BIM can facilitate. “We put our cranes and concrete pumps right into the model,” says Dan Russell, simulated construction manager for Sundt Construction, Phoenix. Sundt is a general contractor that self-performs its concrete work. Russell says incorporating major equipment into the model enables the company to schedule equipment and crews a as an integrated part of the model. As dimensions, materials, or other parameters change, the effects of these changes are reflected a automatically in the schedule. Similarly, schedule changes in one area of construction—for example a delay in completing the plumbing rough in—are reflected throughout the entire model.
Sundt began using BIM about three years ago to better coordinate the mechanical, electrical, and plumbing (MEP) portion o of its projects. As soon as they had the software, it made sense to use it for the concrete work as well.
Today the company uses the BIM model to generate a lift drawing, including embedded plate and rebar information, for every pour. A 3-D picture of each wall also is generated from the model and such things as the square footage of forms and other quantity information are extracted easily. Because all of the information is integrated, if one part of the model changes, the entire model automatically shows the effects of that change. An example of this is if someone changes a concrete wall thickness from 6 to 8 inches, all the affected lift drawings become updated.