Concrete Construction Magazine, December 2008

The Truth About BIM
What building information modeling is and how it can change the way you do business

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.

Additional depth
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.

No need to be big
Midsized contractors, too, have a lot to gain from using BIM. Pompano Beach, Fla.-based Current Builders recently reached a turning point. "We've decided to use BIM for every new project we do," says David Thirlwell, Current Builder's BIM and virtual design and construction manager. The company is a design/build general contractor, which self-performs concrete work. Thirlwell, who for years has been using 3-D modeling, started using BIM about a year ago to prevent coordination problems and produce better field drawings. The company does a lot of parking garages for which model development initially may take two to three weeks. But after that he can easily create a drawing based on any task. "We're seeing huge benefits from it," he says.

One example is a recent design-build parking garage project with a surrounding apartment building. A new, monolithic beam forming system was being used on the project and BIM allowed Thirlwell to generate 2-D section drawings of the garage that provided precise elevation data for placement of each form, saving hundreds of manual calculations and ensuring accuracy. Additionally, BIM revealed conflicting post-tensioning draw points at the ramp-to-column junctions and the surrounding building. These were able to be modified and adjustments made in the production schedule that allowed better constructability. Because the potential conflicts were caught so early in the process, the changes were made without causing any delay in the field.

Although Current Builders is using BIM in the framework of traditional design/bid/build projects, Thirlwell says its benefits are even greater in a design/build environment, especially when coupled with integrated project delivery. Such an environment, where all parties benefit from increased efficiency, encourages sharing as much information as practically possible. Incorporating BIM on a project dramatically expands the practicality of sharing data.

So what is the value for a concrete contractor when a project is using BIM? "As a tool, BIM facilitates coordination of the design and construction processes," says Robert Middlebrooks, AIA, industry programs manager for Autodesk. Specifically, BIM facilitates better communication and accuracy, reduces ambiguity, increases efficiency, and reduces rework. When the designer develops such a model and passes it on to the contractor, the contractor can do takeoffs, scheduling, and other construction planning knowing they are based on information that is current.

Middlebrooks says BIM uses a structure reminiscent of a relational database, and a BIM model often consists of a number of individual models aggregated together. Depending on the particular project, either the architect or design engineer may put together the core model. Others, such as the mechanical and electrical contractors, put together their own models which are then tied into the core model, not unlike layers on a CAD drawing. Embedded in each of the models is any information the user has chosen to include.

Some BIM software is bidirectional and reflects changes made on any of the secondary models throughout the entire model. Other programs are unidirectional, accepting changes made on the secondary models only as imported data to the main model.

Individual BIM programs use a variety of file formats, many of which are company-specific. Some of the BIM programs have built-in translation capabilities-Autodesk and Bentley have an interoperability agreement that allows them to read and write each other's native formats. Most support more than their native file formats. Tekla Structures, for example, supports IFC, DGN, DWG, XML, and other non-proprietary formats for model and data aggregation activities. However, the technology is still at the point where having a good utility program to manage the translation and meld data is worthwhile. One program that several users mentioned is NavisWorks, which earlier this year was acquired by Autodesk. NavisWorks is a nonpropri-etary aggregator that can combines data together from virtually any BIM-related programs. Its various modules allow you to work with the model as well as view it. Whereas the actual BIM programs are the tools for design activities, this aggregator is a good tool for the construction and execution of a project.

Both Sundt and Current use NavisWorks for viewing and investigating models. They also regularly use it for visualizing how concrete elements fit with other building systems and make well-informed decisions. For example, a recent Sundt project called for two 6-foot-square spread footings just 2 feet apart. Rus-sell says ordinarily the crew would consider simplifying that by forming it as a single 6x14-foot placement. However, a quick look at the building model showed floor drains and piping in the 2-foot space, so the project manager was able to alert the field crew to not combine the two footings.

Of course, that's not the only game in town. Adobe Acrobat 9's Professional Extended version supports the IFC format. That means you can convert a BIM model in that format to a PDF with full visualization capabilities and access to the object property data associated with the model.

Origins and destinations
Although the basic BIM concept is common to the various available software products, these products have modifications often stemming from the individual programs' origins. Some examples are, Graphisoft's ArchiCAD developed from an architectural CAD package and so addresses the design process from that perspective. Bentley's Architecture also begins with an architectural approach to BIM. Revit, which is the Autodesk portfolio of BIM software, originally was developed for architectural design and subsequent building construction and management. Tekla's BIM offering, Tekla Structures, is based on the company's structural design and fabrication roots and so has an approach that starts with material properties and analysis in mind. Vico Software offers an integrated package that incorporates modeling, estimating, and scheduling into one product.

Because BIM has the potential to affect such a broad range of design and construction activities, many special interest groups have formed to share thoughts and concerns about and best practices in using BIM as it applies to their areas of specialization. The American Institute of Architects and Associated General Contractors of America (AGC) both have BIM focus groups, and AGC currently is updating its "Contractors' Guide to BIM." The Precast/Prestressed Concrete Institute has an active BIM subcommittee. The American Concrete Institute, through its Strategic Development Council, recently formed a task group on meeting the challenges of BIM.

Several groups also are working toward bringing more standardization to BIM. The Applied Technology Council (www.atcouncil.org) is developing a neutral file format for BIM. In December 2007, the National Institute of Building Sciences (www.nibs.org) released the first part of its U.S. National Building Information Modeling Standard (NBIMS), which is available on its Web site as a free download. Also, its buildingS-MART alliance serves as the North American chapter of the International Alliance for Interoperability (www.iai-international.org), which supports a data representation standard and file format based on industry foundation classes (or IFC).

Current Builders' Thirlwell says that the hardest part of getting into BIM is selecting which software to purchase, but there is no excuse for putting it off. The most important thing, he says, is to just pick one and try it. Several of the software companies offer free trial-use periods, generally 30 to 60 days, during which you can download and use a fully functional copy of the software. Be sure to plan ahead, though, because the downloads can have large file sizes. Also check your hardware against the manufacturer's minimum requirements to ensure you will be able to accurately evaluate the program's performance.

Things That Go Bump
One BIM feature that is most useful for contractors is clash detection, which refers to its ability to identify interferences. Users are able to run a check at any time. To avoid running exhaustive checks of every element each time the clash detection is invoked, the program can be set to check for interferences only between certain portions of the model, for example, mechanical piping and electrical conduits. Wise use of the clash detection feature can eliminate many, if not most, field interference problems before they have a chance to affect the construction schedule.