BIM-boozled

After reading about building information modeling (BIM) in the latest issues of several trade magazines including Structural Engineer, I’ve been trying to understand exactly how it’s supposed to work. I’ve watched web presentations of Tekla and Revit. One thing that disturbs me is the potential for application-specific proprietary formats. Every time I see a program using "wizards" and things like "parametric linking of details," I sense that an application is losing its flexibility.

If BIM is to succeed, it needs to be based on an open-file specification. The simpler this process can be, the better it will be for the users. It may not be all that difficult, perhaps based on using existing 3-D CAD formats, with supplemental database information. A good example of an open-file specification is HTML, used for writing web pages.

However, if BIM works with only one type of software, we will be limiting ourselves. It would be like everyone in the world driving the same type of car. Eventually, the world would look like Cuba, where everyone is driving 1950s, pre-Castro era jalopies!

Likewise, the structural engineering profession is better off having a large choice of software applications for analysis and design that comply with open-file specifications. Without choice, innovation will stagnate.

Karl Hanson, S.E., P.E.
Chicago

Editor’s Note: Let’s continue this BIM-related discussion!

According to Structural Engineer research, only 29 percent of structural engineers are familiar with the term "building information modeling". What’s more, the definition of BIM varies, depending upon who you ask.

Share your comments, ask your questions, and learn what people are saying about BIM at the GoStructural.com Building Information Modeling Forum, sponsored by Autodesk. Also, you can check out the complete report of the Structural Engineer research in Editor Jennifer Goupil, P.E.’s September article, "Building information modeling: The state of practice within structural engineering." Visit the forum at www.gostructural.com/bim.

A difference between codes

Bruce A. Suprenant’s article, "Solution to a stair problem," in the July 2006 issue of Structural Engineer highlights a recurring problem in stairway construction. He cites the difficulties encountered in the stairway construction requirements of the NFPA Life Safety Code, and is to be commended for his suggestions. Construction conflicts often arise during any construction project, and a timely meeting or discussion between the designer, contractor, subcontractors or specialty suppliers, and the building code official may help resolve issues before they become critical. Perhaps a redesign of the stairway (including a different number of treads and risers) prior to construction would have been the solution in the example.

As a brief note, many states and jurisdictions enforce the International Code Council’s family of construction codes, especially the International Building Code (IBC), rather than the Life Safety Code. Here in Virginia, our Virginia Uniform Statewide Building Code adopts the IBC. This is not an argument for using either code in preference to the other; that discussion would be for a different time and place.

I noticed that the NFPA stair riser dimensions and tolerances shown in Figure 1 of the article exceed the IBC maximum allowable riser dimensions, while possibly mis-stating permissible tolerance limits, as given in the 2003 International Building Code Section 1009 Stairways and handrails. Section 1009.3 Stair Treads and Risers requires riser heights to be 7 inches maximum and 4 inches minimum for commercial stairways (other limits that apply to residential stairways fall under the International Residential Code). Section 1009.3.1 Dimensional Uniformity allows a 3/8-inch maximum variation in riser heights between the largest and smallest riser in a flight of stairs, and allows the bottom riser to be less than 4 inches in height where meeting a sloping walkway, for instance, although uniformity is otherwise required.

Dan K. Williams, P.E., CBO
Fairfax County, Va.