Building information modeling (BIM) certainly helps to expand the design decision matrix, facilitating collaboration among the various disciplines and systems, and identifying clashes before construction begins. Incorporating constructability into the design decision matrix has the potential to super-power BIM, help the design team make smarter decisions, and positively impact overall project efficiency and quality. Together, BIM and constructability can deliver projects that integrate design and construction insights in a highly collaborative, owner-friendly format, but only if they are joined by more than a computer screen early in the design process.

BIM is hailed by owners, designers, and constructors as the way to bring the major disciplines to the table to find and solve potential issues before the team gets to the field. While this is a significant advantage of 3D modeling, this modeling does not replace the need for good design. BIM will model bad design solutions just as it will model highly effective designs, and BIM will model designs that are difficult (and expensive) to build. Good design remains the responsibility of the design team, and incorporating the philosophy of constructability enables the design team to incorporate construction knowledge into design decisions, and thereby improve overall design and project results.

Constructability is not value engineering
Constructability has traditionally been viewed as a step in the design/construction process that is very similar to value engineering in that a substantially completed design (such as 90 percent) is reviewed with attention to incorporating construction considerations that could save project costs and/or shorten the construction schedule. However, while value engineering may provide some savings, it is by nature a process that only fine-tunes the individual parts. As such, it cannot achieve a finely tuned project. Further, because it is done late in project development, its ability to influence the project is limited. In contrast, constructability integrates the process by engaging design and construction players at the earliest possible stage, ideally during conceptual planning (as shown in Figure 1) before a substantial design is complete. This takes full advantage of available construction knowledge and experience. The American Institute of Steel Construction (AISC) recently published “Design Guide 23, Constructability of Structural Steel Buildings,” which was authored by Ruby+Associates’ founder, Dave Ruby. In this publication, AISC notes, “This document … is based upon evolving thought on new project delivery systems in the industry and addresses concepts that are appearing in the professional literature on an increasing basis. The author’s ideas involve all construction trades and design disciplines, not just structural engineers and structural steel fabricators, and this document can serve as a primer for structural engineers … who seek new approaches to construction and new ways of doing business.”

AISC Design Guide 23/Ruby + Associates Figure 1: As time progresses on a project, the ability to influence good design efficiently diminishes.

Every building is custom
Every building that is designed and constructed is customized because each site has different subsurface conditions, seismic considerations, and loading criteria (from wind, snow, etc.). Yes, some previously designed solutions can be appropriate, however, each new site usually brings a new challenge that requires some sort of custom solution.

Structural engineers typically face several challenges as design proceeds, including the following:

• Many other building systems connect to the structure and impose load concentrations; the structural engineer must integrate these systems into design considerations.
• Structural systems often must operate in unseen spaces to maintain architectural design integrity, and must share these spaces with high concentrations of mechanical, electrical, plumbing, and communications systems.
• Because a building is not created in its final state, structural design must accommodate changing loads that occur as a structure is constructed.

Integrating BIM and constructability solves potential issues on the design side and prevents problems on the construction side by not only bringing together design disciplines, but also inserting construction knowledge into the design process. Together, BIM and constructability allow the design team to know more about the other systems that connect to the structural design so load concentrations can be better understood throughout construction. BIM facilitates the philosophies of constructability by requiring all of the design team to collaborate in 3D. Therefore, many of the potential issues of co-located systems can be resolved in the 3D model instead of in the field where problems can increase project costs and time to completion. Together, BIM and constructability help the design and construction team to organize “hidden” systems efficiently, maximizing floor-to-ceiling heights and reducing total building costs.

While recognizing the benefits for the design team, it is also important to recognize the advantage of collaboration for the construction team. The construction team still will be faced with making decisions about design intent in the field regardless of BIM’s sophistication and the design team’s expertise. Overall project success still depends upon the ability of the construction team to execute the design. By including key construction staff in the design process, that team is much more capable of making field decisions that accurately reflect design intent. No longer looking at static drawings, the team members understand the thought processes behind the design.

Partnering with the steel fabricator/erector to deliver the structure of the building, Ruby’s structural engineers applied constructability principles and completely redesigned the structural steel component. This redesign saved a significant amount of money, enabling the owner to construct the fourth floor (originally scheduled for future expansion) and still complete the project several hundred thousand dollars under budget.

Two tools intended to expand the design decision matrix
In the ancient days of Rome, the master designers created their structures on paper, and then had them built to see if they would stand. Bad designs fell down; good designs are still around today (to some extent). This methodology of trial and error has come a long way over the past couple of thousand years, and our industry continues to seek tools that improve design before construction begins. Combining BIM with constructability concepts is another step in that evolution.

Both BIM and constructability strive to expand the design decision matrix by incorporating more information and by enabling the designer to make smarter decisions. BIM does this by integrating the entire design team; constructability does this by integrating construction considerations with design. By incorporating input from the construction manager and construction trades, BIM can deliver more complete designs that include considerations that will make construction more efficient.

Together, BIM and constructability provide a powerful tool to bridge design and construction by creating conversation, collaboration, and creativity.

Jay Ruby, P.E., is the president and CEO of Ruby + Associates, a structural engineering consulting firm with offices in Farmington Hills and Grand Rapids, Mich. He can be reached at jruby@rubyusa.com.