Play ball! That was the cry from the D.C. Sports and Entertainment Commission to the Nationals Park design-build team. And, like any baseball fan, they were looking for a home run.
Nationals Park, home to the Washington Nationals baseball team, has received critical acclaim for its speed of construction, making the cover of several popular design and construction journals. With comments like “construction’s equivalent of a grand slam of a 100 mph pitch” and “fastest professional sports stadium ever constructed,” the project is definitely one for the record books. It’s easy to attribute the success of the project to the design-build project delivery method, but this was not your usual design-build. What was most unusual about it? “That it really worked.” says Don Banker, president and owner of the Banker Steel Co. in Lynchburg, Va., the steel specialty contractor for the project.
Banker Steel was part of the design-build team and, more important, a key participant in the structural steel design-assist process. Design-assist, in its true form, puts the specialty designer and the specialty subcontractor working together from the early design phase. In this case, Banker Steel worked closely with the structural steel engineer, New York’s Thornton Tomasetti Inc., beginning in the preconstruction phase of the project. Structural steel design-assist has two major benefits: Economy and value are designed into the project from the start with reasonable assurance that the project will stay within budget, and two critical lead time items — steel detailing and the steel mill order — take place during the early design phase. This allows steel fabrication to begin at, or in this case before, design completion. Both of these benefits were realized on the project largely because the team players were willing to step out of their comfort zones.
One question that often comes up when considering this is “How can I competitively choose a steel contractor without a design to bid on?” The answer is “unit prices.” Banker Steel submitted a series of unit prices for various categories of steel framing. These were based on unit quantities and categories provided by Thornton Tomasetti. Typical categories include raker trusses, moment frames, braced frames, belt trusses, roof bents, gravity columns, floor framing and scoreboard. The unit prices were used with the unit quantities by the design-build joint-venture contractor, Clark/Hunt/Smoot JV, to determine an initial contract value. Through this process Banker Steel demonstrated that they would provide the best value for the project.
The unit prices would be converted to a firm contract amount later in the process. The downside of unit prices is that risk. The unit quantities and unit prices were based on schematic sketches and discussions and the initial contract value would be carried all the way through the project. Banker Steel stuck its neck out, having a seat at the design table but no guarantee that the overall structural steel cost would remain within the unit price budget.
The Order
Having been brought onboard early based on its unit prices, Banker first focused on reserving the mill order — crucial to maintain the fabrication and erection schedule. But it was a challenge. To determine realistic tonnages for the structure so early in the design phase the team agreed that the stadium be divided into seven sectors, and a structural design would be performed on the first sector to compute tonnage. This was then extrapolated to provide a tonnage estimate for the entire structure. This required an extraordinary commitment from the architect, HOK/Devrouax&Parnell. They agreed to lock in the geometry of the ballpark early. This was not a comfortable position for them and, in fact, the architects’ willingness to get out of their comfort zone was instrumental in the success of the project.
The use of Tekla Structures’ 3-D structural design and detailing program aided in the process. This allowed a very detailed early design and helped make the early tonnage estimates much more accurate. The Tekla model also enabled Banker to monitor the unit prices and provide frequent and immediate cost/scope feedback throughout the project. After the mill reservation was made, the owner paid for the mill material — also unusual.
Up to Speed
Weekly meetings started in the preconstruction phase to address and resolve difficult issues to best maintain project budget and schedule. Strong leadership from the general contractor was essential. Their influence helped everyone work together to maintain their GMP. The process is designed to drive each specialty contractor to their unit price, which drives the project to the budget.
Because of the ballpark’s unique layout, the design and construction sequence progressed from right field in toward first base, behind home plate and back out along the left field line — an understandable practice for construction but more uncommon for design. Throughout this process the architects were flexible, making decisions either on the spot or within a day or two. They were also willing to scale back certain features originally envisioned up-front, to maintain the overall project budget.
The architects realized significant value in this early working relationship. Early consultation with the steel detailer, Mountain Enterprises, and by using the Tekla model, they received immediate feedback on the appearance of prominent areas of exposed steel structure.
The Tekla model worked out many scheduling and sequencing issues. Truss assemblies were sized to facilitate economical shipping, and the mill order process was expedited using the in-depth member information contained in the model. The model also provided immediate feedback on the cost of changes and enabled the design-build team to understand the cost impact of changes.
Because steel was ordered early, some subsequent design changes had left some steel shapes unused. Since these shapes were already owned by the project, they were put on a “bone yard” list. To keep the project as efficient as possible, the team utilized steel shapes from the bone yard for the remainder of the project. In one instance, a late scoreboard redesign forced Banker and Thornton Tomasetti to come up with a clever design that utilized only the steel from the bone yard. As a result, there was no unused steel at the end of the project.
Rounding the Bases
Perhaps the toughest challenge that faced the steel team was the design of the connections, which along with details are typically the most expensive part of the structural steel package. It’s a challenge that can break the budget, and is an area where Thornton Tomasetti really demonstrated its value as a team player. In fact, Banker and Thornton Tomasetti worked out a model sharing arrangement where Thornton Tomasetti maintained ownership and control of the Tekla model through the early design phases. Thornton Tomasetti designed many of the major connections with Banker’s input and blessing. Eventually the model was handed over to Banker, where it handled the design of the more typical connections, with Thornton Tomasetti input, and Banker completed the steel detailing.
The Tekla model helped maintain project schedule.
Five separate mill orders were produced as the team worked around the baseball field. The ability to readily extract the advanced bill of material (ABM) from the model expedited the mill order process. Also, the need to get steel quickly into fabrication necessitated the approvals of shop drawings electronically within the Tekla model. Banker also relied on direct download of fabrication data from the model into its CNC fabrication equipment to get the steel through the shop and to the site as quickly as possible.
The continued collaborative effort of the project team throughout the construction phase led to the timely completion of the project and Nationals Park was ready on March 16, 2008, two weeks before opening day.
Tom Faraone is regional engineering manager for Banker Steel Co.