feature

On the Wings of a Dove

Design-Build Glazing Contractor Takes on the Challenge of Peace Building
by Megan Headley

The new U.S. Institute of Peace (USIP) Headquarters in Washington, D.C., sits on the Northwest corner of the National Mall, facing the Lincoln Memorial. The location is visited by millions of tourists each year. The mission of the national center for advancing the study and practice of peace building is clear even as one approaches the building, as it is capped by two curving glass roofs designed to evoke the image of the wings of a dove and an olive branch.

The design, fabrication and installation of those complex roofs was less a lesson in peace than it was in patience—and exacting quality control.

Dovetailed Design
Through a nationwide competition, architect Moshe Safdie and his firm Moshe Safdie and Associates in Somerville, Mass., were chosen to design the USIP facility. The $110 million, five-story, 150,000-square-foot concrete structure ultimately consists of three distinct sections linked together by atriums covered by large-span undulating roofs. The roofs form a dramatic series of wing-like elements constructed of steel frames and nearly 1,500 white insulating glass units (IGUs) fabricated by Bischoff Glas Technik in Germany. The IGUs each feature a translucent interlayer and dotted frit on layer #01 to provide a white glow. The south roof has a 12,000-square-foot surface area and spans 80 feet between buildings; the north roof has a 7,500-square-foot surface area and spans 55 feet.

seele, a German-owned design-build contractor headquartered in the United States in New York, was awarded the installation contract in December 2006, starting the long journey from design-assist to completion.

“During the design-assist phase a close collaboration between seele and the architects was required to develop the desired geometry and meet the design intent during detailing phase. Many structural members and components were adapted during this stage,” says Heiko Mertel, the project manager.

Daylight—and Nightlight—Challenges
As Mertel explains, the architect’s design intent on the USIP was “to provide a translucent white roof system that minimizes the appearance of the faceted components, producing a smooth, dome-like structure when viewed from the exterior.”

It was important that the LEED Silver structure maximize interior daylighting, but was equally important that the illuminated white dome not outshine the nearby memorials. As Mertel explains, the design intent specifically mandated “the intensity of the evening glow of the glass roof will be closely monitored so not to exceed the lumens produce by the Lincoln, Jefferson and Washington Monuments.

“The most critical [challenge] for this building was not just to achieve the highest thermal values, as is standard; the biggest challenge was to achieve the [correct] lighting so as not to exceed the glow of all the memorials all around,” Mertel says. It became a balancing act of very neutral low-E coatings and interlayers.

The fabricated glass underwent a lighting mock-up, in addition to its performance mock testing and testing for high strength bolts and bomb-blast calculations. As Marc Zimmer, vice president of operations for seele, explains, “We developed a matrix of different types of membranes and glass sizes, and from the matrix we built different mock-ups that underwent light testing at our facility. We had the whole consulting team, the owner and the contractor there for the light testing that was performed overnight in order to see the effects between different types of glass systems and membrane systems.”

Design Big-Time Assist/Fabrication
As seele was involved early on in the project, the glazing contractor’s team played a big role in steering the architect toward the best products for requirements such as this “night lighting.”

Even as the materials were decided upon—plans quickly changed.

For example, the team quickly found that the roof overhang on the north side could not be carried on the façade because the façade was directly above the entrance to the underground car park, supported on a long-span reinforced concrete beam. Additional loads would have overstressed the beam.

As Mertel explains, “The initial design was to bolt roof connections to the concrete. Due to high shear forces and reduced space (high amount of rebar), the concrete was not able to allow for bolted connections. Therefore, we had to redesign the connections with complex embeds.”

The solution was a sliding joint between the inward-curving curtainwall and the roof construction, so that no loads are transferred from the roof to the façade.

Multiple-cranked steel sections for the transverse beams were welded together beforehand and bolted to the intermediate beams via end plates during erection. Aluminum glazing bars on top, concealed Sefix retainers and a continuous silicone joint formed an aesthetically sophisticated roof glazing solution.

Installation and Challenges
For the glazing contractors starting construction in June 2009, the USIP’s prime location meant traffic congestion and difficult access.

“It was a congested site, of course, so we had to deal with just-in-time delivery,” Mertel says. Adding to the challenge of storing glass materials onsite was the fact that the deliveries consisted of oversize crates containing preassembled steel frame assemblies. There was no room onsite for those deliveries, and barely room on the street for the trucks.

“We had to close down Constitution Avenue,” Mertel says. “We had to get into the site, which was sometimes very difficult because the site stopped on the road and we had to tear down fences or things like that to get into the site—which meant blocking the road.”

Then there were the days where they couldn’t get to the site at all.

“We had to deal with no-work days during public holidays,” Mertel says. “Usually you don’t think about things like that, you just get deliveries and start with construction,” he adds.

And then there was the record-breaking snowstorm of 2010.

“We had to stop caulking of the roof and planned for better weather in spring,” Mertel recalls.

Upon surmounting these challenges, the glaziers, found, naturally, new hurdles.

“The roof and the curtainwall structure are an integrated structure,” Zimmer explains. “The roof structure acts as a shelf structure. The scaffold had to remain up for the whole period of the installation because it was a support for the roof shell. From an installation perspective, this is not something where you can dismantle a certain area and turn it over—you had the full area [scaffolded] for the entire period in order to perform the installation.”

But in June 2010 the glass installation was complete.

Much like peace building requires close collaboration among all involved, seele’s managers agree that the collaborative approach among all parties led to the ultimate success of this project.

“The collaborative approach by all parties in the project … made this project a unique experience for everyone involved in it,” Mertel says.

Working with BIM
seele had used building information modeling (BIM) software on projects in the past and was familiar with the new capabilities this technology allows.

“[There] are always going to be different parties driving the BIM approach,” says Marc Zimmer, vice president of operations for seele, based on his experience. “There are projects where the owner is requesting the integrated approach, there are other projects where we’ve seen the general contractor implementing BIM for coordination purposes.”

In the case of the U.S. Institute of Peace (USIP) headquarters in Washington, D.C., however, there seemed to be no way to not work with BIM and still achieve the architect’s vision.

As Zimmer says, “We used BIM modeling because the architectural intent was a 3-dimensional, complex shell structure that could not have been devised on paper.”Simplifying the structure might not have been possible without using BIM to coordinate the thousands of pieces. “We worked with different shapes in order to develop the roof structure. The final shape of the wing and the dove was actually devised by the interface of familiar shapes, like balls, doughnuts etc.,” Zimmer elaborates.

Among the challenges in working with BIM, cautions Heiko Mertel, the project manager for the USIP project, is taking those difficult-to-design pieces and turning them into simple-to-fabricate lites.

“In working with BIM, the biggest challenge was from the beginning of the design to get the geometry into a usable solution that can be manufactured in the shop and installed,” he says.

Although the company has used BIM extensively on projects—many of the 200 engineers and architects on staff in its Germany office have the capability to develop BIM models—Mertel points out that the real challenge with BIM is not the model design, but rather the approach to using the model.

For USIP, Mertel says, “The design phase was unique as it fully integrated the BIM approach to the project. The final approval for construction was based on the 3D model and detail drawings rather than a 2D drawing set.”

Zimmer adds, “Different parties need to contribute to one structure that is going to be incorporated into one model. What we had on this project, and I think what’s going to be the direction in the future, is that the approval for starting fabrication was based on the model. In the traditional approach you would issue the drawing and move forward with the drawing.”

Calling Quality into Question

The just-opened U.S. Institute of Peace Headquarters in Washington, D.C., features a complex glass roof that might not have been possible without close attention to quality control. Many professionals say that improved quality control is one of the year’s biggest architectural glass trends (see article page 28).

Insulating glass units were fabricated by Bischoff Glas Technik in Germany, and the structural steel was pre-assembled at seele’s shop in Pilsen, Czech Republic. Although the oversize crates shipped from overseas would provide challenges, it’s unlikely seele will fabricate in the U.S. anytime soon because of those quality control concerns. “Usually with a specialized glass-steel system, we have very tight tolerances, and so we usually decide to produce the steel in our own shop to [ensure] the quality … and so we have the problem with the shipment,” says Heiko Mertel, the project manager for the USIP project.

“The steel was manufactured with machinery that is being used in the car industry. We’re using the same tolerances for the structural steel that we would have supplied to, for example, a car panel—this would be tolerances in a range of millimeters—which then gives us the opportunity in the installation phase to make sure that the structure falls into place,” says Marc Zimmer, vice president of operations for seele. “It’s currently a very limited number of fabricators that actually apply the high tolerance fabrication process to structural steel.”

Megan Headley is the editor of USGlass magazine.

USG
© Copyright 2011 Key Communications Inc. All rights reserved.
No reproduction of any type without expressed written permission.