Whether locals want to hold a farmers market, a picnic, or a summer concert in the park, Washington D.C.'s new G8Way Pavilion was designed to provide them with a place to gather for community events. Thanks to the use of a custom precast concrete solution, the visually stunning structure offers people a place to gain protection from the elements or to get a bird's-eye view of the neighborhood.
"The pavilion creates an instantly iconic, visible, and welcoming view into the site," says Bill Henderson, vice president of operations for Gate Precast Co., the precaster for the project.
The new pavilion features a sloping canopy and rooftop terrace comprising 181 lightweight, precast ultra-high performance concrete (UHPC) panels that are just 1.75 in. (45 mm) thick. The panels have supplemental hollow structural sections attached to their backs to create an aesthetically pleasing yet structurally sound system.
"Because the UHPC premix is made up of fine aggregates, it was possible to cast the panels with strict angular geometries," Henderson says. By increasing the panel dimensions to synchronize with the primary steel structural grid of 15 ft (4.6 m) on center, the architect was able to minimize the number of secondary steel members. "That significantly reduced project costs."
It wasn't easy to build, though. The different geometrical panel shapes and requirements for panel placement made erection extremely difficult.
To avoid errors in the field, all of the teams involved with the project used three-dimensional drafting software to model the structure and compared models regularly throughout design. "That allowed the design team to identify and solve potential problems on the computer before they became problems in the field," Henderson says. As a result, they were able to cast and install the panels in a short period without any significant field modifications or delays.
The collaborative process also allowed for the primary steel frame to be concurrently installed with the UHPC panels and without clashes to further support the aggressive schedule.
Once the design was finalized, the erection crew had to develop a special erection method to adjust the UHPC panels to their intended designed geometrical attitude while keeping the panels suspended before they could be placed on the structure. This was accomplished by employing nylon straps of varying lengths and combinations of chain-falls and come-alongs to set the panels in place.
The erection crew used 30-ton and 50-ton rough terrain cranes to aid in the overall handling and accurate positioning of the panels. Because these types of cranes can be easily moved or relocated on a site, the erector was able to meet an aggressive schedule.
"This was one of the speediest fast-track projects on which we have ever worked," Henderson says. Over the course of just 19 days, 181 UHPC panels were produced, and erection was completed in one month.
"The project really does look great in the field, and it would be difficult not to take pride in that accomplishment," he says. "For us, it's a big feather in our cap."