Custom formwork and box-outs precisely form curvilinear structure
The National Veterans Memorial in Columbus, Ohio will open in the fall of 2018. The elegant, sweeping curves of the three interlaced cast-in-place reinforced concrete rings that define the structure belie the complexity of the project's design and construction. Designed for the Columbus Downtown Development Corporation by Allied Works Architecture, the Memorial Museum occupies seven acres of a 21-acre site along the Scioto River. The structure consists of a collection of concentric arches rising from the earth. The arches cross to create interwoven concrete rings that form the museum walls and support an upper level sanctuary, providing "a path connecting earth to sky". Constructing the asymmetric structure presented many challenges for the project's concrete contractor, Baker Concrete, and formwork supplier, PERI USA.
Individual quality for complex task
"This is the most complicated structure I've ever worked on," said Rob Ford, project manager for Baker Concrete. It is so complicated, in fact, that no dimensions are in the plans. In essence, the entire project is being built from a 3D model, which Ford says made laying things out especially difficult.
"Each of the three rings takes a circular sweep around the building, but they don't do it at any particular radius – it's constantly changing," Ford said. "You can't just pull a tape to back check your coordinates, because there aren't any corners."
But the challenge of designing and building the formwork was even greater. Baker turned to PERI to provide the formwork for this high-profile project with virtually no room for error.
Overall, the project required about 9,000 m² of wall forms, all built using PERI's VARIO system and supported by PERI UP scaffolding and shoring.
In addition to all of the forms being curved, every form panel had to be built to the exact curve and specifications of a particular location on the project.
"There's no repetition," said Adam Shaw, PERI's lead designer on the project. "We could reuse the VARIO components, but each panel was different."
Challenging formwork solution
Perhaps even more challenging and impressive were the 400 void forms required to create the openings in the concrete rings. These plywood box-outs were CNC-cut in PERI's yard and ranged in size from 3 m² to 25 m².
"All the voids also had a knife-edge, tapering about two and a half feet on all the upper edges," Shaw said. Many tapered to zero at the Xs. "This was a major engineering effort for us."
Creating custom formwork in a Virtual Design Construction Environment
Shaw continues "The 400 custom box-outs were designed in 3D along with a significant portion of the wall forms. What made this job unique is that there were no paper drawings for the project – everything was based on a virtual model that was updated by the architect. PERI pulled the relevant geometry and portions of the model, designed the formwork to match, and then submitted it to Baker for geometric confirmation and coordination with the other trades/sequencing. Although PERI produced 2D form drawings for the final submittal, almost all the design work was completed in this VDC (virtual design construction) environment."
Concreting result at its finest
Because of the dense reinforcement and the desire for an architectural quality finish, Baker pumped self-consolidating concrete from the bottom of the forms. The wall geometry dictated a number of very large pours, as long as 36 m and 12 m tall. Steel reinforcement cages – some approaching 50 tons – were assembled on the ground as the formwork was erected, then lifted into place. In many cases, achieving the openings required that the void box-outs had to be put into place after the rebar had been lowered into the formwork.
Almost the entire structure was designed to be exposed architectural concrete, and originally was slated for sandblasting to ensure a uniform surface. However, the early concrete finish turned out so well off the form that the architect decided to forgo the sandblasting.
National Veterans Memorial and Museum
Designed as a tribute to veterans, rather than as a war memorial or military museum, the Memorial Museum will feature interactive and educational exhibits, beautiful landscaping, and iconic architecture, including the spiral processional rising to a rooftop sanctuary. It will also include permanent and temporary exhibits and meeting rooms for veterans groups.
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