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At the Solomon R. Guggenheim Museum in New York City, it's not only the works of art people come to see - it's also the masterpiece of concrete building and design. Opened in 1959, the Guggenheim has attracted visitors from around the world who admire the building's artistic and visionary design. But almost as long as the building has been open, its concrete structure has suffered from cracking. As the building nears its 50th anniversary, a team of architects, engineers, historical conservators and contractors have joined forces to ensure a state-of-the-art renovation for this concrete masterpiece.

The Guggenheim Museum was designed by American architect Frank Lloyd Wright, who oversaw its construction between 1957 and 1959. The Guggenheim was Wright's last project; he died at age 91, shortly before the museum opened. An architectural visionary, his construction and engineering methods were often controversial and anything but normal, putting design above proven building methods of the time. As experienced with many of Wright's other structures that have gone through major renovations, the Guggenheim's unconventional building design required an unconventional repair design.

The original construction
The rotunda of the Guggenheim is a six-story, continuous spiral structure with a 3 percent grade. The walls of the rotunda tip outward and lean out farther as the building gets taller. The contractor working with Wright formed the walls of the rotunda with plywood panels and created the walls with gunite, or shotcrete, a product that at the time was used in structures like parking garages but not thought of as a viable material for an architectural project. The plywood was placed on the outside walls and the gunite shot from the inside. This was a non-typical application for gunite, with most applications being done with the plywood on the inner wall and the material placed from the outside.

The gunite rotunda walls were supported every 30 degrees by a "web wall," a cast-in-place structural pillar found 12 times around the circumference of the rotunda, supporting both the exterior rotunda walls and the interior spiral ramp. Every 10 degrees between the web walls the rotunda is reinforced by an embedded vertical T section, which also supported the original formwork. An additional four layers of steel are buried in the 5-in. rotunda wall - a layer of wire mesh, two layers of rebar and another layer of wire mesh.

One of the most unconventional decisions Wright made with the Guggenheim design was eliminating control joints. He wanted the surface to appear as a monolithic spiral and did not believe he could achieve that with crack control joints.