developed an unexpected problem; it created a wind tunnel effect, and in strong winds the doors could not be opened. Pei was forced to construct a tunnel so visitors could enter the building during high winds. Between 1963 and 1967 Pei designed the Mesa Laboratory for the National Center for Atmospheric Research outside Boulder, Colorado, in an open area at the foothills of the Rocky Mountains. The project differed from Pei's earlier urban work; it would rest in an open area in the foothills of the Rocky Mountains. His design was a striking departure from traditional modernism; it looked as if it were carved out of the side of the mountain. In the late modernist area, art museums bypassed skyscrapers as the most prestigious architectural projects; they offered greater possibilities for innovation in form and more visibility. Pei established himself with his design for the Herbert F. Johnson Museum of Art at Cornell University in Ithaca, New York (1973), which was praised for its imaginative use of a small space, and its respect for the landscape and other buildings around it. This led to the commission for one of the most important museum projects of the period, the new East Wing of the National Gallery of Art in Washington, completed in 1978, and to another of Pei's most famous projects, the pyramid at the entrance of Louvre Museum in Paris (1983–89). Pei chose the pyramid as the form that best harmonized with the Renaissance and neoclassical forms of the historic Louvre, as well as for its associations with Napoleon and the Battle of the Pyramids. Each face of the pyramid is supported by 128 beams of stainless steel, supporting 675 panels of glass, each . Fazlur Rahman Khan In 1955, employed by the architectural firm Skidmore, Owings & Merrill (SOM), he began working in Chicago. He was made a partner in 1966. He worked the rest of his life side by side with Architect Bruce Graham. Khan introduced design methods and concepts for efficient use of material in building architecture. His first building to employ the tube structure was the Chestnut De-Witt apartment building. During the 1960s and 1970s, he became noted for his designs for Chicago's 100-story John Hancock Center, which was the first building to use the trussed-tube design, and 110-story Sears Tower, since renamed Willis Tower, the tallest building in the world from 1973 until 1998, which