If you’re interested in engineering mysteries, The Wall Street Journal has a story for you about I.M. Pei’s East Wing of the National Gallery in Washington, DC. The article goes into fascinating detail to present the engineering whodunit (or, really, whatdunit) behind the marble panels that seem to be popping off the structure:

One or two of the 2-by-5, 438-pound marble panels on the building’s main air shaft were tilting out. At first, gallery officials believed the problem was localized, caused by the freezing of water lodged on the shaft’s deteriorated asphalt lining. But tilted panels soon started cropping up on different parts of the building. To date, the displacement of some 400 of the East Building’s 16,200 exterior panels—about 2.5% of the total—has been observed. That may seem a small amount. But because this is a public venue, and because “we can’t model or predict the rate of failure,” says Susan Wertheim, the gallery’s deputy administrator for capital projects, National Gallery officials decided in 2008 to reinstall all of the panels. They plan on hiring a contractor to oversee the project next year. […] The project is scheduled for completion in 2013 at an estimated cost of $85 million. A cordon sanitaire has been discreetly established by means of wooden entrance pavilions, roped-off entrance steps, and temporary fencing around the building. But visitors can’t identify the problem because newly tilting panels are swiftly wedged back into place with leaden shims.

Ultra Modern Building Shows Signs of Age (Wall Street Journal)