Epoxy Fingered in Boston Big Dig Tunnel Roof Collapse

herald.jpg The US National Transportation Safety Board issued a damming report on Tuesday. It cites a lack of engineering know-how about the epoxy used to hold the anchor bolts holding 4,600-lb ceiling panels in place. The epoxy failed, leading to a ceiling collapse last year in the $14B public works project in whch a woman died. According to the NYT article Collapse of Big Dig Ceiling in Boston Is Tied to Glue ““We’re talking about the wrong glue here, in effect,” said Kitty Higgins, one of the five members of the board, which said that the epoxy selected dried quickly but lost strength weeks later. “The knowledge of the engineering community seems to be deficient,” said Bruce A. Magladry, director of the board’s office of highway safety.” At the time of the collapse last year, engineers speculated wildly in forums online about this engineering who-done-it. Though widely used in a wide range of demanding and critical applications including the assembly of aircraft components, epoxies require a more nuanced understanding than their mechanical counterparts. Design engineers need to know how they perform under specific environmental conditions (moisture, thermal) and the exact mode of loading, as well as curing considerations. So perhaps it’s no surprise that the Big Dig debacle does not set a precedent for the misapplication of epoxy: In one notable example in the automotive industry, the liquid adhesives originally used to bond rearview mirrors in place on car windshields often failed prematurely, causing many mirrors to shear off and wind up in the surprised driver’s lap. (Your’s truly included.) Ford ultimately substituted a high-strength, pressure sensitive tape in that application.

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