This post continues our series on famous structural failures. More details can be found by taking a look at the seminars located on the “articles” page of www.AeroNavLabs.com
The John Hancock tower in Boston, Massachusetts is a sixty-story building consisting of a steel frame and originally covered with 4 1/2 by 11 1/2 foot double-glazed glass panels. These panels had been used before but not on such a tall flexible building. On January 20, 1973 a severe windstorm hit Boston, causing 65 of the double glazed glass panels to fall to the ground. Each panel weighed 500 lbs!
The tower has dimensions of 300 feet by 104 feet, resulting in a very flexible building. When panel failures occur in a high-rise building it is usually assumed that it is due solely to the deflection of the steel frame under the action of the wind. Various tests showed that this was not the primary cause of failure. However, to reduce the building deflections it was decided to add tuned dynamic dampers, each weighing 300 tons, at the top of the building. The damper masses float on a film of oil and are attached via springs to the building. 1,500 tons of steel bracing were also added to increase the building’s lateral stiffness.
The failure of the glass panels, which were correctly installed, was ultimately found to be caused by the design of the double-pane joints. The joint between the inner and outer glazing was so strong that it could not yield and transmit any motions caused by movements of the building frame. To resolve the problem all the 10,344 panels in the tower were replaced with single glazed panels that were more flexible.
It is also interesting to note that during excavation for the building, the ground in the vicinity began to fall as much as 6 feet. It was ultimately discovered that the area selected for the tower was a former swamp and had been filled in with sand and gravel in the 19th Century. Further discussion about this type of issue will be detailed in our coming posts about New Orleans after hurricane Katrina, and the Leaning Tower of Pisa.
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