A lawsuit is currently pending in Chicago – a family is suing over the death of a loved one. A lawsuit in the big city -- that’s nothing new, right? Maybe, except that this woman was killed by a window! As she was walking down a Chicago sidewalk, huge plate-glass windows came showering down on her and killed her. How could such a thing happen? The window did not come loose from the building due to someone popping it out of its frame. The building actually pushed it out all by itself!

This is not the first instance of buildings revolting against their windows. Back in the early 70’s, the John Hancock Tower in Boston went on a similar rampage. This time it wasn’t just a few of its windows that came crashing down to the sidewalk below. Entire blocks of windows were falling from the building, endangering the public and worrying the owners of this beautiful skyscraper. As more and more windows fell to the ground, the owners had to put large sheets of plywood in the empty frames to protect the contents of the offices inside. It was often joked that the Hancock Tower was the “Plywood Tower.” The plywood remained until a group of engineers investigated the building’s strange behavior and proposed an interesting solution.

So what made these windows simply pop out of these modern skyscrapers? How exactly did the building push the windows out? As it turns out, buildings have the ability to oscillate or dance back and forth. These motions occur in many structures all the time but are often not significant enough for you or I to feel. However, in some cases these motions become so extreme that windows fall out or even more serious damage occurs! Most people can’t possibly imagine that something as large as a 1000 ft skyscraper can actually sway and twist about, but the following pages will help you to understand quite simply why buildings (and bridges) do indeed move and what engineers like myself are doing to prevent these types of disasters.

First, let’s try and understand why these giants dance!