World Trade Center structural joint
This damaged structural bracket from the World Trade Center was recovered from the debris pile. Context:
This viscoelastic damper connected a floor truss to an exterior steel column of the World Trade Center. Building movement caused by wind was a major concern to the architects and engineers designing the 110-story towers. They cleverly mitigated apparent building movement by using these dampers to allow the exterior of the building to sway slightly under wind load, while the floor remained largely stationary.
The damper and other floor attachment brackets were also a point of failure leading to the towers' collapse. When the intense fire heated the 60 foot-long floor trusses, they eventually distorted and pulled free of their attachments to the exterior columns. As the upper floors of the towers fell, the weight then “pancaked” the lower floors, breaking floor truss attachments unaffected by heat. Each of these huge towers collapsed in about ten seconds.