John Hancock Center scaffold collapse

December 30, 2006
Publication: Forensic Engineering 2006 - Proceedings of the Fourth Forensic Engineering Congress, ASCE p 97-111
Author(s): Alec Zimmer Glenn Bell

Abstract: On Saturday, 9 March 2002 at approximately 1:45 p.m., a 100-ft long, suspended scaffold platform fell from the west face of the 100-story John Hancock Center in Chicago, dropping debris along an arc from the northwest corner of the building to the building's south face. The scaffold wreckage killed three motorists on East Chestnut Street and severely injured several other passers-by. In early 2000, the building's commercial and residential owners embarked upon a major facade restoration project. They engaged a prime contractor who contracted with a scaffold vendor to design and furnish the scaffold system. The scaffold rig involved in the accident consisted of a 100-ft long, aluminum truss work platform suspended from two outriggers on the roof of the building. On the day of the accident, the contractor determined that it was too windy to work from the platform, and, as had become their custom during off-hours, the contractor's workers moored the work platform on the building's west faceat the 42nd floor. We investigated both the technical and procedural causes of the failure. We determined that under the platform's self-weight and down-draft wind loads acting on it, the cam followers (uplift rollers) and wire rope lashing holding the north outrigger to the building's roof track failed. Without this support, the outrigger overturned, and the scaffold platform dropped. As is the case in many catastrophes of this magnitude, there were many opportunities for the project participants to avert the failure. Many of those parties failed to meet their obligations to the project, and their shortcomings contributed to the accident.