Chicago, IL

John Hancock Center, Scaffold Collapse


On 9 March 2002, a 100 ft long, suspended scaffold platform fell from the 42nd floor of the John Hancock Center.  As the scaffold fell, it dropped debris in an arc from the northwest corner to the building’s south face.  The wreckage killed three motorists on East Chestnut Street and severely injured several others.  The building owners were undertaking a major facade restoration project at the time.  On the day of the accident, the contractor had decided it was too windy to work from the platform.  SGH investigated the causes of the failure.

SGH investigated both the technical and procedural causes of the failure. Our investigation included the following:

  • Examination of the scaffold wreckage to document the condition and compare the existing configuration with the scaffold design documents
  • Preparation of calculations, including estimation of loads at the time of collapse
  • Development of structural analysis models to evaluate the behavior under the combination of static and dynamic loading
  • Laboratory analysis, which included collaborative sessions with other experts, and wind tunnel testing
  • Review of project documents and photographs produced during litigation

The scaffold platform was suspended from two outriggers on the roof. SGH determined that the uplift rollers and wire rope, which held the north outrigger to the building’s roof, failed under the platform’s self weight and down-draft wind loads. Following the failure, the outrigger overturned and dropped the scaffold platform. SGH concluded that the scaffold collapsed because of a combination of construction, operation, and design errors along with shortcomings in project oversight. Based on lessons learned from this accident, the City of Chicago adopted new ordinances related to scaffold design and operation.

Project Summary



Completion Date
Failure Investigation
Structures | Advanced Analysis
Clifford Law Offices
Specialized Capabilities
Temporary Construction | Computational Mechanics | Failure Analysis

Key team members

Alec Zimmer
Alec Zimmer
Associate Principal