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.