In order to construct the retractable roof for the Miller Park baseball stadium in Milwaukee, WI a large, heavy-lift crane was required. The crane chosen for the job, “Big Blue,” was over 500 feet tall, had two crawlers, 2.4 million pounds of counter-weights and 3 operators. On July 14, 1999, while placing a nearly 1 million pound section of the right field roof, “Big Blue” collapsed, resulting in three fatalities and extensive damage to the stadium and construction equipment.
Engineering Systems Inc. was called on to investigate the cause of the collapse. Initial work included on-site inspection, survey and documentation of the on-site wreckage in the weeks after the collapse. ESI then worked with other interested parties and government agencies to facilitate documentation and removal of key pieces of evidence for later laboratory examination and testing.
The investigation was extensive and encompassed many scientific and engineering disciplines. During the course of the accident reconstruction, ESI investigated, tested and analyzed:
- The materials used in the crane;
- Physical signatures and witness marks within the wreckage;
- The winds present at the time of the collapse;
- The drag loads on the crane and roof;
- The strength and stiffness of key portions of the crane;
- The geotechnical aspects of the crane support;
- The response of the entire crane structure to applied loads and support conditions;
- The effects of roof load dynamics on the crane; and
- Applicable industry standards in the U.S. and worldwide.
It was determined that the collapse was the result of many factors, including the wind, the soil underneath the crane, the flexibility of the crane, key structural details within the crane and actions of the operator. When taken individually, any one of these factors would not have resulted in failure of the crane but, when combined, resulted in a catastrophic collapse.