High wind is being suggested as the most likely cause of a crane collapse last month in Milwaukee, USA that killed three workers and injured five others.
Neil F. Lampson Inc’s massive Big Blue crawler was lifting a 400 US ton steel section of the retractable roof on the new Milwaukee Brewers’ baseball stadium just after 5pm on 14 July when the boom and load fell. The crane, weighing 1,200 US ton, was equipped with 567ft of boom and more than 1,000 US ton of counterweight. Designed with a maximum lifting capacity of 1,500 tons, the crane had already made nine similar picks out of a planned total of 31.
The three men killed were working in a man basket suspended from a support crane.
Lampson’s quality assurance manager Bruce Stemp on 19 July said that “all indications are pointing to the wind conditions” and that “any failure of any of the crane components was a result, not a cause of the accident.” Photographs show that the crane’s superstructure had separated from the carbody and such a failure, in the base of the crane, suggests that wind was a factor, according to Al Ghorbanpoor, chairman of the civil engineering department at the University of Milwaukee-Wisconsin.
Lampson president, Bill Lampson, was expected to be on site for several days and a report was expected before the end of the month. Stemp said that before the report was completed there would not be any changes in procedure on Lampson’s other projects as a result of the Milwaukee incident.
Reports of the wind speed at the time of the collapse vary between 23mph and 30mph. On 15 July the Milwaukee Journal Sentinel reported: “Construction officials have said repeatedly that it would be unsafe to do a roof lift in winds of more than 10mph.” It went on to say that the first roof section lift, on 8 January, was delayed for 17 days by the wind and that the second one, due on 5 March, was postponed because of 20mph winds. There has been speculation that pressure to stay on schedule to meet the completion date, or risk financial penalties, could have been a factor.
OSHA, the Occupational Safety & Health Administration, has a maximum of six months to completed its investigation and report on all aspects of the incident. George Ioksas at the Milwaukee office expects it to be “weeks, at minimum”.
