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May 11, 2007

L&I investigation: Flawed engineering design caused tower-crane collapse

TUMWATER — A flawed engineering design was the cause of the Bellevue tower-crane collapse in November, killing one person, a Department of Labor & Industries (L&I) investigation has determined.

The engineered foundation, by Magnusson Klemencic Associates of Seattle, was designed to withstand only about one-fourth of the pressures that the 210-foot tower crane actually required, L&I said today.

Operator error was not a factor. The investigation found the crane operator was well experienced and was operating the crane properly.

“The inadequate design of the tower-crane base clearly led to the collapse of the structure,” said Steve Cant, assistant director for L&I’s Division of Occupational Safety and Health. “The problem was compounded by the failure of the general contractor to maintain and inspect the crane base in accordance with the manufacturer’s specifications.”

The results of L&I’s six-month investigation into the Nov. 16 crane collapse were shared today with the companies involved in the project.

The investigation covered all aspects of the crane’s construction and operation, including the possibility that strong winds may have weakened the crane. The department found no evidence that high winds the night before contributed to the tower-crane collapse. The cause of the collapse was metal fatigue of the steel base frame, which was not strong enough to support the working crane.

The collapse of the crane prompted the Legislature this year to enact new laws establishing a construction-crane-certification program and a crane-operator-certification program, which will be administered by L&I.

“We’re pleased that Gov. Chris Gregoire and the Legislature enacted changes in the oversight of construction cranes, because this kind of tragedy, in which workers and innocent bystanders could be at risk, should not happen again,” said Cant.

Cant said L&I specifically asked that the new construction-crane legislation include a provision that, in any non-standard tower crane base, an independent professional engineer must review and approve the plans.

The Bellevue crane’s base design was unusual in that a typical standard construction-crane base would be a poured concrete pad in which crane anchors would be embedded. The base structure designed for this crane consisted of a configuration of steel I-beams welded and bolted together as an H-frame and attached through a set of collars to four concrete pillars.

Non‑standard bases are necessary in some situations, and they can be engineered to ensure structural integrity and safety. However, in this case the base system design was not strong enough to support all the possible critical load combinations. It needed to be at least four times stronger to operate safely.

As a result of L&I’s investigation, two firms are being cited for workplace-safety violations:

  • Magnusson Klemencic Associates, the engineering firm that designed the base, was cited for failing to ensure that the design specifications met the specific recommendations of the crane manufacturer. The proposed penalty is $5,600.
  • Lease Crutcher Lewis, the general contractor for the Tower 333 project, was cited for failing to conduct periodic inspections to determine that the crane’s deflection limits were not exceeded as specified by the manufacturer. The proposed penalty is $5,600.
  • Lease Crutcher Lewis was also cited for attaching to the tower crane structure advertising banners that exceeded the size recommended by the manufacturer. Oversized signage could potentially affect the control and operation of the crane. The proposed penalty is $3,600.

L&I’s investigation included four other companies — Northwest Tower Crane Service, Morrow Equipment Co., Ness Crane Inc. and Albrecht Birkenbuel Inc.  No violations were found and they were not cited.

The cited companies have 15 business days to appeal the citations.

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For media information: Elaine Fischer, L&I, 360-902-5413 or nele235@LNI.wa.gov, or visit the L&I News and Media Center at www.LNI.wa.gov/News

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