Lock, stock and barrel

30 April 2008

Barnhart was contracted to remove and replace the two lower pool lock gates ‘in the dry’ on a large ship lock in Mobile, Alabama. Each gate measured 85 feet tall, 65 feet wide and 7 feet thick and weighed 360 tons. Matters were further complicated by the tight time constraints on the project–just 30 days.

Barnhart devised a solution comprising a portable, high–capacity bridge crane that would span the dock and include a 500–ton winch. The old gates would be lowered onto a barge, which would also deliver the new ones. Th roughout the lifting procedure this vessel would act as a tailing device.

These lifts provided a range of engineering and planning challenges, not least of which were the span, the weight of the load, and the obstructions of the lock structure. In addition, Barnhart had just three weeks to design, fabricate and test the bridge.

Newly–designed equipment developed for the project comprised the trolley gantry (utilizing the BCR containerized 500 ton hoist) and BCR gripper system with wheel–mounted end trucks. Barnhart also modified existing 60 foot long, 8 foot deep box girders to give the required 150 foot span.

Execution of the project involved three steps: removing each of the two lock gates by rotating them out of their hinges, then lifting them up between the two 8 foot deep trolley girders, and finally lowering them onto the barge. The new gates were delivered by barge and temporarily installed in the reverse of this procedure. With this complete, the lock was temporarily dammed and drained to allow final installation and inspections.

The project was under fixed, lump sum contract, which included an agreement to accept liquidated damages for exceeding scheduled outage days. Barnhart completed assembly, removal, replacement, draining and permanent installation lifting within 15 days–half the originally proposed period.

In addition to its commercial and technical success, the project was outstanding from the safety viewpoint. There were no OSHAreportable incidents and no first aid incidents (throughout all phases–load test, load out, erection and execution). Daily safety meetings, pre–lift meetings, and remotely–controlled operations throughout the entire activities of the project caused the job to exceed Army Corps of Engineers Safety Manual requirements. The result: Barnhart won the Army Corps of Engineers Annual Safety Award.


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