Dam towers

A trio of Potain tower cranes are being used on a hydroelectric dam expansion project in the USA. The project is the Holtwood Dam on the Susquehanna River near Holtwood, Pennsylvania.

General contractor is Walsh Construction, which owns two cranes on the job - an MR 615 and an MR 415. The third unit is an MD 485 B rented from All Erection and Crane Rental. Jib length, at between 131 and 145 feet long, will remain throughout the job.

Nick Everson, Walsh project manager for powerhouse construction, said the cranes are spaced to provide different lifting options. "The construction site is approximately a 150 foot [46 metre] deep hole, 180 feet [55 m] wide and almost 600 feet [103 m] long," Everson said. "We arranged the cranes so that any two cranes can reach almost all areas of the construction site at one time."

Potain's Top Tracing anti-collision and controlled work zone software is used to help manage overlapping operation zones. It also alerts the operator if the crane's jib gets too close to another crane on the site. If the operator doesn't react to this condition, a cut-off switch stops operation to prevent an impact.

For additional safety Walsh configured the three cranes with the cabs all at the same level to allow eye contact between the operators. Uneven terrain, however, means that each crane is a different overall height, standing between 146 and 221 feet (45 and 67 m) tall.

Walsh is working on the underwater section of the two-part powerhouse building. It installed coffer dams on each side of the powerhouse and is now using the cranes, fitted with concrete buckets, to place 60,000 cubic yards of concrete in 10 US ton loads. The cranes will also place the concrete forms and reinforcing steel bar needed in the building process. Some embedded components of the turbines will also be placed using the cranes. Sections of the 15 to 17.5 ton draft tube liners for each turbine will be lifted into place.

The tower trio has been on the job site since October 2010 and will be working to May 2012.