The gantry crane, worth $9.5m, not including assembly, foundations or lifting equipment, can lift a maximum of 5,100USt, is wheel-mounted and travels on steel rails. It is used to lift and carry various lifting frames as well as positioning them for installation on the precast shells. It has the capability to move the lifting frames perpendicular to the crane rails.

“The Olmsted Dam gantry crane is the largest gantry crane of its kind in the world,” according to the US Army Corps of Engineers, Olmsted Resident Office, which is overseeing the project.

The crane, designed and supplied by Ederer LLC, a division of PAR Systems, Seattle, is self-contained, operating off a crane-mounted 300kW Caterpillar diesel generator. The top of the gantry supports stands for 12 strand jacks, the primary lifting mechanism to raise and lower the concrete shells.

Powered by 12 7hp electric motors, the crane is designed such that the two upper most beams, known as strand jack beams, can be hydraulically adjusted to conform to various lifting frame configurations.

Unloaded, the gantry will travel at 20ft/min; loaded, it will travel at 10ft/min.

A total of 64 36in diameter steel wheels are utilised for the movement of the crane. There are four rails, two each side, with a total runway length of 1,200ft.

Other structural components of the gantry crane include eight travel truck assemblies, eight vertical legs and 12 box beams. Approximately 5,000 bolts and welding holds these components together.

Overall dimensions of the crane are 100ft-long from travel truck number one to travel truck number four, 160ft-wide from outside of leg to outside of leg, and 140ft-high from ground level to the top of the strand jacks. This gives interior dimensions of 100 x 130ft.

Pre-erection on the ground of the girders, beams and leg assemblies took approximately one year, while lifting and erection of the main structural members took two months to complete.

Two Manitowoc 4600 crawler cranes were used to lift and place the components. The heaviest lift in this process was a girder, weighing 428,268lbs which put each of the crawler cranes at 95% of their maximum capacity, says the US Army Corps of Engineers.