Bragg Crane & Rigging Overhauls Hydroelectric Facility’s 75-Ton Bridge Cranes

In operation since 1925, the PG&E Pit 3 hydroelectric powerhouse in Burney, California, provides electricity to northern and central parts of the state. In 2021, Bragg Companies undertook a major overhaul of the facility’s two 75-ton bridge cranes that involved innovative rigging solutions, and new and customized equipment.

The challenges for the project were considerable, noted Justin Lambert, general manager of Bragg Crane & Rigging, including:

• The only engineering drawings available were more than 100 years old and lacked details such as the weight of the trolleys, bridge cranes and girders and catwalks.
• The bridge cranes were positioned 53 feet above the floor, leaving almost no headroom below the facility’s concrete roof and steel trusses.
• The bridge crane girders were connected at both ends and had to be removed at the same time.
• No work was allowed above the hydroelectric facility’s turbines, leaving a small 40- by 30-foot work area.
• The facility’s basement and sub-basement restricted floor loading.
• Access was limited to overhead door openings.
• The hydroelectric facility would remain operational throughout the project, requiring an extensive effort to protect against contamination of the watershed.
  

“Working with loads that have to be supported from below rather than lifted, elevates risk,” Lambert said. “By measuring and photographing every part of the facility and using conservative weight estimates based on experience, our teams set out to develop a plan to replace the bridge cranes and catwalks. Every pound and every inch had to be accounted for so we did not overload equipment or exceed available dimensions.”

Bret Hanley, superintendent at Bragg Crane & Rigging was onsite for the duration of the project. To start, he pointed out, crew members were required to complete hydroelectric and substation, boom, scissor lift and gantry training. When the project got underway, he added, the first order of business was to prepare the site for load handling equipment with Masonite, trench plates, mats and cribbing blocks.

“Once that prep work was done, we brought in a 700-ton capacity gantry crane with a 35-foot extension, but even that equipment was still short of the height needed so we added a custom designed subframe to the top of the gantry to make up the difference,” Hanley said. “Skate beams were used as well, along with a range of chain, hoists and other rigging equipment.”

To remove each of the bridge cranes, Bragg used its customized gantry system to lift the trolley within tight tolerances and lower the crane assemblies to the floor where they were moved out of the building with hoist trucks. The process was repeated four times, twice to remove the existing bridge cranes and two more times to install new machines and equipment.

“Everything had to be positioned perfectly in the hoisting area to fit and maintain the center of gravity in a safe position,” Hanley explained. “All of the equipment and the trolleys were bolted and welded in place as well to avoid shifts. Maintaining loads and keeping them level required precise calculations. Successful load transfers onto and off the gantry was dependent on communication at all times.”

In the end, noted Justin Lambert, it took months of planning and execution to complete the project, including 300 hours of engineering time and the production of 185 drawings.

“With the right equipment and custom designed pieces, the hydroelectric powerhouse now has modern bridge cranes and equipment and can more effectively keep up with customer demand for electricity with less time needed for upkeep,” Lambert said. “With rigging expertise, our teams were also able to complete the project under budget, without downtime and most importantly without incidents or injuries.”