Internal climbing setup enables Potain cranes to fast-track Boston tower

Over the past year, the rapidly rising, 43-story One Congress office tower has become a distinct new landmark in Boston’s North End. But going largely unnoticed are the Potain MR 415 and MR 418 A tower cranes that are quietly growing along with the building — and also inside it.

• The developers of One Congress, a 43-floor office block in downtown Boston, wanted to start leasing space on the lower floors while construction was still underway.
• This required an intelligent approach to tower crane installation, so a Potain MR 415 and MR 418 were erected in the core of the building, in an internal climbing configuration.
• This setup also eliminated the need for larger, more expensive tower cranes.

Forming part of the western parcel of the 4.8-acre Bulfinch Crossing mixed-use development, a stone’s throw from Boston City Hall, the imposing new building tops out at around 565 ft and offers spectacular views over the city and harbor. The innovative approach to its construction was a result of the desire to begin leasing space within the tower as quickly as possible, explained Cori Amadon, vice president at James F. Stearns, the leading crane provider for the project.

“We were approached by John Moriarty Associates, the main contractor, to devise a plan that would allow them to start leasing floors six through 25 before the rest of the structure was complete,” he said. “That meant we had to rethink the original plan of tying in tower cranes to the building’s outside perimeter and come up with an interior climbing program instead.”




The solution was to make full use of the building’s concrete slipform core, which grows faster throughout construction than the floors that surround it. Once structural work is complete, the building core will be home to the elevator shafts that provide vertical transportation throughout the building.

The crane climbed another 90 ft during each of the next two stages, with a second diving board added at level 32 during Phase 4 and a third board seven floors later during Phase 5, by which time the structure had reached level 42. For the final push, Phase 6, one last climb of 88 ft would be sufficient to enable topping off in July 2021, with the crane supported by the diving boards on levels 32 and 39.

“One of the unique things about this project is that it has a four-cell system from ground level up to level 25, and then one of the cells ‘disappears’ and it turns into a three-cell core,” Amadon explains. “So, initially we were working internally surrounded by a concrete cell up to level 25, but then we had to come out of that and switch from a four-sided support system to utilizing a diving board system on the outside of the core.”




More options with Potain
These smaller, lighter cranes provided further benefits to a project that might once have relied on the use of larger, more costly models.

“By reducing the loads that are imposed, they give you the flexibility to come up with a different type of support system that’s not as cumbersome as would be needed to support a larger tower crane,” Amadon explained. “You can get great results working with an MR 608 (32 t maximum capacity) from the perimeter, but if you put a 24-ton capacity MR 418 into the core of a building with a shorter boom, you can pretty much get the same benefit.”

Disassembly of the cranes was also straightforward. A derrick crane was placed on the rooftop to remove one of the tower cranes in November 2021, while the 418 A continued placing glass for the tower’s construction. The crane was then removed in an almost exact reversal of its installation, according to Amadon.

With both tower cranes now removed, sixteen floors comprising a total of 1 million ft2 of trophy office space are now available for lease and will be ready for occupancy in 2023. The One Congress project is a partnership between Carr Properties, National Real Estate Advisors, and The HYM Investment Group.

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