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. An ambitious internal climbing configuration was then put in place, in which two Potain cranes were attached to the building’s core.
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.
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 (172 m) 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. This building core will eventually house the elevators that provide vertical transportation throughout the building.
“When we started looking at this project, we thought, ‘Ok, we’ll climb the cranes through the concrete core,’ but the concrete company was initially opposed because they worried it might subtract a lot of their workspace,” Amadon said. “Typically, when developing internal form systems, the concrete contractors design a platform system that covers the entire core that is used for assembling rebar, shaking rebar out, etc., so they can hoist material from the ground and land it on their workspace. They asked us to find a way to put the tower cranes on the outside of the core instead.”
The mutually agreed solution centered around the two Potain luffing-jib tower cranes, which James F. Stearns rented from Maxim Crane Works. James F. Stearns has a long-standing relationship with Maxim on crane rentals for major projects across the northeastern United States.
Core skills
Using Potain MR cranes on the project was an inspired choice. The interchangeability of their bases with those of its sister ranges, the MD and MDT models, increased the number of installation options for internal and external climbing configurations. Also, their uniquely mounted luffing mechanisms and hoists saved space on the jobsite, enabling operation in this confined space.
In collaboration with engineering firm Howard I. Shapiro & Associates, plans were drawn up for each stage of the MR 415’s upward journey. The contractor’s desire for a spacious working platform had left a gap of mere inches around the mast perimeter and the core walls, leaving the riggers with no opportunity to assemble or drop in the mast from above. Instead, the beams were pulled into the bottom of the core through a doorway, assembled at ground level, and then maneuvered into position by crane and/or air tuggers.
More options
These smaller, lighter cranes provided further benefits to a project that might once have relied on the use of larger, more costly models. 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 (92,900 m²) 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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