Inside climbing setup allows Potain cranes to fast-track Boston tower

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Potain’s MR 415 and MR 418 A tower cranes grow quietly with – and within – the building

The imposing new building forms part of the western lot of the 12-acre mixed-use development at Bulfinch Crossing, just a stone’s throw from Boston City Hall, stands approximately 565 feet tall and offers spectacular views over the city and harbor. The innovative approach to construction is the result of a desire to start renting space inside the tower as soon as possible, he explained Cori AmadonVice President at James F Stearnsthe leading crane supplier for the project.

core competencies

Use Potain MR cranes on the project was an inspired choice. The interchangeability of their bases with those of their sister series, the MD and MDT models, increased the number of installation options for internal and external climbing configurations.

During the demolition of an adjacent car park, a series of four interconnected concrete core cells were uncovered, providing fully enclosed support for the Potain MR 415’s climbing mechanism. The MR 418 A was then attached to the outside of the westernmost airframe, where it would soon be deployed, largely obscured by the steel framework of the tower built around it.

Working with engineering firm Howard I. Shapiro & Associates, plans were drawn up for each stage of the MR 415’s upward journey. For Phase 1, the initial installation, the crane would be freestanding, with a nearly 197-foot mast and a similar jib length.

The contractor’s desire for a spacious work platform had left a gap of just a few centimeters around the mast perimeter and core walls, leaving the erectors with no way to erect or install the mast from above. Instead, the girders were pulled through a doorway in the bottom of the core, assembled at ground level, and then maneuvered into position using a crane and/or air tugs.

The crane climbed an additional 90 feet during each of the next two phases, adding a second springboard at Level 32 during Phase 4 and a third board seven stories later during Phase 5, by which time the structure had reached Level 42. For the Final Push, Phase 6, a final climb of 88 feet would be sufficient to allow topping in July 2021, with the crane being 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 floor to level 25, and then one of the cells ‘disappears’ and turns into a three-cell core,” explained Amadon. “So initially we worked 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 using a stepping stone system on the outside of the core.”

The crane climbed an additional 90 feet during each of the next two phases, adding a second springboard at Level 32 during Phase 4 and a third board seven stories later during Phase 5, by which time the structure had reached Level 42. For the Final Push, Phase 6, a final climb of 88 feet would be sufficient to allow topping in July 2021, with the crane being 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 floor to level 25, and then one of the cells ‘disappears’ and turns into a three-cell core,” amadon explained. “So initially we worked 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 using a stepping stone system on the outside of the core.”

More options with Potain

These smaller, lighter cranes offered additional benefits to a project that previously might have relied on the use of larger, more expensive models.

“By reducing the loads imposed, they give you the flexibility to design a different type of support system that is not as cumbersome as would be required to support a larger tower crane.” amadon explained. “You can get great results on the edge with an MR 608 (maximum lifting capacity 32 tonnes), but if you put a MR 418 with a lifting capacity of 24 tonnes in the core of a building with a shorter jib, you can get pretty much the same benefit. “