CASE STUDY
The Final Riverfront Devel- opment Site Salesforce Tower, a 58-story tower named after its pri- mary tenant, provides 1.2 million square feet of office space and completes Wolf Point Plaza, one of the last remaining riverfront sites in downtown Chicago. Salesforce Tower Chicago, IL
Throughout construction of the building, the riverfront location provided access chal- lenges, with only one path in and out of the site through a single, one-way underground tunnel. The Walsh Group turned to the expertise of PERI Formwork Systems, Inc., to deliver a flexible, coordinated formwork solution utilizing just-in-time delivery of all materials and flexibility to climb independently of the tower crane. A Case Study in Complexity Salesforce Tower is a high-rise building with steel structures and a massive, four-cell vertical concrete core which supports the tower. PERI collaborated with the project team to develop a specific sequence and schedule for delivering critical formwork components just-in-time. The schedule allowed for a delivery truck to drive through the tunnel and have work crews unload the formwork products as soon as they arrived. This enabled the truck to back out of the tunnel as soon as all parts had been taken into the work site. The contractor’s schedule and crane availability dictated the timeline for construction, in addition to working backward from when certain elements needed to be complete. To aid in this schedule, PERI preassembled products into the largest shippable units to speed up on-site installation. Since the tower crane operated through one of the cores, PERI worked to achieve additional coordination between the concrete contractor and the steel contractor during construction of the high-rise structure. The ACS Core 400 typically only has one floor, but for Salesforce Tower, an additional, lower one was added so the steel contractors could attach plates to the concrete for connection to the steel beams. To achieve this, the concrete crew was hoisted up to a certain level and then walked up a 150-foot stair tower to the core for work each day. The design of Salesforce Tower features changing geometries with reduced wall thickness on floors 7, 22, and 40, changing the formwork settings on those levels. There is also a transition from a four-core cell to a two-core cell on level 40, decreasing the square footage of the upper levels. After a year of construction to build the first 40 levels, the disassembly sequence began to remove the outer two cores, leaving the middle two cores for the final levels. Based on drawings completed in the planning and assembly phases, a crane removed one piece at a time. On the four-core cell, crews completed a new level of the tower, and the core moved up a level every four days. Once the core was reduced to a two-core cell, construction speed could increase to a new level every three days with a smaller crew size.
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csengineermag.com
November 2021
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