Salesforce Tower Chicago, a 58-story tower named after its primary 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.
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 Chicago 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 as ready-to-use systems just-in-time for use.
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 Chicago, 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 Chicago 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.
Safety, Speed, and Support
The core used PERI VARIO formwork to cast the concrete pour around the tower crane, carried by PERI ACS Core 400 self-climbing formwork system. ACS Core 400 was selected for its hydraulic controls that allow for climbing all four cells together and climbing the core from pour to pour.
VARIO is highly adaptable with freely selectable tie positioning and joint arrangement in accordance with planning specifications that delivers freedom in wall and tie design. It is continuously adjustable through the elongated holes in the walers and couplings with flush, aligned, and tight panel connections, making it the optimal formwork solution for Salesforce Tower Chicago.
The ACS Core 400 was designed for the US high-rise market, featuring a high-capacity single stroke cylinder that climbs to the next level in 20 minutes with less brackets, anchors, and over parts required. ACS Core 400 can support large concrete placing booms that allow for pouring slabs and walls simultaneously.
From ground level to level 40, crews utilized a four-core cell before transitioning to a two-core cell for levels 40 and up. The external panels of the ACS Core 400 system provided safe and comfortable work access while also supporting the load-bearing capacity of additional materials, supplies, and tools, including 100,000 pounds of rebar. This added support and platform space was particularly important since materials could only be delivered once a day.
In addition to the core cells, MULTIPROP vertical shoring was utilized for framing large door box outs for walking into the elevator lobbies and holding up horizontal shoring.
The aluminum MULTIPROP weighs less and carries significantly higher loads than tubular steel slab props. MULTIPROP features a practical wedge connection and an integrated measuring tape on the inner tube to quickly show the complete length of the prop, delivering both time and cost savings.
Open for Business
Proposals for the project began in February 2020, and the first product delivery was in August 2020. PERI provided continuous engineering support for construction management during the entire execution phase, with numerous revisions to the structure from top to bottom.
Construction on Salesforce Tower Chicago is expected to be complete in the first quarter of 2023.
(Photo credit: YoChicago.com)