SalesForce Tower Gets A Start in San Francisco
In a marathon pour on November 8, 2015, the foundation for SalesForce Tower in downtown San Francisco was pumped with seven Schwing boom pumps and more than 1400 loads of concrete. The majority of the concrete was pumped in 12-hours by Conco, Concord, California, which also acted as the concrete contractor on the project. The 1,070-foot tower that will rise from the 12,000 cubic yard monolith will be the tallest occupied office building west of Chicago. While the culmination of the project will occur in 2018 when the tower is completed, the planning goes back nearly a decade.
The building’s history dates from 2007 when Hines was chosen as the developer in a global competition by the Transbay Joint Powers Authority. The winning proposal included a world famous architect Cesar Pelli design. A seven-member jury selected Hines to entitle and purchase the site located at 1st and Mission in downtown San Francisco. In 2012, Boston Properties acquired a 50% stake in the project and in 2013 acquired most of Hines’ remaining interest to become 95% owners of the project. The development was originally contracted on spec with no major tenant lease secured. In April 2014 SalesForce, a customer relationship software company, announced that it signed a lease for 714,000 square feet on floors 1, 3-30, and 61 to become the building’s anchor tenant.
The foundation rests on 42 deep piles that extend 265-feet down to bedrock. Prior to the epic pour, more than six-million pounds of steel were woven into a 14-foot thick reinforcement that includes 2.25 inch diameter #18 rebar. Planning for the pour was started a year ahead to coordinate two ready-mix suppliers and the Conco pumps which were set-up in a challenging urban environment. More than 1400 loads of concrete were required and routes were established to keep two mixers at every concrete pump for at least 12 hours. A 950 yard per hour goal was established for the crew of finishers and pump operators. Normal maintenance was applied to the long booms that would shoulder the continuous pumping.
Conco chose seven Schwing boom pumps from their fleet – three S 58 SX and four S 47 SX models. All the pumps are equipped with 2525H-6 120/85 MPS pumpkits with output to 216 cubic yards per hour. Standard on these models is the Big Rock sequencing valve with extended hopper to easily manage the constant flow of ready-mix. Important to the operation is the pump’s large diameter 10 inch pumping cylinders that operate through a 98-inch stroke. The slow stroking action keeps the boom stable even at maximum output which allowed the hosemen to manage the pour safely in tight quarters surrounded by finishers.
With boom reach measuring 139 feet seven inches for the S 47 SX units and 175 feet two inches for the S 58 SX, the pumps were able to be placed on just two sides of the square block excavation. The Overhead Roll and Fold design of the 4-section booms allowed operators to fully extend to the middle of the pour area and place concrete back to the edge. Also contributing to the efficient placement were the curved telescopic Super X front outriggers on all the pumps that allow set-up in confined areas.
At 12:00 am Sunday morning the read-mix began arriving in Cemex and Central Concrete mixer trucks. Seventy-six mixer trucks were utilized to rapidly discharge their loads and make room for waiting trucks to maintain constant pumping. A washout area near the downtown site, manned by several workers, kept truck drivers in their cabs. The early morning weekend hours were necessary to keep the trucks moving and minimize the impact on downtown San Francisco. Two major thoroughfares were closed to normal traffic during the pour. By noon, the majority of the concrete was in place and Conco was able to pull four pumps from the area. The concrete was pumped without any issues resulting in the largest continuous concrete pour in San Francisco’s history. The three remaining trucks finished the pour by six pm.
The mammoth concrete foundation is part of the structural solution applied to the building by engineering firm Magnusson Klemencic Associates, San Francisco. Using a “performance-based seismic design” approach, the firm is transforming the structural design of tall buildings in regions of high seismicity. A three-story parking garage will bring the subterranean portion of the project to grade level. A uniform steel and glass curtain wall system will wrap the tower’s structural steel framing, which itself will surround a concrete core. Concrete decks will be poured as the building rises to 1,070 feet which will make it the tallest in San Francisco. A time lapse video documents the mat pour. It has received nearly 100,000 views.
The SalesForce tower was a repeat performance as Conco participated in two of the largest pours in California’s history. In April 2014 the company placed 21,200 cubic yards for a foundation that will support the Wilshire Grand, a 1,000 foot highrise being constructed in Los Angeles. Together, the two skyscrapers will not only be the tallest structures in their respective cities, but also the two tallest buildings west of the Mississippi River.
Owner/Developer: Boston Properties, San Francisco
Architect: Pelli Clarke Pelli Architects, San Francisco
General Contractor: Clark/Hathaway Dinwiddie, San Francisco
Concrete Contractor: CONCO, Concord, CA
Concrete Pumping Contractor: CONCO, Concord, CA
Ready-Mix Concrete Providers: Cemex and Central Concrete, San Francisco
Equipment: Three Schwing S 58 SX and four Schwing S 47 SX truck-mounted concrete pumps with placing booms