Salesforce Tower, in San Francisco, has been honored by ASCE as a 2020 Outstanding Civil Engineering Achievement Honor Award recipient.
All 10 Honor Award projects will be showcased at ASCE’s 2020 OPAL Gala, March 13, in Washington, D.C., with two runners-up and the OCEA winner announced at the event.
Salesforce Tower is the tallest office building in a severe seismic zone in the Western Hemisphere. Standing at 61 stories, the tapering tower announces a new standard for office high-rise design. This obelisk totals 1.4 million square feet, and features a first-ever high-performance core spine of carefully configured reinforced-concrete shear-walls, resisting windstorms and earthquakes without the participation of exterior columns. No other building of this height relies only on its core for that.
A wide-open office space is achieved by eliminating structural encumbrances typical of other tall buildings – outriggers, belt trusses, seismic braces and dampers. This design is empirically comfortable and efficient but also provides a much higher level of safety and resiliency than typical commercial office buildings in San Francisco.
The foundation is not only the deepest ever constructed in the city, but at 310 feet, one of the deepest in the United States – socketed 70 feet into bedrock (equivalent to putting a 25-story building below the ground). Salesforce features a design supported by cast in situ concrete deep foundations sometimes referred to as barrettes.
The project has the largest black-water system in a commercial high-rise building in the U.S. and provides underfloor ventilation using 100-percent outside air. The finished site includes a generous bridge connection to a 5.4-acre rooftop public park and a large public plaza. And with the tower’s column-free user spaces, occupants can practically “see around corners.”
The building also serves as the front door to the Salesforce Transit Center, three city blocks long, which is set for full operation in 2028. The transit center and Salesforce Tower are adjacent, yet were being built at the same time, along with other nearby high-rises! Even less common than this circumstance of construction is that Salesforce and its transportation namesake are in direct contact with each other.
What about those continuously changing floor sizes? Every floor above the 26th does have a different geometry, which required intricate coordination. Structural engineer Magnusson Klemencic Associates (MKA) developed custom thrust-stabilized sloping columns to maximize constructability and economy. Happily, the tower’s tapering form was able to showcase an elegant, timeless beauty.
Because MKA, Pelli Clarke Pelli, Kendall/Heaton Associates, and Clark Construction/Hathaway Dinwiddie employed such state-of-the-art solutions in erecting the 1,070-foot-tall tower, the cityscape has been transformed.