Building a supertall skyscraper in one of the most seismically active regions of North
America is not easy.
But with San Francisco's booming tech industry demanding ever more high-end office space,
engineers had to develop ways to push buildings to new heights.
Rising from the corner of First and Mission Streets in San Francisco's South of Market
district is the city's tallest structure; the 326m (1,070 foot) Salesforce Tower.
When the 853 foot, 260m “Transamerica Pyramid” completed in 1972 it joined the Golden Gate
Bridge as a dominant feature on San Francisco’s skyline -
and with building heights capped at 550 feet in the 1980s there was little
to change the city's profile for over 40 years.
But as pressure to densify and revitalise parts of the city has increased, and as the
number of technology companies looking to establish headquarters in Northern California
has risen - San Francisco’s authorities have relaxed height limits in favour of
taller buildings that benefit the public realm.
In this case, the rezoning of land for the Salesforce Tower kick-started the USD $2.25BN
redevelopment of the adjacent “Transbay Transit Center” - a transport hub for the bay area.
The Salesforce Tower is the centrepiece of a wider redevelopment that includes direct
connections to the transit centre and access to a 5.4 acre park on its roof.
Designed by Pelli Clarke Pelli Architects, the tower stands over 200
feet taller than the Transamerica Pyramid - and provides 1.6M square feet of office
space across 61 storeys.
55% of the building is occupied by its main tenant; Salesforce.
To construct a building of such height on land that was reclaimed using landfill and
in a region prone to earthquakes, engineers developed some of the largest foundations
ever used in San Francisco.
In total, some 42 foundation piles - each over 300 feet (or 100m) in length - were drilled
into the underlying bedrock.
On top of this, a 14-foot-thick concrete slab extending across
the tower’s one acre site was constructed.
In total, the foundation slab contains over
2,200 tonnes of steel reinforcement and over 9,000 cubic metres of concrete.
It took over 18 hours of pouring and the continuous flow of 1,300 concrete trucks to complete
the slab, making it the second largest concrete pour ever carried out in the city - the largest
being that for the Transamerica Pyramid back in the 1970s.
From these foundations, a high strength concrete core was constructed to support the building’s
steel frame.
At design stage, the tower’s superstructure model was subjected to 22 different virtual
earthquake simulations, drawn from historical seismic data across the region.
Based on the results of these simulations, the tower was designed with a high strength,
reinforced concrete shear wall core, with walls up to 48 inches thick.
This rigid spine, together with structural steel columns around the tower’s perimeter,
support its composite steel and concrete floors.
The tower culminates in a nine-storey perforated metal and glass crown that “dissolves”
its summit into the sky.
The Salesforce Tower is a truly modern commercial work space - with particular attention paid
to the quality of its indoor environment and occupant wellbeing.
With an advanced natural ventilation system, high performance glazing, integrated louvres
and the largest blackwater treatment plant in a US commercial building - the tower has
been certified as LEED Platinum, becoming the highest rated commercial project in the
United States.
To improve the indoor environment and enhance well being, the tower is divided into a series
of three storey “vertical villages”.
The levels within these villages are linked by
staircases that encourage movement and collaboration between teams.
Each floor has its own social lounge, kitchen and breakout area, as well as a “ mindfulness
zone” where occupants can recharge and unwind.
Additionally, all occupants have access to the building’s 61st floor which features
a cafe and exhibition space, against a backdrop of panoramic city views.
With the 800 foot “181 Fremont Street” and the 900 foot “Oceanwide Centre” both
currently under construction, the now-completed Salesforce Tower stands as the first in a
new generation of skyscrapers rising across the San Francisco skyline.
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