Light and Height in San Francisco

The Salesforce Tower and Transit Center Transform the City with Complex Design

By Jordan Scott

San Francisco’s newest landmarks are redefining people’s image of the city. The $1.1 billion Salesforce Tower is glassy and curved, with a design more complex than it appears at first glance. At 1,070 feet high, it be-came the tallest building in San Francisco when it opened in May 2018. The tower’s companion, the Salesforce Transit Center, is designed to be the gateway to the city for the millions of people using its transit services.

Reaching for the Sky

“We knew this was going to be the tallest building in San Francisco. For an architect that’s a very important assignment,” says Fred Clarke, senior principal at Pelli Clarke Pelli Architects in New Haven, Conn. “It’s an assignment that obviously has a developer intention behind it, but also a civic responsibility that goes beyond the functionality of it.”

The height of the tower is protected by San Francisco’s zoning laws, so there will never be another tower close to the building’s height, according to Clarke. The importance of making such a mark on the San Francisco skyline was not lost on Clarke, who says the firm questioned which qualities make a building appear timeless.

“For us, that means the building needs to be quite simple. It needs to be rather clear and understandable, particularly to laypeople,” he says. “We like to say the most assessable buildings are the ones a child can draw a sketch of because it means you’ve communicated the essence of it very quickly.”

Clarke says one of the firm’s goals was delivering a clear message by having the tower taper as it rises to create a simple gesture against the sky. The building appears white in color to emit the bright quality of light inherent to San Francisco. The curved corners of the building make the tower appear taller and thinner.

“All of those are fundamental characteristics that we think make the building a worthy contribution to the skyline and deserving of being the tall-est building,” says Clarke.

Bent into Shape

Salesforce Tower incorporates nearly 500,000 square feet of Guardian’s Sun-Guard AG 50 coating on both flat and curved clear glass, giving occupants access to views and daylighting.

Regional architectural manager east Leigh Anne Mays worked closely with Pelli Clarke Pelli Architects on the project.

“The taper and curved corners required complex, conical bends in the glass…” says Mays. “There was a lot of careful thought and design work necessary to successfully bring to life the bent glass design and the resulting overall look of this building, which is already proving to be a landmark in the San Francisco skyline.”

According to Mays, Pelli Clarke Pelli requested a crisp, reflective and monolithic look for the building, which would have been lost if the curve was broken by metal or silicone. She says that SunGuard, a high-performance, low-E glass, works well in curved applications.

The glass selection was important for both the aesthetics and performance of the building.

“The tower is LEED platinum, so it’s at the peak of sustainability,” says Clarke. “The California energy code is quite restrictive. We had to obey specific rules of energy conservation and energy usage. It’s a high-performance insulating glass that’s important from a sustainability point of view and extremely important from an aesthetic point of view.”

Tecnoglass S.A. of Colombia, fabricated the flat glass while the Italian company Sunglass fabricated the bent glass.

“Those elements were compounded on Salesforce Tower because the team was globally managing an extremely high volume of glass. Guardian Glass was shipping to two different fabricators and dealing with multiple time zones,” says Mays.

According to Gery Chinzi, sales and project manager at Sunglass, the company was chosen for its ability to maintain coating quality after bending. The largest bends are 20 degrees and the largest glass sizes bent are 6.9 by 13.1 feet.

Complex Installation

Contract glazier Benson Industries of Portland, Ore., was brought on board in 2013 to provide design-assistance. Benjamin Gomez, director of design at Benson, says that the company’s first impression of the tower was that it would be complex, even if the design didn’t reveal that initially.

One major challenge for Benson was that the building was segmented with curved corner units both in plan and section.

“The segmentation in section reduces the footprint floor by floor from level 27 up to level 70—the further up we went, the less typical units there were,” says Gomez. “Curtainwall units had to be parallelograms, curved units ‘tapered’ to deal with the lean back. The challenge was how to assemble the units to create the needed parallelograms, and cold forming the units as they were being set, so that the building geometry would work out in the end. The scoop units at the tower top on all four sides of the building were challenging to design, as there is less than normal curtainwall frame to the unit.”

Gomez says that as the building started to lean back in section, the installation crew had to cold-form the units as they were installing them. This became more pronounced the further the team went up the building.

Skyscraper on Its Side

Clarke says he can’t think of the Salesforce Tower without also thinking of the Salesforce Transit Center, which he describes as a skyscraper lying on its side in front of the tower. The center includes 5.5 acres of green, public space and is longer than the tower is tall. The $2.26 billion transit center features walkable skylights and light columns developed by Greenlite Glass Systems Inc. and Vetrotech Saint-Gobain. It opened in August 2018.

The largest of the light columns forms the central element of the primary public space within the center called the Grand Hall. The column reaches from the park all the way down to the train platforms two stories below grade, providing light to all areas of the 1.2 million-square-foot transit center.

“The building is absolutely full of sun-light and daylight … It’s a big building that goes quite deeply into the ground. We wanted to try to bring daylight even all the way down to the train box below,” says Clarke. “So the light column and the glass around the light column help to bring daylight deeply into the building. When you’re inside the building the glass also allows you to look up and see the park. It couldn’t have been done without that amount of glass.”

Ryan Dennett, owner of Greenlite Glass Systems in Port Coquitlam, British Columbia, says natural light inter-faces with people from many different perspectives, such as how it makes people feel. He says the natural lighting is also important for sustainability be-cause less artificial lighting and heating are needed.

“We added solar controlled coatings to the glass to assist in keeping the Grand Hall space cooler,” he says.

The exterior of the building is a perforated metal, but Clarke says the design originally included a glass exterior.

“When it was glass, the exterior was becoming very expensive because it also had to withstand the possibility of a blast, which made it very thick, heavy and expensive,” he says.

A Walkable Skylight

Contraflam Liteflam XT 120, a walk-able fire-rated glass floor and skylight system, was developed specifically for this project. The floor is the largest fire-rated glass floor in North America.

Kevin Norcross, general manager at Vetrotech Saint-Gobain in Auburn, Wash., says Contraflam Liteflam XT 120 came from a collaborative process. Vetrotech worked closely with Green-lite Glass Systems, glazing contractor Crown Corr and Pelli Clarke Pelli on a design assist to ensure that all the advanced structural and safety requirements were taken into account.

“Because of its location and dual function as a skylight and high-traffic pedestrian walkway, this project had several unique challenges. It had to handle live loads from above; be slip-resistant, weatherproof and water-tight; and meet strict seismic requirements for San Francisco,” says Norcross. “It had to have a two-hour fire rating—something that had never been done before in a glass floor—and be easy and efficient to replace in case of damage without sacrificing safety.”

The floor includes a top layer of sacrificial glass, which Norcross says is the first in the country to be tested for weather cycling. It is made up of several layers of heat-strengthened, translucent laminated glass. The uppermost lite is the walking surface and features solar reflective properties, a translucent light diffusing laminating interlayer and an anti-slip patterned silk print.

“Should the sacrificial layer experience wear and tear or become damaged, the pane can be replaced on site without removal of the lower fire-rated portion,” he says.

To view the laid-in version of this article in our digital edition, CLICK HERE.

 

This entry was posted in Uncategorized. Bookmark the permalink.

Leave a Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.