Articles November 20, 2019

181 Fremont: A Skyscraper Poised for the Big One

Source: Architect Magazine

181 Fremont: A Skyscraper Poised for the Big One

Home to a division of Facebook and a fresh class of urbanites, the 57-story tower designed by Heller Manus Architects sets new precedents in resilience, sustainability, and urban development.

Just four blocks from where the 1989 Loma Prieta earthquake buckled the double-decker Embarcadero Freeway, a model of resiliency and resistance rises 802 feet into the air. The $800 million mixed-use tower at 181 Fremont St. is the third tallest building in San Francisco and the tallest residential building on the West Coast. Home to both Facebook’s Instagram division and 67 condominiums—including a penthouse listed for more than $40 million—the project checks off a litany of firsts: the first REDi (Resilience-based Earthquake Design Initiative) Gold–rated project in the world; the first U.S. building with a fully automated emergency evacuation elevator system; the first mixed-use tower in San Francisco to be LEED Platinum pre-certified; and the first private building in San Francisco to have a graywater recycling system.

The 57-story, glass-encased skyscraper is among the safest and most earthquake resilient in the world, says Jeffrey Heller, FAIA, president and founder of local firm Heller Manus Architects, the project’s designer. But 181 Fremont’s achievements go beyond the technical. Joining the Salesforce Tower and Park Tower at Transbay in a rapidly transforming tech hub recently branded as the East Cut, 181 Fremont is recasting a once-insular San Francisco as a global city.

A Neighborhood Reborn

Cut off from San Francisco’s Financial District by an overpass and serviced by an aging Greyhound bus station, the South of Market district (which includes the East Cut) of the early aughts was ripe for redevelopment. The tower at 181 Fremont has roots in a transit-oriented development plan formulated by San Francisco’s planning department prior to the 2010 demolition of the earthquake-damaged Transbay Terminal, says Dan Kingsley, a managing partner at local commercial real estate firm SKS Partners. That plan ultimately paved the way for the multistory, multimodal Salesforce Transit Center, which sits next to 181 Fremont today. More immediately, the plan galvanized public support for the idea of rezoning the land to host a denser office district in which height limits would double from 350 feet.

Sensing opportunity, SKS purchased the 15,400-square-foot parcel with two existing brick buildings for $15 million in 2007. “We always intended to build a building,” Kingsley says, “but knew there would be an opportunity … to assess the project and decide whether we wanted to build or sell.”

Six years later, SKS cashed in on the property’s skyrocketing value. With schematic and elevation drawings by Heller Manus complete and city approval to build to 700 feet, it sold the undeveloped parcel to the local developer Jay Paul Co. in 2013 for $71.5 million. Eager to get the project underway, Jay Paul brought on Sunnyvale, Calif.–based general contractor Level 10 Construction and global engineering firm (and REDi creator) Arupas geotechnical engineer.

The owner also scored a major coup: a lease with Facebook, whose executive team had balked at earlier offers to lease space in the building. “It was a three- to four-year process,” says Jay Paul chief investment officer Matt Lituchy. “Their team came to us saying, ‘X amount of people are tired of commuting.’ At first, we were looking at 100,000 square feet. Then they came back and said, ‘We’re sorry, but our C-suite isn’t ready to make the move.’ ” Nearly two years later, Facebook was back again, Lituchy continues, “saying that the clamoring was so loud, [they couldn’t] ignore it.”

Eventually, as reported by the San Francisco Business Times, the two parties agreed on 436,000 square feet of office space with an asking rent of $80 per square foot. Lituchy says that 181 Fremont’s compact floor plates could more ably encourage the social encounters Facebook envisioned for its employees while providing the same square footage as the company’s sprawling Menlo Park, Calif., headquarters. Plus, Instagram employees would have direct access, via a pedestrian bridge, to the 5.4-acre elevated park atop the Salesforce Transit Center, San Francisco’s take on New York City’s High Line. “Facebook saw that many other Silicon Valley competitors had major operations in San Francisco,” Lituchy explains. “They realized they needed this type of environment to attract and retain talent.”

From Design Brilliance to Project Resilience

Still, the project would not have happened without the design instincts of Heller and his team. For a 700-foot-tall building, its footprint was tiny—just 125 feet by 137 feet. A structural concrete core like the one used in the nearby Salesforce Tower would have left little space for leasable real estate in a structure with such a dramatic aspect ratio. Forgoing the core, however, would have opened the building and its occupants to greater risks from lateral wind loads and seismic events.

Undeterred, Heller imagined an undulating sea carried across a rigid structure. He recalled the structural braces of I.M. Pei’s Bank of China Tower, Foster + Partners’ Hongkong and Shanghai Bank Headquarters, and 875 N. Michigan Ave. (formerly the John Hancock Center) in Chicago. Thus emerged 181 Fremont’s exoskeleton, a system of eight aluminum-clad steel mega-braces that hug the building and are arranged in triangles—“the strongest form in nature,” Heller says. This form would keep the elevator core compact by taking on much of the latter’s structural burden.

But the tower’s seismic resiliency truly begins 262 feet below street level, where 44 caissons are augered firmly into bedrock, says Heller Manus project manager Ryan Boe, who spent six years on the project: “It is literally the safest building in the city.”

Still, Heller notes, a greater concern for a project of such height and slenderness is wind sway. The project’s original structural engineer, local firm Treadwell & Rollo (acquired in 2010 by global firm Langan), had specified a 700-ton tuned mass damper hung from the tower’s roof to counteract wind vibration—a “giant slug of steel on a pendulum,” as Heller describes it. But the massive weight of the damper would necessitate a stiffer structure, ultimately increasing the building’s vulnerability to seismic forces. This cycle of trade-offs kept Heller up for nights, wondering: Was a slender building this tall possible?

Then, a breakthrough. Ibbi Almufti, associate principal in Arup’s advanced technology and research group, proposed a system of 32 viscous dampers that would allow the building to sway—safely—during heavy winds or an earthquake. With enthusiastic support from Jay Paul, the plan moved forward. The dampers are contained in the mega-braces, each of which comprises three parallel steel beams. The middle beam in each set is functionally rigid. The outer two beams, roughly 12 to 14 feet long and 10 inches in diameter, have built-in dampers at each end. Manufactured by North Tonawanda, N.Y.–based Taylor Devices, the dampers function as pistonlike shock absorbers, allowing for 6 inches of expansion to regulate the building’s sway.

Mapping these braces across the building’s twisting, tapered volume required complex computer modeling. No two floor plates in the tower repeat. On office floors where the dampers occur, the mega-braces thread through Teflon pads—frictionless, sleevelike insertions—installed on each floor to prevent buckling.

The damper system and other seismic design features incorporated by Almufti and Arup saved an estimated 3,000 tons of structural steel—as built, the tower uses approximately 20% less steel than in the original proposal. In addition, the innovative system allowed the relocation of mechanical equipment to the tower’s rooftop, enabling the creation of the spacious penthouse on the double-height top floor.

On the building’s 39th floor, a recessed, open-air terrace defined by an inverted chevron structural frame reduces wind load further while visually and physically separating the upper-level condominiums from the lower 34 commercial floors occupied entirely by Facebook. A wind-load study prepared by Guelph, Ontario–based engineering firm RWDI found a 3.5% to 4% reduction in the acceleration at the top of the building when exposed to projected five-year and 10-year wind loads. This sway reduction resulted from the turbulence generated by the tower’s Sky Lounge. While the impact may appear slight, Heller says, it is noticeable particularly at the top.

In Case of Emergency

Aside from its pioneering structural and resilient design, 181 Fremont still has more innovations on hand—namely, its occupant evacuation operation (OEO) elevators, the first system of its kind in this country. In the event of a fire, according to Heller Manus chief financial officer and principal Eric Lundquist, strobe lights flash, sprinklers activate, and a voice message on an automated system instructs building occupants to leave the building—nothing new there. What is unique is that occupants in this situation will have the option of exiting via the elevators, which can evacuate all occupants, often within minutes. “If you’re in a high-rise building, you don’t want to walk down 70 flights of stairs,” Heller says. “Especially if you’re me and you can’t.”

Synced to the building’s smoke-detection devices, the life safety system alerts occupants to the safest and fastest egress route among three ways: a staircase, 12 passenger elevators, or a service elevator, which also serves as the fire service access elevator (FSAE). Typically, the system evacuates only the floor with the fire and the two floors above and below. In a buildingwide event, the elevator cabs proceed to other floors according to their proximity to the fire. An analysis showed that the five consecutive floors posing the greatest threat can be evacuated in less than 15 minutes, and a fully occupied building in under an hour.

Heller says regulatory changes made following the 9/11 attacks on the World Trade Center in New York motivated the design decision. In particular, the International Building Code required a third egress staircase for towers exceeding 420 feet. A subsequent change formalized in Section 3008 of the 2009 IBC allows for the use of OEO elevators as a means of egress in lieu of this additional stairway.

Installing and testing the system wasn’t easy. New elevator transfer stations for the commercial low-, mid-, and high-rise elevator banks requested by Facebook complicated the approved OEO sequence for elevator operation. The team also had to stage a four-week testing protocol involving the San Francisco Fire Department and subcontractors Thyssenkrupp, Rosendin Electric, and the Pacific Auxiliary Fire Alarm Co. for each phase of occupancy while also coordinating test sequences of the alarm notifications with residents already living in the building, according to Level 10 Construction project executive Mike Castillo.

But the system has already demonstrated its effectiveness. In the world’s first-ever OEO evacuation, Lundquist says, a real fire broke out in the FSAE machine room on the penthouse mechanical level two months after the city’s building inspection department granted 181 Fremont a temporary certificate of occupancy. The smoke activated the fire alarm system and the elevator system went into its automated OEO mode, instructing occupants to leave the building. Occupants on the top floors—closest to the fire—exited first, leaving the building in about two minutes using the residential OEO elevators. Occupants on other residential floors quickly followed, also via the elevators. As the fire was extinguished before presenting a threat, Facebook employees and construction crews on the lower office levels remained in the building. Even with the FSAE out of commission, Lundquist notes, “the system evacuated people without human interaction, like it should.”

The building’s fire containment system helps ease the burden on the OEO elevators by reducing the likelihood that a fire will spread from floor to floor. Developed by Owens Corning subsidiary Thermafiber, 181 Fremont’s custom engineered life safety system is capable of providing up to two hours of fire containment protection. In the event of a fire, the system was designed to keep the fire within its room of origin, preventing it from spreading to higher floors via the void between the exterior, non-rated curtain-wall assembly and the rated floor assembly, according to Angela Ogino, Insolutions technical services leader at Thermafiber.

The 4- to 6-inch voids between 181 Fremont’s curtain wall and floor assemblies are filled with a customized Impasse perimeter fire containment system installed with fire-performance mineral wool components—FireSpan 90 and Safing Insulation. On every building floor, geometrically distinct insulation panels were fit snugly in the irregular openings around the spandrel framing and are secured in place with Thermafiber’s Impasse mechanical fasteners. “If you don’t pay attention to providing containment at these vulnerable openings, it provides a path for fire to spread quickly and uncontrollably at the building’s perimeter,” Ogino says. “Keeping [the fire] contained gives occupants critical time to get out of the building and first responders the time they need to enter the building and extinguish the fire.” The system was developed in compliance with IBC Section 715.4 and meets ASTM E2307, the test method for determining the resistance of a perimeter fire-containment system for multistory structures.

Local building codes mandate that buildings allow for safe occupant evacuation and minimal building damage following a 475-year earthquake, which translates to a mid-7 to -8 magnitude in San Francisco. But Almufti proposed a more rigorous model: Arup’s own REDi standard, which had yet to be piloted after its 2013 publication. Like the building code, a REDi Gold rating requires that occupants be able to evacuate a building safely following a significant earthquake. However, REDi goes one step further, requiring that the building be occupiable immediately after the event.

For 181 Fremont, its combination of design features—its exoskeleton structure, deep foundation, viscous damper system, and transfer trusses between the second and third floors and between the 39th and 40th floors to direct building loads to mega-columns at the tower’s corners—ensured its candidacy for the rigorous standard. Forty-four ground motion trials, using LS-DYNA simulation software showing that building operations could resume the day after a 475-year earthquake on the San Andreas Fault, confirmed its achievement.

Green Matters

Even with 181 Fremont’s numerous complexities, its design does not overlook sustainability. The building achieved LEED Platinum pre-certification in 2014 and is on track to join a short list of skyscrapers that have earned the full designation.

Wolfgang Werner, the New York–based president and CEO of Urban Fabrick, the project’s LEED consultant, says the commitment of Jay Paul to support a graywater-recycling system moved the building’s LEED score past the 80-point needle for a Platinum rating. According to water-reuse calculations submitted to the U.S. Green Building Council, 71% of the building’s collected graywater and rainwater is treated on site in an Aquacell graywater-treatment system. Water from sinks, baths, and washing machines is sent to a basement five floors below grade, where it’s treated before being reused for toilet and urinal flushing and drip irrigation. This saves an estimated 1.4 million gallons of water each year.

Another intriguing energy-saving feature is more visible: 181 Fremont’s sawtooth windows, which begin at the second-floor truss level. Modeled in Autodesk Revit, the windows are mapped onto a pattern-based curtain wall that follows a parametric curve. The result is a series of elliptical waves that span the triangular patterns of the mega-braces as they ascend the tower. At the same time, each window angles slightly side to side to provide self-shading, resulting in a 6% passive heat-gain reduction.

But 181 Fremont’s water-treatment capabilities and window layout only scratch the surface of the project’s high performance. Compared with a baseline building, its glazed envelope and HVAC and lighting systems yield nearly 30% in energy cost savings, and its water-efficient fixtures and fittings reduce water consumption by 28%—a figure that increases to 44% when including 181 Fremont’s on-site graywater reuse.

The Long View

In a city with one of America’s worst housing and homelessness crises but a burgeoning tech community, what does the addition of 181 Fremont mean?

For starters, Heller says, it opens the possibility for increased density in a city that desperately needs it. By building a case for more mixed-use development, it helps counter the strong anti-growth coalition that has persisted in the city for decades—resulting in generic, boxy buildings now known as “Richmond specials,” named after the district in which they originally appeared. Tall buildings and improved mass transit could be part of a multifaceted response to San Francisco’s housing crisis, particularly if tech companies continue to move to the city, thus helping defray the development costs of what are inherently expensive projects.

Densifying, of course, requires San Francisco to go vertical. Even if the voices of the antigrowth coalition have softened in recent years, earthquakes remain a serious risk to high-rise development, particularly when buildings must find footing on small lots due to the limited availability of ground space, and when nearly every local is wary of the next seismic event’s potential for devastation. As Heller knows, no matter how beautiful the building, it must be able to withstand the test of time.

Link to Original Article (may require registration)