The iconic Pacific Telephone Building, now known as 140 New Montgomery, in downtown San Francisco has undergone an adaptive-use project, including a significant seismic retrofit. RienvanRijthoven
The Pacific Telephone Building is transformed into a desirable space for contemporary technology firms thanks to an adaptive-use project that includes a seismic retrofit.
May 13, 2014—When it was completed in the mid-1920s, the Pacific Telephone Building in San Francisco housed the offices of the Pacific Telephone and Telegraph Company, at the time a cutting-edge communications company. Now, following several years of vacancy, the 26-story building is once again a high-tech hub, this time serving contemporary technology firms with operations that would have been unimaginable when the building was constructed. The building’s reboot comes thanks to an adaptive-use project involving significant architectural and structural renovations—including a seismic retrofit—all designed to preserve the building’s original architectural integrity.
Located in San Francisco’s up-and-coming South of Market neighborhood, the 436 ft tall Pacific Telephone Building, now known by its address—140 New Montgomery—was the tallest building in the city when it was completed in 1925. Prominent San Francisco architects Timothy Pflueger and James Miller designed the tower in the neogothic and art deco styles. Among the building’s defining features are its painted, glazed terra-cotta tile facade and such embellishments as a set of eight 13 ft tall eagles perched atop the building’s wedding-cake style crown.
Although the Pacific Telephone and Telegraph Company changed names and owners several times through the years, its offices remained in the building until 2007, when AT&T, its current owner, sold the skyscraper to San Francisco-based Wilson Meany, a privately owned real estate investment and development firm. Wilson Meany initially planned to convert the building into condominiums, but those plans changed when the real estate market devolved as a result of the 2008 economic recession. In 2010 the firm decided instead to renovate the building for office use in hopes of attracting technology tenants from Silicon Valley. The only question was: would today’s technology companies want to relocate to a nearly 90-year-old building with floor plates measuring a maximum of just 13,000 sq ft?
Wilson Meany hired the San Francisco office of Perkins + Will, a global architecture firm with 21 offices nationwide, to lead the project’s architectural design. The developer then invited three engineering firms to submit proposals for the project’s structural design. As a result of that competitive process, it selected the San Francisco-based engineering firm Holmes Culley as the structural engineer of record. The architects, structural engineers, and other team members worked collaboratively with Wilson Meany to develop a design strategy that would bring the building into compliance with current office standards and building codes without jeopardizing its historic character.
The project scope included restoring the building’s lobby to its 1920s elegance, remodeling its two basement levels to accommodate a parking garage and a bicycle storage and repair facility, transforming a service yard at the rear of the building into a garden oasis and courtyard, creating space for two restaurants on the first floor, and reimaging the 2nd through 26th floors as contemporary office space. “The goal was to position the project for what we call ‘The Art of Work’ because it’s in the arts district, in the very same block as the San Francisco Museum of Modern Art and surrounded by several notable galleries and an art school down the block,” says Cathy Simon, F.AIA, LEED BD + C, a design principal of Perkins + Will. “The idea was to make it an artful adaptive reuse and to attract the best tenants.”
The lobby of 140 New Montgomery, formerly known as the Pacific
Telephone Building, in San Francisco, has been restored to its
1920s’ elegance. Tim Griffith
To achieve that objective the structure had to be made safer for its future occupants. The building is located in downtown San Francisco, between the San Andreas and Hayward faults. Research released in 2008 by the U.S. Geological Survey, the Southern California Earthquake Center, and the California Geological Survey indicates that the San Francisco Bay Area has a 63 percent probability of experiencing an earthquake of 6.7 magnitude or greater within the next 30 years. Because the building was not originally designed to withstand such an earthquake, the structural engineering team had to develop a robust seismic retrofit for the structure. It determined that the best way to do that would be through performance-based design, says Zander Sivyer, S.E., a principal and the chief executive officer of Holmes Culley and the structural engineer of record on the project.
The team predominantly drew upon the ASCE standard Seismic Rehabilitation of Existing Buildings, 41-06, (ASCE, 2007) to develop performance criteria for the building, but it also used tall-building design guidelines from both the city of Los Angeles and the Pacific Earthquake Engineering Research Center, a multi-institutional research and education center headquartered at the University of California, Berkeley. Bill Tremayne, S.E., a principal and technical director of Holmes Culley and the project’s lead analyst, explains that the project qualified to be designed for 75 percent of the Basic Safety Earthquake-1 (BSE-1) seismic hazard given in the ASCE document, taking into consideration the California State Historical Building Code and San Francisco city and county codes for the retrofit of existing buildings. “We targeted life-safety performance for the structural system for both the evaluation and retrofit of the existing structure,” he says. “The new elements were evaluated and designed for one hundred percent of [the] BSE-1 hazard.”
Once the performance criteria were established, many elements of the building were subjected to destructive testing to determine the strength and configuration of the existing structure and how it would contribute to the retrofit. The team then created a nonlinear analysis model of the building, incorporating site-specific response spectra and earthquake ground-motion data provided by the geotechnical engineer, San Francisco-based Langan Treadwell Rollo, to understand how the existing building would perform in an earthquake of the predicted magnitude. “Once we had that as a baseline, we understood that the building needed both additional strength and stiffness due to the flexibility of the original structure,” Sivyer says.
Outrigger trusses were incorporated at levels 6 through 8
and 17 through 19 to connect the central core to the
supercolumns at the building’s perimeter, adding stiffness
to the structure. Bill Tremayne
The building’s existing stairs did not comply with the building code for egress, so they were infilled, and new code-compliant stairs were installed near the building’s central elevator core. Several of the building’s restrooms and data-and-server rooms were also consolidated around the core. Those changes required new concrete shear walls at the core, which provided sufficient strength but not sufficient stiffness for the anticipated deflections, Sivyer says. So outrigger trusses were incorporated at levels 6 through 8 and 17 through 19, coupling the central core to the supercolumns at the building’s perimeter. “Those outriggers stiffen that central core and enable it to work double duty over the height of the building because it has multiple points of hinging at not only the base but also at various other points up the height of the building,” Sivyer notes.
Incorporating the retrofit solution into the existing building presented many challenges. For instance, the floors heights are not uniform, so the architects, engineers, and contractors had to collaborate closely on-site to ensure that the new structural elements fit through the structure properly, says Nina Mahjoub, P.E., a project engineer for Holmes Culley and the project engineer. Another challenge stemmed from that fact that the basement is below the water table. To mitigate the risk of penetrating the basement’s waterproof membrane, large spreader walls were incorporated into the building’s two basement levels to distribute the forces from the new structural elements to the existing foundations at the perimeter, Sivyer explains.
No new foundations were required, in part because the outrigger trusses’ diagonal bracing elements are buckling restraint braces (BRB) tuned to provide sufficient stiffness to minimize deflections while also reducing the foundation loads so that no additional support was required under the building’s central core or beneath the supercolumns. “The use of the BRB outriggers to stiffen the core walls was an innovative solution for the retrofit of the existing building,” Tremayne says. “This is the first application I’ve heard of where a combination of BRB outriggers and core shear walls has been used in a building of this height for a seismic retrofit.” Holmes Culley earned an award of excellence in the historic preservation category of the Structural Engineers Association of Northern California’s 2014 Excellence in Structural Engineering Awards for its work on the project.
The new structural system also added stability to achieve the open floor plan desired in most contemporary office spaces. “The work that we did structurally was doing double duty in terms of helping define the architectural spaces,” Sivyer says. The building’s existing office spaces were gutted to expose their ceilings and the interior of the façade’s brick infill walls. The existing 20th-century design of private offices along the building’s perimeter was reconfigured to create an open floor plan at each level. The BRBs were also left exposed in most cases, contributing to the architectural design character. “Holmes Culley developed a system that has as minimal impact as you can have while still meeting the building code requirements for seismic design,” Simon says. “It’s a brilliant approach because it allows amazing open floor plates almost everywhere.”
Project construction began in 2012, and the seismic retrofit was substantially completed in late 2013. Work continues today to build out the remaining offices and outfit the first floor for the two restaurants. Although the developer took a leap of faith by renovating the nearly 90-year-old building for contemporary technology firms, the project has been a success, and the building is now nearly 100 percent leased. Its largest tenant is Yelp, a multinational firm that operates an online business review site and has its headquarters arranged over a dozen floors. Other tenants include Lumosity, a firm that develops online “brain-training” games, and the headquarters of Knoll, a distinguished furniture design and manufacturing firm that has been in business since 1938. “When the building was built, it was about the current high technology of its era,” Simon says. “Now, it once again speaks to that idea of high technology but within a beautiful legacy building that bookends the past and future.”