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Earthquake-Proof Skyscrapers to Crown San Francisco Skyline

Tue October 02, 2007 - Midwest Edition
Frank Hartzell

Since the Gold Rush of 1849, San Francisco has often been a ground-breaking place, capable of launching some spectacular hits, in more ways than one.

There was the building of the Golden Gate Bridge in 1936, the Counterculture of the 1960s and then, of course, Barry Bonds.

Just hours after the Giants slugger hit his record 756th homerun, San Francisco authorities found a surprising new way to break ground, finalizing a competition to build a transit terminal complex that would rival the Empire State Building in height and lead the world in environmental values.

In fact, an unprecedented boom in “green” skyscraper-building is underway in The City by the Bay.

Just yards from the San Francisco-Oakland Bay Bridge, the tallest residential condo tower in the West topped out at 641 ft. (195 m) in August at One Rincon Hill, with a second 645-ft.-tall (195 m) south tower now nearing completion.

On Sept. 20, a final design was picked for a 1,200-ft. (365 m) Transbay Tower, part of the efforts to replace San Francisco’s transit hub, the Transbay Terminal. A cluster of a dozen 40- to 60-story residential and office towers are proposed nearby in an area that is now a mix of eclectic shops, warehouses, crumbling infrastructure from the city’s long-gone glory days as a maritime trade hub, and a high concentration of homeless people.

City officials have decided to consider rezoning the area around the new terminal and will analyze raising the height limit from 550 ft. (167 m).

Mark Choey of Climb Real Estate Group/Vanguard Properties has established to keep track of the flurry of big buildings and new projects, which has come at a time when the residential real estate market has been in decline in California and around the country.

This is all a shockwave — in more ways than one — in a city where the 853-ft. (259 m) Transamerica Tower has been unrivaled for 35 years.

San Francisco is famous for both earthquakes and for what builders call “red tape” and what locals would call “community values.”

This building revolution has proclaimed itself to be as “green” and safe as it is big.

The board of directors of the Transbay Joint Powers Authority voted unanimously in late September to begin negotiations with the Hines development firm and Pelli Clarke Pelli Architects. The team has offered $350 million for a site at First and Mission streets.

The Hines-Pelli proposal was the favorite of a prestigious design jury that reviewed the proposals, not so much because its design was more spectacular and green, but because the team offered $200 million more than its two rivals.

San Francisco Planning Director Dean Macris told the Transbay Joint Powers Authority that permits would be put on an aggressive schedule, with all the paperwork possible in 18 months. However, final permitting could still alter the design in a neighborhood where the current height limit is 550 ft.

The flurry of proposals for tall buildings were covered in media accounts saying that San Francisco would boast taller towers than any city west of the Mississippi and that the Transbay Tower would be the third tallest in the United States, after the Sears Tower in Chicago and the Empire State Building in New York City. These were based on press releases of involved builders, architects and civic boosters.

San Francisco boosters are thrilled anytime they beat bigger, more conservative Los Angeles, whether the competition be baseball or condominium towers.

But they overreached.

If the Transbay were completed tomorrow it would be the third tallest building in the United States. But contrary to popular belief, 9/11 did not put a scare into the high-rise building business. A simple Google search reveals how tall buildings have come back into vogue, and many tall structures are proposed and being built — such as a 2,000-ft. (609 m) Fordham Spire in Chicago, the city which launched the first skyscraper boom at the turn of the last century. Structures the size of the Empire State Building are in the works for Miami and Las Vegas. Even taller buildings and towers are being planned, especially around the Pacific Rim and in the Middle East.

A nearly-finished tower in Dubai is predicted to reach some 2,700 ft. (822 m) with its spire when it is finished next year.

Follow-up news stories about the buildings in San Francisco didn’t use the word “tallest” about any of the buildings still in the planning stages.

Still, San Francisco’s skyscraper boom would still be among the biggest and is certainly the most unexpected.

While environmentalists and preservationists once were unified against towering buildings, the new structures all boast green innovations that will make them certified as gold or even platinum under LEED standards.

The Leadership in Energy and Environmental Design (LEED) Green Building Rating System is the nationally accepted benchmark for the design, construction, and operation of high performance green buildings. LEED promotes a whole-building approach to sustainability by recognizing performance in five key areas of human and environmental health: sustainable site development, water savings, energy efficiency, materials selection, and indoor environmental quality. The Rincon Hill Towers feature solar electrical systems, among other green innovations.

The metal grid of the Transbay building would feature fins that would serve as sun screens that would reduce the tower’s energy needs by 15 percent. The buildings on the site will feature as much natural light as possible, as well as water recycling and innovative pollution reduction methods.

Backers of the big building boom in the Left Coast capital say the cluster of tall residential buildings, transportation and offices also will compose something of a vertical village that will reduce the environmental costs of the commute.

In selecting the Hines-Pelli team, the Transbay Authority also selected the Pelli firm’s design for a new terminal — which would feature a 5.4-acre public park on the roof of the four-story transit barn at First and Fremont streets. The park is at the heart of recycling and temperature-control efforts for the building. Transit buses would enter the third floor of the terminal from a ramp connected to the Bay Bridge. The basement is reserved for future high-speed rail service.

Skyscrapers in San Francisco? For years, the main obstacle was earthquakes.

Recent innovations in earthquake research enable such towers to be built safely, engineers and city planners said. This is done by a combination of flexible foundations that allow buildings to move and dampers high up in the building that reduce that sway.

An innovative device is the liquid tuned damper that tops One Rincon Hill, installed last summer after extensive testing at the University of Western Ontario, London. The water-filled device takes up an entire floor at the top of the tower and resembles a gigantic fish tank. It provides not only dampening of sway in high winds or an earthquake, but also fire protection.

The technology has been used in office buildings in Japan and California, but structural engineer Ron Klemencic told the publication Building Design and Construction that One Rincon Hill will be the first high-rise concrete residential structure in the United States to use it. The design has been validated in full-scale tests at the University of California, Berkeley, to resist seismic forces two-and-a-half times greater than code requirements.

Klemencic told BDC that the liquid damper will save $2 to $4 per square foot over stiffening the building with more concrete, while the seismic bracing will cut $5 per sq. ft. compared to conventional code-prescribed designs.

Tall buildings like the Empire State Building traditionally resisted motion solely by the mass and stiffness of the structure. However, as the structures have become longer, taller and more flexible, the demand for safety has increased, and sway has been incorporated into foundations that move. It has been described as putting the building on contained roller skates.

Researchers are studying new types of cost-efficient dampers for mitigating wind and earthquake induced vibrations in tall buildings and other structures like long-span bridges and offshore structures. The most commonly used auxiliary damping device is the Tuned Mass Damper, which consists of a solid mass attached to the building through a spring and a dashpot, according to university studies. Such systems have been implemented, for example, in the John Hancock tower in Boston and the Citicorp Building in New York City.

However, the use of a liquid, rather than solid mass damper is new, according to the NatHaz laboratory at the University of Notre Dame. Liquid dampers work by controlling the slosh of water with baffles in a way that counteracts the motion from the wind or earthquake.

The liquid damper is cheaper and also can serve as a water supply and for firefighting, engineering publications state.

While the water has been seen as harder to control, its advantages have emerged in research by the NatHaz, and in research projects in Japan.

While no prominent engineers have emerged to publicly call the innovative new skyscraper designs unsafe — as happened with the new Bay Bridge — the San Francisco Chronicle and some bloggers urge caution.

“Public discussion of the three proposals for a new tower at the Transbay Terminal site has so far resembled a beauty contest, with little mention of earthquake risks,” a Chronicle editorial stated.

“When the subject does come up, the usual response from the authorities is that the architects and engineers know how to cope with shaky ground,” the editorial continued. “But the record of structural failures indicates that architects and engineers, despite their admirable achievements, are far from infallible. Each generation assumes that it has the answer on structural matters — until the next generation rewrites the building codes to accord with new information.”

A look into the seismic plans for various San Francisco high-rises shows that earthquake mitigation measures are an interplay between damping and foundation, and that impacts the look and use of the building from top to bottom.

The Rincon towers, for example, have a central core providing the main support for the structure rather than an exterior frame.

The developer of the One Rincon Hill complex is Urban West Associates. The total cost of the project is $290 million.

The 1.3-acre (0.5 ha) site for the two new Rincon Hill towers is bordered by Harrison Street to the west; the Fremont Street off-ramp from Highway 101 to the north; the western approach to the Bay Bridge (Interstate 80) on the east; and the First Street on-ramp to the south. A clock tower, first owned by Union 76 and then Bank of America was originally on the site

A 720-ft. (219 m) tall crane has been an imposing figure on the city skyline over the past year, as the Rincon Towers are built. The towers are offset at angles in an effort not to block views from the Bay Bridge.

Both the north and south towers of the Rincon Hill complex bear a resemblance to The Heritage at Millennium Park in Chicago, a building of a similar height to the south tower designed also by Solomon, Cordwell, Buenz and Associates.

“The design is out of our Chicago office, and does take cues from the architectural tradition of Chicago,” said Chris Pemberton, vice president of Solomon Cordwell Buenz.

“The touch of Chicago could be the building height and simplicity of design — Chicago buildings have a straight forward rational design that we have kept as a guiding principle in the design for One Rincon Hill.”

Bovis Lend Lease is the general contractor for the structures at One Rincon Hill, where many construction innovations have emerged that weren’t known in 1970s — the last national wave of skyscraper building.

Project Executive Peter Read, of Bovis Lend Lease, said his team learned of an Australian high-rise project which employed a cocoon all around the building during construction, providing extra safety for workers and also enabling occupancy of lower floors as the cocoon moves up.

Also used have been lanyard-like harnesses, allowing workers to climb like on a pogo stick when pouring columns of concrete, a task once much more precarious, stated a newsletter published by the developer.

Another new advance is partial occupancy, a new trend that allows complete build-out of entire floors and eventual move-in while higher floors continue to be built above.

The speed with which concrete floors were completed at One Rincon Hill — one every three days — is another recent innovation which saved months of expensive work time there, and potentially at others proposed.

According to Bovis Lend Lease, One Rincon Hill’s construction featured 43,000 cu. yds. (32,800 m) of cast-in-place concrete, weighing 87,075 tons (78,993 t) and 6,271 tons (5,688 t) of reinforcing steel.

The physical rise of One Rincon Hill towers and the very public media campaign to pick a winning design for the Transbay Project have brought the issue of high-rise construction to the forefront in the Bay Area.

Two other teams entered the competition for the Transbay Tower. Rockefeller Group Development Corp. worked with Skidmore Owings & Merrill to propose a slender 1,375-ft. (420 m) tower alongside a new terminal. Forest City Enterprises and Rogers Stirk Harbour + Partners proposed an open-air terminal next to a 1,100-ft. (335 m) glass tower topped by a spectacular wind turbine.

The winning proposal still has a long way to go, with more public meetings planned and construction expected to be complete in 2014.

The approval by the Transbay Joint Powers Authority is a big step. The TJPA Board of Directors is comprised of representatives from the city and county of San Francisco, including the SF Municipal Railway (MUNI), the Office of the Mayor and the Board of Supervisors; the Alameda-Contra Costa Transit District (AC Transit); and the Peninsula Corridor Joint Powers Board-Caltran, composed of the City and County of San Francisco, the San Mateo County Transit District, and the Santa Clara Valley Transportation Authority.

Transbay developer Hines’ portfolio of projects underway, completed, acquired and managed for third parties includes more than 1,000 properties representing approximately 416 million sq. ft. (38 million sq m) of space, including office, residential, mixed-use, industrial, hotel, medical, retail and sports facilities, as well as large, master-planned communities and land developments. With offices in 68 U.S. cities and 15 foreign countries, and controlled assets valued at approximately $19.9 billion, Hines is one of the largest real estate organizations in the world.

Established in 1977, Pelli Clarke Pelli Architects (PCPA) has designed over 80 million sq. ft. of urban, mixed-use projects for prestigious government, private, and corporate clients worldwide, and has received many awards for its LEED certifications. CEG

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