New Towers Designed To Become San Francisco Landmarks

"It is always a challenge to build a high-rise on top of a hill in earthquake country, particularly in San Francisco, which still harbors dark memories of the great quake and fire that destroyed the city 100 years ago. Now the city has complex building codes, and putting up a tower on the top of a hill has special challenges -- not just earthquakes, but strong winds that blow off the Pacific in winter, sometimes over 75 miles an hour, hurricane force on the Beaufort Wind Scale...

Back in the 20th century, a skyscraper would be built around a steel frame, the way a human is built around a skeleton. But now, many tall buildings are built around a concrete core, poured around reinforced steel for strength...One advantage of the core construction as opposed to the steel-frame method is that the condos in the towers would not have structural members obscuring the windows. This means floor-to-ceiling windows and spectacular views. The better the view, the more the developer can charge...

The tower has yet another unusual feature -- on the very top are two water tanks holding about 100,000 gallons combined. Each tank will also have two liquid damper screens to control the flow of the water. The purpose of the tanks is to counter the sway of the building in a high wind...But the design idea is that if the wind tends to move the building one way, the water would provide a counterbalance for stability. This concept has never been used in this country before."