Triangular Towers Get High Marks for Earthquake Safety

People tend to worry about being in tall buildings during an earthquake, often without good reason, providing they’re built to contemporary quality standards, says seismology expert Gary C. Hart. .

“I’d love to be in one of the Century Plaza towers in Century City during an earthquake, enjoying the ride and feeling quite safe,” says the president of Englekirk & Hart Inc., a Los Angeles-based firm of consulting engineers.

He added that, while the 44-storied twin landmark structures do not have a monopoly on earthquake worthiness, they are among the city’s high-rise structures that have the right stuff to endure a stiff jolt.

Hart should know. He’s been monitoring the 2029 and 2049 buildings on Century Park East for some time as part of the U.S. Geological Survey’s monitoring team.

Increased Resistance

“The triangular shape and engineering of those buildings will cause them to sway less during an earthquake than a rectangular building because they offer increased resistance to twisting--often the cause of major damage during a severe earthquake,” he said.

The towers, completed in the mid-1970s, are among several hundred structures that serve as full-scale seismic laboratories for the Geological Survey, Hart said. He noted that the federal approach to structural seismic monitoring differs from the state’s approach in that Survey’s primary interest is in buildings of unusual or unique design, so that they may be studied as research models.

“The federal government’s objective is long-range research. Its efforts focus on learning more about how to design buildings from the data collected here and in other earthquake-prone areas,” Hart said.

Through his 20-year affiliation with UCLA, as a professor of civil engineering specializing in seismic design of buildings, Hart has been a member of monitoring teams on numerous structures both for the Survey and for the state.

“USGS’s continuing program to evaluate the dynamic properties of structures (especially those with novel design features),” Hart said, “has included on-going tests of both forced vibration and ambient vibration on the Century City South Tower building.

“The results for dynamic behavior of the multistory triangular-shaped buildings have been quite favorable, according to a report delivered by the Earthquake Engineering Research Center at UC Berkeley for the National Science Foundation.”

Rising 44 stories, the steel-frame towers face each other at the apex (resembling a bow-tie from the air). At the time they were built they were the world’s only twin triangular towers.

Theme Structures

Architect Minoru Yamasaki’s concept of equilateral triangles (each side 260 feet wide), as dominant theme structures for Century City, were intended to contrast the curved facade of the Century Plaza Hotel, which Yamasaki also designed.

The triangle, Hart noted, has an excellent configuration for support and strength because its three bases are spread out in fairly equal proportions around its central core.

Yamasaki’s use of concentric triangular service cores for the buildings created space that was conventional and rectangular, except for its unusual corner offices.

Samuel H. Kaufman, building manager for the towers, couldn’t be more delighted with the selection of the twin buildings by the U.S. Geological Survey among its study sites in the Los Angeles area.

Special Equipment

“They installed special monitoring equipment (paid for by the National Science Foundation) during final stages of construction of the towers in 1976 and 1977.

“And we were pleased to learn that the equipment registered little or no motion to the buildings during our major earthquake of Oct. 1, 1987,” Kaufman said.

His management team is currently implementing a $200,000 program to reinforce the electrical and other service systems to bring them up to the latest seismic safety technology.

“When we complete the work, our systems will have been upgraded to the modern design criteria set for hospitals, police and fire stations.”