Can tall buildings withstand quakes?
By Jung Min-ho
High-rise apartments are seen in Busan after a magnitude-4.5 earthquake struck the ancient city of Gyeongju, Monday. / Yonhap
After a series of earthquakes hit the southern regions of Korea, many residents of tall buildings are now wondering whether their homes are safe enough to withstand one that hits them.
The question was not asked until two weeks ago, when they felt magnitude-5.8 seismic tremors for the first time in their lives.
Experts say, for most earthquakes, tall buildings are usually safer than low-rise ones because they are designed to withstand seismic motion, although residents may not feel that way high up.
“Tall buildings are relatively safe because their structures are earthquake-resistant,” said Rhie Jun-kee, a professor of the School of Earth and Environmental Sciences at Seoul National University. “The damage risks are bigger for old, low-level buildings, which were not constructed in line with seismic design codes.”
According to the Ministry of Land, Infrastructure and Transport, the number of 30-story or higher buildings in Korea nearly doubled from 753 in 2010 to 1,478 last year. Among them, 307 buildings are in Busan, a metropolitan city 80 kilometers away from Gyeongju, the epicenter of the recent quakes.
Korea adopted a law in 1998 to require structures six stories or higher to be constructed according to seismic design standards. However, the law does not specify how resistant they should be, said Kim Ik-hyun, a construction engineering professor at the University of Ulsan.
“Based on the cases abroad, we can only speculate that buildings can withstand tremors with a magnitude of about 7,” he said.
This quake on Sept. 12 was the first time that their seismic design was seriously tested.
To minimize any forces or deformations during earthquakes, construction engineers use earthquake-resistant materials or structural vibration control technologies.
One of the key factors making tall buildings safer than small ones in quakes is flexibility, which allows them to sway instead of breaking, said Jung Jin-hwan, director of the seismic research center at Pusan National University.
“Many factors affect how resistant buildings are, but importantly, tall buildings are usually more flexible,” he said.
Thus, if earthquakes occur, residents of tall buildings are advised to stay where they are instead of rushing outside while taking shelter under a table until the shaking is over, experts said.
The Ministry of Public Safety and Security said it will set up more detailed standards for seismic design.
Most public facilities, including airports, railways and dams are earthquake-resistant, but only 33.5 percent of other structures (three-stories or higher) are, according to the infrastructure ministry.
The Korea Meteorological Administration said there would be no stronger aftershocks than the magnitude 5.8 one, but there could be aftershocks with magnitude 3 to 4. It said it cannot predict when the aftershocks would stop, adding they may continue for weeks or even months.