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Fri, July 1, 2022 | 02:34
Aerobic exercise blamed for tremor at Techno-Mart
"테크노마트 흔들림 원인은 '태보' 운동"
Posted : 2011-07-19 18:56
Updated : 2011-07-19 18:56
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By Yun Suh-young

A form of aerobic exercise performed by dozens of people caused the vertical vibration felt in certain floors at Techno-Mart, a 39-story shopping mall in Gwangjin-gu, Seoul, two weeks ago, an inspection committee tentatively concluded Tuesday.

A simulation of the exercise was carried out on the 12th floor of the fitness center of the building Tuesday by inspectors to prove that the group exercise caused the building to vibrate. The same number of people, 23, as was there at the time of the shaking on July 5, participated in the simulation exercise.

A professor from the Architectural Institute of Korea who participated in the inspection of the building told a radio program that the most likely cause of the shaking at the mall was from vibrations caused by “taebo,” an aerobic sport which is a mixture of taekwondo and boxing.

“The same kind of vibrations were felt at the higher stories of the building when we performed a simulation of the exercise at the fitness center Sunday,” said Chung Lan, professor of Architectural Engineering at Dankook University at Jukjeon campus.
Vibrations measured on a vibrometer installed at the 38th floor of the building were ten times greater than usual.

The tentative conclusion was the consensus among the six professors from the architectural institute and vibration measurement experts who participated in the building’s inspection, he said.

“We used a laser Doppler vibrometer while performing the same kind of aerobic exercise that was performed at the time of the shaking which occurred on July 5. We noticed that the shaking was felt in the upper floors while the exercise was being performed but no other place showed signs of vibrations,” said Chung.

Mechanical resonance is the most likely explanation for the vibrations, according to the inspectors.

“It just happens to be that the vibration set up by the “taebo” exercises coincided with the resonance frequency unique to the building,” the professor said. When an external vibration hits the resonance frequency of a certain object, the vibration is amplified and causes excess shaking even from slight movement.

“The new fitness instructor apparently carried out the exercise twice as hard as usual. That must have been the reason,” said Chung.

However, the conclusion drew public criticism. Many bloggers and Twitter users posted messages critical of the inspection outcome.
“If the real cause of the vibration was the exercise, then shouldn’t the people who built the shoddy building be held accountable?” tweeter Stefanet quipped.

Another tweeter honeypooh37 said, “It’s really ridiculous that a building shook due to an exercise at a gym.”
The final results of the detailed safety inspection will be released in two months by the Architectural Institute of Korea.

"테크노마트 흔들림 원인은 '태보' 운동"
군무 시연 때 38층서 흔들림 관측…"안전성 문제 없어" 39층 높이의 서울 광진구 테크노마트 건물 고층부에서 나타난 흔들림 현상은 당시 12층 운동시설에서 단체로 했던 '태보' 운동 때문인 것으로 드러났다. 대한건축학회와 테크노마트 건물주인 프라임산업은 19일 오후 2시 테크노마트 사무동에서 진동 원인규명 설명회를 열고 "피트니스 센터에서 평상시와 다른 군무(群舞)를 한게 흔들림의 원인일 가능성이 크다"고 밝혔다. 학회 측은 이날 한국시설안전공단이 5일 발생한 건물 흔들림 원인으로 추정한 사무동 12층 피트니스 센터에서 당시와 비슷한 23명을 동원, 태권도 동작을 응용한 '태보' 운동을 하는 공개 시연을 했다. 그 결과 38층에 설치된 진동계측기에는 상시진동수(평상시 진동 크기)의 10배 정도 되는 흔들림이 관측됐다. 진단에 참여한 이동근 성균관대 건축공학과 교수는 "군무를 시연해본 결과 평상시보다 매우 큰 진동이 고층부에서 관측된 것"이라며 군무가 원인이라고 잠정 결론을 내렸다. 이 교수는 "조사해본 결과 평소와 달리 지난 5일 태보 수업에서 같은 동작을 20분간 반복했다고 한다"며 "건물의 고유 진동수와 당시 실시된 태보 운동의 박자와 일치하는 2.7㎐ 박자에 맞춰 바닥을 구르는 운동을 재연한 것"이라고 설명했다. 그는 "이는 건물 고유의 특성인 진동 주기가 하중(외부 흔들림) 진동과 일치하면 에너지가 누적돼 진동이 커지는 '공진' 현상"이라며 "1831년 영국 브로스턴 다리를 군대가 발을 맞춰 행진하자 갑자기 무너진 적도 있다"고 덧붙였다. 하지만 "지금처럼 강한 정도의 태보 운동으로 진동이 계속 전달돼도 사람들이 불편하게 느끼는 '사용성'을 해칠 수는 있겠지만 건물 '안전성'에 지장을 주는 정도는 아니다"며 건물 붕괴 등 우려에 대해서는 선을 그었다. 정란 단국대 교수는 "구조적으로 문제가 생겨서 생긴 진동이라면 잠깐 충격적으로 오고 말지만, 이번 진동은 10분간 지속됐기 때문에 내부에서 원인을 찾아야 한다고 판단해 진단을 실시했다"고 설명했다. 정 교수에 따르면 당시 진동의 주기는 대략 0.3∼0.4초로 추정됐는데, 각 층의 공조기(에어컨)와 기계실, 4D 영화관 등의 진동은 40∼60볼트로 빨랐기 때문에 피트니스 센터가 원인으로 지목됐다. 정 교수는 "일부에서 바람때문에 건물이 흔들렸다는 의견을 제시했지만, 바람의 진동은 5∼7초로 이번 흔들림과 맞지 않다"고 지적했다. 학회와 프라임산업 측은 앞으로 상시진동과 태풍이 올 때의 진동 등을 계측하고 정밀진동해석, 정밀안전진단 등을 통해 건물 사용성과 안전성을 보다 정밀하게 평가하고서 2∼3개월 뒤 최종 결론을 내놓을 예정이다. (연합)
Emailysy@koreatimes.co.kr Article ListMore articles by this reporter
 
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