Nagoya Television Tower, which is currently undergoing seismic reinforcement work, saw the completion of the process of cutting off its four pedestals from its underground concrete foundation on Oct. 23, making it look as if it is floating in the air.
The work was conducted to create space to insert seismic isolators underneath the 180-meter-high tower, which weighs 4,000 tons. The pedestals are temporarily supported by four hydraulic jacks.
The tower was completed in 1954 as the nation’s first transmission tower. Due to aging, there is a danger that part of its steel frames will fracture during an earthquake measuring an upper 5 on the Japanese shindo scale, although the tower itself is unlikely to collapse.
The seismic reinforcement work is part of the project to renovate the tower, including building a hotel and a high-end restaurant inside, before it reopens in July 2020.
The pedestals were cut off from the foundation at about 5 meters underground after they were bound together by steel frames to prevent them from spreading due to the weight of the tower. After 2-meter-high jacks were inserted, the old concrete foundation was cut off by wire saws.
“There are various types of seismic enforcement works for buildings, but as for seismic isolation of steel towers, it is necessary to make sure that the pedestals won’t spread outwards due to the load,” said Toru Tokuno, head of the construction office of Takenaka Corp.’s Nagoya branch in charge of the project.
After seven seismic isolators of four different types, including laminated rubber, are installed under each pedestal, the jacks will be removed by the end of this year.
According to the tower’s operator, by adopting this construction method, it becomes possible to reduce the extent of drilling and dismantling, thus saving on construction costs. The seismic reinforcement work is expected to total some ¥900 million.
After work is completed, the damage to the tower will be minimized even in the case of an earthquake measuring an upper 6, they said. The government predicts there is a 70 percent to 80 percent chance of a massive earthquake occurring along the Nankai Trough close to the Tokai region within the next 30 years.
“This is the only way to conduct seismic isolation works without changing the appearance of the tower,” said Kazuhiro Osawa, president of the operating company. “It was a big day in history, since the tower legs were separated from the earth and the tower will born again.”
This section features topics and issues from the Chubu region covered by the Chunichi Shimbun. The original article was published on Oct. 24.