＊ Professor, Department of Architecture and Architectural Engineering, College of Industrial Technology, Nihon UniversityKeywords: Demolition, Skyscraper, Steel Structure, JapanIn Japan, there are currently more than 700 skyscrapers with a height of 100m (328 ft) or more. The function and performance of the skyscrapers that were at the forefront a couple decades ago at the beginning of construction were obsolete after 30-40 years. In recent years, it has been discovered that long-period ground motion during an earthquake is a problem in high-rise buildings. There is a limit to the reinforcement and renewal, and it is expected that reconstruction of super high-rise buildings will increase in the future.In 2012-2013, the new building of Akasaka Prince Hotel in Tokyo (39 floors above ground, 1 floor of penthouse, 2 floors of basement, 138.9m (456ft) in height) was demolished. In Japan, as well as from the international community, the general public were intrigued and the news was widely featured on TV and newspapers. Demolition of a skyscraper that exceeds 100m (328 ft) in height leads to unresolved issues in the conventional demolition method that needs to be addressed. Skyscrapers are mostly located in urban areas, and there are many restrictions on demolition work compared to suburban and rural lands. There is a wide variety of issues that must be resolved: the wind in the sky being several times higher than that on the ground, the work of installing and removing temporary scaffolds, curing materials being a dangerous task at high places, dust being scattered over a wide area, the risk of dismantling members getting injured increasing, noise complaints and the propagation of vibration.The five major general contracting companies in Japan have been paving the way in proposing the demolition skyscrapers through various technological developments. The outline of each company will be introduced based on the materials released by the Japan Construction Federation and the information published on the website regarding the demolition of skyscrapers. Jacks installed at each pillar position in the lower floor support the entire building and demolishes the lower floor. For each column, the jack is promptly operated to support the load on the upper floor for each demolished layer, and when the demolishing of the same layer of the entire building is completed, the entire building is brought down with all jacks. This is a method of repeating demolition work by repeating this procedure. With this method, noise and dust scattering can be suppressed compared to the conventional demolition methods. In addition, because constant work is always repeated near the ground, it is not necessary to refill environmental measures equipment and construction equipment. Also, the factors affecting the surrounding environment can be ensured at a fixed place and can be addressed steadily. Effective measures are taken to improve safety by reducing work in high places. The jacks installed on the lower floor will support the entire load of the upper floors, but to prevent earthquakes, a reinforced concrete core wall is installed before dismantling and seismic resistance is secured by the seismic mechanism using load transfer beams. This procedure was first applied in 2008 in the demolition work of the former Kajima Corporation （Received February 27, 2021）─ 29 ─日本大学生産工学部研究報告Ａ2021年 12 月 第 54 巻 第 ２ 号1. Introduction2. Kajima Corporation “Kajima Cut and Down Method”: Fig.1DocumentNoboru YUASA＊Demolition of Skyscrapers in Japan
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