support the hydraulic excavator, it is common to connect the upper and lower slabs with a support pipe and to support them with multiple layers. However, instead of this support pipe, there is also a method to place unreinforced concrete in place of this support pipe and to demolish the floor slab in the end. Since it is straight, it is easy to break and the prices are reasonable.The Japan Demolition Contractors Association provided research grants and is working on the evolution of demolition technology, and plans to hold a research presentation once a year that summarizes research results. Although my laboratory also uses this grant, it is expected that the level of the industry as a whole will be improved by sharing the technology developed within the industry and to incorporate it into a common technology system.Research on demolition method also contains the integrated aspect of joint research with other general contractors, but since demolition technology itself is owned and accumulated by the demolition business, general contractors will help systematize the demolition technology by thinking about the mechanism. By doing so, it seems that the roles of demolition technology can be shared evenly with each other. Even during the demolition work of the Akasaka Prince Hotel, which has attracted the attention of society in recent years3), it was the general contractor that constructed the entire system, but the demolishing contractor was in charge of the elemental technological areas such as crushing and cutting/disconnecting. At present, it has been said that out of all the existing technology, “crushing”, is the most used demolition technology. Most of the buildings can be demolished using the crushing technology and is considered the most efficient out of all existing technologies. However, it seems that there are many cases in which another method is deemed fit when the crushing technique is not enough. Use of wire saws and manual crushing are also important techniques, but they are only for auxiliary positions. Since many experiences and knowledge have been accumulated through crushing, the motivation to actively adopt new technologies are not at its highest priority at this point.Looking back, the crushing method was once a new technology, and demolition work started with the breaking of concrete using chisels, so one can say that great progress has been made since then. It may not be possible to expect any further evolution from this crushing technology.Challenges the current demolition methods will face in the future includes: (1) increasing the number of layers and (2) measures for higher strength.Around the year 2010, major general contractors have simultaneously developed practical use of demolition methods for skyscrapers. It is preferred to look at the details separately, but there are differences between “demolition from above” and “demolition from below”. Nonetheless, there are correlations when you look as a whole. Perchance, general contractors realized the need for noise, vibration and waste countermeasures that demolition work up till now has unaddressed. I presume that general contractors would appeal new strategies of demolition work with the subject being skyscrapers. However, these construction methods are presumably steel frame construction and it is difficult to apply them onto reinforced concrete constructions or steel frame reinforced concrete construction.High-rise buildings in urban areas are often in close proximity to neighboring buildings, and the construction conditions for demolition work are very strict. It is necessary to minimize the impact on the surrounding environment due to noise, vibration, carry-out of by-products, etc., and consider the scattering of harmful substances such as asbestos and dioxins. In the demolition method for skyscrapers, panels are used to cover the demolition floor to prevent scattering outside, and the demolition work is performed in a closed construction environment but recently, similar measures have been taken for high-rise buildings. Regarding soundproof panels, it seems that the conventional general soundproof panels are sufficient, rather than developing special ones for demolition.Compressive strength tests in Japan are performed on φ20 × 100 mm cylindrical specimens. Therefore, for countries using 100×100×100 mm test specimens, the following Japanese values need to be multiplied by an estimated ×1.2. The standard compressive strength of concrete used in general reinforced concrete buildings ranges from 18-36 N/mm2, but with the evolution of concrete technology, high-strength concrete of 60 N/mm2 class has spread in Japan, and currently there are ultra-high-strength concrete exceeding 150 N/mm2 which has also been put to practical use. In the past, super-high-rise buildings were mainly made of steel but with the progress of higher strength and ultra-high strength of concrete, high-strength reinforced concrete construction has become more mainstream. This is due to great merits in terms of 4.1 Response to High-rise Buildings (Skyscrapers) 4.2 Measures for Higher Strength ─ 23 ─4. Future Issues of Demolition Method
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