5. Layout for Disassembly and Demolition habitability, especially in housing complexes.In the case of a steel frame structure, the steel frame member is disassembled by cutting, but in the case of a reinforced concrete structure, it is common to crush the concrete with the reinforcing bar inside. However, if the strength of concrete becomes high and the diameter of the reinforcing bar becomes larger, it becomes difficult to crush the concrete and cut the reinforcing bar. Machines would wear out faster, and construction efficiency will be reduced.In my laboratory, we make 150-180N/mm2 class specimens to conduct experiments. In conclusion, the current crushing technology can be used. The reason behind this being, crushing is a method of breaking not by compressive force but by tensile force (concrete tensile strength does not change much even if the compressive strength increases).However, the practical limit of adoption, which commensurate with the economic activity of the crushing method, is up to a standard strength of 60 N/mm2 or less, and above that, the load on the attachment would be too large, and there would be difficulties due to noise and vibration.Therefore, for parts that exceed the standard strength of 60 N/mm2, (1) at the dismantling site, use a cutter or wire saw method to cut the target parts into a size that can be placed on a truck and carried out, (2) reuse or crush/classify the materials in the work field to be used as a high-quality recycled material.In many cases, parts that use ultra-high strength/high strength concrete are often limited to parts of the lower floors rather than the entire building. In addition, ultra-high-strength and high-strength level concrete is rich in cement, has high recycling value, and can be a high-grade recycled aggregate.Furthermore, I would like to introduce the research that concludes these points given another opportunity.I have once asked several demolition contractors whether they could use parts of the reinforced concrete columns and beams for the next planned structure. Their answers didn’t meet my hopeful expectations and were responded with either “not profitable” or “I have no idea”. It seems more realistic now to break it down into smaller pieces and recycle, rather than to cut it clean and reuse it. Many of the buildings that are to be demolished are ineligible existing buildings, and there is also the point that they will not be suitable as diverted members in light of the current seismic regulations.I mentioned the demolition of high-strength concrete, but the higher the strength level of a new structure, the more convenient the method of bringing in PCa (precast) parts to the site and constructing them rather than casting-in-place due to construction management. However, I have wondered if demolishing still can be done if we see the light of this unfavorable situation. Although the old ones have limitations, it seems to me that the technical level and management level are high enough that the constructed structural parts can be diverted enough now into the future. In addition, the higher the strength and the harder it is to break, the higher the added value as a diversion part should be.Perhaps it is not so difficult to devise a joint of parts at the time of design so that it can be used both during construction and demolition. When we incorporate proper measures during the designing phase of construction, it is possible to realize the benefits: facilitated demolition and reduced by-products.A systematic and safe disassembly must be considered and general contractors should definitely think in that direction. In a few years, there may be new advertisements in this direction.Both at the Great Hanshin-Awaji Earthquake in 1995 and the Great East Japan Earthquake in 2011, the biggest issue for early recovery and reconstruction was the early processing/treatment of debris.Many demolition contractors own a lot of heavy equipment and has a technology where you can move/discard debris. There was an agreement with the local government, and in such an emergency, the contractors dispatched quickly and have devoted their efforts to debris disposal. All of these contributions have been recognized and they were awarded by the Ministry of Land, Infrastructure, Transport and Tourism and the Ministry of Environment.With this recurring revision of the Construction Business Act, there is still a concern that there will be a shortage of future workers due to an increase in the number of employees leaving the workforce and a decrease in the number of young employees entering the field. In response to this issue, proper construction during demolition and security of the people who carry these works need to be addressed. The market in the demolition business will continue to increase in the future. It is important to improve the working environment and working conditions and to promote proper education of human resources in order to recruit young and enthusiastic skilled workers and retain skilled workers.Until now, demolition work was included in the civil ─ 24 ─When Newly Established6. Expectations for the Demolition Work
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