4. Year 1965-1980 (From Wrecking Ball Method to Larger Breaker Method, and an Era of Pollution-Free Demolition Method)for demolition of foundations, floating slab foundations (slab-on-grade) and pavements. On the other hand, attempts were also made to drop the wrecking ball by using a triad (three-pronged) structure, and it seems that the reinforcing bars in concrete were often collected after separating concrete into small mass. Along with this came the domestic production of picks and breakers that were light and durable.Around 1965, among crane trucks and other large machineries, the use of wrecking balls as a demolition method has been more so established. In other words, it is a method of hitting the floor slab from the upper floor in subsequent order, pulling out the beams, cutting the beams, and finally pulling down the columns and walls.During the demolition work of the head office in the Bank of Japan from 1968 to 1969, a crawler crane/truck crane was used to vertically drop or shake a 1-2.5-ton weight (wrecking ball) to knock down concrete parts. (Fig. 4). In addition, a thick and heavy hose was laid around, and concrete was broken using many of the hand-held pneumatic breakers (Fig. 5). In this demolition work, iron mesh concrete in the vault (8mm wide and 6mm thick expanded metal sheets were stacked at intervals of about 25mm and pea gravel concrete was poured) were demolished. However, since around 1970, due to the social changes accompanied with an increase of vibration, noise and dust pollution, demolition methods of reinforced concrete structures using wrecking balls has become more desirable and fit.As a result, jacking method using hydraulic pressure Fig. 4 Demolition due to a wrecking ball (Bank of Japan Head Office around 1970)Fig. 5 Demolitions due to a hand breaker (Bank of Japan Head Office around 1970)Fig. 7 Crushing Method around 1978─ 37 ─Fig. 6 Jacking Method
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