PROBLEM TO BE SOLVED: To prevent a crack of concrete by returning its height to the same height as a receiving stand of the other place after concrete is placed in a condition where outer shell sheet plate is made higher than the periphery. ;SOLUTION: When concrete is placed on a lower floorboard 5 of a synthetic structure caisson 1 composed of an outer shell steel plate 2 where T shape steel 7 having a projection is welded to the inside surface side and concrete 3 placed on the side to which the T shape steel 7 is welded, the concrete 3 is placed by holding a height of a receiving stand 12 of a part where an upper surface of the concrete 3 receives tensile force at supply time in a condition of being made higher than a receiving stand 11 of the other place. After the concrete 3 is hardened, the height of the receiving stand 12 is returned to the same height as the other receiving stand 11. Therefore, since prestress froce acts on a concrete surface by deflection of dead weight, when this prestress froce is offset to tensile force at supply time, a crack can be prevented.;COPYRIGHT: (C)1997,JPO
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