Study on the Improvement in Bearing Capacity and Deformability of Prestressed High Strength Concrete Pile

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This report is the summary of the experimental study about the Prestressed High Strength Concrete Pile (PHC Pile) subjected to lateral load. The objective of this study was to investigate the reinforcing method by which the brittle failure could be prevented and the deformability of the pile could be improved.The B-type PHC piles of the Japanese Industrial Standard were mainly tested. The outer diameter of the pile was 30 cm. The magnitude of axial load was determined assuming that the pile was supported on firm stratum where the Standard Penetration Test Number was about 50. That is, 35 tf was for sustained loading. 0 tf and 70 tf were for temporary loading. 105 tf corresponded to the limit bearing load of the pile. The shear span to outer diameter ratio of pile was 3.0 assuming that pile head was fixed in the footing and the surrounding soil was fairly soft.As for the B-type PHC pile generally used in site, the amount of spiral hoop should be increased in order to prevent the brittle … More failure. It could not be prevented, however, under 105 tf of axial force, even if the pile was laterally reinforced by seven times amount of spiral hoop as much as that of generally used pile. So the specimens were reinforced as follows: the hollow part was filled with concrete and they were reinforced by high tension spiral hoop. The amount of spiral hoop was about 25 times as much as that of generally used pile. As the results, it was confirmed that the axial force of 105 tf could be kept until the displacement reached above 1/20 rad. in rotation angle of member.Furthermore, the experiment was carried out concerning the connection between the pile head and footing, in order to solve the problems generated by the rupture of longitudinal reinforcement and the cut-off of the pile head and to improve the deformability. As the results, the following method was proved to be effective for improving the axial load carrying ability and deformability: the amount of spiral hoop was increased, the pile head was cut off including longitudinal reinforcement of pile, the hollow part of the pile was filled with concrete, the deformed bars were longitudinally arranged in the filled concrete and they were bonded in the footing.The stress transfer mechanism in the pile-footing connection was analyzed. As a result, the fundamental data concerning the aseismic design of pile foundation subjected to lateral load. Less