| Summary: | 碩士 === 高苑科技大學 === 土木工程研究所 === 104 === A kind of unstable friction force existed in the interface between pile-cap core concrete and the inner surface of pile wall. Traditionally, the above friction force used by pile-cap treatment of pre-stressed concrete piles to be the transmit mechanism to take the forces came from upper foundation structure. Many cases show that it cannot be quantified and exist risks and potential instability defective. By pre-embedded horizontal shear reinforcement into the pile wall at pile-cap position, they could be a stable, completely and strong joint model with the cast-in-place concrete and vertical anchor reinforcement. The engineer could choice the diameter, layers, numbers of reinforcement to suit for the tension force in the pile-cap.
For this study, having a horizontal reinforcement in the pile-cap core concrete structure, use the pile-cap core pullout testing to determine the pulling force and calculate their theory capacity. It will be compared with the traditional pile-cap structure. The pile-cap anti- pullout testing use 2.0m as the depth of pile-cap core concrete, and multi-layer of horizontal reinforcements as shear reinforcement friction perfusion between the inner wall and the cast-in-place pile-cap core concrete, according to theUltimate Strength Design method (USD method).
Clearly defined a tension transmission model based in this research results that is different from the traditional model of foundation and pile-cap. The horizontal shear reinforcements provided a shear-friction results up to 371 tons when this pile-cap use 6 layers*2*2 of #6 rebar (D19) under a reduce factor of Φ=0.65 for allowable shear force capacity. The result of pile-cap anti-pullout testing shown that the ultimate anti-pullout force would be reach more than 371tons.
Because the allowable anti-pullout force of traditional pile-cap structure is to recommended as a value of 49 tons, the modified pile-cap can take anti-pullout tension force more than 7.6 times. The conclusions of this study include: using these horizontal shear reinforcements as improved structural components in bored pre-stressed concrete piles would get an anti-pullout force 7.6 times more than the traditional pile-cap structure, and it’s sufficient to provide adequate and stable bond behavior of the pile-cap. In practice, the design engineers can decide the diameter, layers and numbers of horizontal shear reinforcements to suit for the designed anti-pullout tension force in pile-cap. The deep foundation structures reveal a more stable and more solid pile-cap processing performance to withstand a total of three force of direct bearing load, reversed pullout tension and horizontal shear force came from upper structure.
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