| At the background of National Important Project, HongKong-ZhuHai-Macao Bridge, the large diameter steel tubular composite (STC) pile model tests are conducted. Shear-ring, drilling mud skin and anti-corrosion coating are considered under complex force combinations in an attempt to specify the different performances. Research results provide theoretical and testing reference to STC pile design.The detailed works include:1. Nine STC piles tests were performed with different combinations of shear-ring, drilling mud skin and anticorrosion coating. Bearing capacity and the deformation of reinforced concrete pile see better improvement when the STC pile is applied.(1)The bearing capacity of the STC piles with shear-ring, drilling mud skin and anticorrosion coating is 1.9 times of the reinforced concrete piles. So the STC piles obviously have a better capacity.(2) Drilling mud skin and anticorrosion coating could induce the reduction of deformation characteristics and carrying capacity of STC pile. Experimental results show that, compressive stiffness and decreased by 3% and 1% respectively (thickness of about 0.1 mm). Flexural rigidity fell by around 1% and 1%～2% respectively. The influence is relatively small and manageable.(3) Deformation performance and carrying capacity of pipe and core concrete of pile are improved significantly by shear-ring. Under the experimental conditions in which shear-ring spacing is set from 1D to 3D, cross-sections see inverted "v" or "m" distribution of train. It indicates the stress from core concrete is effectively transferred to pipe by shear-ring. In addition, performances are best improved if shear-ring spacing is set as 2D (60cm)2. Based on the test results, systematic research begins in an effort to find the collaborative work performance, working principle, confining effects and the bearing capacity of the STC piles. Different combinations of the drilling mud skin, anticorrosion coating and shear-ring are considered under the compressing-bending-shear forces.(1)The confining effect increases the strength of core concrete due to the co-working of drilling mud skin, anticorrosion coating and shear-ring (spacing of the shearing ring is 3D).(2)The complex carrying capacity of STC pile is greater than the total carrying capacity of steel pipe and core concrete pile. Under the experimental condition, STC pile (with shear-ring, drilling mud skin, anticorrosion coating, D/t=100, shear-ring spacing=3D) carrying capacity increased by 9.8% compared with the sum of steel pipe and concrete pile.(3)The stiffness formula of the STC pile during the elastic deformation phase by the principle of superposition, and the effluence of the shearing ring on the stiffness is explored. Under the experimental conditions, accretive effect of shear-rings and their space are showed with a hyperbolic relationship.(4)Finally, the formula is proposed when the STC piles are loaded by the axial forces, the inner limiting capacity of the STC pile with shear-ring, drilling mud skin, anticorrosion coating can be calculated by the code ACI(2005).3. Five push-out tests provide essential materials to perform separate studies of the cohesive mechanism in pipe-concrete interface and distribution discipline of cohesive forces. Conclusively, drilling mud skin, anticorrosion coating and shear-ring all prove viable in improving bong-slip behaviors of the STC pile.(1)Pipe-concrete cohesion indicates to be 0.242～0.404MPa and a less than 0.2mm figure is found in relative slippage when cohesion area collapses, with all tests conducted under force-bending-shear force.(2)Shear-ring leads cohesion rises 66.7% when drilling mud skin, anticorrosion coating and shear-ring(spacing<2D) are all involved in the tests, indicating the cohesion at pipe-concrete is thus liable.(3)In theory, the dependence between pipe stress, cohesion at pipe-concrete interfaces and relative slippage are analyzed. Exponential relationship between cohesion and length of interface is assumed in effort to deduce the analytical expression of steel pipe stress, cohesion and relative slippage. Thus, a bong-slip constitution model is proposed and verified through the test results.4. FEM software ABAQUS proves to be applicable to perform a deeper research of performance of the STC pile under force-bending-shear forces.Validation of FEM model is verified by selecting appropriate FEM model. Based on the fundamental model, sensibility of parameters such as shear ring spacing, cross-section format and steel thickness is analyzed in the study. |
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