Mechanical Behavior Research Of Abnormal Shaped Anchorage Zone Of Cable-stayed Bridge Pylon

Anchorage zone is the key area of cable-stayed bridge pylon. The analysis of the mechanical performance of the anchorage zone is widely studied in the cable-stayed bridge, and the anchorage zone is the technological difficulty in the design and construction of cable-stayed bridge. Although many research of the anchorage zone of cable-stayed bridge pylon has been conducted in recent years, and those achievements provide valuable references for the design and construction of cable-stayed bridge, some problems still exist and need to be solved, such as:many researches focused on the pylons with rectangular section, whereas the researches regarding the abnormal shaped section are scarce; finite element analysis is usually based on the linear elastic theory and ignores the long-term effects of concrete; and the design and optimization methods for the anchorage zone of cable-stayed bridge pylon are very rare, etc. Therefore, studies on the mechanical performance and optimization method for the abnormal shaped anchorage zone of cable-stayed bridge pylon are necessary and significant in practical engineering.Based on the full-scale segment model test on the abnormal shaped anchorage zone of Maling River cable-stayed bridge pylon, the abnormal shaped anchorage zone of cable-stayed bridge pylon are studied by using finite element method (FEM), strut-and-tie method (STM) and mathematics programming method, etc. The studies are focused on four parts:full-scale segment model test on the abnormal shaped anchorage zone of Maling River cable-stayed bridge pylon, overall analysis of the anchorage zone of Maling River cable-stayed bridge pylon, optimization analysis of anchorage zone and thermal analysis of the anchorage zone of Maling River cable-stayed bridge pylon. These studies are concluded as:(1) The full-scale segment model test on the abnormal shaped anchorage zone of Maling River cable-stayed bridge pylon and its FEM analysis indicate that the outside of the joints between the polyline long side and short side, and the inside of polyline long side are the most dangerous zones, which require being strengthened. Cracking resistance of the polyline long side is weaker than that of the linear long side. The inside corner of linear long side cracks at load level 1.6 F0, whereas the inside corner of polyline long side cracks at load level 1.4 F0. Stress redistribution occurs in the outside of polyline long side. Before cracking, the stress was linear with load and its value was close to the theoretical one, which validate the finite element model. Cracking resistance coefficient of the full-scale segment model is no less than 1.3 and the destruction coefficient is no less than 1.6, which means the structure has an adequate safety capacity.(2) The comparison of the theoretical result of the segment model and the whole pylon model indicates that the stress distribution of the segment model and the whole pylon model is generally similar and the conclusions are the same, which mean the theoretical analysis of the segment model is correct, and the segment model and its boundary condition are viable in the FEM analysis. There exists prestress blind zone in the outside of the long side around the tendons anchorage zone, and great additional tensile stress occurs in the blind zone under the cable force. In consequence, the horizontal hoop reinforcement is suggested to be strengthened in the blind zone to withstand the great additional tensile stress. The decay of the stress effect of prestressed tendons and that of the cable force along the pylon in the whole pylon model are analyzed. The stress decay effect in short side is remarkable than the long side's, which indicates that the stress effect transfers in a small area in the short side and concentrates in the cable anchorage. As a result, the hoop prestressed tendons should be disposed around the cable anchorage to achieve good stress capacity.(3) Strut-and-tie method (STM) is an accurate and reliable design and optimization method for the anchorage zone of cable-stayed bridge pylon. Based on the internal flows of forces in the anchorage zone, the STM analysis reflects the real stress field in the anchorage zone which accords with the actual need of a structure. The STM analysis not only saves the quantity of the prestressed tendons, but also optimizes the layout of the tendons. For example, the quantity is reduced by 21%, the tendons is preferable to lay near the outside of the short side and lay near the inside of the long side. The section shape of the anchorage remarkably influences the layout of the prestressed tendons and the mechanical performance of the pylon structure, optimal section obtained by STM not only reduces the tendons' quantity by 26.3%, but also enhances the cracking resistance coefficient to 1.6. It means that the optimal pylon section could not only saves the prestressed tendons but also strengthens the cracking resistance.(4) Considering the influence of sun radiation, the sun radiation can be regarded as the rising of the air temperature, and thus the third kind boundary condition can be achieved to take thermal analysis of the anchorage zone. When the worst temperature distribution of the anchorage zone in summer or winter is obtained, the stress distribution of the anchorage zone under the temperature load and the cable load can be analyzed. Regardless in summer or in winter, the anchorage zone of Maling River cable-stayed bridge pylon will not crack.The paper focuses on the mechanical performance and the optimization design of the abnormal shaped anchorage zone of Maling River cable-stayed bridge pylon. It provides references for such abnormal shaped anchorage zone as nonaxisymmetrical sexangle section. Due to the limitation of testing conditions, in this paper, we study relevant problems based on Maling River cable-stayed bridge pylon, some problems such as the development of design tools based on STM, multi-factors optimization considering section shape, dimension and line shape of the tendons, nonlinear ultimate analysis of the anchorage zone and long term effect analysis considering creep, etc. deserves further research.