Study On Key Issues In The PC Pylon Of Long-Span Cable-Stayed Bridge

Two key issues in prestressed concrete pylons of long-span cable-stayed bridges were studied in this thesis.In view of the phenomenon that the actual elongation of small radius U-shaped prestressing tendons in anchorage zone of pylons is slightly greater than the theoretic elongation, the following researches were mainly done:The factors that influence the elongation of the U-shaped tendons were analyzed and the constitution feature of the tensioning elongation of the U-shaped tendons was pointed out.Based on the research of the position change of small radius U-shaped prestressing tendons in the corrugated pipe during the tensioning process, the variation in geometric length of the tendons from the ideal state to that before the deformation of corrugated pipe was obtained. The compression factor ξ was introduced, and the formula to calculate the additional elongation of the U-shaped tendons was presented.The results show that expressing the geometry elongation induced by the deformation of the corrugated pipe as πS (S was the radial compression deformation of the corrugated pipe) is inappropriate, which exaggerats the geometry elongation of the corrugated pipe. Thus, a calculation method of the geometry elongation of small radius U-shaped prestressing tendons which caused by the deformation of the corrugated pipe was proposed.A general calculation method for the theoretical elongation of small radius prestressing tendons was developed, which could reflect the variety of effects and factors. The developed method for calculating the tensioning elongation was verified by the data obtained by field tests. The results show that the deviation of between measured value and calculated value of elongation can be controlled within the range (±6%) from the technical specification, which can fully satisfy the control requirements of tensioning small radius prestressing tendons.Using the compression factor ξ as a variable in the calculation of the theoretical elongation of small radius prestressing tendons was reasonable through the test of goodness of fit.The following aspects were mainly done for getting the formula to calculate the prestressing force in the wall of box pylon:According to the optimization principle of strut-and-tie model(STM), the STM of single anchor was established by means of force method. On the basis of the STM of single anchor, using firstly topology optimization result (Ft2=0)and force method, the STM in the facade wall was comprehensively solved. The relation of interference and independence between vertical components of the adjacent cables was revealed. Thus, the distribution of compressive and tensile stresses in the facade wall under the action of vertical component of cable force was accurately reflected.By the example study, the parameter α3=23.30was determined, and the STM in the facade wall was simplified with better engineering precision.The force and position of each member of the STM under the action of vertical component of cable force in the side wall were originally determined by using the geometric relationship of members in the STM. The whole STM of pylon anchorage zone in the side wall under the action of vertical component of cable force was firstly established.Based on the mathematical statistics and analysis of a large number data of horizontal dimension of pylons, a series of credible horizontal models were established. By vectorizing shape topology results of horizontal models, the whole horizontal STM of pylon was established. The variation rule of model parameters with width-thickness radio of the facade wall was explored, and the calculation formula of the maximum rod force under the action of horizontal component of cable force was presented.On the basis of study on vertical STM and horizontal STM of pylon anchorage zone, the general calculation formula of the prestressing force in the pylon wall was proposed, which can serve to design tendons for the pylon wall quantitatively and to determine pylon size and arrangement of prestressing tendon, which can greatly simplify the tendons design for the pylon wall.