Research On Construction Key Technology Of A-shaped Pylon Of Hybrid Girder Cable-stayed Bridge

Pylon as the main load-bearing component of cable-stayed bridge,the importance of it is self-evident.The ignorance of the function and quality of the pylon has caused some cable-stayed bridge pylons to appear crack,temporary transverse bracing or tie rod appear breakage or failure,and there was even an extreme case of the collapse of pylon B of the Chirajara Bridge in Colombia.Therefore,it is very necessary to study the force behavior of the cable-stayed bridge pylon and its construction technology.This article takes the A-shaped cable tower of a 530m main span double-pylon hybrid girder cable-stayed bridge as the engineering background,researches are carried out on the optimization of A-shaped pylon construction plan,the optimization of synchronous construction of pylon and girder construction plan and the analysis of influencing factors,the line shape of the cable pylon and the determination of the anchor point and pylon exit point coordinates of the cable stayed on the pylon.The main work and results are as follows:(1)According to the difference between the synchronous and asynchronous construction of the pylon limb and the middle beam,and the setting of the transverse bracing,three construction schemes of the pylon are optimized.After comparative analysis,It is determined that the synchronous construction of the pylon limb and the middle beam and the installation of 6 transverse bracing is the optimal plan,and the optimal plan was analyzed for the whole construction process,and it was verified that the stress of the pylon under this construction plan is in a safe range,and the rigidity and stability of the construction transverse bracing also fulfill the requirements.(2)Through the comparative analysis of the synchronous construction of pylon and girder before or after the construction of the middle beam,it is determined that the synchronous construction of pylon and girder after the construction of the middle beam is better.Establishing the finite element model of the full bridge for the construction of pylon first and girder late and synchronous construction of pylon and girder respectively,and analyze the stress and displacement of the main structure of the two construction methods during the construction process and the completed state of the bridge,and verify synchronous construction of pylon and girder under girder construction condition of asymmetry double cantilever of the mixed girder cable-stayed bridge is safe and feasible.However,the synchronous construction of pylon and girder has a greater impact on the longitudinal displacement of the pylon.In the completed state of the bridge,synchronous construction of pylon and girder is smaller than construction of pylon first and girder late,and the difference between the two longitudinal displacement of top pylon is-52mm.(3)The static wind load of the pylon has a great influence on the stress and displacement of the pylon.In the maximum cantilever of synchronous construction of pylon and girder construction stage,the longitudinal and transverse wind loads generated by the design wind speed of the 20-year return period will make the outside section of the connecting part of the pylon limb and the middle beam appear tensile stresses of 1MPa and 1.49MPa.In the completed state of the bridge,the longitudinal bridge-direction displacement of the pylon top is increased by 224mm under the influence of the longitudinal bridge-direction wind load generated by the design wind speed during the 100-year return period.Therefore,the pylon lofting for the synchronous construction of pylon and girder should carry out at low wind speeds as much as possible,and should closely monitor the deviation of the pylon during the construction process.(4)In the maximum cantilever of synchronous construction of pylon and girder construction stage,the-5℃ temperature gradient of the pylon cause a tensile stress of 1.29 MPa on the outside section of the connecting part of the pylon limb and the middle beam.The positive solar temperature difference of the main girder(T1 is 14℃,T2 is 5.5℃)cause a tensile stress of 1.59 MPa on the upper edge of the mid-span Z7 beam section.,and the solar negative temperature difference of the main girder(T1 is-7.5℃,T2 is-2.75℃)cause a tensile stress of 1.09 MPa at the upper edge of the side span B7 beam section.Therefore,during synchronous construction of pylon and girder construction process should closely monitor the temperature and stress changes of the structure to prevent excessive tensile stress from causing cracks in the pylon and main girder.(5)Setting the necessary amount of lateral pre-offset to ensure that the line shape of the pylon reaches the design line shape.Deducing the calculation formula for the anchor point and pylon exit point coordinates of the stay cable of the pylon,and set the necessary anchor point pre-lifting amount,finally use the coordinate calculation formula to calculate the anchor point and pylon exit point coordinates of the stay cable of the pylon after the anchor point pre-lifted.It provides theoretical coordinates for the construction positioning of stay cables.