Research On Technique Of Construction Surveying Of Single Tower Cable-stayed Bridge

Cable-stayed bridge has become the fastest growing and the most competitive bridge type in modern bridge construction for its excellent spanning ability, rational stress system and novel structure. The cable tower is the primary load-carrying member and an important component of cable-stayed bridge. Almost all of the mobile load and permanent load of cable-stayed bridge pass through the cable tower down to the tower pier and foundation. Therefore, the stress on the cable tower is very complex. Only ensuring the geometrical shape and spatial location of the tower complying with the design requirements and specifications and the precise positioning of cable ducts, can an ideal geometric shape and rational state of internal force be achieved. All of these require strict cable tower measurement. As its height raises during the tower construction, the atmospheric refraction coefficient and daily deformation caused by sun exposure affect the measurement greatly, which thus requires in-depth research into the measurement method of cable tower, daily deformation rule and the atmospheric refraction coefficient, to ensure the quality of cable tower.This paper first studies commonly-adopted methods of measurement during the construction of cable tower and analyzes the advantages and disadvantages of each method and makes comparison. Based on the actual conditions, it also adopts precise zenith datum method, steel hanging elevation transferring method, relative datum coordinate and spatial linear formula 3-D coordinate method for cable tower measurement and the precise positioning of cable ducts of Liang-Ji Canal, ensuring positioning accuracy and expediting construction.The temperature distribution fit formula for cable towers of Liang-Ji Canal bridge is obtained through field measurement of the temperature of each wall of cable towers under different sun exposure and the section temperature distribution fit of cable towers based on measured data. Computation models for cable towers of 50 m, 75 m and 102 m high are constructed respectively through ANSYS, and a systematic analysis of the deformation rule under different temperature is made. Through calculational analysis and comparison with measured data, the basic daily deformation rule of cable towers of different heights is obtained. The deformation of cable tower becomes greater as the tower becomes higher. The maximum displacement is about 3.5cm in south-north direction and its general variation is consistent:the swing direction of cable tower is basically consistent with the rotation of the sun, the direction of deformation lagging behind the direction of sunlight.Finally, the analysis of the atmospheric refraction coefficient experiment shows that the atmospheric refraction coefficient is closely related with underlaying surface and meteorological factors. Its change shows obvious daily rule provided the stable external environment. Some measures to reduce the impact of refraction coefficient during measurement are put forward.