Movable Formwork Wider Girder Box Beam Simulation And Control Parameter Sensitivity Analysis

Movable formwork method has been adopted widely to construct multi-span continuous bridges with high piers and medium spans since it has the attributes of fast construction speed, high mechanization degree, small floor occupation and less disturbance to navigation. In recent years, using this method to construct the constant section box-girder bridges and the relevant research have been excessively studied, but any application and research are hardly reported for varying section bridges.In this paper, a cast-in-situ varying section and width prestressed concrete continuous bridge is used as the support project. A method, which incorporate finite element simulation with orthogonal test, is utilized to analyze the influences of several design parameters on girder deflection in construction phase and service phase. A sensitivity coefficient of each parameter to the girder deflection and its formula are proposed. Then the coefficient of different parameter to different joint’s deflection in the construction phase and service phase when the bridge is constructed by varying width movable formwork. Finally, the importance of each parameter and the key joints are determined to provide theoretical basis and guidance to alignment control in PC continuous bridges, which are constructed by movable formwork method. Moreover, that will give experience and references for similar projects in the future. The details of research content and relevant results are shown as follows:1)On the basis of the shear flexible beam grid method theory, the construction process of a varying width PC continuous box-girder bridge with 5 spans and varying sections in the Xiutu interchange of the Quanzhouwan Bay Bridge, which is constructed by the down-moving movable formwork, is simulated and analyzed. Subsequently, the reliability of using the beam grillage theory to simulate alien wide girder structure is validated.2) In order to mitigate the hogging of the cantilever end during the movable formwork construction phase, the unknown load factor method is adopted to calculate reverse punch forces at each cantilever ends. These forces are optimized, aiming at keeping the deflection value of cantilever end within ± 5mm during the construction process and fulfilling a smooth vertical alignment.3) The formula of sensitivity coefficient of each design parameter to different joint’s deflection is proposed The coefficients of several parameters, such as concrete density and elastic modulus, prestressing tendon’s tensioning stress and the influence coefficient of pipe local deviations per meter on friction, relative humidity of environment, load age, temperature fluctuations and movable formwork stiffness, to the vertical deflections of certain joints on girder are calculated. The results indicate that the end point of the third cantilever is sensitive to most of the aforementioned parameters, while the 3L/4 joint on the two middle spans and the first cantilever end point are less sensitive to those parameters than the third cantilever end but still significant.4) Multi-level-factor orthogonal test is utilized to a further study. A comparison analysis is conducted to discuss the sensitivities of seven different parameters to the vertical deflection of the most sensitive points, the third cantilever end point, when the PC continuous box-girder bridge is constructed by down-moving movable formwork. The results show that the vertical deflection of that point is sensitive to prestressing tendon’s tensioning stress, concrete density and elastic modulus, among which the first one is the most important factor.