Study On Construction Monitoring Of Prestressed Concrete Low-pylon Cable-stayed Bridge

Low-pylon cable-stayed bridge, characterized by low pylons, stiff girders and cables of low vertical load sharing rate, is a new type of bridge developed in the last 30 years. The low-pylon cable-stayed bridge must be monitored during construction to ensure the safe bridge structure and to achieve the desired completion state. Construction monitoring includes theoretical parameters such as alignment and stress calculations in construction stages and practical data collection and analysis. Construction is based on the theoretical control parameters. Then the control parameters should be adjusted according to the deviation between the actual structure state and the theoretical structure state to ensure the desired completion bridge state.In order to understand the alignment and stress state at any construction stage, the finite element analysis software Midas Civil was used to bridge construction simulation calculation, and the factors which affect the accuracy of modeling calculations were analyzed. According to calculations, the material parameters in the model, the location of prestressed steel strands, construction loads and construction scheme have great effect on the analysis result. So they must be same with the actual structure.A perfect monitoring system was established in Nanping Bridge Monitoring to monitor the alignment and stress effectively. The sunshine temperature differences have a significant impact on the alignment and stress. Measuring and lofting should be in the morning or at night to avoid the effect of the sunshine temperature difference as much as possible. The stress meter measuring result includes the impact of concrete shrinkage and creep, which must be deducted when analyzing the data. The value of concrete shrinkage and creep can be calculated in the model. It is a very effective method to deduct the value of concrete shrinkage and creep.Frequency method can measure cable force easily, but there are some measuring errors. With a small dip, the cable of Low-pylon cable-stayed bridge is affected by self-weight sag. Besides, the cable is affected by bending rigidity greatly due to the short cable. Measuring result shows the error of the first four cables is longer than last long cable. Different orders of frequency iterative method can avoid the effect of bending stiffness effectively. When the bridge alignment or stress deviates from the ideal state, the cable force should be adjusted. Matrix method and unstressed cable length method are important methods to calculate the value of cable adjustment. They can satisfy the requirements of cable adjustment calculating very well if they are used in combination.Sometimes cable duct is misalignment with cable, and this will inevitably affect the cable's performance and work life. Through the analysis of factors affecting the cable duct location change, cable duct positioning parameters correction formula was established to ensure the accuracy of cable duct's position and angle.