Construction Control Study On Cables Replacement Project Of Concrete Cable-stayed Bridge

For many years, as cable wire corrosion and fatigue, anchor loose, concrete shrinkage and creep, bearing in settling bit, and the construction, maintenance and many other reasons, which lead to the bridge structure in some force security risks, many cable-stayed bridges builting in the last century have been or are facing the problem for cable replacement. At present, there are more than 100 cable-stayed bridges, only more than 10 cable-stayed bridges replaced the cables, it suggests that the remaining bridge will gradually need for replacing cables, so construction control for cables replacement of cable-stayed bridge will become an important research topic. In this paper, to take cables replacement project of the JiaoPingdu cable-stayed bridge as an example, it mainly studys on construction control for cables replacement of small and medium span cable-stayed bridge, the results are as follows:Firstly, we summarize and analyze current construction state for cables replacement of demestic and abroad cable-stayed bridges and dicuss the construction control theory, which includes construction control principles, methods, content, impact factors and simulation analysis for cables replacement of cable-stayed bridge; the paper also summarizes the characteristics and scope of parameters prediction methods on construction control for cables replacement of cable-stayed bridge and introduces the structure, learning, design and analysis of BP neural network. By comparing various prediction methods, BP neural network method will be used in construction control for cables replacement of concrete cable-stayed bridge.Secondly, according to the technical data of JiaoPingdu cable-stayed bridge, using structural analysis software named Dr. Bridge V3.0, which developed by Tongji University, builds the bridge plane frame model and simulates the construction process of cable replacement project. The cables replacement project calculated from two cases with different number of cables and different construction process and analyzed various situations effect on the internal force of the main beam and the tower, by comparision with the monitoring results of construction control, it summed up the various parameters changeable laws of construction control for cables replacement project, So it can be applied to similar cables replacement project.Finally, by using numerical analysis software MATLAB7.1 to compile the main beam deflection and cable tension prediction program that is based on the BP neural network method and building two-parameter prediction model of the construction process, it obtains predictive parameters values of the construction stage. By comparision with test values, The results showed that:the maximum difference of predictive values and measured values of cable tension is not more than±2 kN and the relative error is within±2%; the maximum difference of predictive values and measured values of main beam deflection is less than±0.3mm, they meet the accuracy requirements for construction control of cables replacement project, so predictive control is reasonable.After replacing the cables of JiaoPingdu cable-stayed bridge, the construction control results for:the elevation of main beam(measure point Y4 and S10)raised 4 to 5 millimeter in comparison with its former condition, the bridge linearity is improved after changing cables; the error rate between measured values and design values of cable tension is within 3%,and the cable force distributed steadily; the process of cables replacement affected less on the cable around and the concrete stress state of main beam, so the main beam is secure.