Abstract:Built in 1964, Nanning Bridge is one of the earliest cantilever reinforced concrete thin-walled box urban Bridges in China. Due to the limitation of the design concept at that time and the influence of the increasing traffic volume, the design load grade of the bridge is low and can not meet the requirements of the current load. In addition, after 45 years of operation, various diseases have emerged. OVM unbonded external prestressing system is adopted to reduce the secondary damage to the original structure in the process of reinforcement. In the design, the structure of the tooth plate is optimized to make the force of the tooth plate in a good state. At the same time, the construction method is optimized to make the connection between the new tooth plate and the original structure reliable; In the tensioning process, the "suspension" tensioning method is used to effectively prevent the damage to the working clip during the tensioning process. By adopting the above main strengthening measures such as unbonded external prestressing, the structural force is improved.

Abstract:The roof of the National Stadium adopts the two-way tensioned grid structure, and its prestressed construction has certain difficulty. The prestressed construction scheme and some preparatory work in the early stage of construction are introduced, such as construction simulation calculation and the design of tensioning tools. This paper briefly introduces the prestressed construction monitoring scheme and the synchronous control measures in the tensioning process, and combines the results of simulation calculation and field monitoring, puts forward the prestressed construction technology and characteristics of this kind of structure.

Abstract:A series of experiments were carried out to determine the process parameters of steel fiber reinforced concrete centrifugal forming. The effects of centrifugal time, centrifugal acceleration, coarse aggregate grading, steel fiber length and volume ratio on the distribution pattern of steel fiber in the cross section and longitudinal section of components were studied through the section test of centrifugally formed ring-section steel fiber concrete specimen, and the range of parameters for the application of centrifugally formed steel fiber concrete to the pole of power transmission line was determined To provide scientific research basis.

Abstract:Corrosion of steel bar caused by chloride invasion is one of the common diseases of concrete structure, so the ability of concrete to resist chloride invasion has an important influence on its durability. Chloride ion erosion test is an effective means to study the law of chloride ion invasion, but most of the current research results are aimed at ordinary concrete without stress, and there are few studies on concrete under stress. In order to study the chloride invasion resistance of concrete under stress, the concrete was soaked in salt solution and salt spray test. The test results of uncracked specimens under different water-cement ratio, stress state, stress level and working environment were obtained, and the results were compared and analyzed. The test results show that reducing the water-cement ratio can improve the chloride ion erosion resistance of concrete. The content of chloride ion in tensile stress state is higher than that in non-stress state. The content of chloride ion under compressive stress depends on the level of compressive stress. The effect of salt soaking environment on concrete structure is much more serious than that of salt spray.

Abstract:In this paper, the causes of concrete cracking and floor cracking of continuous rigid frame bridge box girder are analyzed, the mechanical mechanism of this phenomenon is deduced, and the suggestions and countermeasures to prevent such cracking are put forward.

Abstract:This paper points out the importance of antifall beam device for simply-supported beam Bridges in seismic-active areas, introduces the main application type of antifall beam device, its characteristics, selection methods and precautions, and describes the design steps, specific structures and engineering application examples of commonly used type of antifall beam device in our country. It is considered that the installation of anti-fall beam device will provide reliable guarantee for the safety of bridge structure in China under strong earthquake action.

Abstract:Cable force monitoring provides an important basis for the overall evaluation of cable technical status and then the performance of bridge overall structure. However, cable force monitoring is a long-term process, how to ensure the service life and test accuracy of the sensor in the long operation period is an urgent problem to be solved. The magnetic flux sensor cable force monitoring system solves the problem of sensor stress fatigue through non-contact measurement, and realizes data calibration of operating state through analog calibration, which has good durability and long-term performance.

Abstract:Based on the basic structure of bridge health monitoring system, a software of cable-stayed bridge health monitoring system is developed by using labwindows/CVI software. Its basic modules include data acquisition, GPRS wireless transmission, data storage and processing, etc. The software is successfully applied in a cable-stayed bridge project, and its effectiveness is verified.