FRICTION TEST AND PARAMETER ANALYSIS OF PRESTRESSED CONCRETE CONTINUOUS BEAM BRIDGE

The prestressed ducts of prestressed concrete continuous girder bridges are usually three-dimensionally distributed and long in length. The control of prestress loss during construction is very important. In order to ensure the effect of prestress tensioning, the test and analysis of friction parameters of prestressed ducts are particularly important. Based on the tension process of a prestressed concrete continuous beam bridge, the initial tension stress, loading time and channel friction parameters of the prestressed concrete continuous beam bridge are tested by field tests. Combined with the measured friction parameters, the finite element software Midas / Civil is used to analyse the influence of friction parameters on the mechanical properties of prestressed concrete continuous beam bridge. The results show that when the prestressed steel with bending angle not more than 40° and length not more than 70 m is stretched, the initial tension stress is suggested to be set as 20 % of the tension control force and the loading time is 5 min. The measured tunnel friction parameters are larger than the standard value, and the tension control force should be adjusted during the formal tension construction；The deflection of the key section of the main beam increases with the increase of the friction parameters, and the roof stress decreases with the increase of the friction parameters. The change of channel deviation coefficient has a greater impact on the deflection and roof stress than the change of friction coefficient

Research on the Prediction of Rigid Frame-Continuous Girder Bridge Deflection Using BP and RBF Neural Networks

To solve the problem of excessive deflection in the post-operation process of a rigid frame-continuous girder bridge and provide a basis for the setting of its initial camber, this paper, based on the results of finite element analysis, uses three methods to predict and verify the deflection of a rigid frame-continuous girder bridge. The results show that the average deflection method can be used to fit the average deflection value for a relatively long period of time and predict the average deflection value for the next longer period of time. Both the back-propagation (BP) neural network model and the radial basis function (RBF) neural network model can predict deflection well, but the RBF neural network model has higher prediction accuracy, with a mean absolute error (MAE) of 2.55 cmm and a relative error not exceeding 1%. The prediction model established by the RBF neural network has higher stability, better generalization ability, and better overall prediction performance. The established model has some reference significance for similar engineering projects and can achieve the optimization of structural parameters

FIELD EXPERIMENTAL STUDY ON EXTERNAL PRESTRESSING REINFORCEMENT OF A 420M PC CONTINUOUS BEAM BRIDGE

In this paper, the practical engineering of a 420 m PC continuous beam bridge is taken as the research object, and an external prestressing reinforcement method is proposed to reinforce the damaged and cracked girder. The paper is to study the structural performance of PC continuous beam bridge before and after reinforcement. The heavy vehicle loading test of reinforced PC continuous beam bridge was carried out. A total of three test spans were selected, and each test span selected seven deflection test section and a strain test section. The corresponding finite element model was established and verified by the test results. Finally, it was concluded in this study that the external prestressing reinforcement method has a good effect on improving the loading capacity and overall performance of damaged bridges

EFFECT OF VEHICLE QUALITY AND SPEED ON THE IMPACT CHARACTERISTICS OF AN OVERPASS BRIDGE PIER

To study the impact of the mechanical characteristics of heavy trucks on piers under different masses and speeds, a new equivalent simplified model of heavy trucks is proposed in this paper. The reliability of the calculation model is verified by studying the pier of the G1011 Ha-Tong high-speed K302+095 separated overpass, which was subjected to impact by a heavy truck. A finite element model of a heavy truck and a pier is established using the finite element software ABAQUS, and the influence of heavy truck load and impact speed on the impact force and pier stress is analysed. Results show that the peak of impact force increases with the increase in the mass and impact speed of heavy trucks. The high-stress area of the pier is concentrated in the root and the impact position, and an inclined through-crack is formed at 45° with the pier axis. The results also reveal the influence law of the quality of heavy trucks and impact speed on the impact force and stress of the pier and provide a new theoretical basis for the anti-collision design of piers and the limitation of current specifications on the high-speed impact of heavy trucks on piers

FIELD LOADING-TEST BASED SHM SYSTEM SAFETY STANDARD DETERMINATION

Structural health monitoring (SHM) allows for real-time structural response monitoring and online data acquisition of bridge structures. This data reflects the operational and environmental conditions of the bridge, which is important in identification of possible anomalous changes. In order to effortlessly determine the safety condition of the bridge directly through the transferred data without data analysis, a five-level safety standard system will be established for real-time safety warning in this paper. The threshold of each safety levels will be determined through field loading tests results on an external prestressing rehabilitated continuous rigid frame bridge, of which permanent structural health monitoring system was instrumented. After overall evaluation, we come to the conclusion that the rehabilitation is successful and that the bridge is under safe operating condition. A novel, simplified safety standard thresholding technique is proposed based on static loading test results as well as ultimate limit state of the bridge. This technique is simple yet very practical in daily bridge monitoring

PERFORMANCE ANALYSIS OF HIGH STEEL TUBE LATTICE SUPPORT SYSTEM IN TYPHOON AREA

Research on safety of high steel tube lattice support systems in typhoon areas is still in the preliminary stage. The purpose of this paper is to study the overall buckling and overturning stability of the high steel tube lattice support systems in typhoon area. By constructing the spatial finite element model of the high steel tube lattice support system via MIDAS Civil, the optimal design of the steel tube lattice support system is carried out through the analysis of the main influencing parameters. The stability of steel pipe lattice support system is calculated theoretically, and the optimal design of steel pipe lattice support system is studied by finite element numerical method in Typhoon area. The calculation results show that Critical buckling load coefficient increases with the increase in diameter of the steel tube when the δ/d ratio of steel pipe structure is fixed. The critical load factor of the six-limb support system is slightly larger than that of the four-limb support system. When the transverse space of the support system is from 5 m to 7 m, stability increases rapidly. The best stability of the support system is obtained when the transverse space is approximately 7 m. The diagonal brace can significantly improve the stability of the steel tube lattice falsework

MONITORING AND ANALYSIS OF CANTILEVER JACKING OF HIGH SLOPE PRESTRESSED CONCRETE CONTINUOUS BOX GIRDER

Due to the rapid development of the transportation industry and economy, an increasing number of bridges have been unable to meet the demands of traffic. Demolishing and rebuilding bridges can lengthen the construction period, waste a lot of resources, and increase construction costs. Based on the lifting renovation project of the old Harbin Dongsan Ring Expressway viaduct, this paper combines finite element analysis and on-site testing to analyze the construction process. The bridge alignment, elevation, and deviations were monitored during the construction process, and a correction system was developed to address such issues. Structural analysis was conducted to evaluate the internal forces when uneven jacking occurred. The construction process described in this paper can effectively solve the jacking problems of urban continuous bridges with large tonnage, high slopes, and heights. The successful implementation of the jacking retrofitting project has verified the reliability of the measures taken