Performance Evolution And Reliability Assessment Of Existing Highway Bridges

As an important part of road traffic,bridges play an important role in ensuring the trafficsafety and efficiency.However,after concrete bridges are built and put into use,due to load,material aging,damage accumulation,environmental effects and other factors,various diseases in bridges arise,resulting in bridge structure safety and performance decreasing with time.Supported by ministry of transport construction technology projects“ Research and development of technical system and equipment of reliability evaluation of existing concrete beam bridge ” and “Research of long-term concrete beam bridge performance(LBBP)”,main factors that affected the performance of medium and small span concrete bridges were analyzed from three aspects as in bridge safety,crack and deformation.The safety assessment model,crack evolution analysis model and deformation evolution analysis model were established.The main contents and conclusions are as follows:1.The factors affecting safety of concrete bridge were analyzed from the aspects of material,construction,environment,maintenance and repair.The calculation formulas of time variant reliability indexes and reliability indexes were established.The reliability evaluation methods based on different bridge test results were established.The annual failure probabilities of highway bridges in China in recent 10 years were analyzed.The results show that,for the bridge bearing capacity evaluation method specified in “Specification for inspection and evaluation of load-bearing capacity of highway bridges(JTG/T J21-2011)”,the decline range of reliability indexes of structural members is 2.0~ 3.0 when the carrying capacity deterioration coefficient is 0 as the scale of bearing capacity check coefficient reducing from 1 to 5.The actual failure probability of the bridge is far more than the limit specified in “Unified standard for reliability design of highway engineering structures(GB/T50283—1999)”.2.According to engineering investigation,the forms,types,main influencing factors,main positions and forming reasons of common bridge cracks were analyzed.Shrinkage crack evolution analysis model of constraint RC members and bending load crack evolution analysis model were established.Examples were given to prove the feasibility of these models.3.Main factors affecting short-term deformation and long-term deformation of bridges were analyzed.An analysis model of bridge deflection was established.Based on theoretical analysis and experimental data,the approximate linear relationship between crack width and deflection was established.The results show that the mid span deflection of pre-stressed concrete beam calculated by the current code is smaller than that calculated by creep theory.When the actual effective stress of pre-stressed concrete beam is not up to the value calculated according to the code,the inverted arch value decreases,and the long-term vertical deflection increases.The change degree of above indexes is related to actual effective prestress.