Research On Monitoring Technology Of Assembled Small And Medium-Span Bridges After Reinforcement

Some assembled small and medium-span bridges built in the early days are not competent for the increasing traffic volume,and the reinforcement and maintenance of assembled small and medium-span bridges have also attracted extensive attention from relevant departments and researchers.Traditional regular manual inspection will consume a lot of manpower and material resources and can not grasp the operating state and structural damage of bridges in real time.The bridge health monitoring system can effectively make up for the shortcomings of manual inspection.At present,there is little research and practice on health monitoring of assembled small and medium-span bridges and their reinforcement,and it is not applicable to establish a monitoring system for assembled small and medium-span bridges after reinforcement based on the practical experience of existing long-span bridge monitoring systems.The main contents and conclusions of this paper are as follows:(1)By consulting the literature,the common diseases and causes of assembled small and medium-span bridges are classified,and several common reinforcement methods of assembled small and medium-span bridges are introduced.Using Midas/civil software grillage method,the finite element modeling method of assembling small and medium-span bridges is put forward,and the simulation method of boundary conditions in finite element modeling of various reinforcement methods is put forward.(2)The assembled simply-supported T-beam is selected as the research object,and the finite element modeling of simply-supported T-beam strengthened by longitudinal steel plate sticking method,transverse steel plate sticking method and external prestressing reinforcement method is carried out.The response laws of bridge stress and vertical displacement under constant load,vehicle load,temperature gradient load,shrinkage and creep during operation period are calculated and analyzed.The results show that the effects of constant load,shrinkage and creep can be ignored,and the effects of vehicle load and temperature gradient can be mainly considered for assembled small and medium-span bridges strengthened after many years of service.The load test of an assembled T-beam bridge is carried out,and the results show that the finite element calculation values are in good agreement with the load test data.(3)According to the analysis and calculation results of bridge structure,some suggestions are put forward on the routine monitoring content,point layout and sensor selection of assembled medium and small span bridges.The routine monitoring contents of assembled small and medium-span bridges should include deflection,strain,temperature and crack indicators.Deflection and strain sensors should be arranged in the middle of the bridge,and can be added at L/4 and 3L/4.Strain sensors should be arranged at the bottom of the beam to reduce the influence of temperature.Aiming at the assembled small and medium-span bridges strengthened by different reinforcement methods,a targeted monitoring scheme is proposed in addition to the conventional monitoring content.(4)Analyze the composition of bridge monitoring data and the time scale of action effect,extract the load effect and temperature effect of bridge vehicles by using wavelet analysis technology,and put forward a method to set the early warning threshold of assembled small and medium-span bridges by combining the finite element calculation value and bridge inspection coefficient.The concept of correlation coefficient is introduced to characterize the cooperative working performance between two precast beams.The monitoring data of the actual bridge are analyzed and calculated,and the lateral cooperative working performance of each beam of the bridge is good,which provides reference for the setting of monitoring and early warning threshold and the evaluation of lateral working performance of assembled small and medium-span bridges after reinforcement.