Experimental Study Of Safety Assessment Before And After The Strengthening Of The Reinforced Concrete Slab Bridge

China built many Bridges in the 1970 s and 1980 s,and a large part of it was a bridge of three or four roads.Due to the low design load,the lack of maintenance and other reasons,a large proportion of the age-old bridges are facing the potential security risks and failing to meet operational requirements.Therefore,how to accurately assess the reliability of such bridges is a very important issue,this is related to people's lives and property safety and the bridges' economic efficiency.This article belongs to the Yunnan Provincial Department of Transportation Science and Technology Project "Yunnan in service for many years small span beam bridge safety re-use test" sub-topics.The mechanical properties of the reinforced concrete slab bridge in Yunnan for nearly 30 years are studied.A static load test was conducted to study the two states.First,the state before reinforcement is not removed,including steel plate reinforcement,steel and beam roof concrete reinforcement of the two cases;the second is to remove all reinforcements,that is regarded as the state before reinforcement.The study consists of four parts.First,the static load test was carried out before and after the demolition and reinforcement of bridge,to evaluate whether the bridge's current performance meet the requirements or not.Second,the mechanical properties of the bridge are analyzed.Third,the destructive test is undertaken on all bridge without reinforcement,analyzing the mechanism of bridge stress in the loading procedure.Finally,a three-dimensional finite element simulation model is established to simulate the static load test and the destructive test,and the theoretical data and measured Data are compared and analyzed.The main research contents and achievements are as follows:(1)In this paper,the non-destructive testing method and theory are introduced.The strength test of concrete,the depth of concrete carbonation and the corrosion of steel are tested respectively.The results show that the strength of concrete is slightly lower than the design value.The depth of concrete carbonation of bridge floor is between 5.0mm and 6.0mm,but it is greater than 10 mm in the sides of bridge.And the level of steel corrosion is between-300 m V and-400 m V,indicating that the corrosion probability of steel is more than 90%.The preliminary evaluation of the bridge's existing situation provides a reference for experimental analysis.(2)The static load test of the original state of reinforced bridge is analyzed.The results show that the measured values of strain-controlled section's measuring points are larger than the theoretical value in the load test.According to Specification for Inspection and Evaluation of Load-bearing Capacity of Highway Bridge,the load capacity of this reinforced bridge cannot meet these requirements.(3)The static load test data of the bridge before and after reinforcement are compared and analyzed.The static load test is done after dismantling the concrete reinforcement of bridge,in which the strain and deflection value increase rapidly,but they are increasing smoothly after further removing the steel plate.The test results presents that the stiffness of the reinforced concrete is stronger than that of the steel plate.(4)The finite element model is used to simulate and analyze the static load test and loading destructive test.This paper presents the methods and points of the actual reinforced concrete structure in the simulation.By comparing the calculated theoretical value with the measured data,the applicability of the calculation model is verified and has some reference significance.(5)In this paper,the initial condition of unreinforced bridge is studied.Considering the influence of the steel corrosion factors,the time-varying load effect and the time-varying structure resistance are compared and analyzed.The results show that the bridge has a large bearing capacity reserve.The time-dependent reliability of the bridge is calculated by MATLAB program.Through the comparison and analysis of the target reliability index,the reliability of the bridge can not meet the requirement in 90 years.