Research On Optimization Of The Girder Bridge On Whole Life Based On Reliability

Since 21 st century,with the rapid development of domestic economy in the past twenty years,the task faced by bridge engineers has been gradually changing from designing new bridges to the maintenance and management of existing bridges.If the existing bridges can’t meet the normal traffic conditions,it is bound to face a choice of reinforcement and maintenance for existing bridges or demolition and reconstruction.There are some questions to be considered,such as what methods should be used in reinforcement and maintenance,which indicators need to be followed,how many times we should perform the reinforcement and maintenance,whether the effect of reinforcement can be assured after reinforcement,and what standard that evaluates if reinforcement scheme is suitable or not we should use.Focusing on reinforced concrete girder bridge and considering structural deterioration model of time-varying effect,this paper makes in-depth analysis for structural bearing capacity before and after strengthening and the changes of performance indices(such as deflection).Based on Reliability Theory,Fuzzy Math and Engineering Economics,the study gives the optimal maintenance plan from perspective of life cycle maintenance.The researches and conclusions are as follows:(1)In the state of ultimate bearing capacity,with the structure anti-bent capacity as target function,the paper considers time-varying differences of degradation model of reinforced concrete beam itself between the stick steel reinforcement and stick carbon fiberboard reinforcement before and after reinforcement.Integrating the time-varying characteristics of reinforcement material itself,it researches reliable degrees index of changes before and after the reinforcement,and finds that upgrade efficiency of the stick steel reinforcement against bent hosted the capacity is higher.The former is around 1% higher than the latter.(2)In the state of the normally utilized limit,the fuzzy information "allow flexibility" is quantified with fuzzy math.Reliability index change before and after reinforcement is studied combined with the reliability theory,taken deflection as target function.The paper finds that the way of sticking steel reinforcement is 3.3 times of CFRP bonded reinforcement for rigidity improved efficiency.(3)Based on established time-dependent reliability assessment models,the rein-forced concrete girder bridge which has served for five years is reinforced by steel-bonded reinforcement and CFRP bonded reinforcement only for once.The rest service life of the bridge has been forecasted and finds that the service life for gluing CFRP reinforcement is 1.5 times of steel-bonded reinforcement.(4)Under the premise of basically consistent sequent service life and less reinforcement times,it compares and analyzes the differences among four different reinforcement ways-single multiple plate,one more than a multiple carbon fiber sheet,plate prior to carbon fiber and carbon fiber sheet reinforcement plate.It is found that the second way can’t guarantee to improve the rigidity,there is basically the same performance to improve rigidity between the latter two ways and the reinforcement times of single steel plate is slight more.(5)Life reinforcement cost objective function is established with the consideration of the discount rate.It also increases the reconstruction programme.Under the premise of the basically same bridge age,the cost of plate after the first carbon fiber sheet reinforcement scheme can be saved almost a half compared with the first carbon fiber plate.