Optimization Of PC Bridge Life Cycle Comprehensive Maintenance Strategy Considering Climate Change

In recent years,long-span PC continuous rigid frame bridges have been widely used.However,the problem such as over deflection of the continuous rigid frame bridge is becoming more and more serious.Research shows that the continuous downward deflection of the rigid frame bridge is affected by the creeping development of concrete and the effective prestress loss,and the temperature is one of the main environmental factors affecting the creep of concrete.According to the fifth report of the Intergovernmental Panel on Climate Change(IPCC),urbanization will lead to a significant increase in atmospheric C02 concentrations and temperature over the next 100 years,with which will lead to aggravating of the development of concrete creep shrinkage and deteriorating the structural durability.Consequently,the failure probability of the bridge due to the deterioration of structural performance will increase and cause more maintenance cost and environmental impact during the service life.Therefore,it is very important to propose the optimization repair and reinforcement strategy of bridge considering structural safety,applicability and durability under the background of climate change.Considering the influence of the increasing CO2 concentration and temperature on the safety,durability and applicability of long-span PC continuous girder bridges,an improved carbonization and creep contraction prediction model is established.From the perspective of reliability,structural damage is considered.The degree of influence on the reliability index increment after reinforcement is established,and the time-varying reliability model under the bearing capacity and normal use limit state is established.Considering the maintenance behavior based on performance control and time-based control,the optimal strategy for bridge life cycle maintenance and reinforcement is proposed using environmental impact,cost and comprehensive cost as the optimization goals.The research work of this paper mainly includes the following aspects:(1)For the existing durability models of concrete structures,the influence of time-varying effect of temperature,CO2 concentration and relative humidity on material properties cannot be considered at the same time.Based on the climate change data provided by the IPCC report,the temperature and C02 concentration in the next 100 years are considered.The time-varying effect and the influence of relative humidity on the carbonization rate are considered,and an improved concrete carbonization model is proposed.(2)Referring to the B4 model,the influence of temperature change on the creep rate is introduced into the shrinkage and creep prediction model,which improves the Chinese standard on the calculation model of creep shrinkage and its resulting effective prestress loss.In addition,based on the improved carbonation and creep contraction prediction model,considering four climate change reduction scenarios,the reliability analysis of-main structure of the main span of a continuous rigid frame bridge under the normal use limit state and the ultimate limit of the flexural load capacity is conducted.(3)Under the different climate change reduction scenarios,consider the degree of structural performance degradation,four commonly used performance-based reinforcement methods are considered.Scenario analysis is carried out for the limit increment of the reliability index after reinforcement.Two time-based maintenance methods are considered to mitigate the degradation rate of reliable indicators after reinforcement.(4)Based on the life cycle assessment method,environmental impacts of the bridge during the material production phase,transportation phase,construction phase and maintenance and reinforcement phase are quantitatively analyzed.With the goal of 60%reduction of carbon emissions per unit of GDP promised by the Chinese government in the 2016 Paris Agreement,a calculation model for the failure probability of bridge life cycle carbon emission reduction suitable for China's national conditions is established.In addition,in accordance with the "System Integrated Environmental and Economic Accounting",a reasonable and feasible environmental cost calculation model is proposed.(5)Finally,an optimized life cycle maintenance strategy is proposed,considering the maintenance method based on performance and time-based control,with economic cost,environmental cost and environmental impact as the objective function.