Research Of Offshore Bridge Maintenance Strategy Based On Life-Cycle Seismic Performance

With the development of society,people's awareness of earthquake prevention and disaster reduction is constantly improving and the seismic design theory of bridge is also gradually improved.However,because of the inevitable adverse service environment of most bridges in the life cycle including complicated environmental effect and earthquakes,a large number of structures break down without reaching expected service life time.The offshore bridge structure has also been in a complex sea erosion environment for a long time,and its seismic performance is deteriorating with time under the action of chloride induced corrosion.Therefore,life-cycle seismic performance evaluation for bridges considering chloride induced corrosion appropriately is significant to ensure the safety of the offshore bridge structures under sudden earthquakes.For bridges in earthquake-prone areas,seismic performance is dominant in safety assessment.With service time increasing,the seismic performance of bridge degenerates so a lot of maintenance and retrofit need to be done to ensure the seismic performance satisfy safety target.Reasonable maintenance strategy can effectively improve the seismic performance of the bridge in the life cycle.On the contrary,it will not only cause a lot of economic losses,but also make the bridge face a huge risk of failure under the earthquakes.Therefore,it is very necessary to formulate effective seismic maintenance strategy for the use and management of bridge in life cycle.Based on the background above,the seismic vulnerability curve of the life cycle of the bridge considering the chloride induced corrosion is established in this paper and the change of seismic reliability with time is also studied.Considering the degradation of seismic reliability of bridges,a life cycle maintenance strategy based on essential maintenance and preventive maintenance is proposed.Main study includes:(1)Reinforced concrete rigid frame bridges are taken as examples and 10 bridge models are established in OpenSees.Considering the uncertainty of structural material parameters,Latin hypercube sampling(LHS)method is used to extract the relevant parameters independently and hierarchically.For each bridge model,12 seismic waves with the peak ground acceleration uniformly distributed in 0-1.2g are input respectively,and the seismic vulnerability of each example bridge in the initial state is analyzed.(2)In this paper,the diffusion model of chloride ion in reinforced concrete members is introduced and the probability distribution of corrosion initiation time of reinforcement in piers is determined considering the uncertainty of the environment and material parameters of the structure.The Monte Carlo method is used to study the time-varying characteristics of the mechanical properties of reinforced concrete materials and the area loss of reinforcement in piers and columns based on the pitting corrosion.(3)Considering the pitting corrosion of chloride ion,finite element models of bridge in each life stage are established and the nonlinear dynamic time history analysis is carried out to withdraw the change of seismic vulnerability with time.Combining the seismic vulnerability curve with the current code for seismic design of highway bridges in China,the seismic intensity and the value of peak acceleration of ground motion corresponding to the seismic fortification of E1 and E2 are calculated,and the variation trend of bridge failure probability and seismic reliability index with time under the action of two fortification earthquakes is studied.(4)The essential maintenance strategy and preventive maintenance strategy are established based on the change of seismic reliability in the life cycle of bridge examples.The steel jacket reinforcement method and the concrete cover repair method are selected as maintenance methods,and nonlinear dynamic time history analysis is used to calculate the seismic vulnerability of the bridge before and after maintenance.The time-varying curve of seismic reliability of the bridge after maintenance is drawn,and the mean value of seismic reliability and the present value of maintenance cost in the life cycle is calculated.Therefore,the influence of several given maintenance strategies on the seismic performance and cost of bridge in the life cycle is compared and analyzed.