Study On Probabilistic Seismic Damage Characteristics Of Offshore Cable-stayed Bridge Under Environmental Corrosion

Chloride ion erosion will lead to serious performance degradation of reinforced concrete and cables,which poses a huge threat to the structural safety of cable-stayed bridges located in coastal areas.In addition,many cable-stayed bridges are located in earthquake-prone areas.Several major earthquakes have caused serious damage to bridges.At present,the seismic research of cable-stayed bridges at home and abroad is mostly based on intact structures,while the research on seismic vulnerability of bridges considering material corrosion mostly focuses on the small and medium-sized girder bridges or a single component of cable-stayed bridges.The research on the overall seismic performance of cable-stayed bridges under the effect of material corrosion degradation is still in the initial stage.With the continuous planning and construction of cable-stayed bridges in coastal areas,it is of great theoretical and practical significance to study the time-varying deterioration of seismic performance of cable-stayed bridges.This paper took a single-tower cable-stayed bridge in offshore area of China as the research object.Considering the corrosion of chloride ions on cables and reinforced eoncrete,the time-varying eomponents and systems seismic vulnerability of eable-stayed bridges were systematically discussed.The main contents of this paper are as follows:(1)The time-varying deterioration characteristics of main tower,pier and cables have been considered in this paper,based on OpenSees platform,several three-dimensional finite element models of cable-stayed bridge under different service times were established,and the accuracy of OpenSees model was verified by SAP2000 software.The natural vibration periods of cable-stayed bridge under different service times were analyzed.The results show that the performance deterioration of reinforced concrete and cables will lead to the increase of the natural vibration period of cable-stayed bridge,but the increase rate is small.(2)100 earthquake waves were selected to evaluate the ground motion intensity indices(spectral acceleration corresponding to the basic period of the bridge Sa(T1)and PGA),and Sa(T1)was chosen as the ground motion intensity index of cable-stayed bridge.On the basis the four damage levels of cable-stayed bridge,the damage indices of each component(main tower,pier,pile,supports and cables)were quantified,and the time-varying seismic capacities of the main tower and pier were studied by moment-curvature analysis.(3)Based on the incremental dynamic analysis method,the components seismic vulnerability curves of cable-stayed bridges under different service times were established.It is found that the damage probability of components(main tower,pier,pile,support and cables)under slight damage,moderate damage,severe damage and complete damage conditions increase in varying degrees during the whole corrosion service period of cable-stayed bridge.The increase of damage probability of deteriorated components(main tower,pier and cable)are higher than that of components(pile,support)without considering performance degradation.(4)The theoretical of structural system reliability was used to describe the cable-stayed bridges system.Based on the analysis of cable failure modes,a hierarchical series reliability model of cable-stayed bridge is proposed.(5)The time-varying system seismic vulnerability of cable-stayed bridge was studied by using the boundary method.The results show that the damage probability of cable-stayed bridge system is higher than that of any single component,and the damage probability of system increases with service times.When the damage probability of one component is much higher than that of other components,the system damage probability of cable-stayed bridge is very close to that of the component.The system damage probability is greatly affected by the support damage under the conditions of slight damage and medium damage.In the condition of severe damage and complete damage,the system damage probability is greatly affected by pile damage.