Life-cycle Seismic Performance Analysis Of Marine Bridge Piers Under Multi-earthquakes

Marine Bridges have characters of large investment, long-service time, severe working condition and high risk of suffering earthquakes. With the great growing need and investment on new infrastructures recently in China, the construction work in marine bridges is becoming more and more enormous. As the most important force-bearing component of marine bridges, it is very significant for bridge piers to behave safe and sound during their whole service lives. Historical materials of earthquakes and research work of domestic and oversea scholars have shown that marine bridge piers may suffer from effects of serious chlorine ions corrosion and multi-earthquakes during their whole service lives.(1) Based on historical materials of earthquakes, seismic risk analysis model and statistics, the probability of the appearance of multi-earthquakes during service life is discussed. The analytical results have shown that building structures have extreme low probability of suffering twice or more unrelated earthquakes or earthquake sequences during their whole service lives. However, they have very large probability of suffering one earthquake sequence which composes many earthquakes. Therefore, it is quite necessary to do some research on the effects of earthquake sequences.(2) Based on the method of constituting earthquake sequences proposed by oversea scholars, ten new earthquake sequences are formed using real mainshock and aftershock records of the same record stations acquired from PEER ground motion database. These newly formed earthquake sequences are inputted into the finite element model to do nonlinear dynamic time-history analysis in order to consider cumulative damage of bridge piers under the effect of multi-earthquakes.(3) The chlorine ions corrosion effect, which is the most important factor that influences marine bridge piers’durability, is discussed in detail. Then the steel corrosion condition in high performance concrete which is used in marine environment is analyzed using Life-365 software. The analytical result shows that though marine bridge piers have taken some protective measures like using high performance concrete, inhibitors, etc., bridge piers are inevitable suffering chlorine ions corrosion during its 100 years’service time. Thus steel would corrode and seismic performance of bridge piers would be affected.(4) Based on incremental dynamic analysis and seismic fragility method, seismic performance behaviors of bridge piers in initial period, the 60th,80th, and 100th service year after steel began to corrode are compared and analyzed. The seismic performance behaviors of bridge piers under single earthquake and earthquake sequence are also compared in this article. The analytical results indicate that bridge piers perform linear reactions mostly in slight damage state. The effect of service time and earthquake sequence is quite small in this state. In the state of moderate damage, extensive damage and complete damage, bridge piers behave plastically. In this state, service time and earthquake sequence have very large effect on piers’ displacement reaction and fragility curves, and piers are easier to enter dangerous conditions.