Abstract
For offshore bridges, the most prominent problem in the whole life cycle is that it is in an earthquake prone zone and an offshore corrosion environment at the same time. A nonlinear dynamic analysis model is set up for an offshore multispan and continuous rigid frame bridge based on the OpenSEES platform. The fragility surface of the bridge pier, bearing, bridge platform, and system are established by selecting a reasonable damage constitutive model of the material durability and a damage index analysis that studies the damage of the bridge durability to time‐varying seismic fragility of bridge components and the system of the whole life cycle in offshore environment. The results show that the durability damage will lead to a constant decline in seismic capacity of the pier and an increase of the seismic demand under earthquake action as well as the probability to reach the ultimate failure state; compared to high piers, a low pier is more vulnerable to the offshore corrosion environment; the seismic fragility of bridge platform is higher than that of simply bearing; and the influence of offshore corrosion on environment is relatively large. With the prolongation of service period, the effect of durability damage on the seismic fragility of bridge system cannot be ignored in the coastal environment and it is necessary to make a reasonable evaluation on the seismic fragility of bridge structure during the whole life period.
Highlights
The offshore and cross sea bridges have been widely built around the world, such as the Ming Shi channel bridge in Japan, the Waal bridge in Netherland, and the Oakland Harbour Bridge in New Zealand
The exceeding probability of 1#, 4#, and 5# piers under four damage states in the first 20 years is significantly less than that in the latter 80 years for the initial corrosion time of the hoop reinforcement is about 14 years and the initial corrosion time of the longitudinal reinforcement about 19 years, which shows that the mechanical behavior of reinforcement is the main factor to affect the seismic performance of piers
The probability of pier to exceed all kinds of damage states during service period is increasing affected by chloride ion erosion and concrete carbonation in the offshore environment; that is, the actual seismic capacity of the pier will continue to decrease, while the seismic demand for seismic action and the probability to reach the limit state of failure will be continuously increasing
Summary
The offshore and cross sea bridges have been widely built around the world, such as the Ming Shi channel bridge in Japan, the Waal bridge in Netherland, and the Oakland Harbour Bridge in New Zealand. The existing studies [3] show that as the service time of the bridge extends, the concrete carbonization and chloride ion erosion effect will cause durability damage to the bridge structure and lead to degradation of the seismic performance. Considering the degradation effect of chloride ion erosion on the properties of reinforcing steel bars and by analyzing the seismic fragility of a two-span bridge, Choe and others [10] conclude that the corrosion of reinforcing steel bars will have a certain effect on the seismic performance of concrete bridges. Cui et al [22] present an improved reinforced concrete reinforcing steel bar deterioration model that incorporates pitting corrosion and considers the change in after-cracking corrosion rate to assess the time-dependent seismic fragility of RC bridge substructures in marine environments. Some bridges cannot reach the design service life and need to be repaired and strengthened to maintain their normal function, leading to a lot of economic losses
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