Multi-objective Optimization In Life-Cycle Analysis For Offshore Bridges Based On Preference Of Seismic Performance

The southeastern coastal area of China is in the Circum Pacific seismic belt where frequent earthquake disasters have seriously affected the safety of offshore bridges and caused huge economic losses.It is very significant for offshore bridges to carry out multi-objective optimization based on life-cycle seismic performance,to strike a balance between the seismic safety and life-cycle cost.Furthermore,chloride-indued corrosion is able to generate the structural performance degradation,and then affects the seismic safety and reliability of offshore bridges.Multi-objective optimization decision making of offshore bridges based on life-cycle seismic performance is utilized to conduct the systematic research.Seismic performance-based preference is converted into value function and integrated into interactive optimization model.The effects on damage cost under earthquake and life-cycle seismic optimization of corrosion are also taken into account.The main contents and conclusions are listed as follows:(1)Taking a single-column pier as an example,a multi-objective seismic optimization model that can simultaneously consider the economic performance and safety performance of the entire life under seismic hazard is established.The design variables and constraints are section parameters and meeting requirements of guidelines,respectively.The obtaining results show that:for seismic design with low dimension,the designer is provided more choices by the algorithm which is capable of balancing such as seismic safety and economy,and generating a well-distributed Pareto optimal set.For high-dimensional problem,however,it may be failing to cover the satisfied region from designers.(2)Seismic performance preference based on ductility is presented and converted into the corresponding value function,which is combined with interactive multi-objective optimization for the seismic design of bridges.The results illustrates that by successively introducing preference information of designers,the proposed interactive seismic model is able to focus on the interested region of seismic performance and progressively search for until finding out the global optimal design satisfying the corresponding preference.(3)Based-on seismic performance preference of ductility,the two preference introduced ways of 'posterior' and 'interactive' are utilized into seismic design of bridge pier.For low-dimensional design,a sufficient number of populations is needed for the posterior algorithm to obtain the solutions meeting requirements.And for high-dimensional design,the final solutions attained by the algorithm may be locally optimal.Whereas,the computational accuracy of results by the interactive algorithm is less affected by the number of optimization objectives and its advantages become more significant as the number of objectives increases.Even when there are too many objectives,the results with the interactive model can converge to the globally optimal design corresponding with the seismic performance preferences.(4)The calculation formulas of seismic damage cost,life-cycle cost and average annual cost are derived under chloride-induced corrosion.The cost preference and durability service life are incorporated into interactive seismic optimization model.It is indicated that when considering the effects of corrosion,annual cost model,compared with life-cycle cost model,can be more accurately and reasonably applied to weigh the benefits of extending durability service life against its cost.