Research On Bridge Resilience Under Multi-hazard Of Earthquake And Blast Loads

Bridges will encounter a variety of natural or man-made hazards during their lifecycle.Among many hazards,earthquake is the most common natural hazard which causes structural damage.Besides,accidents caused by vehicles make blast loads be one of the potential threats to the continued functionalities of bridges.Consideration of the effect of earthquakes and blasts is not only beneficial to preserve the functionalities of bridges,but also important to support economic activities and people’s lives.Recently,research on improving resilience of structures has become a new trend in the field of hazard prevention and reduction for civil engineering.As an important transportation hub,bridges play a vital role in the transportation network.Thus,the resilience of bridges under hazards is the main emphasis of the ongoing research.However,the most of the investigations on hazard prevention and reduction at this stage consider the impact of single hazard applied on the bridges,without giving enough consideration to the complex scenarios with multi-hazard.This kind of design and analysis method is in a static,definite and limited style without consideration based on the lifecycle of bridges.It ignores the high uncertainties of hazards,degradations of structural performance caused by environmental factors,and can’t effectively control the effect of hazards on the safety,society,environment and economy of the structural systems.The method can’t meet the objective needs of establishing resilient structures.Based on the weakness of current research,the dissertation investigates the bridge resilience under multiple hazards.The study consists of the analytical studies that considers typical reinforced concrete girder bridge using the softwares and programs Open Sees,MATLAB and Python.Specifically,this dissertation considers the effects of earthquake and blast loads for the lifecycle of bridges.It considers the complex multihazard scenarios,the probability of hazards occurrence,the time-dependent degradation of structural performance caused by environmental factors,extends the concept of hazard resilience of the existing engineering structures and proposes multi-dimensional evaluation and decision criteria.The main contents and conclusions are as follows:(1)Research on generalized resilience analysis and decision-making of bridges under multi-hazard.The resilience of bridges under multi-hazard is studied considering the lifecycle,risk and cost based on the extended concept of resilience which considers the structural function recovery as the only meaning.The method to investigate generalized resilience of bridges is proposed and how the results will affect the decision-making process is discussed,which covers hazard analysis,fragility analysis,structural recovery and possible impact on safety,society,environment and economy.The paper provides a practical example of resilience analysis and evaluation of bridges under multi-hazard considering the hazard effects of earthquake and blast loads and degradation of structural performance.The results of analysis find the significance of bridge resilience based on multi-hazard,lifecycle,risk and cost.The method proposed in this paper is not only applicable to earthquake and blast,but also applicable for other types of hazards such as strong wind,flood,scouring.The proposed method has potential applications for other types of structures,such as buildings,dams,and transmission towers.(2)Research on improved seismic fragility analysis based on Box-Cox transformation and Bayesian Updating(BC-BI-BLR).An improved fragility method is proposed based on Box-Cox transformation,Bayesian Inference and Binomial Logistic Regression to comprehensively processing the original data by eliminating the heteroscedasticity problems,which leads to the improved fitting of the probabilistic seismic demand model.By using Bayesian Inference,the uncertainty of the model can be considered to obtain the parametric distribution of seismic demand and capacity model,so as to avoid over-fitting.It is discussed that,when the intensity of earthquake is large,the traditional fragility method underestimates the risk of damage to the bridges.The improved method based on BC-BI-BLR can mitigate such underestimations.(3)Research on bridge resilience under multi-hazard of earthquake and blast considering complex hazard scenarios.Considering the uncertainty of hazards’ intensities,occurrence sequences and times,the parameters that can adjust the fragility functions for damage analysis of bridges are obtained on the basis of resistance reduction.Monte Carlo method is used to establish the complex multi-hazard scenarios and resilience analysis is carried out at the end.The results reveal that bridge resilience decreases with the increase of intensity of earthquake and blast loads,and the hazard occurred during the structural recovery period has a great impact on bridge resilience.The occurrence sequence of hazards will affect the estimation of structural resilience to some extent.Furthermore,the recovery time needed for bridge repair is found to be related to the types of hazards and structural damage modes.The distribution of functional curves in the time domain obtained from the multi-hazard scenarios with“blast first and earthquake later” is different from the multi-hazard scenarios with“earthquake first and blast later”.When two type of hazards occur successively,the estimated value of resilience is the smallest.When the time interval between the two hazards is long,the damages of structures are relatively small and the estimated value of resilience is relatively large.(4)Research on bridge resilience under multi-hazard of earthquake and blast considering occurrence probability of hazard.The influence of multiple hazards and its annual occurrence rate are considered for long-term resilience based on the lifecycle of bridges to clarify the dominant scenario with highest economic loss.Five hazard scenarios have been proposed after obtaining the annual occurrence probability of earthquake and blast.The performance of bridges,in terms of resilience and economic loss,is studied using the Poisson renewal process during the lifecycle of bridges.The results show that among the 5 different hazard scenarios in the service life of bridges,the earthquake with a return period of 100 years causes the greatest economic loss,although the long-term resilience is heavily affected when the oil tank explosion is considered.This implies that both long-term resilience and economic loss need to be considered in the damage prevention and maintenance of bridges.In other words,the long-term effect of structural safety and economic loss can’t be balanced by making decisions according to only one aspect.In addition,the long-term economic loss of bridges under hazards is related to occurrence and intensity of hazards,remaining service life of bridges and discount rate for money.The value of these parameters should be carefully selected.(5)Research on bridge resilience under earthquake and blast considering degradation of properties of bridge component.The influence of chloride corrosion on the long-term structural resilience based on the lifecycle of bridges is investigated.The damage of chloride to bridges is analyzed based on probabilistic method.The paper finds that with the increase of service life,the corrosion of chloride to piers is intensified which causes the degradation of structural performance,thus having impact on the longterm resilience of bridges.The resilience of bridges under earthquake and blast is related to the occurrence time of hazards.At the initial stage of service life,the aseismic and anti-blast performance of bridges remains relatively untouched.As the increase of service life,the hazard capacity and displacement ductility of piers are gradually reduced due the corrosion of chloride,the failure probability of bridges in different damage states becomes larger and the structural resilience becomes smaller.