Failure Risk Assessment Of Masonry Structures In Villages And Towns Under The Combined Action Of Flood And Earthquake

China is a country prone to natural disasters.It has the characteristics of many types of disasters,high frequency of occurrence,and a wide range of impact.The combined effects of floods and earthquakes may be suffered during the time.In structural design,usually only one kind of disaster or simple superposition of loads through the combination of disaster load coefficients is considered,and the interaction between various disasters is not fully considered.More and more scholars have begun to study the evaluation and design methods of structures under the action of multiple disasters,respectively from the perspectives of disaster risk and structural vulnerability.Based on the idea of risk,this paper studies the disaster probability model under the combined action of flood and earthquake and the assessment of the failure risk of typical village and town buildings.Based on these,the following research work has been carried out in this paper:(1)Summarize the distribution model of single random variable and the joint distribution model of multidimensional random variable.Introduce the types of multivariate joint distribution in detail,including: Moran method,Feiyongfa method,FGM method,empirical frequency method,non-parametric method,Copula function method,and summarize the applicable scope of each method.(2)Propose a joint flood-seismic distribution model based on Copula theory.Based on the events of the coupling of flood and earthquake between 1970 and 2019 in Sichuan Province,the edge distribution function and edge probability density function of the two disasters were obtained respectively,and the joint probability distribution function of the two disasters was obtained using Copula theory.Square root error and AIC criterion determine the optimal joint probability distribution function and recurrence period.(3)Based on the risk theory,a failure risk assessment method for the masonry structures of villages and towns under the combined action of flood erosion and earthquake is proposed.Comprehensively considering the disaster risk and structural fragility of flood erosion and earthquake,the fragility function and the two disaster probability density functions are integrated in the disaster domain to obtain the failure overrun probability of the structure under different damage states,and the loss ratio and The cumulative failure probability of the structure,and then obtain the reliability index under the full performance state,and compare with the target reliability index to conduct structural performance evaluation.(4)Take the two-story masonry structure as an example to show the establishment process of the failure risk assessment method.The results show that the erosion has little impact on the vulnerability of the structure to slight damage and moderate damage,and is vulnerable to severe damage and collapse.The impact of flooding is greater;the impact of flood erosion on the seismic performance of the structure has a greater impact.Compared with considering only the action of earthquakes and considering the combined action of flood erosion and earthquakes,the probability of failure under various damage states of the structure is increased.And as the degree of damage increases,erosion has a greater and greater impact on the probability of structural failure.