Seismic Pounding Fragility And Risk Assessment Method Of Nonlinear Adjacent Structures

Adjacent buildings exist in practical engineering widely,a large number of seismic damage investigation results show that pounding between adjacent structures is one of the important factors causing structural damage or even collapse.Earthquakes have high uncertainty.In order to adapt to the development of performance-based earthquake engineering and seismic design theory,it is necessary to develop a more advanced,accurate and efficient method based on reliability method to evaluate seismic pounding risk of adjacent buildings.However,probabilistic seismic pounding risk assessment methods are limited to multi-degree-of-freedom linear structures,and the safety levels of existing procedures to determine a minimum separation distance is unknown.Therefore,the aim of this study is to propose a probabilistic performance-based procedure for assessing fragility of seismic pounding between nonlinear adjacent buildings.The main contents and conclusions of the thesis are as follows:(1)By defining the seismic pounding failure probability of adjacent structures,an efficient small failure probability method,i.e.,subset simulation,is proposed to be used for calculation of the pounding risk of adjacent buildings.The probability of pounding between linear single-degree-of-freedom systems is estimated by the proposed methodology,which is validated against those computed from analytical and simulation methods.Furthermore,the proposed method is illustrated by assessing the pounding risk of adjacent buildings modeled as nonlinear multi-degree-of-freedom systems with substantially different dynamic properties.Seismic fragility curves of nonlinear and linear adjacent buildings with different separation distances are compared.The results show that the seismic pounding fragility curve of nonlinear adjacent structures is increasing in general,but there will be small fluctuation.When the structures spacing is greater than a certain value,the failure probability will not reach 1 even if the peak ground acceleration increases.The larger the structural spacing,the greater the difference between the failure probabilities of adjacent buildings with and without considering the elastoplastic behavior.(2)The seismic pounding fragility of multi-degree-of-freedom adjacent structures linked by spring elements is analyzed using the proposed method.The results show that when the structure enters the elastoplastic stage and the peak ground acceleration is greater than a certain value,if the stiffness of the spring element is not large enough,the failure probability of the structure pounding will be increased.The seismic fragility analysis of single structure considering pounding force is analyzed using the proposed method.The results shows that when the separation distance between adjacent structures is small,the seismic fragility of single structure considering pounding is greater than that without considering pounding.(3)The proposed method for seismic pounding fragility and risk assessment of adjacent structures based on subset simulation is applied to the nonlinear finite element models of 6-storey and 5-storey adjacent frame structures and 6-storey and 4-storey adjacent frame structures using Matlab and OpenSees interaction.The seismic pounding fragility and risk of the two cases of adjacent structures under different separation distances are assessed.The incremental dynamic analysis method which is usually used to assss fragility of single structures is proposed to be used to assess the seismic pounding fragility of adjacent structures.Seismic fragilty curves of the studied adjacent frame structures derived from the two methods are compared,it is suggested that the most disadvantageous results of the two methods should be chosen in practical application.Finally,the failure probabilities of the adjacent frame structures with the minimum code-specified separation distance under earthquakes of different intensities are evaluated,when the adjacent structure spacing is the the minimum code-specified separation distance,the pounding probability under rare earthquake is higher,and the greater the dynamic difference of adjacent structures,the greater the probability of seismic pounding.