Bi-directional Seismic Analysis And Fragility Evaluation Of A Nuclear Containment Building

The containment building being the last barrier to prevent nuclear leakage is very important for seismic safety and integrity of nuclear power plant.According to the composition of different materials,the containment can be divided into steel containment,non-prestressed concrete containment,and prestressed concrete containment.At present,the non-prestressed concrete containment still exists in all over the world,such as China Qinshan PWR containment,Japan hamaoka and Shimane BWR containment,Korea PWR containment,the United States Clinton,big bay,BWR containment,and the small scale PWR containment proposed by the American Energy Agency.Therefore,the research on seismic performance of external non-prestressed concrete containment is of great importance for improving the seismic safety of nuclear power plant system.The object of this thesis was the external non-prestressing reinforced concrete containment which is represented by the Qinshan nuclear power plant.Different from general frame and shear wall structure,the geometrical characteristics of nuclear containment are characterized by small depth-width ratio and large width-thickness ratio,which probably results in the shear failure mode of nuclear containment under seismic action.Therefore,how to adopt or put forward an appropriate numerical modeling method or theoretical analysis method for the research of nuclear power plant containment is of great significance for throughly understanding its seismic performance.Because of the multidimensional nature of the ground motion,the direction of inertia force of the containment due to earthquake excitations always changes.The preceding studies have shown that bidirectional seismic loading may have an adverse effect on general structure,but the failure mechanism of nuclear power plant containment under bidirectional seismic action has not been further studied.Therefore,how to accurately assess the seismic capacity of the nuclear power plant containment under bidirectional earthquakes and determine the suitability of parameter is also worth studying.This thesis focused on the modeling method,bidirectional seismic response,performance state under bidirectional loading path,the simplified model considering shear coupling,and seismic vulnerability analysis and determination of HCLPF capacity for nuclear containment building.Main research contents and conclusions are as follows:(1)In order to consider the material damage caused by cyclic loading and effectively simulate the hysteretic response of containment,the concrete plastic damage theory was applied on the smeared crack model and a two-dimensional concrete constitutive model was developed and embeded into ABAQUS software.Finally,the concrete model was verified through the scaled nuclear containment test.The results showed that the developed constitutive two-dimensional concrete can be used for numerical simulation of nuclear containment building.(2)The dynamic characteristics of nuclear containment building were firstly obtained.Based on the information corresponding to the seismic hazard of site,the ground motions matched with constant hazard spectrum were selected.Using the bidirectional ground motion records,the seismic response of containment building was studied in detail.The results showed that with the increase of the earthquake intensity level,the structure entered into a more serious plastic state;bidirectional seismic loading caused the structure's greater deformation;when the earthquake intensity increased,the concrete cracking occured more earlier than unidrectional seismic excitation;and compared to the deformation,the damage energy dissipation due to bidirectional earthquake excitation was more significant than unidirectional earthquake excitation.(3)Obtaining the hysteretic results for specimen 1 under uniaxial,square,circular,diamond,and infinite load paths,the effects of load paths on the cracking,yielding,and collapse capacity and displacement were investigated.After researching the influence of single parameter on structure strength and displacement,the peak intensity ratio,peak displacement ratio,and ultimate displacement ratio formulas were established through numerical verification.The results showed that different loading path may induce different hysteretic performance;compared with the unidirectional loading path,the asceding branch significantly slowed down after the yield and the deceding branch occured significantly in advance;The change of the total base shear in bidirectional load path was more obvious than that of unidirectional load path due to the same energy dissipation;the established expression for the peak strength ratio,the peak displacement ratio,and the ultimate displacement ratio can be used to predict the performance state of the nuclear containment building under bidirectional load path effectively.(4)The Takeda hysteretic rule was developed using the Opensees software and the previous Takeda hysteretic rule was extended to hysteretic rule due to biaxial loading,which was also developed using the Opensees software.Finally,the results for scaled nuclear containment building test,the finite element model,and the simplified model were compared due to unidirectional load path and the square,diamond,round,and infinite load paths,verifying the validity and rationality of the developed model.The results showed that the simplified model considering shear coupling can predict the response of nuclear containment building effectively.(5)Through the introduction of a large number of bidirectional earthquake intensity parameters,the dispersion among bidirectional seismic intensity measures used to represent the structural response was compared and the representative earthquake intensity measure was determined.Then seismic vulnerability assessment for the nuclear containment building under bidirectional earthquake excitation was studied and the fragility curves corresponding to cracking,peaking,and ultimate states were obtained.The selected bidirectional earthquake intensity index was used to determine the HCLPF value.Finally,a comparison of the ultimate capacity between unidirectional and bidirectional earthquake excitation was carried out.The results showed that the parameter Rot D50(Sa)can be used as a bidirectional seismic intensity to calibrate the nuclear containment HCLPF ability.