Numerical Simulation And Analysis Of Masonry Structure Collapse Under Earthquake

Based on the previous work,numerical processing and spectrum characteristics of seismic wave,establishment of discrete masonry finite element model,deformation and crack mode of masonry walls under cyclic load as well as destruction of masonry buildings under earthquake are simulated and analyzed.The following work is completed:1.The long history of masonry and the current situation of masonry in China are stated as well as the reason of earthquake vulnerability of masonry is explained.The failure modes and mechanical mechanism of masonry under earthquake action are discussed.Researches of analysis of masonry using numerical method are investigated.Then the purpose,content and significance of this paper are proposed.2.The basic principle of finite element method is introduced,and the numerical characteristics and convergence conditions of explicit time integral are expounded.In view of the complicated topological relations and massive element of discrete models,3D reduction integral brick element is implemented considering the balance of calculation precision and calculation efficiency.Zero energy mode and restraints are described.Some mainstream commercial finite element software are introduced.The LS-DYNA code,which is known as explicit nonlinear calculation,is selected as the calculation tool to simulate and analyze.3.Due to environmental and human factors,the original seismic wave acceleration signal is usually mixed with noise,resulting in untruthfulness of earthquake analysis.According to the basic principle of seismic wave processing,the ground acceleration of Wenchuan earthquake is fixed using band-pass filtering and regression analysis,and the ground velocity and ground displacement are calculated.The results show that the baseline drift of the seismic wave is corrected after revise,which is in accordance with the actual situation of ground motion.In order to study the change of the seismic wave properties before and after the numerical correction,the response spectrum is calculated.Results show that the response of structures induced by the processed signal is similar to that of the original one.It can be concluded that the processing method adopted in this paper has little effect on the spectral characteristics of the seismic wave acceleration signal.4.Considering the material properties of brick and mortar,appropriate constitutive relations are chosen to describe their mechanical behavior,and the specific material parameters are given.Finite element models of masonry walls are established,mechanical behavior under cyclic loading is simulated and analyzed.Results show that the deformation pattern of the wall as well as the distribution of the fracture are in good agreement with the experimental results,and the validity of the discrete model is proved.It is found that although the low strength and rigidity of the masonry,it exhibits certain ductility and energy dissipation under cyclic loading.Comparing the continuous wall and the walls with opening,early degradation phenomenon is found on the walls with opening design.5.The discretization models of two-story masonry structures with three different reinforcement schemes(no reinforcement,1st floor reinforcement and double floor reinforcement)are established.The mechanical response and collapse behavior under earthquake action are simulated and analyzed.The results show that the nonreinforcement masonry structure without reinforcement can barely maintain integrity under earthquake action due to its low strength and rigidity,which is prone to crack and collapse.After strengthening the first floor with structural column,the overall stiffness of the structure is improved and the seismic capacity is enhanced as no integral collapse is observed,however local destructions of masonry walls can be noted.Due to the ductility and energy absorption capacity of masonry,the first floor dissipates some of the seismic wave energy,and the cracking degree of the second floor of the structure is reduced.Structural column are set up in the upper and lower layers as well as the masonry reinforcement,structural strength and stiffness are significantly improved.Only local failure of brick and mortar is observed under earthquake action,the structure shows good seismic capacity.