Refined Numerical Substructure Methods For Seismic Inelastic Analyses Of Tall Building Structures

Tall building structures may progressive collapse due to damage of key support members under the extreme loads in nature,especially under strong earthquakes,resulting in great economic losses and casualties.China is a country with many earthquakes,and it is of great significance to study the dynamic disaster mechanism and perform elastoplastic analysis for tall building structures under strong earthquakes.Finite element numerical simulation is the most effective analytical method for dynamic disaster simulations of tall buildings,but considering two factors:firstly,the computational efficiency of nonlinear analyses of large-scale structures is extremely low;secondly,the numerical accuracy of key support members of the tall building structure under strong earthquakes is not enough,therefore,it is a challenging problem for engineers that the dynamic disaster numerical simulation of tall building structures.In this paper,the computational efficiency and numerical accuracy of the tall building structure are studied.Firstly,in Chapters 2 and 3,efficient numerical methods are presented to speed up the computation of the whole structure.Secondly,in Chapters 4 and 5,refined nonlinear finite element numerical models and non-local Peridynamics models are developed and proposed to capture the strong nonlinear behaviors and discontinuous damage and failure of the key support member.In Chapter 6,the efficient numerical method combined with the refined nonlinear numerical models is used to perform the seismic analysis of tall buildings.The main contents of this paper are as follows:(1)A novel numerical substructure method(NSM)for seismic elastoplastic analyses of tall building structures is proposed.In this method,structural dynamic responses are firstly calculated by using a linear elastic FE model of the whole structure,named as master structure,then based on the structural displacement field,elastoplastic states of all structural components or elements are determined.Once the structural component or element yields,it will be isolated and simulated in a substructure model.In the substructure,the actual resisting force of the yield component or element is computed and then transferred to the master structure.Subsequently,an equivalent external force calculated from the resisting force is applied to the master structure,and finally,the actual structural dynamic responses are re-calculated by an equivalent linear elastic analysis(ELEA)of the master structure.According to the degree of nonlinearity of the structural component,a conventional nonlinear element,refined FE substructure,and Peridynamics model are respectively used to simulate the common structural component with a low degree of nonlinearity,the local component with a high degree of nonlinearity,and the component with discontinuous damage and fracture.In this paper,the governing equation for ELEA of the master structure is derived,three different computational algorithms are designed,and the ELEA computation platform is established and integrated into the OpenSees.Taking the plane steel frame and reinforced concrete(RC)frame structure as examples,the accuracy,reliability,and efficiency of the ELEA for the master structure are verified.(2)An efficient parallel numerical substructure method(PNSM)is developed for nonlinear analysis of large-scale structures.The proposed method combines the above numerical substructure method and conventional domain decomposition method,thus the limitation of the serial computation method can be omitted.The large-scale structural system is divided into several independent,parallel computing and small-scale subdomains by using domain decomposition,and yield structural components in each subdomain are analyzed in an isolated nonlinear substructure.The governing equations for ELEA of the main-and subdomains are derived,and their computational algorithms and analytical processes are designed and introduced in detail,respectively,finally,the parallel computation platform of the ELEA for the master structure is established and integrated into the OpenSees.The seismic elastoplastic time-history analysis of plane steel frame and RC frame structures are performed,the results show that the PNSM is accurate,reliable,and efficient,and has the ability to analyze nonlinear structures with much larger scale.(3)A refined numerical substructure calculation analysis platform is established,in which conventional elastoplastic behaviors of structural key components can be captured using isolated cross-platform substructure models.In order to accurately simulate the strong nonlinear behavior of local key components,refined FE models of general components,such as buckling restrained braces and RC shear walls,are developed and proposed,and their accuracies are verified by comparing their simulations with experimental results.Boundary(displacement and reaction)treatment methods of the refined FE models of the isolated substructures are derived,and the cross-platform simulations between OpenSees and OpenSees and that between OpenSees and ABAQUS are developed using the CS and text read-write techniques,respectively.Take the plane steel frame with braces as an example,the results show that refined simulation of isolated substructure can accurately capture the damage behavior of local key components and improve the numerical accuracy of the whole structure.(4)Based on the theory of Peridynamics,local discontinuous damage and failure of structural key components can be captured using isolated cross-platform substructure models.Based on Peridynamics theory,local cracking behaviors of general components can be accurately simulated,and an efficient and accurate coupled analytical model with finite element master structure and Peridynamics substructure model is established.The generalized Peridynamics substructure is developed based on the OpenSees,the boundary treatment method of the Peridynamics substructure model is described in detail,dynamic and static equivalent equilibrium equations of master structure and substructures are derived,and an efficient dynamic explicit and static implicit algorithm are designed.Through the refined simulation of plane concrete cantilever beams with local cracks,the results show that the coupled model with FE master structure and Peridynamics substructure can efficiently and accurately simulate the local discontinuous damage and fracture of the local key components.(5)The applicability and effectiveness of the refined numerical substructure simulation method are verified by seismic elastoplastic refined numerical substructure analyses of two tall building structures.Two tall building steel frames with common and buckling restrained braces and a tall building frame-RC shear wall structure are taken as the research objects and analyzed by using the numerical substructure method.A coarse FE model is built in the master structure,and in the isolated substructures,yield beam and column components are simulated by nonlinear fiber elements,while yield braces and RC shear walls are calculated by using the above developed and proposed refined finite element models.The results show that the proposed numerical substructure method can accurately capture the damage and fracture behavior of the local key component in the tall building structure under strong excitations,and effectively simulate the plastic zone extension,damage evolution,and failure modes of the whole structure.