Finite element flexibility method of reinforced concrete frame three dimensional inelastic seismic response
Three dimensional structure of inelastic response has been the law in the field of seismic research important topics. As structural testing by pilot scale and number of constraints, the overall structure of the prototype, the current mainly rely on computer simulation to study it, and test methods for components and small scale structure model.
For reinforced concrete frame, the current findings can not fully meet the actual needs, still left a lot of problems to be solved. In this paper, three dimensional reinforced concrete frame structure seismic response of inelastic dynamic analysis of several key issues that exist have been studied.
These issues include how to ensure the objectivity required parameter input, reinforced concrete columns under complex loading paths in the axial force and two way coupling between moments as well, including high axial compression ratio, variable axial impact, reinforced concrete columns softened inelastic buckling a series of complex issues.
Around these goals, this paper completed the following work: ① respectively, based on truss structure and nonlinear finite element stiffness method flexibility methods basic theory, model simulations using fiber multiaxial loading conditions rod cross section of the complex between force and deformation non linear relationship was established for material and geometrically nonlinear analysis of spatial beam unit as a basis for the preparation of the reinforced concrete frame structure inelastic response dimensional dynamic analysis procedures.
Each program of different fiber rod unit can have different material properties, ease of processing such as reinforced concrete structures constructed from different materials rod unit problem; Users simply enter the fiber material uniaxial stress strain relationship, parameter input objectivity and ease compliance requirements; program output in addition to the usual structure, unit and section level a lot of information, but also outputs the specified fiber stress or strain history such detailed information for researchers to conduct seismic Performance studies provide more convenience.
② The method based on the finite element stiffness and flexibility method of nonlinear spatial beam unit conducted a systematic comparative research. Studies show that: As usual stiffness method based on the use of a two node beam element is based on the lateral displacement of the Hermite cubic polynomial interpolation, linear interpolation Lagrange axial displacement assumption, only to meet the deformation compatibility condition and the junction point of the equilibrium conditions, is difficult to describe in reinforced concrete members strongly nonlinear stage of the actual state of deformation and accuracy to meet the equilibrium conditions inside the cell, it is difficult to effectively simulate such as reinforced concrete columns under complex loading paths in the axial force and bending moment between the two way coupling phenomena as well as softening, non elastic buckling force and other complex phenomena.
Although this problem can theoretically grid through encryption, about a cell is subdivided into several units addressed in a manner, which results in a calculated level of work times of growth, but also in a larger structure may numerical calculations lead to instability and convergence problems.
The rule is based on the compliance unit sectional force field is assumed as a starting point for establishing units for axial and bending deformation dominated beam unit, this assumption is usually able to get exactly satisfied, which is not subject to the nonlinear state unit effects, even after the unit enters the softening phase strongly nonlinear problems, equilibrium conditions inside the unit can still be strictly satisfied, thus compared with the stiffness method to analyze the efficiency and effectiveness has greatly improved.
③ The finite element flexibility method only in the material by the application of nonlinear problems in expanding into the material and geometrically nonlinear problems in the application. Based on Euler Bernoulli beam theorys basic assumption, combined with the finite element flexibility method presents the basic idea can be considered material and geometrically nonlinear analysis method for general nonlinear beam column unit. Several classic problems through numerical simulation and structural testing to verify the correctness of the proposed method.
④ The paper prepared by the nonlinear analysis procedures, including reinforced concrete bending structures cyclic loading test and six story reinforced concrete space frame shaking table test structure, including the number of instances of a numerical simulation experiment analysis, validation of the program The validity and reliability.
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