Finite Element Flexibility Method Based Shear-Critical Nonlinear Analysis Of Reinforced Concrete Frame Structures

Reinforced concrete frame is one of the most widely used structural system ofreinforced concrete structure, and it is also an important part of the other structuralsystem, although it has a long history and many researchers have in-depth study, thereare still many problems have not been solved. Nonlinear analysis of reinforced concreteframe, usually doesn’t consider the shear performance, but when the shear span isrelatively small and shear effect is significant, especially under the seismic actionshould not ignore the impact of the non-elastic shear deformation.The element analysis model with shear effect includes the solid finite elementmodel and bar member analysis model. Among which the finite element model of thebar member analysis model combined with the cross-section analysis model-fiber model,can not only overcome the shortcomings of the solid finite element model, but alsobetter reflect the structural and element‘s nonlinear phenomenon. Due to the assumeddisplacement shape function based on the theory of finite element model of thetraditional stiffness method is difficult to describe the element actual displacement fieldin the strongly nonlinear stage, so it is difficult to effectively simulate the nonlinearshear effect, to get high accuracy results, it is necessary to discrete the structuralmember into more elements, but the specific number of units is not known in advance,which needs trial constantly to get a better simulation results, and with the increase ofthe number of units, the computing workload will be doubled and redoubled, may causethe instability of the numerical analysis. The flexibility method selected in this papertakes the force interpolation functions as a starting point, the assumed cross-sectionforce distribution is always in line with the actual internal force distribution, which hasnothing to do with the element state, and it is able to achieve the desired simulationresults without an increase in the number of units, the flexibility method is significantlybetter than the stiffness method in the analysis of the efficiency and accuracy.Based on the finite element theory, along with the line as the material, section,element and structure, following the idea of macroscopic to microcosmic, local to thewhole, combined with the flexibility method theory, the fiber model, modifiedcompression field theory (MCFT), this paper establishes the flexibility-shearbeam-column element model and incorporates the model into the FEAP programplatform, so that can be used for the nonlinear analysis of reinforced concrete frame. In order to verify the correctness of the theory and reliability of the program, this paper hasrespectively completed numerical simulation analysis in two levels of component andstructure. From the results of the simulation, the force interpolation functions of theflexibility-shear beam-column element model can accurately describe the distribution ofthe force field of the various stages of the unit, can simulate the nonlinear characteristicsof the structure and component under the influence of shear effect, and has successfullysimulated the coupling phenomenon among the axial force, bending moment and shearsforce, it has greatly improved the analysis efficiency and accuracy compared to thestiffness-shear element model. But in this paper there are some problems needed furtherresearch such as using a simplified cross-section shear strain distribution, did notconsider the role of the longitudinal reinforcement pin bolt, stiffness after peakdecreased too fast etc.