Panel Zone Behavior And Theoretical Research In Beam-column Connections To Square Concrete-filled Tubes

It is of great importance to understand the panel zone behavior in steel-concrete composite structures analysis.This paper focused on panel zone in beam-column connections to square concrete-filled tubes.Direct shear test,fine finite element model analysis,multi-scale finite element model analysis,theoriotical analysis and macro model analysis were conducted.Major research achivements includes:(1)Panel zone direct shear test was designed and performed.Based on stress state investigation,direct shear test which would reflect the main features of panel zone was promoted.13 specimens with different parameters were fabricated and tested.Thus,panel zone shear behavior was acquired and lay the foundation of fine finite element model analysis.(2)Suitable fine finite element model was suggested for panel zone analysis.Taking engineering practicity and calculation accuracy into account,concise parameters were adopted including a revised core concrete shear retension factor.The model was calibrated by the direct shear test and showed good performance.(3)Multi-scale finite element model for internal beam-column connections was suggested.Multi-scale connection subroutines were coded,therefore mechanisms and errors were comprehensively analyzed.Combined with the understanding of internal beam-column connection,dependable multi-scale finite element model was proposed and compared with experiments reported.(4)Loading mechanism,capacity calculation method,deformation feature and macro spring model were proposed.With the help of multi-scale finite element models,influences of different parameters to the panel zone behavior were investigated.Meanwhile,reasonable mechanism was suggested to derive a proper calculation method for panel zone shear capacity.Furthmore,equation which could reflect the relationship between the shear force and the shear deformation was promoted.Using this equation,a macro spring model with simplicity and efficiency was finally set up.This model could be applied in complicated cyclic loading situation and presented acceptable performance compared to the multi-scale model and experiments.In conclution,this paper proposed a new effective testing method for panel zone behavior investigation,a pratical fine finite element model with calibrated parameters,an efficient multi-scale model based on comprehensive analysis,an explaination of panel zone shear mechanisms and a marco spring model which was applicable for structural analysis with member system.This paper was of significant value in improving our understandings for panel zone and instructing corresponding engineering design in beam-column connections of squared concrete-filled tubes.