Eccentric Compressive Behavior Of GFRP Tube-Confined Concrete-Encased Cross-Shaped Steel Composite Column

In the past two decades fiber-reinforced polymers(FRP)have been widely used a confining material for the strengthening and seismic retrofit of reinforced concrete columns.More recently,the use of FRP tubes as a confining device as well as a corrosionresistant skin has also been widely explored for new construction.FRP tube-confined concrete encased cross shaped steel columns(FCCSCs)are a new form of hybrid columns has been developed recently.An FCCSC consists of a square FRP outer tube,a cross shaped steel section and concrete filled in between.The limited researches on axial compressive behavior of FCCSC have demonstrated that this sectional configuration ensures that the concrete is very effectively confined despite the square shape of column.In addition,the cross shaped steel section serves as the ductile longitudinal reinforcement for the loads in two lateral directions and its possible buckling is constrained by FRP outer tube and the concrete leading a column that is highly ductile.In order to further investigate the eccentric compressive behavior of FCCSCs,this research presents finite element(FE)simulation of FCCSC using ABAQUS.The main contents of research are:The present work demonstrates the nonlinear finite element analysis(NLFEA)of eccentrically loaded FCCSC specimens.The variable parameters of eccentricity,slenderness ratio,and thickness of outer GFRP tube were considered in the analysis.To establish the finite element model of FCCSC specimens,the confined concrete was modeled using non-linear concrete damaged plasticity(CDP)model,the steel section was modeled as a bilinear elastoplastic material,and the GFRP outer tube was modeled as a linear elastic material.The accuracy of established finite element model was verified by comparing with the existing axial compressive experimental results.The compassion shows that the simulation results agree well with the test results.Based on the verified finite element model,parametric analysis was carried out to investigate the influence of eccentricity,slenderness ratio,and thickness of FRP tube.The eccentricity was varied from 0 to 100 mm with increment of 25 mm,while the slenderness ratio was varied from 3.0 to 6.0 and the thickness of FRP tube was 3 and 4 layers of thickness.On this basis,the influence of eccentricity,slenderness ratio and FRP tube thickness on the eccentric compression performance of FCCSCs is analyzed and obtained.The analysis results demonstrate that the concrete is effectively confined by the GFRP tube and cross-shaped steel and the buckling of steel section was completely constrained,resulting in the excellent eccentric compressive behavior.On the basis of analytical results,the axial force-bending moment(N-M)interaction diagram of FCCSCs is finally developed.From the N-M interaction diagram,it can be found that the balanced failure between large and small eccentricity will occurred when the eccentric ratio reached to 0.5 for all the FCCSCs with the slenderness ratio of 3 and 6.In this case,the confined concrete in the compressive zone reached to ultimate compressive strain and the cross-shaped steel in the tensile zone yield at the same time.