Experimental Study On The Axial Compressive Behavior Of GFRP-High Strength Concrete-High Strength Steel Composite Columns

With the rapid development of society,traditional materials and structures have been unable to meet the needs of the latest infrastructure construction.Therefore,a variety of new materials and structures emerge at the right moment.Through the combination of various new materials with superior performance,the mechanical properties of structures can be greatly improved.In recent years,the composite structure of FRP,Steel and Concrete has become the focus of research.Existing studies have shown that the innovative structural form combining FRP with traditional materials such as Steel and Concrete has the advantages of high cost efficiency and high performance.FRP-Confined Concrete Filled Steel Tube(FCCFST),Fiber confined steel-reinforced concrete column(FCSRC),and Double-skin Tubular column(DSTC)are typical composite columns.At present,there are many researches on innovative structural forms,but there are few researches on the application of high-performance materials such as high-strength concrete and high-strength steel to such composite columns.Based on this,an experimental Study on the Axial Compressive Behavior of GFRP-High strength concrete-High strength steel composite column has carried out.Parameters including the section form of steel(cross section steel,steel tube),the intensity of steel(Q345,Q460,Q690),concrete strength(normal-strength concrete,high strength concrete)and GFRP tube layer(0,4,8).Finally,The influence of the above parameters on the structural strength,stiffness,ductility and the interaction between FRP,concrete and steel was studied.This test mainly includes 54 specimens.18 of them are GFRP-High strength concrete-High strength cross section Steel composite Columns,including 12 FRP Confined steel-reinforced Concrete columns(FRSRC)and 6 Steel-reinforced Concrete columns(SRC).Another 30 specimens are GFRP-High strength concrete-High strength Steel tube composite Columns,including 12 Double-skin Tubular columns(DSTC),12 Double-tube Concrete Column with an FRP External Tube and a Steel Internal Tube(DTCC),6 Concrete-filled Steel tubes(CFST).4 Concrete filled FRP tubes(CFFT)and two Concrete columns(CC)were used as the control group.The results show that in GFRP-High strength concrete-High strength steel composite columns,the steel section does not affect the strain distribution of GFRP tube.Comparing to GFRP-High strength concrete-Normal strength steel composite column,the yielding of high strength steel is delayed,the ultimate axial load and ductility of the structure are improved,and the expansion speed of the structure is decreased.The use of high-strength concrete can increase the ultimate axial load and the stiffness of the structure,but cause the reducing of structure ductility and the increasing of structure expansion speed.With the GFRP layers increased,the ultimate axial load、ductility and deformation capacity of the structure increased,the expansion speed decreased.GFRP layers have no obvious effect on the stiffness.Under the same condition of steel strength,concrete strength and GFRP layer number,the ultimate axial load of FCSRC is lower than DTCC but higher than DSTC,the ductility of DSTC is lower than DTCC but higher than FCSRC,the expansion speed of DTCC is lower than FCSRC but higher than DSTC.The results also show that in GFRP-Normal strength concrete-High strength steel composite columns,the combined effect between GFRP、concrete and steel of DSTC is worse than DTCC but greater than FCSRC,The three material in DTCC combined very well,and the actual mechanical properties is significantly better than the theoretical mechanics performance.DSTC performs second and FCSRC is relatively weak.The combined effect order in GFRP-High strength concrete-High strength steel composite columns is DTCC、FCSRC、DSTC.Using high-strength steel and increasing GFRP layer can improve the composite effect.