Research On Axial Compressive Behavior Of Fiber Reinforced Polymer (FRP) Concrete-filled Steel Tubes With Timber Infills

The new FRP-concrete-filled steel tube with timber infill composite column is composed of fiber-reinforced polymer(FRP)cloth or tube,wood core,concrete,and steel tube.This paper uses experimental research,numerical simulation,and theoretical analysis methods to study the axial compressive behavior of the new composite column.The main research contents and conclusions are as follows:(1)With wood core diameter,GFRP(Glass Fiber Reinforced Polymer)layer thickness,and layer angle,10 composite column specimens were designed,and the axial compression test was carried out.The failure process of each specimen was roughly divided into two stages:linear elastic stage and elastoplastic stage.For different wood core-sized specimens,the surface of the test piece bulges,and elephant feet appear in many places.With the increase in the number of external GFRP cloth layers,the internal concrete is scattered due to the presence of steel pipes.With different laying angles of GFRP cloth,the outer GFRP cloth appeared wrinkled and warped,and elephant feet appeared in many places.From the load-displacement curve of the specimen,it can be seen that all specimens are ductile failure.(2)when the size of the wood core of the composite column specimen increases,and the ultimate bearing capacity of the composite column(P_u)decreases,the initial stiffness(K)of each specimen has a decreasing trend,but the ductility performance(DI)and energy consumption performance(TA)are significantly improved;An average reduction 29.6%,and the load-to-weight ratio(P_u)only decreased by 18.1%on average.The average K value decreased by 21.3%,while the average K/W value decreased by only 7.9%;DI increased by43.9%on average,and(DI/W)increased by 69.8%on average.TA increased by 27.8%on average,TA/W increased by 48.1%on average.The wood core can effectively improve the load-to-weight ratio and ductility of the composite column.(3)Using the finite element analysis software ABAQUS to establish a new FRP-concrete filled steel tube with timber infill composite column axial compression finite element analysis model,simulate the displacement loading process of the specimen,analyze the deformation and stress cloud diagram of the component,and pass the ultimate bearing capacity.The simulation value is compared with the test result.The maximum error between the simulated value and the test value is 15.2%and the average error of the test piece is 5%.The ultimate bearing capacity of the composite column decreases with the increase of the diameter of the wood core and increases with the increase of the GFRP layer thickness and the layer angle.(4)Based on the limit equilibrium theory,establish a new type of composite column force analysis model,considering the main parameters such as wood core diameter,GFRP ply thickness,and ply angle.The formula for calculating the ultimate axial bearing capacity of a new FRP-concrete-filled steel tube with timber infill composite column is given.