Research Of Mechanical Behavior Of GFRP Confined Steel Tube Recycled Concrete Stub Columns

Recycled Aggregate Concrete(RAC)is a innovative concrete made by recycling waste concrete into recycled aggregates(mainly coarse aggregates),mixed with gradation in a certain proportion,is a new green material with significant social significance,economic and environmental value,but compared to ordinary concrete,its strength and stiffness is lower,density is smaller,creep shrinkage is large,durability is poor,currently in the actual project is mainly used in non-stressed or less stressed structures.Steel tube recycled concrete is filled with recycled concrete inside the steel tube,and the structure of the steel tube and recycled concrete are jointly stressed,which can make up for the deficiencies of each when they are separately stressed,and has positive significance in avoiding or delaying the premature local buckling of the steel tube,and the outer steel tube provides strong restraint to the recycled concrete,which improves the mechanical properties of the core recycled concrete with high bearing capacity and good ductility,and is an effective way to solve the problem of construction waste dumping and the scarcity of natural aggregates.GFRP(Glass-Fiber Reinforced Plastic)has the advantages of light weight,high strength,anti-corrosion candle and fatigue resistance,etc.It not only improves the restraint effect of regenerated concrete of steel pipe,improves the bearing capacity and ductility of the member,but also reduces the amount of steel used in the member,reduces the self-weight of the member and solves the problem of exposed corrosion of steel tubes.This paper takes the GFRP-confined steel tube recycled concrete composite member as the research object and carries out the research on the mechanical behavior of its composite member,and its main research work and findings include the following:(1)The axial compression tests of 24 GFRP confined steel tube recycled concrete stub columns and 12 steel tube recycled concrete stub columns were completed to analyze the effects of parameters such as recycled aggregate replacement rate,recycled concrete strength,steel tube thickness and number of GFRP layers on the axial compression performance of the combined columns.The results show that the axial compression damage pattern of the GFRP-confined steel tube recycled concrete stub columns shows that the specimens are damaged by bulging and deformation in the middle.With the increase of recycled aggregate replacement rate,the bulging deformation of the specimens intensified,and the specimen stiffness and bearing capacity decreased,but the later ductility became better;GFRP could improve the bearing capacity and ductility of the specimens;the thickness of steel tube and the strength of recycled concrete could effectively improve the preliminary stiffness and ultimate bearing capacity of the specimens,but the later ductility decreased significantly.(2)Based on the axial compression test of GFRP conffined steel tube recycled concrete stub column,the equation of axial compressive load capacity of GFRP conffined steel tube recycled concrete stub column is proposed by equilibrium theory,and the calculation results are compared with the existing research equation and the equation of this paper,which takes into account the influence of recycled concrete on the mechanical properties of the combined column,and the calculated value of the equation of this paper is in better agreement with the test value and has higher safety.ABAQUS was used to conduct finite element simulations of axial compression tests on tube columns of GFRP confined steel tube recycled concrete,to analyze the stress development law of each part of the material in the process of axial compression,to compare the calculation and test results,and to establish a computational model that can be used to analyze its axial compression for theoretical and practical engineering reference.(3)The seismic model of GFRP confined steel tube recycled concrete composite column was established by using Open Sees,and seven parameters such as axial compression ratio,aspect ratio,recycled aggregate replacement rate,number of GFRP layers,recycled concrete,thickness of steel tube and yield strength of steel were designed.The seismic hysteresis curves and skeleton curves of the members with different parameters were analyzed systematically to elaborate the influence law of each parameter on the seismic performance of the specimens.The results show that the GFRP confined steel tube recycled concrete composite columns exhibit stable force performance and excellent energy dissipation capacity.Increasing the steel strength and steel tube thickness can significantly improve the seismic performance of the composite column;appropriately reducing the length-to-diameter ratio of the members has some improvement on the seismic performance of the members;the replacement rate of recycled aggregate,GFRP thickness and the strength of recycled concrete have no significant effect on the hysteresis capacity of the specimens;increasing the axial pressure ratio will lead to a significant decrease in the seismic performance of the composite members.