Finite Element Analysis On Axial Compressive Stability Bearing Capacity Of FRP-concrete-steel Tubular Composite Long Columns

In recent years,fiber reinforced composites(Fiber Reinforced Plastic)have attracted more and more attention in the field of civil engineering because of their unique material properties and rich structural forms,which can well meet the requirements of modern structures for long span,heavy load,light weight and high strength.For example,the use of external paste FRP to repair and strengthen the structure,the use of FRP materials combined with traditional building materials to form new structural members,and so on.FRP-concrete-steel tube composite column(FRP-concrete-steel double-skin tubular columns,referred to as DSTC column)is proposed by Professor Teng Jinguang of Hong Kong Polytechnic University under this background.Considering the good performance characteristics and broad development prospects of DSTC columns,it is of great significance to study this new type of composite columns.This paper is based on the long column of DSTC.According to the relevant mechanical research results of axial compression,eccentric compression and seismic behavior of DSTC columns,the stability of composite long column structures under axial compression is studied by using the finite element software ANSYS.The specific research contents and results are as follows:In this paper,the stress of each part of FRP tube-concrete-steel tube composite long column is analyzed in the process of axial compression instability.The results show that the whole section is compressed and there is no axial tension in the process of load increasing to stable bearing capacity.For FRP pipe,before reaching the stable bearing capacity,the axial compressive strain on the larger compression side increases continuously,while the axial compressive strain on the less compressed side increases at first and then decreases.When the load reaches the stable bearing capacity,the tensile strain of the larger side of the span in the central direction is still much smaller than the ultimate fracture strain in the circumferential direction.For the steel pipe,the steel pipe on the larger side of the compression will yield before the load reaches the stable bearing capacity,but due to the constraint of concrete,there is no local buckling of the steel pipe.For concrete,due to the restraint of FRP pipe,steel pipe and axial pressure,the strength of concrete is improved,and the axial compressive stress of concrete is less than the peak stress after the increase of strength in the whole loading process.The influence of the material size of each part of the section of FRP pipe-concrete-steel tube composite long column on the stability bearing capacity of the structure is studied.The main factors to be considered include steel pipe thickness,FRP pipe thickness,hollow heart rate under fixed steel pipe wall thickness,hollow heart rate under equal diameter-to-thickness ratio and structure slenderness ratio.The results show that under the same column height,the stability bearing capacity and stability coefficient increase with the increase of steel pipe wall thickness.With the increase of the thickness of FRP pipe,the stability bearing capacity of members also increases,but the stability coefficient decreases with the increase of the thickness of FRP pipe.When the hollow heart rate of the member section is changed by the fixed steel pipe wall thickness,the stability bearing capacity reaches the maximum when the hollow heart rate is 0.65,and the stability coefficient increases with the increase of the hollow heart rate.Under the condition that the diameter-thickness ratio of steel pipe is constant,when the hollow heart rate of the member section is changed,the stability bearing capacity and stability coefficient increase with the increase of the hollow heart rate.For different column height,that is,corresponding to different slenderness ratio,the higher the column height is,the larger the slenderness ratio is,and the smaller the stable bearing capacity is.