Finite Element Simulation Of Mechanical Properties Of FRP-confined Reinforced Concrete Column Under Steel Corrosion

Fiber Reinforced Polymer(FRP)composites have been widely used in seismic reinforcement and durability enhancement of concrete structures in recent years due to characteristics of light weight,high strength,corrosion resistance,easy construction and low maintenance cost.At present,a large number of studies have been carried out on the axial compressive performance of FRP-confined concrete columns at home and abroad,but the following problems still exist:1.In order to load conveniently,most of the existing tests take small size short column as the standard specimen,while the research on medium or large size long column is not enough.2.Most of the existing stress-strain models of FRP-confined concrete are based on the axial compression test results of FRP-confined concrete cylinder,which cannot accurately simulate the inevitable joint constraint of steel bar and FRP in engineering.3.In engineering,most structures are under eccentric load or flexural action.At present,there is a lack of thorough research on the mechanical properties of FRP-confined reinforced concrete under eccentric compression and pure flexural action.In order to more accurately understand the FRP-confined large-size reinforced concrete columns under eccentric compression and pure bending,it is necessary to continue to carry out research work,improve the stress-strain model of confined concrete,analyze the whole process of FRP-confined reinforced concrete columns,and provide technical support for the reinforcement design of concrete structures.In this paper,a finite element model considering plastic damage is established for FRP-reinforced composite confined concrete.The accuracy of the stress-strain model was verified by comparing with the axial compression and eccentric compression test data of FRP-confined reinforced concrete columns in the literature.The mechanical properties of 136 FRP-confined concrete columns under axial compression,eccentric compression and pure bending were systematically studied.The main research contents are as follows:1.When the concrete is subjected to FRP-reinforced composite constraints,the stress of the concrete is complex.it is difficult to obtain accurate internal force distribution and limit state in the simulation of FRP-constrained reinforced concrete columns by the previous FRP-confined analysis model.The correction method of FRP reinforced composite plastic damage model of confined concrete,through the calculation of FRP restraint stiffness of specimen and restrained reinforced equivalent stiffness,and allocation in proportion to the model,the stress and strain of confined concrete under axial compression,eccentric compression,pure bending of reinforced concrete column FRP constraint has carried on the finite element simulation,accurate simulation of FRP constraint force process and limit state of reinforced concrete column.2.Due to the influence of various factors such as the accuracy of test equipment and material uniformity,many previous experimental studies have not fully proved the influence of loading path on the limit state.This paper verified that the stress path has no significant influence on the ultimate bearing capacity of FRP-confined concrete,and the eccentric axial displacement loading and the axial force + angular displacement loading has no significant influence on the stress distribution in the ultimate state.3.For FRP-confined reinforced concrete columns,with the increase of load eccentricity,the area with the highest principal stress ratio(intermediate principal stress/minimum principal stress)gradually moves to the maximum compression area of concrete,but its size does not increase gradually.With eccentric compression,the axial stress-strain curve of the mid-height section along the eccentric direction is different from that of the FRP restraint concrete column,and the axial stress of the stirrup area in the compression zone is the largest.The maximum point of external FRP circumferential strain corresponding to two local adjacent stirrups is located between the cross-section of equal vertical distance between the two stirrups and the cross-section of the adjacent stirrups.With different axial load,the eccentricity of the bearing capacity limit state,there are two possible when axial displacement is small,load eccentricity on the surface of the concrete compression zone largest FRP fracture,split concrete destroyed rapidly,while the breaking point for the bearing capacity limit state,when the larger axial displacement load eccentricity,FRP are not broken,but the column has reached the ultimate bearing capacity,then the ultimate bearing capacity corresponds to the ultimate state.4.Before steel corrosion,the axial stress of concrete near the steel bar is the highest,followed by the core area and the lowest at the protective layer.As stirrups continue to rust,the axial stress of concrete in the core area continues to decrease,and finally is lower than that of concrete in the protective layer.The axial compression bearing capacity of the column decreases significantly,but the bending bearing capacity does not change significantly.With the continuous corrosion of the longitudinal bars,the axial stress of the concrete near the reinforcement and in the core area continues to decrease,and finally is lower than that of the concrete in the protective layer.The axial compression capacity and bending capacity of the column decrease significantly.5.After reinforcement corrosion occurs when the reinforced concrete column strengthened with FRP earnings ratio depends on the kind of reinforcement and bearing capacity of corroded degree,to give priority to with axial compression specimens,stirrups corrosion is serious,the benefits of FRP reinforcement is lower,to give priority to with the bending specimen,longitudinal reinforcement corrosion is more serious,the benefits of FRP reinforcement is lower,if not for the above two cases,the more serious the corrosion is,the higher the FRP reinforcement benefit will be.The greater the number of FRP reinforced layers,the greater the increase in axial compression capacity,but the little increase in flexural capacity.Increasing the strength of concrete will significantly improve the axial compression capacity of FRP constrained reinforced concrete columns,but the increase of flexural capacity is small.The greater the column slender-to-slender ratio is,the lower the axial bearing capacity of FRP constrained reinforced concrete columns is,and the change of the flexural bearing capacity is not obvious.