| In reinforced concrete structural members under seismic loading,the reinforcement may be subjected to large repeated tensile and compressive strains,which can lead to large lateral deformation of the reinforcement,i.e.,buckling of the reinforcement,under the compression of the damaged concrete if the restraint of the reinforcement is insufficient.Buckling of longitudinal reinforcement in reinforced concrete columns can also lead to rapid loss of reinforcement strength under compression,which has a significant impact on the seismic performance of the column,including ductility,energy dissipation capacity and stiffness degradation process.In order to prevent premature buckling of longitudinal reinforcement in reinforced concrete columns,steel casing,fiber casing restrained reinforcement,which is filled with high-strength concrete or mortar to retard or prevent buckling has been proposed.FRP-confined concrete core-encased rebar is a Composite component made of steel,high-strength concrete or mortar,and fiber composite material,referred to as FCCC-R.This paper uses one-way glass fiber cloth combined with epoxy resin adhesive This paper investigates the effects of winding angle,number of layers and length to slenderness ratio on the Buckling and hysteretic properties of FCCC-R specimens using unidirectional glass fiber cloth combined with epoxy resin adhesive to wrap the mortar and core reinforcement.The main work and results are as follows.（1）The Buckling properties of FCCC-R specimens were investigated experimentally.It is shown that the FCCC-R specimens show an obvious secondary rising segment of the compressive load-displacement curve compared with the pure steel specimens.Changing the winding angle,the number of layers of composite material and the length to thin ratio of the specimen have less effect on the first linear phase of the load-displacement curve of FCCC-R specimens and more effect on the second rising phase.The length and peak load of the second rising phase of the load-displacement curve of FCCC-R specimens are positively related to the number of wrapped layers of composite material and inversely related to the length-to-density ratio（L/d）of the specimen.（2）The hysteresis performance of FCCC-R specimens was investigated experimentally.It is shown that the FCCC-R specimens are divided into two stages under reciprocating load compared with the pure steel specimens,which are the pre-buckling stage（reinforced section）and the post-buckling stage of the specimens.When no buckling damage occurs in FCCC-R specimens,the hysteresis performance of FCCC-R specimens is enhanced compared to that of pure reinforcing steel specimens mainly due to the improvement of compressive properties.After flexural damage of the FCCC-R specimen,the hysteresis performance of the FCCC-R specimen is similar to that of the pure reinforcement during subsequent loading due to the damage of the composite material.By applying reciprocal loading to the FCCC-R specimens,when the inner layer of the specimen is wound at 0°,the specimens are only improved in compressive properties compared to the reinforcement,and the tensile properties are not changed.The enhanced hysteresis performance of FCCC-R specimens increases with the increase of FRP layer thickness,and the enhanced hysteresis performance of FCCC-R specimens decays faster with the increase of specimen length-to-density ratio（L/d）.（3）Based on ABAQUS,finite element numerical simulations were performed for the flexural properties of FCCC-R specimens.The finite element software ABAQUS was used to simulate the axial compression of FCCC-R specimens,and the results showed that the load-displacement relationship of the specimens and the damage of the fibers could be simulated more accurately by the finite element software.The results show that the FRP lamination angle and the initial defect size can be used to extend the axial pressure of the specimen.The design curve equation of FRP restraint thickness and specimen length-to-density ratio L/d for the FCCC-R specimen with two FRP lamination angles is obtained by the finite element simulation. |
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