Research Of The Flexural Behavior Of High-strength Concrete Beams And The Seismic Performance Of High-strength Concrete Columns Reinforced With Hybrid High-strength Steel And CFRP Bars

Carbon fiber reinforced plastic(CFRP)is a new high-performance material with the advantage of light weight,high strength and corrosion resistance.The high-strength steel and CFRP bars are both used in high-strength concrete structural members to not only improve the durability of RC members but also reduce the brittleness of high-strength concrete.Because of the elastic properties of CFRP bars,it can also reduce the residual deformation and improve the post-yield stiffness of the RC members,then further improve the recoverability of the structure and better exert the respective advantages of materials,which can decrease the use of building materials,and provide an effective way for energy conservation and emission reduction.To study the flexural behavior of high-strength concrete beams and the seismic performance of high-strength concrete columns reinforced with high-strength steel and CFRP bars,the high-strength concrete,high-strength steel fiber reinforced concrete and reactive powder concrete(RPC)was used in the experiment respectively.The study is mainly divided into two aspects:(1)the three-point bending test was conducted in two high-strength concrete beams reinforced with high-strength steels and five high-strength concrete beams reinforced with high-strength steel and CFRP bars.The finite element model was established by considering the constitutive relations of different materials.The accuracy of the model was verified by the comparison with experimental results.Parametric analysis was carried out on the basis of the verified model,and various parameters were obtained to study the flexural behavior of hybrid reinforced high-strength concrete beams.(2)The seismic performance tests were carried out on two high-strength concrete columns reinforced with high-strength steel bars and seven high-strength concrete columns reinforced with high-strength steel and CFRP bars.The effects on seismic performance and recoverability of the hybrid reinforced high-strength concrete columns were studied by various factors,such as different concrete types,different axial compression ratios and the bond stress in CFRP bars surface.The bearing capacity,deformation ability and failure mode were also analyzed.The variation rules of indexes related to seismic performance such as displacement ductility,stiffness degradation and energy dissipation capacity of the specimens were studied.The finite element model and parametric analysis was carried out to study the skeleton curves of three high-strength concrete columns reinforced with high-strength steel and CFRP bars,the results of the finite element model was studied by the comparison with experimental results,and various parameters were obtained to study the seismic performance of hybrid reinforced high-strength concrete columns.The main conclusions are as follows:1.The results showed that the failure mode of all high-strength RC beams was bending failure,high-strength concrete beams reinforced with steel and CFRP bars have a good ductility and energy-dissipating capacity.The flexural capacity of hybrid reinforced high-strength concrete beams was lower than that of high-strength RC beams with the same nominal longitudinal reinforcement ratio,but the deformation ability of which was obviouslyimproved,and the load-displacement curve shows a characteristic of bilinearity.The addition of steel fibers in high-strength concrete improved the flexural capacity of specimen.The flexural capacity of the hybrid reinforced high-strength concrete beam with unbonded CFRP bars was significantly lower than the specimen with bonded CFRP bars,with the number of cracks decreased and the crack spacing increased,however the deformation capacity was basically the same.The theoretical calculation results of all specimens with measured material strength values are lower than test results,and the simulation results can be basically fitted with the test values.Parametric analysis shows that the bearing capacity of hybrid reinforced high-strength concrete beams increased with the reinforcement ratio of high-strength steel and CFRP bars,the stiffness increased with the increase of the reinforcement ratio of the high-strength steel bars.2.Except for the control specimen with low reinforcement ratio,the failure mode of other high-strength RC columns were bending failure in the low-cycle reciprocating pseudo-static test,and the steel fiber concrete columns and RPC columns showed a good ductility and energy-dissipating capacity,and the flexural capacity and deformation ability of which were also significantly improved,the specimen had a stable post-yield stiffness.The flexural capacity,deformation ability and ductility of hybrid reinforced high-strength concrete columns with bonded CFRP bars were obviously higher than that of specimen with unbonded CFRP bars,after the addition of steel fiber,the seismic performance of latter improved.With the increase of axial compression ratio,the flexural capacity of hybrid reinforced high-strength concrete columns increased,but the ductility and energy-dissipating capacity were significantly reduced.Under the low axial compression ratio,hybrid reinforced high-strength concrete columns with bonded CFRP bars had a stable post-yield stiffness;under the medium and high axial compression ratio,hybrid reinforced high-strength concrete columns exhibited a negative post-yield stiffness.The post-yield stiffness of hybrid reinforced high-strength concrete column with unbonded CFRP bars can keep stable first,but decreased latter.Under low axial compression ratio,the simulative skeleton curve of hybrid reinforced high-strength concrete columns can be well fitted with the experimental results.The parametric analysis of skeleton curves of hybrid reinforced high-strength concrete columns under low axial compression ratio shows that the elastic stiffness of the specimen improved with the increase of the reinforcement ratio of the high-strength steel bars;the ultimate displacement of the hybrid reinforced high-strength concrete columns increased with the increase of the CFRP reinforcement ratio,but decreased with the increase of the strength of steel bars.