| Due to the shortcomings of large self-weight and difficult transportation during construction,the concrete-filled steel tube(CFST)arch structure makes it difficult to apply in certain roadway environments with relatively poor conditions.Therefore,this paper developed a new CFRP-confined concrete arch structure,and carried out axial compression,eccentric compression and pure bending tests of CFRP-confined concrete elements.Then,the test results were compared with that of CFST and concrete-filled geotextile tube(CFGT)confined with carbon fiber mesh fabric.Taking the data measured in the laboratory tests as parameters,a series of numerical simulation tests were carried out,which could obtain the stress-strain responses under the influence of multiple factors.Based on the deformation law obtained from the laboratory tests and the numerical simulation tests,the working mechanism of CFRP-confined concrete under different load conditions was analyzed,and the theoretical study of the bearing capacity calculation of the tested specimens.The relevant conclusions were summarized as follows:(1)Comparative study on axial compression bearing behavior of members of CFRP-confined concrete arch structureThe ultimate load of CFRP-confined concrete under axial compression is 1850 kN.The results of axial compression tests show that the confinement of CFRP can not only improve the bearing capacity,but also significantly affect the failure mode.Compared with other confinements of concrete,the ultimate bearing capacity of CFRP-confined concrete is higher than that of CFGT and lower than that of CFST.A significant correlation between the strain characteristics of confinement materials and the overall strain characteristics of confined concrete is found by analyzing the strain community distribution of concrete with different confinements.A numerical simulation test under axial compression is established,where the simulation parameters are set according to the axial compression tests and material tests.The numerical simulation results show that the number of CFRP layers and concrete strength levels can significantly affect the ultimate axial compression bearing capacity of the specimens.The ultimate load of specimens with 6 CFRP layers and 9 CFRP layers increases by 37.8%and 73.9%,respectively,compared with the specimen with 3 CFRP layers.The ultimate load of specimens with concrete strength levels of C40 and C50 increases by 13.6%and 27.1%,respectively,compare with the specimen with concrete strength levels of C30.Based on the deformation laws obtained from the laboratory tests and the numerical simulation tests,a theoretical model of axial bearing capacity calculation of CFRP-confined concrete is proposed.The model analysis shows that the number of CFRP layers is positively correlated with the ultimate bearing capacity of the specimens,while the radius of concrete is negatively correlated with the stress of internal concrete.However,the elastic modulus of the concrete will not have a significant effect on the stress of internal concrete.(2)Comparative study on eccentric compression bearing behavior of members of CFRP-confined concrete arch structureThe ultimate load of CFRP-confined concrete under eccentric compression is 910.2 kN,which is higher than that of CFGT and lower than that of CFST.CFRP mainly improves the ultimate bearing capacity of the specimen by reinforcing the concrete in the tensile zone.Through the strain analysis of each section,the strain of compressive side of the CFRP-confined concrete specimen in middle section is greater than that of tension side.The average growth rate of the axial strain on the compressive side and the tensile side is 4.39 times and 2.52 times of the neutral side,respectively,while the average growth rate of the hoop strain is 1.92 times and 0.57 times of the neutral side.Compared with CFST and CFGT,the crushed concrete is found in the compressive zone of the CFST and CFRP-confined concrete,while the crushed concrete is found in the tensile zone of the CFGT.The increment of axial strain of CFRP-confined concrete is more linear than that of CSFT,while the plastic deformation characteristics during the yield stage is more obvious.A numerical simulation test under eccentric compression is established,where the simulation parameters are set according to the axial compression tests and material tests.The numerical simulation results show that the ultimate load of specimens with 6 CFRP layers and 9 CFRP layers increases by 71.56%and 120.59%,respectively,compared with the specimen with 3 CFRP layers.The ultimate load of specimens with eccentricity of 0.4 and 0.6 decreases by 10.5%and 31.5%,respectively,compare with the specimen with eccentricity of 0.2.Based on the deformation laws obtained from the laboratory tests and the numerical simulation tests,a theoretical model of eccentric bearing capacity calculation of CFRP-confined concrete is proposed.The model analysis shows that the increasing of number of CFRP layers leads to the improvement of the ultimate bearing capacity of the specimens,and the number of CFRP layers obviously affects on the movement of neutral axis.The movement angle of the neutral axis towards the tensile zone increases with the number of CFRP layers.(3)Comparative study on the pure bending bearing behavior of members of CFRP-confined concrete arch structureThe ultimate load of CFRP-confined concrete under pure bending load is 64.25 kN·m,which is higher than that of CFGT and lower than that of CFST.The maximum axial strain of all the three confined concrete occurs in the tensile zone in lower section,where the ratio of tensile strain and compressive strain of CFRP-confined concrete,CFST,and CFGT is 1.637,2.15,and 11.34,respectively.Taking the ratio of tensile strain and compressive strain as the main index,a reinforcement coefficient which could characterize the reinforcement performance of the confined concrete members is proposed.The comparison results show that the reinforcement performance of CFRP-confined concrete is significantly better than that of CFST and CFGT.A numerical simulation test under eccentric compression is established,where the simulation parameters are set according to the eccentric compression tests and material tests.The numerical simulation results show that the ultimate load of specimens with 6 CFRP layers and 9 CFRP layers increases by 57.1%and 105.7%,respectively,compared with the specimen with 3 CFRP layers.The ultimate load of specimens with concrete strength levels of C40 and C50 increases by 25.5%and 36.4%,respectively,compare with the specimen with concrete strength levels of C30.Based on the deformation laws obtained from the laboratory tests and the numerical simulation tests,a theoretical model of pure bending bearing capacity calculation of CFRP-confined concrete is proposed.The model analysis shows that the increasing of number of CFRP layers leads to the improvement of the ultimate moment of the specimens,and the relation between them is approximately linear.Moreover,when the CFRP-confined concrete is under pure bending load,the reinforcement of CFRP plays a crucial role in improving the ultimate bearing capacity of specimens.(4)Comparative study on the bearing characteristics of CFRP-confined concrete under different loadsThere is also a significant difference of the bearing characteristics between CFRP and other types of confinements under different loading conditions.Under the axial load,the bearing capacity of CFRP-confined concrete is 68.5%of CFST.and 113.3%of CFGT.Under the eccentric load,the bearing capacity of CFRP-confined concrete is 96.3%of CFST,and 169.7%of CFGT.Under pure bending load,the bearing capacity of CFRP-confined concrete is 42.9%of CFST,and 569.9%of CFGT. |
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