Tests of 4 simply supported unbonded prestressed truss concrete composite beams encased with circular steel tube were carried out. It is found that the ratio of the stress increment of the unbonded tendon to that of t...Tests of 4 simply supported unbonded prestressed truss concrete composite beams encased with circular steel tube were carried out. It is found that the ratio of the stress increment of the unbonded tendon to that of the tensile steel tube is 0.252 during the using stage,and the average crack space of beams depends on the ratio of the sum of the bottom chord steel tube's outside diameter and the secondary bottom chord steel tube's section area to the effective tensile concrete area. The coefficient of uneven crack distribution is 1.68 and the formula for the calculation of crack width is established. Test results indicate that the ultimate stress increment of unbonded tendon in the beams decreases in linearity with the increase of the composite reinforcement index β0. The pure bending region of beams accords with the plane section assumption from loading to failure. The calculation formula of ultimate stress increment of the unbonded tendon and the method to calculate the bearing capacity of normal section of beams have been presented. Besides,the method to calculate the stiffness of this sort of beams is brought forward as well.展开更多
A theoretical model to analyze the nonlinear circumferential guided wave(CGW) propagation in a composite circular tube(CCT) is established. The response features of nonlinear CGWs to early damage [denoted by variation...A theoretical model to analyze the nonlinear circumferential guided wave(CGW) propagation in a composite circular tube(CCT) is established. The response features of nonlinear CGWs to early damage [denoted by variations in third-order elastic constants(TOECs)] in an inner layer of CCT are investigated. On the basis of the modal expansion approach, the second-harmonic field of primary CGW propagation can be assumed to be a linear sum of a series of double-frequency CGW(DFCGW) modes. The quantitative relationship of DFCGW mode versus the relative changes in the inner layer TOECs is then investigated. It is found that the changes in the inner layer TOECs of CCT will obviously affect the driving source of DFCGW mode and its modal expansion coefficient, which is intrinsically able to influence the efficiency of cumulative second-harmonic generation(SHG) by primary CGW propagation. Theoretical analyses and numerical simulations demonstrate that the second harmonic of primary CGW is monotonic and very sensitive to the changes in the inner layer TOECs of CCT, while the linear properties of primary CGW propagation almost remain unchanged. Our results provide a potential application for accurately characterizing the level of early damage in the inner layer of CCT through the efficiency of cumulative SHG by primary CGW propagation.展开更多
The feasibility of using the nonlinear effect of primary circumferential guided wave(CGW)propagation for characterizing the change of inner layer thickness of a composite circular tube(CCT)has been investigated.An app...The feasibility of using the nonlinear effect of primary circumferential guided wave(CGW)propagation for characterizing the change of inner layer thickness of a composite circular tube(CCT)has been investigated.An appropriate mode pair of the fundamental and double-frequency CGWs(DFCGWs)has been selected to enable the second harmonics of primary wave mode in the given CCT to accumulate along the circumferential direction.When changes in the inner layer thickness(described as the equivalent inner layer thickness)take place,the corresponding nonlinear CGW measurements are conducted.It is found that there is a direct correlation between change of equivalent inner layer thickness of the CCT and the relative acoustic nonlinearity parameter(Δβ)measured with CGWs propagating through one full circumference,and that the effect of second-harmonic generation(SHG)is very sensitive to change in the inner layer thickness.The experimental result obtained demonstrates the feasibility for quantitatively assessing the change of equivalent inner layer thickness in CCTs using the effect of SHG by primary CGW propagation.展开更多
The effects of microstructure on quasi-static transverse loading behavior of 3D circular braided composite tubes were studied. Transverse loading tests were conducted. Transverse load-deflection curves were obtained t...The effects of microstructure on quasi-static transverse loading behavior of 3D circular braided composite tubes were studied. Transverse loading tests were conducted. Transverse load-deflection curves were obtained to analyze the effects of braiding parameters including the braiding angle, the wall thickness, and the diameter on the transverse loading of 3D circular braided composite tubes. Breaking loads, moduli and strengths had also been used to describe the transverse loading behaviors. The failure morphologies were shown to reveal damage mechanisms. From the results, the increase in braiding angle, wall thickness and diameter increases the ability of anti-deformation and breaking load of braided tubes. The breaking load of specimen with a braiding angle of 45° is about 1.68 times that of specimen with a braiding angle of 15°. The breaking load of specimen with 4 layers of yarns is about 2.15 times that of specimen with 2 layers of yarns. The breaking load of the tube with a diameter of 25.5 mm is about 2.39 times that of the tube with a diameter of 20.5 mm.展开更多
文摘Tests of 4 simply supported unbonded prestressed truss concrete composite beams encased with circular steel tube were carried out. It is found that the ratio of the stress increment of the unbonded tendon to that of the tensile steel tube is 0.252 during the using stage,and the average crack space of beams depends on the ratio of the sum of the bottom chord steel tube's outside diameter and the secondary bottom chord steel tube's section area to the effective tensile concrete area. The coefficient of uneven crack distribution is 1.68 and the formula for the calculation of crack width is established. Test results indicate that the ultimate stress increment of unbonded tendon in the beams decreases in linearity with the increase of the composite reinforcement index β0. The pure bending region of beams accords with the plane section assumption from loading to failure. The calculation formula of ultimate stress increment of the unbonded tendon and the method to calculate the bearing capacity of normal section of beams have been presented. Besides,the method to calculate the stiffness of this sort of beams is brought forward as well.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11834008,11474361,11632004,and 11622430)
文摘A theoretical model to analyze the nonlinear circumferential guided wave(CGW) propagation in a composite circular tube(CCT) is established. The response features of nonlinear CGWs to early damage [denoted by variations in third-order elastic constants(TOECs)] in an inner layer of CCT are investigated. On the basis of the modal expansion approach, the second-harmonic field of primary CGW propagation can be assumed to be a linear sum of a series of double-frequency CGW(DFCGW) modes. The quantitative relationship of DFCGW mode versus the relative changes in the inner layer TOECs is then investigated. It is found that the changes in the inner layer TOECs of CCT will obviously affect the driving source of DFCGW mode and its modal expansion coefficient, which is intrinsically able to influence the efficiency of cumulative second-harmonic generation(SHG) by primary CGW propagation. Theoretical analyses and numerical simulations demonstrate that the second harmonic of primary CGW is monotonic and very sensitive to the changes in the inner layer TOECs of CCT, while the linear properties of primary CGW propagation almost remain unchanged. Our results provide a potential application for accurately characterizing the level of early damage in the inner layer of CCT through the efficiency of cumulative SHG by primary CGW propagation.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12074050,11834008,and 11704410).
文摘The feasibility of using the nonlinear effect of primary circumferential guided wave(CGW)propagation for characterizing the change of inner layer thickness of a composite circular tube(CCT)has been investigated.An appropriate mode pair of the fundamental and double-frequency CGWs(DFCGWs)has been selected to enable the second harmonics of primary wave mode in the given CCT to accumulate along the circumferential direction.When changes in the inner layer thickness(described as the equivalent inner layer thickness)take place,the corresponding nonlinear CGW measurements are conducted.It is found that there is a direct correlation between change of equivalent inner layer thickness of the CCT and the relative acoustic nonlinearity parameter(Δβ)measured with CGWs propagating through one full circumference,and that the effect of second-harmonic generation(SHG)is very sensitive to change in the inner layer thickness.The experimental result obtained demonstrates the feasibility for quantitatively assessing the change of equivalent inner layer thickness in CCTs using the effect of SHG by primary CGW propagation.
文摘The effects of microstructure on quasi-static transverse loading behavior of 3D circular braided composite tubes were studied. Transverse loading tests were conducted. Transverse load-deflection curves were obtained to analyze the effects of braiding parameters including the braiding angle, the wall thickness, and the diameter on the transverse loading of 3D circular braided composite tubes. Breaking loads, moduli and strengths had also been used to describe the transverse loading behaviors. The failure morphologies were shown to reveal damage mechanisms. From the results, the increase in braiding angle, wall thickness and diameter increases the ability of anti-deformation and breaking load of braided tubes. The breaking load of specimen with a braiding angle of 45° is about 1.68 times that of specimen with a braiding angle of 15°. The breaking load of specimen with 4 layers of yarns is about 2.15 times that of specimen with 2 layers of yarns. The breaking load of the tube with a diameter of 25.5 mm is about 2.39 times that of the tube with a diameter of 20.5 mm.
