Expansive concrete is used in the steel tube of Concrete-filled steel tubular(CFST)columns to solve the problem of steel-to-concrete debonding.Self-stress is generated between concrete and steel plate due to concrete ...Expansive concrete is used in the steel tube of Concrete-filled steel tubular(CFST)columns to solve the problem of steel-to-concrete debonding.Self-stress is generated between concrete and steel plate due to concrete expansion,which can effectively improve the mechanical performance of CFST columns.Deformation tests were conducted on concrete and CFST columns,respectively.The free deformation of concrete and circumferential deformation of steel tubes were measured and analyzed.A calculation method was proposed to evaluate the hoop strain,self-stress and creep deformation of the CFST columns.The test and calculation results indicate that the proper addition of expansion agent in the internal concrete can keep concrete expansive and generate self-stresses for a long time.The expansion and self-stresses prevent the debonding between the steel tube and the internal concrete.Increasing the dosage of expansive agents and reducing the curing age both increase the expansive deformation and self-stress of CFST columns.Increasing the tube thickness reduces the expansive deformation and increases the initial self-stress of CFST columns.展开更多
Based on reanalyzing test results of uniaxial compressive behavior of concrete at constant high temperatures in China, with the compressive cube strength of concrete from 20 to 80 MPa, unified formulas for uniaxial co...Based on reanalyzing test results of uniaxial compressive behavior of concrete at constant high temperatures in China, with the compressive cube strength of concrete from 20 to 80 MPa, unified formulas for uniaxial compressive strength, elastic modulus, strain at peak uniaxial compression and mathematical expression for unaxial compressive stress-strain relations for the concrete at constant high temperatures were studied. Furthermore, the axial stress-axial strain relations between laterally confined concrete under axial compression and multiaxial stress-strain relations for steel at constant high temperatures were studied. Finally, based on continuum mechanics, the mechanics model for concentric cylinders of circular steel tube with concrete core of entire section loaded at constant high temperatures was established. Applying elasto-plastic analysis method, a FORTRAN program was developed, and the concrete-filled circular steel tubular (CFST) stub colunms at constant high temperatures were analyzed. The analysis results are in agreement with the experiment ones from references.展开更多
Existing analytical methods of buried steel pipelines subjected to active strike-slip faults depended on a number of simplifications.To study the failure mechanism more accurately,a refined strain analytical methodolo...Existing analytical methods of buried steel pipelines subjected to active strike-slip faults depended on a number of simplifications.To study the failure mechanism more accurately,a refined strain analytical methodology was proposed,taking the nonlinear characteristics of soil-pipeline interaction and pipe steel into account.Based on the elastic-beam and beam-on-elastic-foundation theories,the position of pipe potential destruction and the strain and deformation distributions along the pipeline were derived.Compared with existing analytical methods and three-dimensional nonlinear finite element analysis,the maximum axial total strains of pipe from the analytical methodology presented are in good agreement with the finite element results at small and intermediate fault movements and become gradually more conservative at large fault displacements.The position of pipe potential failure and the deformation distribution along the pipeline are fairly consistent with the finite element results.展开更多
The high-frequency interference exists obviously in low strain integrity testing of large-diameter pipe pile when a transientpoint load is applied. An analytical solution of vertical vibratory response of large-diamet...The high-frequency interference exists obviously in low strain integrity testing of large-diameter pipe pile when a transientpoint load is applied. An analytical solution of vertical vibratory response of large-diameter pipe piles in low strain testing isdeduced in this paper. The analytical solution is verified by both numerical simulation and model test results. The time-domainvelocity responses on pile top are analyzed. The calculation results indicate that the time-domain responses at various pointssuffer different high-frequency interferences, thus the peak values and phases of different points are different. The influence ofvibratory modes on high-frequency interference is analyzed. It is found that the high-frequency interference at 90° point main-ly derives from the second flexural mode, but for other points it mainly originates from the first flexural mode. The factors af-fecting the frequency and peak value of interference waves have been investigated in this study. The results indicate that thelarger radius angle between the receiving and 90° points leads to greater peak value of high frequency wave crest. The leasthigh-frequency interference is detected at the angle of 90°. The frequency of interference waves is decreased with the increaseof pile radius, while the peak value is almost constant. The frequency is also related to pile modulus, i.e. the larger pile modu-lus results in greater frequency. The peak value varies with impulse width and soil resistance, i.e., the wider impulse width andlarger soil resistance cause smaller peak value. In conclusion, the frequency of interference waves is dependent on the geomet-rical and mechanics characteristics of the piles such as pile radius and modulus, but independent of the external conditionssuch as impulse width and soil resistance. On the other hand, the peak value of interference waves is mainly dependent on theexternal conditions but independent of the geometrical and mechanics characteristics of the piles. In practice, some externalmeasures should be adopted to weaken high-frequency interference such as using soft hammer, hammer cushion and adoptingsuitable receiving point.展开更多
基金The National Key R&D Program of China(No.2017YFC0703705)the National Natural Science Foundation of China(No.51778183)Jiangsu Planned Projects for Postdoctoral Research Funds(No.2020Z088).
文摘Expansive concrete is used in the steel tube of Concrete-filled steel tubular(CFST)columns to solve the problem of steel-to-concrete debonding.Self-stress is generated between concrete and steel plate due to concrete expansion,which can effectively improve the mechanical performance of CFST columns.Deformation tests were conducted on concrete and CFST columns,respectively.The free deformation of concrete and circumferential deformation of steel tubes were measured and analyzed.A calculation method was proposed to evaluate the hoop strain,self-stress and creep deformation of the CFST columns.The test and calculation results indicate that the proper addition of expansion agent in the internal concrete can keep concrete expansive and generate self-stresses for a long time.The expansion and self-stresses prevent the debonding between the steel tube and the internal concrete.Increasing the dosage of expansive agents and reducing the curing age both increase the expansive deformation and self-stress of CFST columns.Increasing the tube thickness reduces the expansive deformation and increases the initial self-stress of CFST columns.
基金Projects(50438020 50578162) supported by the National Natural Sceince Foundation of China
文摘Based on reanalyzing test results of uniaxial compressive behavior of concrete at constant high temperatures in China, with the compressive cube strength of concrete from 20 to 80 MPa, unified formulas for uniaxial compressive strength, elastic modulus, strain at peak uniaxial compression and mathematical expression for unaxial compressive stress-strain relations for the concrete at constant high temperatures were studied. Furthermore, the axial stress-axial strain relations between laterally confined concrete under axial compression and multiaxial stress-strain relations for steel at constant high temperatures were studied. Finally, based on continuum mechanics, the mechanics model for concentric cylinders of circular steel tube with concrete core of entire section loaded at constant high temperatures was established. Applying elasto-plastic analysis method, a FORTRAN program was developed, and the concrete-filled circular steel tubular (CFST) stub colunms at constant high temperatures were analyzed. The analysis results are in agreement with the experiment ones from references.
基金Project(50439010) supported by the National Natural Science Foundation of ChinaProject(DUT10ZD201) supported by the Fundamental Research Funds for the Central Universities in China
文摘Existing analytical methods of buried steel pipelines subjected to active strike-slip faults depended on a number of simplifications.To study the failure mechanism more accurately,a refined strain analytical methodology was proposed,taking the nonlinear characteristics of soil-pipeline interaction and pipe steel into account.Based on the elastic-beam and beam-on-elastic-foundation theories,the position of pipe potential destruction and the strain and deformation distributions along the pipeline were derived.Compared with existing analytical methods and three-dimensional nonlinear finite element analysis,the maximum axial total strains of pipe from the analytical methodology presented are in good agreement with the finite element results at small and intermediate fault movements and become gradually more conservative at large fault displacements.The position of pipe potential failure and the deformation distribution along the pipeline are fairly consistent with the finite element results.
基金supported by the National Natural Science Foundation of China(Grant No.51008115)the Provincial Science Foundation of Jiangsu(Grant No.BK2008040)
文摘The high-frequency interference exists obviously in low strain integrity testing of large-diameter pipe pile when a transientpoint load is applied. An analytical solution of vertical vibratory response of large-diameter pipe piles in low strain testing isdeduced in this paper. The analytical solution is verified by both numerical simulation and model test results. The time-domainvelocity responses on pile top are analyzed. The calculation results indicate that the time-domain responses at various pointssuffer different high-frequency interferences, thus the peak values and phases of different points are different. The influence ofvibratory modes on high-frequency interference is analyzed. It is found that the high-frequency interference at 90° point main-ly derives from the second flexural mode, but for other points it mainly originates from the first flexural mode. The factors af-fecting the frequency and peak value of interference waves have been investigated in this study. The results indicate that thelarger radius angle between the receiving and 90° points leads to greater peak value of high frequency wave crest. The leasthigh-frequency interference is detected at the angle of 90°. The frequency of interference waves is decreased with the increaseof pile radius, while the peak value is almost constant. The frequency is also related to pile modulus, i.e. the larger pile modu-lus results in greater frequency. The peak value varies with impulse width and soil resistance, i.e., the wider impulse width andlarger soil resistance cause smaller peak value. In conclusion, the frequency of interference waves is dependent on the geomet-rical and mechanics characteristics of the piles such as pile radius and modulus, but independent of the external conditionssuch as impulse width and soil resistance. On the other hand, the peak value of interference waves is mainly dependent on theexternal conditions but independent of the geometrical and mechanics characteristics of the piles. In practice, some externalmeasures should be adopted to weaken high-frequency interference such as using soft hammer, hammer cushion and adoptingsuitable receiving point.