Background:The Taylor Spatial Frame(TSF)has gained popularity among orthopedic surgeons for treating open fractures.However,a key challenge is the timely and safe removal of the frame.This study assessed the efficacy ...Background:The Taylor Spatial Frame(TSF)has gained popularity among orthopedic surgeons for treating open fractures.However,a key challenge is the timely and safe removal of the frame.This study assessed the efficacy and safety of axial load-share ratio(ALSR)testing to evaluate callus healing strength after TSF treatment of open tibial fractures.Methods:A retrospective case-control study was conducted,analyzing 180 adult patients with open tibial fractures treated at Tianjin Hospital’s Orthopedic Limb Correction Unit between August 2019 and August 2022.All patients underwent TSF external fixation surgery,and were divided into two groups based on ALSR testing.Group I(92 patients)underwent ALSR testing,with frame removal if the test value fell below 5%.Traditional methods were used for fixator removal guidance in Group II(88 patients).Clinical outcomes,including fixation duration,complications after fixator removal,and Johner-Wruhs functional scores,were compared between the two groups.Results:The groups showed no statistically significant differences(P>0.05)in sex,age,injury side,body mass index,surgery timing,or fracture type.Group I had a significantly shorter fixation duration(25.85±5.57 weeks)compared to Group II(31.82±6.98 weeks)(P<0.05).Following fixator removal,Group I demonstrated superior Johner-Wruhs scores compared to Group II,indicating better outcomes(P<0.05).Complication rates did not differ significantly between the groups at the last follow-up(P>0.05).Conclusion:Regular postoperative ALSR testing could safely and effectively guide TSF removal following open tibial fracture treatment.This method significantly reduced fixation duration compared to traditional guidance methods while maintaining efficacy and safety.展开更多
The Initial Imperfection Amplified Criterion is applied toinvestigate the geometric nonlinear dynamic buckling of staticallypreloaded ring-stiffened cylindrical shells under axial fluid-solidimpact. Tak- ing account o...The Initial Imperfection Amplified Criterion is applied toinvestigate the geometric nonlinear dynamic buckling of staticallypreloaded ring-stiffened cylindrical shells under axial fluid-solidimpact. Tak- ing account of the effects of large deformation andinitial geometric imperfection, the governing equations are obtainedby the Galerkin method and solved by the Runge-Kutta method. Theeffects of static preloading (uniform external radial pressure) onthe buckling features and the load-carrying ability of ring-stiffenedcy- lindrical shells against axial impact are discussed.展开更多
To investigate the seismic performance of a composite frame comprised of steel reinforced ultra high-strength concrete (SRUHSC) columns and steel reinforced concrete (SRC) beams, six interior frame joint specimens...To investigate the seismic performance of a composite frame comprised of steel reinforced ultra high-strength concrete (SRUHSC) columns and steel reinforced concrete (SRC) beams, six interior frame joint specimens were designed and tested under low cyclically lateral load. The effects of the axial load ratio and volumetric stirrup ratio were studied on the characteristics of the frame joint performance including crack pattern, failure mode, ductility, energy dissipation capacity, strength degradation and rigidity degradation. It was found that all joint specimens behaved in a ductile manner with flexural-shear failure in the joint core region while plastic hinges appeared at the beam ends. The ductility and energy absorption capacity of joints increased as the axial load ratio decreased and the volumetric stirIup ratio increased. The displacement ductility coefficient and equivalent damping coefficient of the joints fell between the corresponding coefficients of the steel reinforced concrete (SRC) frame joint and RC frame joint. The axial load ratio and volumetric stirrup ratio have less influence on the strength degradation and more influence on the stiffness degradation. The stiffness of the joint degrades more significantly for a low volumetric stirrup ratio and high axial load ratio. The characteristics obtained from the SRUHSC composite frame joint specimens with better seismic performance may be a useful reference in future engineering applications.展开更多
To investigate the seismic behavior of I-section columns made of 460 MPa high strength steel (HSS), six specimens were tested under constant axial load and cyclic horizontal load. The specimens were designed with di...To investigate the seismic behavior of I-section columns made of 460 MPa high strength steel (HSS), six specimens were tested under constant axial load and cyclic horizontal load. The specimens were designed with different width-to-thickness ratios and loaded under different axial load ratios. For each specimen, the failure mode was observed and hysteretic curve was measured. Comparison of different specimens on hysteretic characteristic, energy dissipation capacity and deformation capacity were further investigated. Test results showed that the degradation of bearing capacity was due to local buckling of flange and web. Under the same axial load ratio, as width-to-thickness ratio increased, the deformation area of local buckling became smaller. And also, displacement level at both peak load and failure load became smaller. In addition, the full extent of hysteretic curve, energy dissipation capacity, ultimate story drift angle decreased, and capacity degradation occurred more rapidly with the increase of width-to-thickness ratio or axial load ratio. Based on the capacity of story drift angle, limiting values which shall not be exceeded are suggested respectively for flange and web plate of 460 MPa HSS I-section columns when used in SMFs and in IMFs in the case of axial load ratio no more than 0.2. Such values should be smaller when the axial load ratio increases.展开更多
BACKGROUND The response to axial physiological pressure due to load transfer to the lumbar spine structures is among the various back pain mechanisms.Understanding the spine adaptation to cumulative compressive forces...BACKGROUND The response to axial physiological pressure due to load transfer to the lumbar spine structures is among the various back pain mechanisms.Understanding the spine adaptation to cumulative compressive forces can influence the choice of personalized treatment strategies.AIM To analyze the impact of axial load on the spinal canal’s size,intervertebral foramina,ligamenta flava and lumbosacral alignment.METHODS We assessed 90 patients using three-dimensional isotropic magnetic resonance imaging acquisition in a supine position with or without applying an axial compression load.Anatomical structures were measured in the lumbosacral region from L1 to S1 in lying and axially-loaded magnetic resonance images.A paired t test atα=0.05 was used to calculate the observed differences.RESULTS After axial loading,the dural sac area decreased significantly,by 5.2%on average(4.1%,6.2%,P<0.001).The intervertebral foramina decreased by 3.4%(2.7%,4.1%,P<0.001),except for L5-S1.Ligamenta flava increased by 3.8%(2.5%,5.2%,P<0.001),and the lumbosacral angle increased.CONCLUSION Axial load exacerbates the narrowing of the spinal canal and intervertebral foramina from L1-L2 to L4-L5.Cumulative compressive forces thicken ligamenta flava and exaggerate lumbar lordosis.展开更多
The Local Joint Flexibility(_(LJF))of steel K-joints reinforced with external plates under axial loads is investigated in this paper.For this aim,firstly,a finite element(FE)model was produced and verified with the re...The Local Joint Flexibility(_(LJF))of steel K-joints reinforced with external plates under axial loads is investigated in this paper.For this aim,firstly,a finite element(FE)model was produced and verified with the results of several experimental tests.In the next step,a set of 150 FE models was generated to assess the effect of the brace angle(θ),the stiffener plate size(ηandλ),and the joint geometry(γ,τ,ξ,andβ)on the_(LJF)factor(f_(LJF)).The results showed that using the external plates can decrease 81%of the f_(LJF).Moreover,the reinforcing effect of the reinforcing plate on the f_(LJF)is more remarkable in the joints with smallerβ.Also,the effect of theγon the f_(LJF)ratio can be ignored.Despite the important effect of the f_(LJF)on the behavior of tubular joints,there is not available any study or equation on the f_(LJF)in any reinforced K-joints under axial load.Consequently,using the present FE results,a design parametric equation is proposed.The equation can reasonably predict the f_(LJF)in the reinforced K-joints under axial load.展开更多
In this paper,the influence of geometric parameters on the stress concentration factors due to three different types of axial loading on 81 TY tubular structures is studied.Our results reveal that,geometric parameters...In this paper,the influence of geometric parameters on the stress concentration factors due to three different types of axial loading on 81 TY tubular structures is studied.Our results reveal that,geometric parameters have a considerable impact on the variation of stress concentration factors on tubular TY-joints under axial loads.Thus,the highest stress concentration factor values are observed on the vertical brace than on the inclined one.The finite element results of the tubular structures were verified by parametric equations and experimental data.A parametric study was carried out by analyses using the nonlinear regression method to obtain parametric equations.These equations are used to calculate stress concentration factors and to analyse the fatigue resistance of TY-joints due to axial loads.展开更多
This paper describes a nonlinear finite element (FE) analysis of high strength concrete (HSC) columns, and verifies the results through laboratory experiments. First, a cyclically lateral loading test on nine cant...This paper describes a nonlinear finite element (FE) analysis of high strength concrete (HSC) columns, and verifies the results through laboratory experiments. First, a cyclically lateral loading test on nine cantilever column specimens of HSC is described and a numerical simulation is presented to verify the adopted FE models. Next, based on the FE model for specimen No.6, numerical simulations for 70 cases, in which different concrete strengths, stirrup ratios and axial load ratios are considered, are presented to explore the effect of these parameters on the behavior of the HSC columns, and to check the rationality of requirements for these columns specified in the China Code for Seismic Design of Buildings (GB 50011- 2001). In addition, three cases with different stirrup strengths are analyzed to investigate their effect on the behavior of HSC columns. Finally, based on the numerical results some conclusions are presented.展开更多
The behavior of square-tubed reinforced concrete (STRC) short columns subjected to axial compression was studied in detail with an accurate nonlinear finite element model (FEM) . Different width to thickness ratios (D...The behavior of square-tubed reinforced concrete (STRC) short columns subjected to axial compression was studied in detail with an accurate nonlinear finite element model (FEM) . Different width to thickness ratios (D/t = 50 150) of the steel tube and the compressive strength of concrete (C80 and C50) were adopted in this research. The axial load strength,steel tube strain and load-shortening response were determined from FEM and the analysis results from FEM were compared with those from experiment. The analysis and test results indicate that the concrete strength little affectes the confinement of the steel tube on the concrete. The transverse stress of the tube at the axial load point increases with the increment in the width to thickness ratio. Based on the results from FEM and experiment,a formula for the prediction of the axial load strength was proposed in this paper.展开更多
A theoretical description of instability of saturated soil under axial load is presented with a set of equations describing the deformation based on the two phase continuous media theory. It is shown that all parame...A theoretical description of instability of saturated soil under axial load is presented with a set of equations describing the deformation based on the two phase continuous media theory. It is shown that all parameters of water and soil influence the instability and two types of instability may exist. One of them is dominated by pore pressure softening, while the other by strain softening. Finally, a practical application is discussed.展开更多
The measurement of pile axial load is of great significance to determining pile foundation design parameters such as skin friction and end bearing capacity and analyzing load transfer mechanisms.Affected by the temper...The measurement of pile axial load is of great significance to determining pile foundation design parameters such as skin friction and end bearing capacity and analyzing load transfer mechanisms.Affected by the temperature and ice content of frozen ground,the interface contact relationship between pile foundation and frozen soil is complicated,making pile axial load measurements more uncertain than that in non-frozen ground.Therefore,it is necessary to gain an in-depth understanding of the current pile axial load test methods.Four methods are systematically reviewed:vibrating wire sensors,strain gauges,sliding micrometers,and optical fiber strain sensors.At the same time,the applicability of the four test methods in frozen soil regions is discussed in detail.The first two methods are mature and commonly used.The sliding micrometer is only suitable for short-term measurement.While the Fiber Bragg grating(FBG)strain gauge meets the monitoring requirements,the Brillouin optical time-domain reflectometer(BOTDR)needs further verification.This paper aims to provide a technical reference for selecting and applying different methods in the pile axial load test for the stability study and bearing capacity assessment of pile foundations in cold regions.展开更多
The limitations of several existing classical rock damage models were critically appraised. Thereafter, a description of a new model to estimate the response of rock was provided. The results of an investigation lead ...The limitations of several existing classical rock damage models were critically appraised. Thereafter, a description of a new model to estimate the response of rock was provided. The results of an investigation lead to the development and confirmation of a new index parabola damage model. The new model is divided into two parts, fictitious damage and real damage and bordered by the critical damage point. In fictitious damage, the damage variable follows the index distribution, while in the real damage a parabolic distribution is used. Thus, the so called index parabola damage model is derived. The proposed damage model is applied to simulate the damage procedure of marble under uni axial loading. The results of the tests show that the proposed model is in excellent agreement with experimental data, in particular the nonlinear characteristic of rock deformation is adequately represented. [展开更多
In this paper,the local buckling of cylindrical long shells is discussed under axial pulse loads in a Hamiltonian system.Using this system,critical loads and modes of buckling of shells are reduced to symplectic eigen...In this paper,the local buckling of cylindrical long shells is discussed under axial pulse loads in a Hamiltonian system.Using this system,critical loads and modes of buckling of shells are reduced to symplectic eigenvalues and eigensolutions respectively.By the symplectic method,the solution of the local buckling of shells can be employed to the expansion series of symplectic eigensolutions in this system.As a result,relationships between critical buckling loads and other factors,such as length of pulse load,thickness of shells and circumferential orders,have been achieved.At the same time,symmetric and unsymmetric buckling modes have been discuss.Moreover,numerical results show that modes of post-buckling of shells can be Bamboo node-type,bending type,concave type and so on.Research in this paper provides analytical supports for ultimate load prediction and buckling failure assessment of cylindrical long shells under local axial pulse loads.展开更多
It is confirmed that tandem-blade configurations have potential to enlarge the flow turning in two-dimension(2D) studies. However, the potential of tandem blades to enlarge the design space for highly loaded axial com...It is confirmed that tandem-blade configurations have potential to enlarge the flow turning in two-dimension(2D) studies. However, the potential of tandem blades to enlarge the design space for highly loaded axial compressors was rarely investigated in open literatures. The present work aims to show the capability of tandem blades to break the loading limit of conventional blades for highly loaded compressors. The 2D models of the maximum static pressure rise derived in previous work were validated by a large amount experimental data, which showed a good agreement. An E parameter was defined to evaluate the stall margin of compressor based on the theoretical models, which indicated that the tandem blade was able to increase the loading limit of axial compressors. A single-blade stage with a loading coefficient of 0.46(based on the blade tip rotating speed) was designed as the baseline case under the guidance of the E parameter. A tandem-blade stage was then designed by ensuring that the velocity triangles were similar to the single-blade stage. The performances of both stages were investigated experimentally. The results showed that the maximum efficiency of the tandem-blade stage was 92.8%, 1% higher than the single;the stall margin increased from 16.9% to 22.3%. Besides, the maximum pressure rise of tandem rotors was beyond the loading limit of 2D single-blade cascades, which confirmed the potential of tandem blades to break the loading limit of axial compressors.展开更多
Composite columns of steel and concrete have been used and studied world wide, but filled tubular columns need more attention. This paper presents an experimental study on the behavior of short concrete filled steel t...Composite columns of steel and concrete have been used and studied world wide, but filled tubular columns need more attention. This paper presents an experimental study on the behavior of short concrete filled steel tubular columns (CFT) axially loaded in compression to failure. A total of 28 specimens (16 were filled with concrete and 12 were kept hollow) with different cross-sections were tested to investigate the load capacity. The length-to-diameter ratios of these columns were between 4 and 9. Parameters for the tests were tube shape and diameter-to-thickness ratio. Some of the concrete filled columns had internal bracing of #3 deformed bars. The test results are compared with the theoretical results and previous studies. The results show that the confinement effect on concrete does play a role in increasing the compressive strengths to almost 60% in some cases. Based on the test results, an equation to estimate the ultimate axial compressive loading capacities is also proposed for square CFT columns.展开更多
The problem of finite deformation of an incompressible rectangular rubber ring with an internal rigid body, where the ring is subjected to equal axial loads at its two ends, is examined. A reasonable mathematical mode...The problem of finite deformation of an incompressible rectangular rubber ring with an internal rigid body, where the ring is subjected to equal axial loads at its two ends, is examined. A reasonable mathematical model is formulated by using the nonlinear field theory and the implicit analytical solutions are derived. Then numerical simulations are implemented to further illustrate the results and obtain some meaningful conclusions. The deformation of the lateral surface of the ring becomes larger with the increasing axial loads, the decreasing ratio of the inner and outer radii and the increasing height of the ring.展开更多
The transverse stiffness and vibration characteristics of discontinuous beams can significantly differ from those of continuous beams given that an abrupt change in stiffness may occur at the interface of the former.I...The transverse stiffness and vibration characteristics of discontinuous beams can significantly differ from those of continuous beams given that an abrupt change in stiffness may occur at the interface of the former.In this study,the equations for the deflection curve and vibration frequencies of a simply supported discontinuous beam under axial loads are derived analytically on the basis of boundary,continuity,and deformation compatibility conditions by using equivalent spring models.The equation for the deflection curve is solved using undetermined coefficient methods.The normal function of the transverse vibration equation is obtained by separating variables.The differential equations for the beam that consider moments of inertia,shearing effects,and gyroscopic moments are investigated using the transfer matrix method.The deflection and vibration frequencies of the discontinuous beam are studied under different axial loads and connection spring stiffness.Results show that deflection decreases and vibration frequencies increase exponentially with increasing connection spring stiffness.Moreover,both variables remain steady when connection spring stiffness reaches a considerable value.Lastly,an experimental study is conducted to investigate the vibration characteristics of a discontinuous beam with a curvic coupling,and the results exhibit a good match with the proposed model.展开更多
A total of 540 nonlinear steady-state finite element analyses were performed to study the influence of temperature and dimensionless geometrical parameters(β,γ,θ,andτ)on the ultimate strength,failure modes,and ini...A total of 540 nonlinear steady-state finite element analyses were performed to study the influence of temperature and dimensionless geometrical parameters(β,γ,θ,andτ)on the ultimate strength,failure modes,and initial stiffness of two-planar tubular KT-joints.The joints were analyzed under two types of axial loading and five different temperatures(20℃,200℃,400℃,550℃,and 700℃).So far,there has not been any equation available for calculating the ultimate strength of two-planar tubular KT-joints at elevated temperatures.Hence,after parametric study,a set of design formulas were developed through nonlinear regression analyses,to calculate the ultimate strength of two-planar tubular KT-joints subjected to axial loading at elevated temperatures.展开更多
When diaphragm wall is used as the permanent vertical bearing structure,design standard of the bored pile adopted has to induce the risk or iste. The vertical load transfer mechanism and bearing capacity of the diaphr...When diaphragm wall is used as the permanent vertical bearing structure,design standard of the bored pile adopted has to induce the risk or iste. The vertical load transfer mechanism and bearing capacity of the diaphragm wall are examined by a field testing program at the site in Shanghai soft clays. Test results indicate that the diaphragm wall almost behaves as a rigid body under the vertical load. It induces that the skin friction and the toe resistance of the wall develop simultaneously. The skin friction resistance carries the large portion of the vertical load,and the toe resistance of the wall provides about 9.2% of vertical bearing load. Toe-grouting technique is found to achieve a remarkable increase in skin friction and toe resistance. The toe resistance of the grouted wall provides about 17.5% of vertical load.展开更多
基金funding support from Natural Science Foundation Key Project of Tianjin(20JCZDJC00600)Tianjin Health Research Project(TJWJ2023QN050)+2 种基金Applied Basic Research Foundation of Tianjin(22JCQNJC00230,22JCQNJC00360)Beijing-Tianjin-Hebei Basic Research Cooperation Project(J230007/23JCZXJC00050)Tianjin Municipal Health Commission Key Discipline Specialization(TJWJ2024XK015).
文摘Background:The Taylor Spatial Frame(TSF)has gained popularity among orthopedic surgeons for treating open fractures.However,a key challenge is the timely and safe removal of the frame.This study assessed the efficacy and safety of axial load-share ratio(ALSR)testing to evaluate callus healing strength after TSF treatment of open tibial fractures.Methods:A retrospective case-control study was conducted,analyzing 180 adult patients with open tibial fractures treated at Tianjin Hospital’s Orthopedic Limb Correction Unit between August 2019 and August 2022.All patients underwent TSF external fixation surgery,and were divided into two groups based on ALSR testing.Group I(92 patients)underwent ALSR testing,with frame removal if the test value fell below 5%.Traditional methods were used for fixator removal guidance in Group II(88 patients).Clinical outcomes,including fixation duration,complications after fixator removal,and Johner-Wruhs functional scores,were compared between the two groups.Results:The groups showed no statistically significant differences(P>0.05)in sex,age,injury side,body mass index,surgery timing,or fracture type.Group I had a significantly shorter fixation duration(25.85±5.57 weeks)compared to Group II(31.82±6.98 weeks)(P<0.05).Following fixator removal,Group I demonstrated superior Johner-Wruhs scores compared to Group II,indicating better outcomes(P<0.05).Complication rates did not differ significantly between the groups at the last follow-up(P>0.05).Conclusion:Regular postoperative ALSR testing could safely and effectively guide TSF removal following open tibial fracture treatment.This method significantly reduced fixation duration compared to traditional guidance methods while maintaining efficacy and safety.
基金the National Natural Sciences Foundation of China(No.19802017)
文摘The Initial Imperfection Amplified Criterion is applied toinvestigate the geometric nonlinear dynamic buckling of staticallypreloaded ring-stiffened cylindrical shells under axial fluid-solidimpact. Tak- ing account of the effects of large deformation andinitial geometric imperfection, the governing equations are obtainedby the Galerkin method and solved by the Runge-Kutta method. Theeffects of static preloading (uniform external radial pressure) onthe buckling features and the load-carrying ability of ring-stiffenedcy- lindrical shells against axial impact are discussed.
基金National Natural Science Foundation of China Under Grant No.50878037
文摘To investigate the seismic performance of a composite frame comprised of steel reinforced ultra high-strength concrete (SRUHSC) columns and steel reinforced concrete (SRC) beams, six interior frame joint specimens were designed and tested under low cyclically lateral load. The effects of the axial load ratio and volumetric stirrup ratio were studied on the characteristics of the frame joint performance including crack pattern, failure mode, ductility, energy dissipation capacity, strength degradation and rigidity degradation. It was found that all joint specimens behaved in a ductile manner with flexural-shear failure in the joint core region while plastic hinges appeared at the beam ends. The ductility and energy absorption capacity of joints increased as the axial load ratio decreased and the volumetric stirIup ratio increased. The displacement ductility coefficient and equivalent damping coefficient of the joints fell between the corresponding coefficients of the steel reinforced concrete (SRC) frame joint and RC frame joint. The axial load ratio and volumetric stirrup ratio have less influence on the strength degradation and more influence on the stiffness degradation. The stiffness of the joint degrades more significantly for a low volumetric stirrup ratio and high axial load ratio. The characteristics obtained from the SRUHSC composite frame joint specimens with better seismic performance may be a useful reference in future engineering applications.
基金the National Natural Science Foundation of China under Grant No.51478244
文摘To investigate the seismic behavior of I-section columns made of 460 MPa high strength steel (HSS), six specimens were tested under constant axial load and cyclic horizontal load. The specimens were designed with different width-to-thickness ratios and loaded under different axial load ratios. For each specimen, the failure mode was observed and hysteretic curve was measured. Comparison of different specimens on hysteretic characteristic, energy dissipation capacity and deformation capacity were further investigated. Test results showed that the degradation of bearing capacity was due to local buckling of flange and web. Under the same axial load ratio, as width-to-thickness ratio increased, the deformation area of local buckling became smaller. And also, displacement level at both peak load and failure load became smaller. In addition, the full extent of hysteretic curve, energy dissipation capacity, ultimate story drift angle decreased, and capacity degradation occurred more rapidly with the increase of width-to-thickness ratio or axial load ratio. Based on the capacity of story drift angle, limiting values which shall not be exceeded are suggested respectively for flange and web plate of 460 MPa HSS I-section columns when used in SMFs and in IMFs in the case of axial load ratio no more than 0.2. Such values should be smaller when the axial load ratio increases.
文摘BACKGROUND The response to axial physiological pressure due to load transfer to the lumbar spine structures is among the various back pain mechanisms.Understanding the spine adaptation to cumulative compressive forces can influence the choice of personalized treatment strategies.AIM To analyze the impact of axial load on the spinal canal’s size,intervertebral foramina,ligamenta flava and lumbosacral alignment.METHODS We assessed 90 patients using three-dimensional isotropic magnetic resonance imaging acquisition in a supine position with or without applying an axial compression load.Anatomical structures were measured in the lumbosacral region from L1 to S1 in lying and axially-loaded magnetic resonance images.A paired t test atα=0.05 was used to calculate the observed differences.RESULTS After axial loading,the dural sac area decreased significantly,by 5.2%on average(4.1%,6.2%,P<0.001).The intervertebral foramina decreased by 3.4%(2.7%,4.1%,P<0.001),except for L5-S1.Ligamenta flava increased by 3.8%(2.5%,5.2%,P<0.001),and the lumbosacral angle increased.CONCLUSION Axial load exacerbates the narrowing of the spinal canal and intervertebral foramina from L1-L2 to L4-L5.Cumulative compressive forces thicken ligamenta flava and exaggerate lumbar lordosis.
文摘The Local Joint Flexibility(_(LJF))of steel K-joints reinforced with external plates under axial loads is investigated in this paper.For this aim,firstly,a finite element(FE)model was produced and verified with the results of several experimental tests.In the next step,a set of 150 FE models was generated to assess the effect of the brace angle(θ),the stiffener plate size(ηandλ),and the joint geometry(γ,τ,ξ,andβ)on the_(LJF)factor(f_(LJF)).The results showed that using the external plates can decrease 81%of the f_(LJF).Moreover,the reinforcing effect of the reinforcing plate on the f_(LJF)is more remarkable in the joints with smallerβ.Also,the effect of theγon the f_(LJF)ratio can be ignored.Despite the important effect of the f_(LJF)on the behavior of tubular joints,there is not available any study or equation on the f_(LJF)in any reinforced K-joints under axial load.Consequently,using the present FE results,a design parametric equation is proposed.The equation can reasonably predict the f_(LJF)in the reinforced K-joints under axial load.
文摘In this paper,the influence of geometric parameters on the stress concentration factors due to three different types of axial loading on 81 TY tubular structures is studied.Our results reveal that,geometric parameters have a considerable impact on the variation of stress concentration factors on tubular TY-joints under axial loads.Thus,the highest stress concentration factor values are observed on the vertical brace than on the inclined one.The finite element results of the tubular structures were verified by parametric equations and experimental data.A parametric study was carried out by analyses using the nonlinear regression method to obtain parametric equations.These equations are used to calculate stress concentration factors and to analyse the fatigue resistance of TY-joints due to axial loads.
基金National Nature Science Foundation of China Under Grant No. 50621062
文摘This paper describes a nonlinear finite element (FE) analysis of high strength concrete (HSC) columns, and verifies the results through laboratory experiments. First, a cyclically lateral loading test on nine cantilever column specimens of HSC is described and a numerical simulation is presented to verify the adopted FE models. Next, based on the FE model for specimen No.6, numerical simulations for 70 cases, in which different concrete strengths, stirrup ratios and axial load ratios are considered, are presented to explore the effect of these parameters on the behavior of the HSC columns, and to check the rationality of requirements for these columns specified in the China Code for Seismic Design of Buildings (GB 50011- 2001). In addition, three cases with different stirrup strengths are analyzed to investigate their effect on the behavior of HSC columns. Finally, based on the numerical results some conclusions are presented.
基金Sponsored by the National Natural Science Foundation of China (Grant No. 50708027)the National Key Technology Research and Development Program of China (Grant No.2006BAJ01B02)
文摘The behavior of square-tubed reinforced concrete (STRC) short columns subjected to axial compression was studied in detail with an accurate nonlinear finite element model (FEM) . Different width to thickness ratios (D/t = 50 150) of the steel tube and the compressive strength of concrete (C80 and C50) were adopted in this research. The axial load strength,steel tube strain and load-shortening response were determined from FEM and the analysis results from FEM were compared with those from experiment. The analysis and test results indicate that the concrete strength little affectes the confinement of the steel tube on the concrete. The transverse stress of the tube at the axial load point increases with the increment in the width to thickness ratio. Based on the results from FEM and experiment,a formula for the prediction of the axial load strength was proposed in this paper.
文摘A theoretical description of instability of saturated soil under axial load is presented with a set of equations describing the deformation based on the two phase continuous media theory. It is shown that all parameters of water and soil influence the instability and two types of instability may exist. One of them is dominated by pore pressure softening, while the other by strain softening. Finally, a practical application is discussed.
基金This study was supported by the Strategic Priority Research Program of the Chinese Academy of Science(Grant No.XDA20020102)Science and Technology Project of State Grid Corporation of China(Contract No.SGQHDKYOSBJS201600077)+1 种基金National Natural Science Foundation of China(Grant No.41101065)the State Key Laboratory of Frozen Soil Engineering Foundation(Grant No.SKLFSE-ZT-34)。
文摘The measurement of pile axial load is of great significance to determining pile foundation design parameters such as skin friction and end bearing capacity and analyzing load transfer mechanisms.Affected by the temperature and ice content of frozen ground,the interface contact relationship between pile foundation and frozen soil is complicated,making pile axial load measurements more uncertain than that in non-frozen ground.Therefore,it is necessary to gain an in-depth understanding of the current pile axial load test methods.Four methods are systematically reviewed:vibrating wire sensors,strain gauges,sliding micrometers,and optical fiber strain sensors.At the same time,the applicability of the four test methods in frozen soil regions is discussed in detail.The first two methods are mature and commonly used.The sliding micrometer is only suitable for short-term measurement.While the Fiber Bragg grating(FBG)strain gauge meets the monitoring requirements,the Brillouin optical time-domain reflectometer(BOTDR)needs further verification.This paper aims to provide a technical reference for selecting and applying different methods in the pile axial load test for the stability study and bearing capacity assessment of pile foundations in cold regions.
文摘The limitations of several existing classical rock damage models were critically appraised. Thereafter, a description of a new model to estimate the response of rock was provided. The results of an investigation lead to the development and confirmation of a new index parabola damage model. The new model is divided into two parts, fictitious damage and real damage and bordered by the critical damage point. In fictitious damage, the damage variable follows the index distribution, while in the real damage a parabolic distribution is used. Thus, the so called index parabola damage model is derived. The proposed damage model is applied to simulate the damage procedure of marble under uni axial loading. The results of the tests show that the proposed model is in excellent agreement with experimental data, in particular the nonlinear characteristic of rock deformation is adequately represented. [
基金This research is funded by the grants from Dalian Project of Innovation Foundation of Science and Technology(No.2018J11CY005)Research Program of State Key Laboratory of Structural Analysis for Industrial Equipment(No.S18313).
文摘In this paper,the local buckling of cylindrical long shells is discussed under axial pulse loads in a Hamiltonian system.Using this system,critical loads and modes of buckling of shells are reduced to symplectic eigenvalues and eigensolutions respectively.By the symplectic method,the solution of the local buckling of shells can be employed to the expansion series of symplectic eigensolutions in this system.As a result,relationships between critical buckling loads and other factors,such as length of pulse load,thickness of shells and circumferential orders,have been achieved.At the same time,symmetric and unsymmetric buckling modes have been discuss.Moreover,numerical results show that modes of post-buckling of shells can be Bamboo node-type,bending type,concave type and so on.Research in this paper provides analytical supports for ultimate load prediction and buckling failure assessment of cylindrical long shells under local axial pulse loads.
基金the support of National Natural Science Foundation of China(Nos.51806004 and 51790511)National Science and Technology Major Project,China(No.2017-Ⅱ-0001-0013)。
文摘It is confirmed that tandem-blade configurations have potential to enlarge the flow turning in two-dimension(2D) studies. However, the potential of tandem blades to enlarge the design space for highly loaded axial compressors was rarely investigated in open literatures. The present work aims to show the capability of tandem blades to break the loading limit of conventional blades for highly loaded compressors. The 2D models of the maximum static pressure rise derived in previous work were validated by a large amount experimental data, which showed a good agreement. An E parameter was defined to evaluate the stall margin of compressor based on the theoretical models, which indicated that the tandem blade was able to increase the loading limit of axial compressors. A single-blade stage with a loading coefficient of 0.46(based on the blade tip rotating speed) was designed as the baseline case under the guidance of the E parameter. A tandem-blade stage was then designed by ensuring that the velocity triangles were similar to the single-blade stage. The performances of both stages were investigated experimentally. The results showed that the maximum efficiency of the tandem-blade stage was 92.8%, 1% higher than the single;the stall margin increased from 16.9% to 22.3%. Besides, the maximum pressure rise of tandem rotors was beyond the loading limit of 2D single-blade cascades, which confirmed the potential of tandem blades to break the loading limit of axial compressors.
文摘Composite columns of steel and concrete have been used and studied world wide, but filled tubular columns need more attention. This paper presents an experimental study on the behavior of short concrete filled steel tubular columns (CFT) axially loaded in compression to failure. A total of 28 specimens (16 were filled with concrete and 12 were kept hollow) with different cross-sections were tested to investigate the load capacity. The length-to-diameter ratios of these columns were between 4 and 9. Parameters for the tests were tube shape and diameter-to-thickness ratio. Some of the concrete filled columns had internal bracing of #3 deformed bars. The test results are compared with the theoretical results and previous studies. The results show that the confinement effect on concrete does play a role in increasing the compressive strengths to almost 60% in some cases. Based on the test results, an equation to estimate the ultimate axial compressive loading capacities is also proposed for square CFT columns.
基金supported by the National Natural Science Foundation of China (Nos. 10872045, 10721062 and 10772104)the Program for New Century Excellent Talents in University (No. NCET-09-0096)the Fundamental Research Funds for the Central Universities
文摘The problem of finite deformation of an incompressible rectangular rubber ring with an internal rigid body, where the ring is subjected to equal axial loads at its two ends, is examined. A reasonable mathematical model is formulated by using the nonlinear field theory and the implicit analytical solutions are derived. Then numerical simulations are implemented to further illustrate the results and obtain some meaningful conclusions. The deformation of the lateral surface of the ring becomes larger with the increasing axial loads, the decreasing ratio of the inner and outer radii and the increasing height of the ring.
基金Support provided by the Ministry of Industry and Information Technology of China(Grant No.JSZL2016204B102)the National Natural Science Foundation of China(Grant Nos.51575022 and 11772022).
文摘The transverse stiffness and vibration characteristics of discontinuous beams can significantly differ from those of continuous beams given that an abrupt change in stiffness may occur at the interface of the former.In this study,the equations for the deflection curve and vibration frequencies of a simply supported discontinuous beam under axial loads are derived analytically on the basis of boundary,continuity,and deformation compatibility conditions by using equivalent spring models.The equation for the deflection curve is solved using undetermined coefficient methods.The normal function of the transverse vibration equation is obtained by separating variables.The differential equations for the beam that consider moments of inertia,shearing effects,and gyroscopic moments are investigated using the transfer matrix method.The deflection and vibration frequencies of the discontinuous beam are studied under different axial loads and connection spring stiffness.Results show that deflection decreases and vibration frequencies increase exponentially with increasing connection spring stiffness.Moreover,both variables remain steady when connection spring stiffness reaches a considerable value.Lastly,an experimental study is conducted to investigate the vibration characteristics of a discontinuous beam with a curvic coupling,and the results exhibit a good match with the proposed model.
文摘A total of 540 nonlinear steady-state finite element analyses were performed to study the influence of temperature and dimensionless geometrical parameters(β,γ,θ,andτ)on the ultimate strength,failure modes,and initial stiffness of two-planar tubular KT-joints.The joints were analyzed under two types of axial loading and five different temperatures(20℃,200℃,400℃,550℃,and 700℃).So far,there has not been any equation available for calculating the ultimate strength of two-planar tubular KT-joints at elevated temperatures.Hence,after parametric study,a set of design formulas were developed through nonlinear regression analyses,to calculate the ultimate strength of two-planar tubular KT-joints subjected to axial loading at elevated temperatures.
基金the National Natural Science Foundation of China(No.50679041)the Shanghai Leading Academic Discipline Project(No.B208)
文摘When diaphragm wall is used as the permanent vertical bearing structure,design standard of the bored pile adopted has to induce the risk or iste. The vertical load transfer mechanism and bearing capacity of the diaphragm wall are examined by a field testing program at the site in Shanghai soft clays. Test results indicate that the diaphragm wall almost behaves as a rigid body under the vertical load. It induces that the skin friction and the toe resistance of the wall develop simultaneously. The skin friction resistance carries the large portion of the vertical load,and the toe resistance of the wall provides about 9.2% of vertical bearing load. Toe-grouting technique is found to achieve a remarkable increase in skin friction and toe resistance. The toe resistance of the grouted wall provides about 17.5% of vertical load.