Fibre-reinforced polymer(FRP)has the advantages of high strength,light weight,corrosion resistance and convenient construction and is widely used in repairing and strengthening damaged concrete columns.Most of the exi...Fibre-reinforced polymer(FRP)has the advantages of high strength,light weight,corrosion resistance and convenient construction and is widely used in repairing and strengthening damaged concrete columns.Most of the existing strength models were built by regression analysis of experimental data;however,in this article,a new unified strength model is proposed using the Hoek-Brown failure criterion.To study the strength of FRP-confined damaged and undamaged concrete columns,900 test data were collected from the published literature and a large database that contains the cross-sectional shape of each specimen,the damage type,the damage level and the FRP-confined stiffness was established.A new strength model using the Hoek-Brown failure criterion was established and is suitable for both circular and square columns that are undamaged,load-damaged and fire-damaged.Based on the database,most of the existing strength models from the published literature and the model proposed in this paper were evaluated.The evaluation shows that the proposed model can predict the compressive strength for FRP-confined pre-damaged and undamaged concrete columns with good accuracy.展开更多
The nonlinear Hoek-Brown failure criterion was introduced to limit analysis by applying the tangent method. Based on the failure mechanism of double-logarithmic spiral curves on the face of deep rock tunnels, the anal...The nonlinear Hoek-Brown failure criterion was introduced to limit analysis by applying the tangent method. Based on the failure mechanism of double-logarithmic spiral curves on the face of deep rock tunnels, the analytical solutions of collapse pressure were derived through utilizing the virtual power principle in the case of pore water, and the optimal solutions of collapse pressure were obtained by using the optimization programs of mathematical model with regard of a maximum problem. In comparison with existing research with the same parameters, the consistency of change rule shows the validity of the proposed method. Moreover, parametric study indicates that nonlinear Hoek-Brown failure criterion and pore water pressure have great influence on collapse pressure and failure shape of tunnel faces in deep rock masses, particularly when the surrounding rock is too weak or under the condition of great disturbance and abundant ground water, and in this case, supporting measures should be intensified so as to prevent the occurrence of collapse.展开更多
In the past few decades,the navigation performance of ships and structures in ice-covered waters has not been fully studied,especially the influence of ice mechanical properties on icebreaking ability.Ice bending stre...In the past few decades,the navigation performance of ships and structures in ice-covered waters has not been fully studied,especially the influence of ice mechanical properties on icebreaking ability.Ice bending strength is a key ice parameter for predicting ship ice loads,and accurate ice bending strength is also the key to scaling model tests results to real ship.However,numerical simulation studies on model ice bending strength of ice tanks are often neglected.In this paper,an explicit finite element method model is used to simulate the ice cantilever beam test,and the failure load and bending strength of the ice are obtained.In this model,the Tsai-Wu failure criterion is used as the material constitutive model,and the required simulation parameters are obtained from the model ice test in ice tank.Parameter sensitivity analysis shows that the cantilever beam size of the model ice has a significant effect on the flexural strength.The results show that proper rounding at the root of the cantilever beam is beneficial to reduce stress concentration and obtain more accurate bending strength;the thickness,width and length of the cantilever beam should conform to a certain ratio,and consistent with the ITTC recommended reference.Therefore,the results of this study can promote model ice experiments and numerical studies and provide ice strength data support for ship design and polar ship maneuvering.展开更多
Ground reinforcement is crucial for tunnel construction, especially in soft rock tunnels. Existing analytical models are inadequate for predicting the ground reaction curves (GRCs) for reinforced tunnels in strain-sof...Ground reinforcement is crucial for tunnel construction, especially in soft rock tunnels. Existing analytical models are inadequate for predicting the ground reaction curves (GRCs) for reinforced tunnels in strain-softening (SS) rock masses. This study proposes a novel analytical model to determine the GRCs of SS rock masses, incorporating ground reinforcement and intermediate principal stress (IPS). The SS constitutive model captures the progressive post- peak failure, while the elastic-brittle model simulates reinforced rock masses. Nine combined states are innovatively investigated to analyze plastic zone development in natural and reinforced regions. Each region is analyzed separately, and coupled through boundary conditions at interface. Comparison with three types of existing models indicates that these models overestimate reinforcement effects. The deformation prediction errors of single geological material models may exceed 75%. Furthermore, neglecting softening and residual zones in natural regions could lead to errors over 50%. Considering the IPS can effectively utilize the rock strength to reduce tunnel deformation by at least 30%, thereby saving on reinforcement and support costs. The computational results show a satisfactory agreement with the monitoring data from a model test and two tunnel projects. The proposed model may offer valuable insights into the design and construction of reinforced tunnel engineering.展开更多
The swinging-loading process is essential for automatic artillery loading systems.This study focuses on the problems of reliability analysis that affect swinging-loading positioning accuracy.A dynamic model for a mult...The swinging-loading process is essential for automatic artillery loading systems.This study focuses on the problems of reliability analysis that affect swinging-loading positioning accuracy.A dynamic model for a multi degree-of-freedom swinging-loading-integrated rigid-flexible coupling system is established.This model is based on the identification of key parameters and platform experiments.Based on the spatial geometric relationship between the breech and loader during modular charge transfer and the possible maximum interference depth of the modular charge,a new failure criterion for estimating the reliability of swinging-loading positioning accuracy is proposed.Considering the uncertainties in the operation of the pendulum loader,the direct probability integration method is introduced to analyze the reliability of the swinging-loading positioning accuracy under three different charge numbers.The results indicate that under two and four charges,the swinging-loading process shows outstanding reliability.However,an unstable stage appears when the swinging motion occurred under six charges,with a maximum positioning failure probability of 0.0712.A comparison between the results obtained under the conventional and proposed criteria further reveals the effectiveness and necessity of the proposed criterion.展开更多
This study investigates the instability characteristics of dynamic disasters resulting from disruption caused by extracting resources underground. Utilizing the split Hopkinson pressure bar (SHPB) system, the dynamic ...This study investigates the instability characteristics of dynamic disasters resulting from disruption caused by extracting resources underground. Utilizing the split Hopkinson pressure bar (SHPB) system, the dynamic response mechanism of coal energy evolution is examined, and the energy instability criterion is established. The validity of the instability criterion is explored from the standpoint of damage progression. The results demonstrate that the energy conversion mechanism undergoes a fundamental alternation under impact disturbance. Moreover, the energy release rate as well as the energy dissipation rate undergo comparable changes across distinct levels of impact disturbance. The distinction between the energy release rate and the energy dissipation rate (DRD) increases as coal mass deformation grows. Prior to coal facing instability and failure, the DRD experienced an inflection point followed by a sharp decrease. In conjunction with the discussion on the damage evolution, the physical and mechanical significance of DRD remains clear, which can essentially describe the whole impact loading process. The phenomenon that the inflection point appears and DRD subsequently suddenly decreases can be employed as the energy criterion prior to the failure of instability. Furthermore, this paper provides significant reference for the prediction of dynamic instability of coal under dynamic disturbance.展开更多
基金Project(2017M622540)supported by the China Postdoctoral Science FoundationProject(51808419)supported by the National Natural Science Foundation of China+1 种基金Project(2019CFB217)supported by the National Natural Science Foundation of Hubei Province,ChinaProject(201623)supported by the Science and Technology Project of Wuhan Urban and Rural Construction Committee,China。
文摘Fibre-reinforced polymer(FRP)has the advantages of high strength,light weight,corrosion resistance and convenient construction and is widely used in repairing and strengthening damaged concrete columns.Most of the existing strength models were built by regression analysis of experimental data;however,in this article,a new unified strength model is proposed using the Hoek-Brown failure criterion.To study the strength of FRP-confined damaged and undamaged concrete columns,900 test data were collected from the published literature and a large database that contains the cross-sectional shape of each specimen,the damage type,the damage level and the FRP-confined stiffness was established.A new strength model using the Hoek-Brown failure criterion was established and is suitable for both circular and square columns that are undamaged,load-damaged and fire-damaged.Based on the database,most of the existing strength models from the published literature and the model proposed in this paper were evaluated.The evaluation shows that the proposed model can predict the compressive strength for FRP-confined pre-damaged and undamaged concrete columns with good accuracy.
基金Project(2013CB036004)supported by National Basic Research Program of ChinaProjects(51178468,51378510)supported by National Natural Science Foundation of ChinaProject(CX2013B077)supported by Hunan Provincial Innovation Foundation for Postgraduate,China
文摘The nonlinear Hoek-Brown failure criterion was introduced to limit analysis by applying the tangent method. Based on the failure mechanism of double-logarithmic spiral curves on the face of deep rock tunnels, the analytical solutions of collapse pressure were derived through utilizing the virtual power principle in the case of pore water, and the optimal solutions of collapse pressure were obtained by using the optimization programs of mathematical model with regard of a maximum problem. In comparison with existing research with the same parameters, the consistency of change rule shows the validity of the proposed method. Moreover, parametric study indicates that nonlinear Hoek-Brown failure criterion and pore water pressure have great influence on collapse pressure and failure shape of tunnel faces in deep rock masses, particularly when the surrounding rock is too weak or under the condition of great disturbance and abundant ground water, and in this case, supporting measures should be intensified so as to prevent the occurrence of collapse.
文摘In the past few decades,the navigation performance of ships and structures in ice-covered waters has not been fully studied,especially the influence of ice mechanical properties on icebreaking ability.Ice bending strength is a key ice parameter for predicting ship ice loads,and accurate ice bending strength is also the key to scaling model tests results to real ship.However,numerical simulation studies on model ice bending strength of ice tanks are often neglected.In this paper,an explicit finite element method model is used to simulate the ice cantilever beam test,and the failure load and bending strength of the ice are obtained.In this model,the Tsai-Wu failure criterion is used as the material constitutive model,and the required simulation parameters are obtained from the model ice test in ice tank.Parameter sensitivity analysis shows that the cantilever beam size of the model ice has a significant effect on the flexural strength.The results show that proper rounding at the root of the cantilever beam is beneficial to reduce stress concentration and obtain more accurate bending strength;the thickness,width and length of the cantilever beam should conform to a certain ratio,and consistent with the ITTC recommended reference.Therefore,the results of this study can promote model ice experiments and numerical studies and provide ice strength data support for ship design and polar ship maneuvering.
基金Projects(52208382, 52278387, 51738002) supported by the National Natural Science Foundation of ChinaProject(2022YJS072) supported by the Fundamental Research Funds for the Central Universities,China。
文摘Ground reinforcement is crucial for tunnel construction, especially in soft rock tunnels. Existing analytical models are inadequate for predicting the ground reaction curves (GRCs) for reinforced tunnels in strain-softening (SS) rock masses. This study proposes a novel analytical model to determine the GRCs of SS rock masses, incorporating ground reinforcement and intermediate principal stress (IPS). The SS constitutive model captures the progressive post- peak failure, while the elastic-brittle model simulates reinforced rock masses. Nine combined states are innovatively investigated to analyze plastic zone development in natural and reinforced regions. Each region is analyzed separately, and coupled through boundary conditions at interface. Comparison with three types of existing models indicates that these models overestimate reinforcement effects. The deformation prediction errors of single geological material models may exceed 75%. Furthermore, neglecting softening and residual zones in natural regions could lead to errors over 50%. Considering the IPS can effectively utilize the rock strength to reduce tunnel deformation by at least 30%, thereby saving on reinforcement and support costs. The computational results show a satisfactory agreement with the monitoring data from a model test and two tunnel projects. The proposed model may offer valuable insights into the design and construction of reinforced tunnel engineering.
文摘The swinging-loading process is essential for automatic artillery loading systems.This study focuses on the problems of reliability analysis that affect swinging-loading positioning accuracy.A dynamic model for a multi degree-of-freedom swinging-loading-integrated rigid-flexible coupling system is established.This model is based on the identification of key parameters and platform experiments.Based on the spatial geometric relationship between the breech and loader during modular charge transfer and the possible maximum interference depth of the modular charge,a new failure criterion for estimating the reliability of swinging-loading positioning accuracy is proposed.Considering the uncertainties in the operation of the pendulum loader,the direct probability integration method is introduced to analyze the reliability of the swinging-loading positioning accuracy under three different charge numbers.The results indicate that under two and four charges,the swinging-loading process shows outstanding reliability.However,an unstable stage appears when the swinging motion occurred under six charges,with a maximum positioning failure probability of 0.0712.A comparison between the results obtained under the conventional and proposed criteria further reveals the effectiveness and necessity of the proposed criterion.
基金Projects(51934007,12072363,52004268) supported by the National Natural Science Foundation of ChinaProject(22KJD440002) supported by the Natural Science Fund for Colleges and Universities in Jiangsu Province,China。
文摘This study investigates the instability characteristics of dynamic disasters resulting from disruption caused by extracting resources underground. Utilizing the split Hopkinson pressure bar (SHPB) system, the dynamic response mechanism of coal energy evolution is examined, and the energy instability criterion is established. The validity of the instability criterion is explored from the standpoint of damage progression. The results demonstrate that the energy conversion mechanism undergoes a fundamental alternation under impact disturbance. Moreover, the energy release rate as well as the energy dissipation rate undergo comparable changes across distinct levels of impact disturbance. The distinction between the energy release rate and the energy dissipation rate (DRD) increases as coal mass deformation grows. Prior to coal facing instability and failure, the DRD experienced an inflection point followed by a sharp decrease. In conjunction with the discussion on the damage evolution, the physical and mechanical significance of DRD remains clear, which can essentially describe the whole impact loading process. The phenomenon that the inflection point appears and DRD subsequently suddenly decreases can be employed as the energy criterion prior to the failure of instability. Furthermore, this paper provides significant reference for the prediction of dynamic instability of coal under dynamic disturbance.
