Throughout the previous studies,none of them are involved in analysing the downwash flow effect on the control surface of the Flapping Wing Rotor(FWR).An overset CFD numerical model is built up and validated to study ...Throughout the previous studies,none of them are involved in analysing the downwash flow effect on the control surface of the Flapping Wing Rotor(FWR).An overset CFD numerical model is built up and validated to study the downwash flow’s effect on the stability of the FWR.After simulation,a cone like self-lock region which acts as the critical condition determining the stability of FWR is found.Only when the flow’s resultant velocity acting on the control surface lies in the stable region,the FWR can keep stable.The size of the cone like self-lock stable region can be enlarged by increasing the maximum feasible deflection angle constrained by mechanical design or enhancing the equivalent downwash flow velocity.Among all the simulated cases,when J=2.67(f=5 Hz,■=5 r/s),the largest average equivalent downwash flow velocities are found.On the other hand,the recovery torque could be enhanced due to the increase of the arm of the lateral force.According to these simulation results,a 43 g FWR model with two control surfaces and two stabilizers is then designed.A series of flight tests is then conducted to help confirm the conclusion of the mechanism research in this work.Overall,this study points out several strategies to increase the flight stability of the FWR and finally realizes the stable climb flight and mild descent flight of the FWR.展开更多
The negative Poisson’s ratio(NPR)bolt is an innovative support element distinguished by its high strength,elongation,and a slightly negative Poisson’s ratio.Unlike conventional prestressed(PR)bolts with a positive P...The negative Poisson’s ratio(NPR)bolt is an innovative support element distinguished by its high strength,elongation,and a slightly negative Poisson’s ratio.Unlike conventional prestressed(PR)bolts with a positive Poisson’s ratio,the NPR bolt exhibits a quasi-ideal plastic response without a prominent yield platform,enabling it to sustain high prestress with a substantial safety margin,which is particularly advantageous for jointed rock masses.However,investigations into the shear resistance mechanisms of NPR bolts under varying prestress levels remain limited.This study conducted full-scale double shear tests to assess the shear strength,deformation behavior,energy absorption,and failure mechanisms of NPR bolts under different prestress conditions.To ensure a fair comparison with PR bolts,a prestress utilization coefficient(PUC)was introduced.The results reveal that at a PUC of 0.25,the NPR bolt achieved peak axial force,shear displacement,and peak shear force values that are 2.41,1.88,and 2.13 times greater than those of the PR bolt,respectively.Shear performance was optimized at a prestress level of 100 kN,with energy absorption reaching 47.1 kJ,which is 2.8 times that of the PR bolt.Furthermore,the necking ratio was significantly reduced,indicating more distributed plastic deformation and delayed failure.Field applications verified the superior performance,resulting in a 27.4%reduction in roof settlement and enhanced structural integrity.These findings confirm that NPR bolts possess excellent shear resistance,energy absorption,and deformation adaptability,and optimizing prestress significantly enhances their support performance,providing a strong basis for geotechnical engineering applications.展开更多
A unilateral self-locking mechanism(USM) was proposed to increase the tractive ability of the inchworm in-pipe robots for pipeline inspection.The USM was basically composed of a cam,a torsional spring and an axis.The ...A unilateral self-locking mechanism(USM) was proposed to increase the tractive ability of the inchworm in-pipe robots for pipeline inspection.The USM was basically composed of a cam,a torsional spring and an axis.The self-locking and virtual work principles were applied to studying the basic self-locking condition of the USM.In order to make the cooperation between the crutch and telescopic mechanism more harmonical,the unlocking time of the USM was calculated.A set of parameters were selected to build a virtual model and fabricate a prototype.Both the simulation and performance experiments were carried out in a pipe with a nominal inside diameter of 160 mm.The results show that USM enables the robot to move quickly in one way,and in the other way it helps the robot get self-locking with the pipe wall.The traction of the inchworm robot can rise to 1.2 kN,beyond the limitation of friction of 0.497 kN.展开更多
BACKGROUND Cervical degenerative disc(CDD)disease is a common type of spondylosis.Although anterior cervical discectomy and fusion(ACDF)is the preferred treatment for CDD disease,internal fixation with a titanium plat...BACKGROUND Cervical degenerative disc(CDD)disease is a common type of spondylosis.Although anterior cervical discectomy and fusion(ACDF)is the preferred treatment for CDD disease,internal fixation with a titanium plate may cause various complications.The invention of the ACDF with a self-locking fusion cage(ROI-C)has effectively decreased the incidence of postoperative complications.AIM To observe the outcomes of CDD disease treated by ACDF with a ROI-C.METHODS Ninety patients with CDD disease treated at our hospital from March 2019 to March 2021 were included.They were divided into two groups(control group and observation group,n=45 in each)using a random number table.Patients in the control group received ACDF plus internal fixation with a titanium plate.Those in the observation group received ACDF+ROI-C placement.The two groups of patients were compared in terms of surgical parameters,pain,cervical spine function,range of motion,and complications.RESULTS The two groups of patients showed no significant differences in surgical time,blood loss,drainage volume,and length of hospital stay(P>0.05).No significant differences in the visual analogue scale(VAS),Japanese Orthopedic Association(JOA),and neck disability index(NDI)scores were observed between the two groups before surgery(P>0.05).The VAS and NDI scores in the observation group were considerably lower than those in the control group after surgery;however,the JOA scores in the observation group were significantly higher than those in the control group(P<0.05).No significant differences were observed in cervical disc height and the range of motion of the superior or inferior adjacent vertebrae between the two groups before surgery(P>0.05).The disc height in the observation group was larger than that in the control group after surgery.The range of motion of both the superior and inferior adjacent vertebrae was significantly smaller in the observation group than in the control group(P<0.05).The incidence of complications was only 2.22% in the observation group compared to 15.56% in the control group,and the difference was statistically significant(P<0.05).CONCLUSION Cervical spine function restoration was better with ROI-C with internal fixation in ACDF than with conventional titanium plates in ACDF for CDD disease.展开更多
This article focuses on the control of cracks in prestressed concrete structures.It explains the stress characteristics,influencing factors,and causes of crack formation during construction.The article introduces adva...This article focuses on the control of cracks in prestressed concrete structures.It explains the stress characteristics,influencing factors,and causes of crack formation during construction.The article introduces advanced technologies such as intelligent prestressed tensioning,highlights key aspects like high-performance concrete mix design,and discusses various monitoring and control methods.It also covers their practical applications and achievements in real-world projects,and looks ahead to future development directions.展开更多
As prestressed concrete(PC)structures age,long-termeffects,e.g.,creep,shrinkage,and prestress losses,compromise their structural performance.Strengthening these aged PC beams has become a crucial matter.One effective ...As prestressed concrete(PC)structures age,long-termeffects,e.g.,creep,shrinkage,and prestress losses,compromise their structural performance.Strengthening these aged PC beams has become a crucial matter.One effective solution is to use externally bonded fiber-reinforced polymer(FRP)sheets;however,limited research has been done on aged PC beams using the FRP,especially for beams with unbonded prestressing strands(UPC beams).Therefore,this research investigates the flexural strengthening efficacy of external FRP sheets on aged UPC beams with unbonded tendons.Aging minimally affected the failure modes of UPC beams,with nonstrengthened beams showing flexural failure via rebar yielding and concrete crushing,and FRP-strengthened beams failing due to FRP debonding and tensile reinforcement yielding,though tendons in the aged beams did not yield due to prestress losses,unlike the new beams.The U-wrap anchor curbed widespread debonding,leading to tensile reinforcement yielding and FRP rupture.Aging hastened crack growth and stiffness loss,increasing deflections and reducing load resistance,but FRP reinforcement mitigated these effects,enhancing cracking resistance by 14%over the unstrengthened aged beams and 7%over the new beams while boosting ultimate resistance by 9%above the non-strengthened new beams.Compared to the new FRP-strengthened beams,the aged counterparts had lower cracking resistance,stiffness and capacity—showing 20%higher deflections,7–9%lower serviceability loads,7%–17%reduced ultimate strength and 17%less deformability—due to prestress losses and premature FRP debonding.展开更多
Understanding the reinforcement effect of the newly developed prestressed reinforcement components(PRCs)(a system composed of prestressed steel bars(PSBs),protective sleeves,lateral pressure plates(LPPs),and anchoring...Understanding the reinforcement effect of the newly developed prestressed reinforcement components(PRCs)(a system composed of prestressed steel bars(PSBs),protective sleeves,lateral pressure plates(LPPs),and anchoring elements)is technically significant for the rational design of prestressed subgrade.A three-dimensional finite element model was established and verified based on a novel static model test and utilized to systematically analyze the influence of prestress levels and reinforcement modes on the reinforcement effect of the subgrade.The results show that the PRCs provide additional confining pressure to the subgrade through the diffusion effect of the prestress,which can therefore effectively improve the service performance of the subgrade.Compared to the unreinforced conventional subgrades,the settlements of prestressreinforced subgrades are reduced.The settlement attenuation rate(Rs)near the LPPs is larger than that at the subgrade center,and increasing the prestress positively contributes to the stability of the subgrade structure.In the multi-row reinforcement mode,the reinforcement effect of PRCs can extend from the reinforced area to the unreinforced area.In addition,as the horizontal distance from the LPPs increases,the additional confining pressure converted by the PSBs and LPPs gradually diminishes when spreading to the core load bearing area of the subgrade,resulting in a decrease in the Rs.Under the singlerow reinforcement mode,PRCs can be strategically arranged according to the local areas where subgrade defects readily occurred or observed,to obtain the desired reinforcement effect.Moreover,excessive prestress should not be applied near the subgrade shoulder line to avoid the shear failure of the subgrade shoulder.PRCs can be flexibly used for preventing and treating various subgrade defects of newly constructed or existing railway lines,achieving targeted and classified prevention,and effectively improving the bearing performance and deformation resistance of the subgrade.The research results are instructive for further elucidating the prestress reinforcement effect of PRCs on railway subgrades.展开更多
China's railway prestressed concrete bridge has more than 600000 holes,prestressed engineering is a key force system affecting the safety and durability of the prestressed concrete bridge structure,its constructio...China's railway prestressed concrete bridge has more than 600000 holes,prestressed engineering is a key force system affecting the safety and durability of the prestressed concrete bridge structure,its construction quality is easily affected by traditional manual operation technology,resulting in low construction efficiency and control accuracy,easy to form a hidden danger of quality and safety,it is difficult to meet the needs of less humanized,standardized intelligent construction trend.Based on the research on the intelligent prestressed construction control and testing technology and equipment for railway bridges,this paper proposes the integration of intelligent prestressed tension control and tunnel friction test of railway bridges,intelligent grouting control of tunnel and intelligent testing of beam construction quality,and sets up a complete technical system and integrated equipment for intelligent prestressed construction of bridges based on the industrial Internet of Things(IoT).Overall,improve the quality and efficiency of bridge production,construction,and management.展开更多
The stress gradient of surrounding rock and reasonable prestress of support are the keys to ensuring the stability of roadways.The elastic-plastic analytical solution for surrounding rock was derived based on unified ...The stress gradient of surrounding rock and reasonable prestress of support are the keys to ensuring the stability of roadways.The elastic-plastic analytical solution for surrounding rock was derived based on unified strength theory.A model for solving the stress gradient of the surrounding rock with the intermediate principal stress parameter b was established.The correctness and applicability of the solution for the stress gradient in the roadway surrounding rock was verified via multiple methods.Furthermore,the laws of stress,displacement,and the plastic zone of the surrounding rock with different b values and prestresses were revealed.As b increases,the stress gradient in the plastic zone increases,and the displacement and plastic zone radius decrease.As the prestress increases,the peak stress shifts toward the sidewalls,and the stress and stress gradient increments decrease.In addition,the displacement increment and plastic zone increment were proposed to characterize the support effect.The balance point of the plastic zone area appears before that of the displacement zone.The relationship between the stress gradient compensation coefficient and the prestress is obtained.This study provides a research method and idea for determining the reasonable prestress of support in roadways.展开更多
The operational and regional conditions to which the prestressed concrete sleeper(PCS)is subjected in a railway track significantly contribute to its performance and durability.Maintaining the health of PCS poses chal...The operational and regional conditions to which the prestressed concrete sleeper(PCS)is subjected in a railway track significantly contribute to its performance and durability.Maintaining the health of PCS poses challenges,and one of these issues involves the potential occurrence of longitudinal cracks in reinforcing bars,which can be caused by various constructional,functional,and environmental factors.Longitudinal cracks in PCS compromise the structural performance,resulting in a reduced capacity to withstand the loads exerted by moving vehicles.The current evaluations not only fail to yield a precise parameter for estimating the behavior and response of the PCS,but they also overlook the specific conditions of the PCS,such as prestressing,and only provide limited information regarding existing damage.Balancing the need for accurate evaluation with consideration of costs and resources,and making informed decisions about maintenance and track performance enhancement,has become a multifaceted challenge in ensuring a robust PCS assessment.This research introduces a novel methodology to improve the evaluation of mechanical and geometrical parameters of PCS over their operational lifespan.The objective is to enhance the accuracy of PCS performance estimation by concentrating on detecting longitudinal cracks.The suggested approach seamlessly integrates model updating methods and the finite element(FE)approach to achieve an accurate and timely assessment of PCS conditions.This comprehensive examination scrutinizes the methodology by applying artificial cracks to the PCS.In addition to introducing this assessment approach,a detailed examination is conducted on a laboratory-simulated PCS featuring various combinations of longitudinal cracks measuring 40,80,and 120 cm in length.This systematic and rigorous approach ensures the reliability and robustness of the methodology.Ultimately,the parameters of cross-sectional area,moment of inertia,and modulus of elasticity,which significantly impact the performance of this sleeper,are explored and demonstrated through functional methodologies.The findings suggest that assessing and addressing damage should be conducted through a comprehensive and integrated procedure,taking into account the actual conditions of the PCS.Longitudinal cracks lead to a substantial decrease in the performance of these components in railway tracks.By applying the proposed methods,it is anticipated that the evaluation error for these components will be reduced by approximately 30%compared to visual inspections,particularly in predicting the extent of damage for cracks measuring up to 120 cm.This research has the potential to significantly enhance the evaluation of PCS performance and mitigate the impact of longitudinal cracks on the safety and longevity of ballasted railway tracks in desert areas.展开更多
The surrounding rock is prone to large-scale loosening and failure after the excavation of shallow large-span caverns because of the thin overlying strata and large cross-section span.The rational design of bolt suppo...The surrounding rock is prone to large-scale loosening and failure after the excavation of shallow large-span caverns because of the thin overlying strata and large cross-section span.The rational design of bolt support is very important to the safety control of surrounding rock as a common support means.The control mechanism and design method of bolt support for shallow-buried large-span caverns is carried out.The calculation method of bolt prestress and length based on arched failure and collapsed failure mode is established.The influence mechanism of different influencing factors on the bolt prestress and length is clarified.At the same time,the constant resistance energy-absorbing bolt with high strength and high toughness is developed,and the comparative test of mechanical properties is carried out.On this basis,the design method of high prestressed bolt support for shallow-buried large-span caverns is put forward,and the field test is carried out in Qingdao metro station in China.The monitoring results show that the maximum roof settlement is 6.8 mm after the new design method is adopted,and the effective control of the shallow-buried large-span caverns is realized.The research results can provide theoretical and technical support for the safety control of shallow-buried large-span caverns.展开更多
基金supported by the following funding organizations in China:National Natural Science Foundation of China(Grant No.52375116 and Grant No.52105285)the Aeronautical Science Foundation of China(Grant No.ASFC-20230023052001)+3 种基金China Postdoctoral Science Foundation(Grant No.2024M754237)National Key Research and Development Program of China(2024YFB470920001)Science and Technology Plan Project of Wenzhou Municipality(Grant No.ZG2024001)Basic Public Welfare Research Program of Wenzhou(Grant No.G2023046).
文摘Throughout the previous studies,none of them are involved in analysing the downwash flow effect on the control surface of the Flapping Wing Rotor(FWR).An overset CFD numerical model is built up and validated to study the downwash flow’s effect on the stability of the FWR.After simulation,a cone like self-lock region which acts as the critical condition determining the stability of FWR is found.Only when the flow’s resultant velocity acting on the control surface lies in the stable region,the FWR can keep stable.The size of the cone like self-lock stable region can be enlarged by increasing the maximum feasible deflection angle constrained by mechanical design or enhancing the equivalent downwash flow velocity.Among all the simulated cases,when J=2.67(f=5 Hz,■=5 r/s),the largest average equivalent downwash flow velocities are found.On the other hand,the recovery torque could be enhanced due to the increase of the arm of the lateral force.According to these simulation results,a 43 g FWR model with two control surfaces and two stabilizers is then designed.A series of flight tests is then conducted to help confirm the conclusion of the mechanism research in this work.Overall,this study points out several strategies to increase the flight stability of the FWR and finally realizes the stable climb flight and mild descent flight of the FWR.
基金supported by the State Key Laboratory of Intelligent Construction and Healthy Operation and Maintenance of Deep Underground Engineering(Grant No.SDGZ2505)the Postdoctoral Fellowship Program of the China Postdoctoral Science Foundation(Grant No.GZB20250742)the General Program of the China Postdoctoral Science Foundation(Grant No.2025M773213).
文摘The negative Poisson’s ratio(NPR)bolt is an innovative support element distinguished by its high strength,elongation,and a slightly negative Poisson’s ratio.Unlike conventional prestressed(PR)bolts with a positive Poisson’s ratio,the NPR bolt exhibits a quasi-ideal plastic response without a prominent yield platform,enabling it to sustain high prestress with a substantial safety margin,which is particularly advantageous for jointed rock masses.However,investigations into the shear resistance mechanisms of NPR bolts under varying prestress levels remain limited.This study conducted full-scale double shear tests to assess the shear strength,deformation behavior,energy absorption,and failure mechanisms of NPR bolts under different prestress conditions.To ensure a fair comparison with PR bolts,a prestress utilization coefficient(PUC)was introduced.The results reveal that at a PUC of 0.25,the NPR bolt achieved peak axial force,shear displacement,and peak shear force values that are 2.41,1.88,and 2.13 times greater than those of the PR bolt,respectively.Shear performance was optimized at a prestress level of 100 kN,with energy absorption reaching 47.1 kJ,which is 2.8 times that of the PR bolt.Furthermore,the necking ratio was significantly reduced,indicating more distributed plastic deformation and delayed failure.Field applications verified the superior performance,resulting in a 27.4%reduction in roof settlement and enhanced structural integrity.These findings confirm that NPR bolts possess excellent shear resistance,energy absorption,and deformation adaptability,and optimizing prestress significantly enhances their support performance,providing a strong basis for geotechnical engineering applications.
基金Project(2007AA04Z256) supported by the National High-Tech Research and Development Program of China
文摘A unilateral self-locking mechanism(USM) was proposed to increase the tractive ability of the inchworm in-pipe robots for pipeline inspection.The USM was basically composed of a cam,a torsional spring and an axis.The self-locking and virtual work principles were applied to studying the basic self-locking condition of the USM.In order to make the cooperation between the crutch and telescopic mechanism more harmonical,the unlocking time of the USM was calculated.A set of parameters were selected to build a virtual model and fabricate a prototype.Both the simulation and performance experiments were carried out in a pipe with a nominal inside diameter of 160 mm.The results show that USM enables the robot to move quickly in one way,and in the other way it helps the robot get self-locking with the pipe wall.The traction of the inchworm robot can rise to 1.2 kN,beyond the limitation of friction of 0.497 kN.
文摘BACKGROUND Cervical degenerative disc(CDD)disease is a common type of spondylosis.Although anterior cervical discectomy and fusion(ACDF)is the preferred treatment for CDD disease,internal fixation with a titanium plate may cause various complications.The invention of the ACDF with a self-locking fusion cage(ROI-C)has effectively decreased the incidence of postoperative complications.AIM To observe the outcomes of CDD disease treated by ACDF with a ROI-C.METHODS Ninety patients with CDD disease treated at our hospital from March 2019 to March 2021 were included.They were divided into two groups(control group and observation group,n=45 in each)using a random number table.Patients in the control group received ACDF plus internal fixation with a titanium plate.Those in the observation group received ACDF+ROI-C placement.The two groups of patients were compared in terms of surgical parameters,pain,cervical spine function,range of motion,and complications.RESULTS The two groups of patients showed no significant differences in surgical time,blood loss,drainage volume,and length of hospital stay(P>0.05).No significant differences in the visual analogue scale(VAS),Japanese Orthopedic Association(JOA),and neck disability index(NDI)scores were observed between the two groups before surgery(P>0.05).The VAS and NDI scores in the observation group were considerably lower than those in the control group after surgery;however,the JOA scores in the observation group were significantly higher than those in the control group(P<0.05).No significant differences were observed in cervical disc height and the range of motion of the superior or inferior adjacent vertebrae between the two groups before surgery(P>0.05).The disc height in the observation group was larger than that in the control group after surgery.The range of motion of both the superior and inferior adjacent vertebrae was significantly smaller in the observation group than in the control group(P<0.05).The incidence of complications was only 2.22% in the observation group compared to 15.56% in the control group,and the difference was statistically significant(P<0.05).CONCLUSION Cervical spine function restoration was better with ROI-C with internal fixation in ACDF than with conventional titanium plates in ACDF for CDD disease.
文摘This article focuses on the control of cracks in prestressed concrete structures.It explains the stress characteristics,influencing factors,and causes of crack formation during construction.The article introduces advanced technologies such as intelligent prestressed tensioning,highlights key aspects like high-performance concrete mix design,and discusses various monitoring and control methods.It also covers their practical applications and achievements in real-world projects,and looks ahead to future development directions.
基金support by the Ministry of Education and Training of Vietnam for this research,under grant no.B2023-MBS-02.
文摘As prestressed concrete(PC)structures age,long-termeffects,e.g.,creep,shrinkage,and prestress losses,compromise their structural performance.Strengthening these aged PC beams has become a crucial matter.One effective solution is to use externally bonded fiber-reinforced polymer(FRP)sheets;however,limited research has been done on aged PC beams using the FRP,especially for beams with unbonded prestressing strands(UPC beams).Therefore,this research investigates the flexural strengthening efficacy of external FRP sheets on aged UPC beams with unbonded tendons.Aging minimally affected the failure modes of UPC beams,with nonstrengthened beams showing flexural failure via rebar yielding and concrete crushing,and FRP-strengthened beams failing due to FRP debonding and tensile reinforcement yielding,though tendons in the aged beams did not yield due to prestress losses,unlike the new beams.The U-wrap anchor curbed widespread debonding,leading to tensile reinforcement yielding and FRP rupture.Aging hastened crack growth and stiffness loss,increasing deflections and reducing load resistance,but FRP reinforcement mitigated these effects,enhancing cracking resistance by 14%over the unstrengthened aged beams and 7%over the new beams while boosting ultimate resistance by 9%above the non-strengthened new beams.Compared to the new FRP-strengthened beams,the aged counterparts had lower cracking resistance,stiffness and capacity—showing 20%higher deflections,7–9%lower serviceability loads,7%–17%reduced ultimate strength and 17%less deformability—due to prestress losses and premature FRP debonding.
基金supported by the National Natural Science Foundation of China(Grant Nos.51978672 and 52308335)the Natural Science Funding of Hunan Province(Grant No.2023JJ41054)the Natural Science Research Project of Anhui Educational Committee(Grant No.2023AH051170)。
文摘Understanding the reinforcement effect of the newly developed prestressed reinforcement components(PRCs)(a system composed of prestressed steel bars(PSBs),protective sleeves,lateral pressure plates(LPPs),and anchoring elements)is technically significant for the rational design of prestressed subgrade.A three-dimensional finite element model was established and verified based on a novel static model test and utilized to systematically analyze the influence of prestress levels and reinforcement modes on the reinforcement effect of the subgrade.The results show that the PRCs provide additional confining pressure to the subgrade through the diffusion effect of the prestress,which can therefore effectively improve the service performance of the subgrade.Compared to the unreinforced conventional subgrades,the settlements of prestressreinforced subgrades are reduced.The settlement attenuation rate(Rs)near the LPPs is larger than that at the subgrade center,and increasing the prestress positively contributes to the stability of the subgrade structure.In the multi-row reinforcement mode,the reinforcement effect of PRCs can extend from the reinforced area to the unreinforced area.In addition,as the horizontal distance from the LPPs increases,the additional confining pressure converted by the PSBs and LPPs gradually diminishes when spreading to the core load bearing area of the subgrade,resulting in a decrease in the Rs.Under the singlerow reinforcement mode,PRCs can be strategically arranged according to the local areas where subgrade defects readily occurred or observed,to obtain the desired reinforcement effect.Moreover,excessive prestress should not be applied near the subgrade shoulder line to avoid the shear failure of the subgrade shoulder.PRCs can be flexibly used for preventing and treating various subgrade defects of newly constructed or existing railway lines,achieving targeted and classified prevention,and effectively improving the bearing performance and deformation resistance of the subgrade.The research results are instructive for further elucidating the prestress reinforcement effect of PRCs on railway subgrades.
基金Scientific and Technological Development Project of China Railway Design Group Co.,Ltd.(No.2022A02480005)Technology Development Project of China Railway Design Group Co.,Ltd.(No.2023A0248001).
文摘China's railway prestressed concrete bridge has more than 600000 holes,prestressed engineering is a key force system affecting the safety and durability of the prestressed concrete bridge structure,its construction quality is easily affected by traditional manual operation technology,resulting in low construction efficiency and control accuracy,easy to form a hidden danger of quality and safety,it is difficult to meet the needs of less humanized,standardized intelligent construction trend.Based on the research on the intelligent prestressed construction control and testing technology and equipment for railway bridges,this paper proposes the integration of intelligent prestressed tension control and tunnel friction test of railway bridges,intelligent grouting control of tunnel and intelligent testing of beam construction quality,and sets up a complete technical system and integrated equipment for intelligent prestressed construction of bridges based on the industrial Internet of Things(IoT).Overall,improve the quality and efficiency of bridge production,construction,and management.
基金Project(52274130)supported by the National Natural Science Foundation of ChinaProject(ZR2024ZD22)supported by the Major Basic Research Project of the Shandong Provincial Natural Science Foundation,China+2 种基金Project(2023375)supported by the Guizhou University Research and Innovation Team,ChinaProject(Leading Fund(2023)09)supported by the Natural Science Research Fund of Guizhou University,ChinaProject(JYBSYS2021101)supported by the Open Fund of Key Laboratory of Safe and Effective Coal Mining,Ministry of Education,China。
文摘The stress gradient of surrounding rock and reasonable prestress of support are the keys to ensuring the stability of roadways.The elastic-plastic analytical solution for surrounding rock was derived based on unified strength theory.A model for solving the stress gradient of the surrounding rock with the intermediate principal stress parameter b was established.The correctness and applicability of the solution for the stress gradient in the roadway surrounding rock was verified via multiple methods.Furthermore,the laws of stress,displacement,and the plastic zone of the surrounding rock with different b values and prestresses were revealed.As b increases,the stress gradient in the plastic zone increases,and the displacement and plastic zone radius decrease.As the prestress increases,the peak stress shifts toward the sidewalls,and the stress and stress gradient increments decrease.In addition,the displacement increment and plastic zone increment were proposed to characterize the support effect.The balance point of the plastic zone area appears before that of the displacement zone.The relationship between the stress gradient compensation coefficient and the prestress is obtained.This study provides a research method and idea for determining the reasonable prestress of support in roadways.
文摘The operational and regional conditions to which the prestressed concrete sleeper(PCS)is subjected in a railway track significantly contribute to its performance and durability.Maintaining the health of PCS poses challenges,and one of these issues involves the potential occurrence of longitudinal cracks in reinforcing bars,which can be caused by various constructional,functional,and environmental factors.Longitudinal cracks in PCS compromise the structural performance,resulting in a reduced capacity to withstand the loads exerted by moving vehicles.The current evaluations not only fail to yield a precise parameter for estimating the behavior and response of the PCS,but they also overlook the specific conditions of the PCS,such as prestressing,and only provide limited information regarding existing damage.Balancing the need for accurate evaluation with consideration of costs and resources,and making informed decisions about maintenance and track performance enhancement,has become a multifaceted challenge in ensuring a robust PCS assessment.This research introduces a novel methodology to improve the evaluation of mechanical and geometrical parameters of PCS over their operational lifespan.The objective is to enhance the accuracy of PCS performance estimation by concentrating on detecting longitudinal cracks.The suggested approach seamlessly integrates model updating methods and the finite element(FE)approach to achieve an accurate and timely assessment of PCS conditions.This comprehensive examination scrutinizes the methodology by applying artificial cracks to the PCS.In addition to introducing this assessment approach,a detailed examination is conducted on a laboratory-simulated PCS featuring various combinations of longitudinal cracks measuring 40,80,and 120 cm in length.This systematic and rigorous approach ensures the reliability and robustness of the methodology.Ultimately,the parameters of cross-sectional area,moment of inertia,and modulus of elasticity,which significantly impact the performance of this sleeper,are explored and demonstrated through functional methodologies.The findings suggest that assessing and addressing damage should be conducted through a comprehensive and integrated procedure,taking into account the actual conditions of the PCS.Longitudinal cracks lead to a substantial decrease in the performance of these components in railway tracks.By applying the proposed methods,it is anticipated that the evaluation error for these components will be reduced by approximately 30%compared to visual inspections,particularly in predicting the extent of damage for cracks measuring up to 120 cm.This research has the potential to significantly enhance the evaluation of PCS performance and mitigate the impact of longitudinal cracks on the safety and longevity of ballasted railway tracks in desert areas.
基金Project(2023YFC3805700) supported by the National Key Research and Development Program of ChinaProjects(42477166,42277174) supported by the National Natural Science Foundation of China+2 种基金Project(2024JCCXSB01) supported by the Fundamental Research Funds for the Central Universities,ChinaProject(KFJJ24-01M) supported by the State Key Laboratory of Explosion Science and Safety Protection,Beijing Institute of Technology,ChinaProject(HLCX-2024-04) supported by the Open Foundation of Collaborative Innovation Center of Green Development and Ecological Restoration of Mineral Resources,China。
文摘The surrounding rock is prone to large-scale loosening and failure after the excavation of shallow large-span caverns because of the thin overlying strata and large cross-section span.The rational design of bolt support is very important to the safety control of surrounding rock as a common support means.The control mechanism and design method of bolt support for shallow-buried large-span caverns is carried out.The calculation method of bolt prestress and length based on arched failure and collapsed failure mode is established.The influence mechanism of different influencing factors on the bolt prestress and length is clarified.At the same time,the constant resistance energy-absorbing bolt with high strength and high toughness is developed,and the comparative test of mechanical properties is carried out.On this basis,the design method of high prestressed bolt support for shallow-buried large-span caverns is put forward,and the field test is carried out in Qingdao metro station in China.The monitoring results show that the maximum roof settlement is 6.8 mm after the new design method is adopted,and the effective control of the shallow-buried large-span caverns is realized.The research results can provide theoretical and technical support for the safety control of shallow-buried large-span caverns.
