Waterproof performance of gaskets between segments is the focus of shield tunnels.This paper proposed an analytical method for determining seepage characteristics at tunnel-gasketed joints based on the hydraulic fract...Waterproof performance of gaskets between segments is the focus of shield tunnels.This paper proposed an analytical method for determining seepage characteristics at tunnel-gasketed joints based on the hydraulic fracturing theories.First,the mathematical model was established,and the seepage governing equation and boundary conditions were obtained.Second,three dimensionless parameters were introduced for simplifying the expressions,and the seepage governing equations were normalized.Third,analytical expressions were derived for the interface opening and liquid pressure.Moreover,the influencing factors of seepage process at the gasketed interface were analyzed.Parametric analyses revealed that,in the normalized criterion of liquid viscosity,the liquid tip coordinate was influenced by the degree of negative pressure in the liquid lag region,which was related to the initial contact stress.The coordinate of the liquid tip affected the liquid pressure distribution and the interface opening,which were analyzed under different liquid tip coordinate conditions.Finally,under two limit states,comparative analysis showed that the results of the variation trend of the proposed method agree well with those of previous research.Overall,the proposed analytical method provides a novel solution for the design of the waterproof in shield tunnels.展开更多
In this article,the mechanical properties of tunnel joints with curved bolts are studied and analyzed using the research methods of full-scale testing and finite element numerical simulation.First,the experiment resul...In this article,the mechanical properties of tunnel joints with curved bolts are studied and analyzed using the research methods of full-scale testing and finite element numerical simulation.First,the experiment results were analyzed to find out the development law of stress and strain of concrete in each part of the tunnel fragment when bearing.The damage process of the joint of the tunnel fragment was described in stages,and the characteristic load value that can reflect the initial bearing capacity in each stage was proposed.Afterward,using the ABAQUS three-dimensional(3D)finite element numerical modeling software,a numerical model corresponding to the experiment was established.The mid-span deflection was used to observe the change in loading and the destruction of each stage,comparing it to the proposed form to verify the reasonableness of the numerical model.Finally,the numerical models were used to analyze the change in material parameters and external loads from two aspects.It is concluded that the damage process of tunnel joints under curved bolt connection can be divided into concrete elasticity stage,inner arc cracking stage,overall joint damage stage,and ultimate joint damage stage,and the initial load of the adjacent stages is defined as the characteristic load value.After concrete cracking occurs,the bolts start to become the main load-bearing components,and the bolt stress grows rapidly in stage II.The strain development of the concrete on the outer arc is greater than the strain value of the concrete on the side due to mutual contact and extrusion.The parameters were changed for material properties,and it was found that increasing the concrete strength and bolt strength could improve the shield fragment joint bearing performance.The optimal effect of improving the mechanical properties of the shield fragment joint would be obtained when the concrete strength grade is C60,and the bolt strength grade is 8.8.Increasing the size of the axial force and bolt preload has the most obvious effect on the load-carrying capacity in the initial elastic phase.This can reduce the joint angle and thus improve joint stiffness.Meanwhile,increasing the axial force has a greater effect on the performance of the tunnel joint than the bolt preload.展开更多
We develop assembled reinforcement structures(ARSs)composed of connection parts,connecting rods,and straight bolts to strengthen segmental joints in the lining of shield tunnels.Through full-scale bending experiments ...We develop assembled reinforcement structures(ARSs)composed of connection parts,connecting rods,and straight bolts to strengthen segmental joints in the lining of shield tunnels.Through full-scale bending experiments and numerical simulations,we investigate the deformation and failure characteristics of segmental joints strengthened by ARSs,and propose a novel optimization method for ARSs.The experimental results show that the ARSs can effectively limit the opening of a segmental joint,but also that separation can occur during loading if the connection between the ARSs and segments is not designed properly.Importantly,this connection can be improved by embedding anchor parts in the concrete.In numerical modeling,we investigate the failure modes of segmental joints strengthened by ARSs for both positive bending and negative bending loading cases.In the case of positive bending loading,first the concrete around the anchor parts cracks,and subsequently the concrete on the external side of the joint is crushed.The joint failure is caused by the crushing of concrete on the external side of the joint.While the un-strengthened segmental joint fails with an opening of 5.884 mm,the strengthened segmental joint only opens by 0.288 mm under the same loading,corresponding to a reduction of 95.1%.In the case of negative bending loading,the concrete around the anchor parts first cracks,and then the amount of joint opening exceeds a limiting value for waterproofing(6 mm),i.e.,the joint’s failure is caused by water leakage.While the opening of the un-strengthened segmental joint is 9.033 mm and experiences waterproofing failure,the opening of the strengthened segmental joint is only 2.793 mm under the same loading,corresponding to a reduction of 69.1%.When constructing a new shield tunnel,anchor parts could be embedded in the concrete segments in tandem with ARSs for improved resistance to joint opening.For existing shield tunnel linings,anchor parts cannot be embedded in the concrete segments;therefore,the connections between the ARSs and concrete need to be optimized to strengthen the segmental joint.展开更多
Quantitative analysis of clinical function parameters from MRI images is crucial for diagnosing and assessing cardiovascular disease.However,the manual calculation of these parameters is challenging due to the high va...Quantitative analysis of clinical function parameters from MRI images is crucial for diagnosing and assessing cardiovascular disease.However,the manual calculation of these parameters is challenging due to the high variability among patients and the time-consuming nature of the process.In this study,the authors introduce a framework named MultiJSQ,comprising the feature presentation network(FRN)and the indicator prediction network(IEN),which is designed for simultaneous joint segmentation and quantification.The FRN is tailored for representing global image features,facilitating the direct acquisition of left ventricle(LV)contour images through pixel classification.Additionally,the IEN incorporates specifically designed modules to extract relevant clinical indices.The authors’method considers the interdependence of different tasks,demonstrating the validity of these relationships and yielding favourable results.Through extensive experiments on cardiac MR images from 145 patients,MultiJSQ achieves impressive outcomes,with low mean absolute errors of 124 mm^(2),1.72 mm,and 1.21 mm for areas,dimensions,and regional wall thicknesses,respectively,along with a Dice metric score of 0.908.The experimental findings underscore the excellent performance of our framework in LV segmentation and quantification,highlighting its promising clinical application prospects.展开更多
Sn/Ni-Sn/Sn sandwich joining piece was developed and applied to fabricate segmented half-Heusler/skutterudite thermoelectric joints,and high-temperature service behavior of the joints was studied.The microstructure an...Sn/Ni-Sn/Sn sandwich joining piece was developed and applied to fabricate segmented half-Heusler/skutterudite thermoelectric joints,and high-temperature service behavior of the joints was studied.The microstructure and contact resistance of the joint before and after aging were investigated.The joints are well bonded and no cracks appear at the interfaces of the joint before and after aging,which can be attributed to the formation of high-melting point intermetallic compounds.The electrical resistance crosses the joining layer smoothly and the contact resistance is low.These results show that the sandwich joining piece is effective and flexible,and promising for the preparation of segmented thermoelectric devices.展开更多
Passive dynamic walking has been developed as a possible explanation for the efficiency of the human gait. This paper presents a passive dynamic walking model with segmented feet, which makes the bipedal walking gait ...Passive dynamic walking has been developed as a possible explanation for the efficiency of the human gait. This paper presents a passive dynamic walking model with segmented feet, which makes the bipedal walking gait more close to natural human-like gait. The proposed model extends the simplest walking model with the addition of fiat feet and torsional spring based compliance on ankle joints and toe joints, to achieve stable walking on a slope driven by gravity. The push-off phase includes foot rotations around the toe joint and around the toe tip, which shows a great resemblance to human normal walking. This paper investigates the effects of the segmented foot structure on bipedal walking in simulations. The model achieves satisfactory walking results on even or uneven slopes.展开更多
The mechanical properties of the steel-plate-reinforced segmental lining are generally determined by the load-bearing capacity of rein-forced joints.However,there is a lack of valid calculation methods for compression...The mechanical properties of the steel-plate-reinforced segmental lining are generally determined by the load-bearing capacity of rein-forced joints.However,there is a lack of valid calculation methods for compression-bending bearing capacity,and researchers mainly rely on experience and analogy for the design of reinforced joints.This paper proposes an analytical model based on the deformation and stress characteristics of the joint surface to calculate the compression-bending capacity of the steel-plate-reinforced joint.After verifying the applicability of this analytical model through finite element simulations,the evalution rules of the load-bearing capacity of the rein-forced joint were attained,followed by a quantitative investigation into the influence of joint parameters on it.The results show that:(1)the bearing capacity curve of the reinforced joint under different axial forces can be separated into two parts,with the maximum ultimate bending moment found at the demarcation point,where the steel plate yielding and joint failure occur simultaneously;(2)the steel plate strength and cross-sectional area have a strong infuence on the bearing capacity of the reinforced joint when the axial force is under 0.15RFF,where RFF is the axial force at pure-compression failure;(3)the concrete strength and segment width have a prominent influ-ence on the curve when the axial force is over 0.30RFF;(4)the impact of the fictitious strain,bolt strength,bolt diameter,and bolt loca-tion on the bearing capacity is minimal in range and amplitude.展开更多
In circular shield tunnels bearing high inner pressure or rectangular shaped shield tunnels,as the axial force at the segmental lining decreases,the bolt load at the segmental joint increases.It is essential to adopt ...In circular shield tunnels bearing high inner pressure or rectangular shaped shield tunnels,as the axial force at the segmental lining decreases,the bolt load at the segmental joint increases.It is essential to adopt high-stiffness segmental joints to improve the bearing capacity and control the deformation at the joint position.When designing high-stiffness segmental joints,the selection of ductileiron joint panel is crucial.In this study,two types of segmental joints with different joint panels were fabricated,and the effects of joint panel stiffness on the mechanical properties of segmental joints were analyzed through full-scale sagging and hogging bending tests.The results showed that the failure mode of high-stiffness segmental joint was similar to that of large eccentric compression section.According to the difference of panel stiffness,the failure modes can be specified into two types.If the stiffness is sufficient,the joint failure occurs due to the yielding of bolts;otherwise,it occurs due to the large deformation of ductile-iron joint panels.As for the design requirement of segmental joint,the stiffness of joint panel should be sufficient,i.e.,the opening and failure of the joints are finally induced by the bolt deformation.Otherwise,before the plastic deformation of the bolts,the large deformation of the joint panels will occur under a bendingmoment-dominant load,and the bearing capacity of the joints will greatly decrease.展开更多
Rocks encountered in foundations of heavy structures are invariably intersected by discontinuities(joints).In the past,several studies have been performed by researchers to incorporate the effect of fully persistent j...Rocks encountered in foundations of heavy structures are invariably intersected by discontinuities(joints).In the past,several studies have been performed by researchers to incorporate the effect of fully persistent joints in the assessment of the load-carrying capacity of rocks.However,in the field,the joints are non-persistent,and an assumption of full persistency will underestimate the capacity.Recently,Shaunik&Singh have studied the influence of non-persistency,number of joint segments and discontinuity orientation on the strength behaviour of rock specimens(Shaunik and Singh,2019).Bell’s approach can be used to obtain the bearing capacity of shallow foundations placed in jointed rocks.In the present study,results of the experimental work(Shaunik and Singh,2019)conducted by Shaunik&Singh have been used to suggest expressions by extending Bell’s approach for computing bearing capacity of the foundation placed near the crown of a rock slope.Easy to use design charts are also presented for field application.Finally,a real-life problem from Indian Garhwal Himalayas is considered,and the approach suggested in this study is utilised to obtain the bearing capacity of a bridge foundation as a function of uniaxial compressive strength(UCS)of intact rock,joint friction,spacing and orientation of joint,nonpersistency and number of joint segments.展开更多
Micromechanics aims mainly at establishing the quantitative relation between the macroscopic mechanical behavior and the microstructure of heterogeneous materials.
This paper studies spectral density estimation of a strictly stationary r-vector valued continuous time series including missing observations. The finite Fourier transform is constructed in L-joint segments of observa...This paper studies spectral density estimation of a strictly stationary r-vector valued continuous time series including missing observations. The finite Fourier transform is constructed in L-joint segments of observations. The modified periodogram is defined and smoothed to estimate the spectral density matrix. We explore the properties of the proposed estimator. Asymptotic distribution is discussed.展开更多
The emergence of curved shield tunnels poses a significant construction challenge.If the quality of the segment assembly is not guaranteed,many segment cracks and damage will result from the stress concentration.Sensi...The emergence of curved shield tunnels poses a significant construction challenge.If the quality of the segment assembly is not guaranteed,many segment cracks and damage will result from the stress concentration.Sensing the contact stresses between segmental joints is necessary to improve the quality of segments assembled for shield tunnel construction.Polyvinylidene difluoride(PVDF)piezoelectric material was chosen for the sensor because it can convert contact stresses into electrical signals,allowing the state of the segmental joints to be effectively sensed.It matches the working environment between the segmental joints of the shield tunnel,where flexible structures such as rubber gaskets and force transfer pads are present.This study proposes a piezoelectric sensing method for segmental joints in shield tunnels and conducts laboratory tests,numerical analyses,and field tests to validate the feasibility of the method.The results indicate that the PVDF film sensor can effectively sense the entire compression process of the gasket with different amounts of compression.The piezoelectric cable sensor can effectively sense the joint offset direction of the gasket.For differently shaped sections,the variation in the force sensed by the piezoelectric cable sensors was different,as verified by numerical simulation.Through the field test,it was found that the average contact stress between the segmental joints was in the range of 1.2–1.8 MPa during construction of the curved shield tunnels.The location of the segmental joints and the type of segment affect the contact stress value.The field monitoring results show that piezoelectric sensing technology can be successfully applied during assembly of the segments for effective sensing of the contact stress.展开更多
The waterproofing capacity of segmental joints is an essential indicator for the long-term service performance of shield tunnels.The segmental joints with double gaskets have been adopted to improve the waterproof per...The waterproofing capacity of segmental joints is an essential indicator for the long-term service performance of shield tunnels.The segmental joints with double gaskets have been adopted to improve the waterproof performance for certain tunnels with high water pressure,especially water-conveyance tunnels.This paper presents a series of waterproofing tests on joints with different settings of double gaskets via an improved test apparatus.Four cases are investigated,including(i)double gaskets with equal high/low waterproof capacity,(ii)the outer gasket with higher waterproof capacity,and(iii)the outer gasket with lower waterproof capacity.Different joint openings are also considered.Moreover,the water pressures at two cavities are continuously monitored to highlight the waterproofing mechanism and failure pattern of double gaskets.The results demonstrate that the gasket with the higher waterproofing capacity dominates the overall waterproofing capacity of joint with double gaskets;only a little enhancement of the waterproofing capacity is found for the joint with the same double gaskets.The waterproofing capacity of joints with double gaskets decreases with the increase of the joint opening.The failure pattern depends on the arrangement of double gaskets,and four stages can be identified during the whole failure process.The advantages of double gaskets in case of joint rotation are also discussed.展开更多
The integrity and bearing capacity of segment joints in shield tunnels are associated closely with the mechanical properties of the joints.This study focuses on the mechanical characteristics and mechanism of a bolted...The integrity and bearing capacity of segment joints in shield tunnels are associated closely with the mechanical properties of the joints.This study focuses on the mechanical characteristics and mechanism of a bolted circumferential joint during the entire bearing process.Simplified analytical algorithms for four stress stages are established to describe the bearing behaviors of the joint under a compressive bending load.A height adjustment coefficient,α,for the outer concrete compression zone is introduced into a simplified analytical model.Factors affectingαare determined,and the degree of influence of these factors is investigated via orthogonal numerical simulations.The numerical results show thatαcan be specified as approximately 0.2 for most metro shield tunnels in China.Subsequently,a case study is performed to verify the rationality of the simplified theoretical analysis for the segment joint via numerical simulations and experiments.Using the proposed simplified analytical algorithms,a parametric investigation is conducted to discuss the factors affecting the ultimate compressive bending capacity of the joint.The method for optimizing the joint flexural stiffness is clarified.The results of this study can provide a theoretical basis for optimizing the design and prediciting the damage of bolted segment joints in shield tunnels.展开更多
基金Project(52278421)supported by the National Natural Science Foundation of ChinaProject(2024ZZTS0754)supported by the Fundamental Research Funds for the Central Universities of Central South University,China+2 种基金Project(2023CXQD067)supported by the Central South University Innovation-Driven Research Programme,ChinaProject(2022QNRC001)supported by Young Elite Scientists Sponsorship Program by CASTProject(2023TJ-N24)supported by the Youth Talent Program by China Railway Society and the Hunan Provincial Science and Technology Promotion Talent Project。
文摘Waterproof performance of gaskets between segments is the focus of shield tunnels.This paper proposed an analytical method for determining seepage characteristics at tunnel-gasketed joints based on the hydraulic fracturing theories.First,the mathematical model was established,and the seepage governing equation and boundary conditions were obtained.Second,three dimensionless parameters were introduced for simplifying the expressions,and the seepage governing equations were normalized.Third,analytical expressions were derived for the interface opening and liquid pressure.Moreover,the influencing factors of seepage process at the gasketed interface were analyzed.Parametric analyses revealed that,in the normalized criterion of liquid viscosity,the liquid tip coordinate was influenced by the degree of negative pressure in the liquid lag region,which was related to the initial contact stress.The coordinate of the liquid tip affected the liquid pressure distribution and the interface opening,which were analyzed under different liquid tip coordinate conditions.Finally,under two limit states,comparative analysis showed that the results of the variation trend of the proposed method agree well with those of previous research.Overall,the proposed analytical method provides a novel solution for the design of the waterproof in shield tunnels.
基金financial support provided by the National Natural Science Foundation of China under(Grant Nos.51978019 and 52278382)the Natural Science Foundation of Beijing Municipality(No.8222004).
文摘In this article,the mechanical properties of tunnel joints with curved bolts are studied and analyzed using the research methods of full-scale testing and finite element numerical simulation.First,the experiment results were analyzed to find out the development law of stress and strain of concrete in each part of the tunnel fragment when bearing.The damage process of the joint of the tunnel fragment was described in stages,and the characteristic load value that can reflect the initial bearing capacity in each stage was proposed.Afterward,using the ABAQUS three-dimensional(3D)finite element numerical modeling software,a numerical model corresponding to the experiment was established.The mid-span deflection was used to observe the change in loading and the destruction of each stage,comparing it to the proposed form to verify the reasonableness of the numerical model.Finally,the numerical models were used to analyze the change in material parameters and external loads from two aspects.It is concluded that the damage process of tunnel joints under curved bolt connection can be divided into concrete elasticity stage,inner arc cracking stage,overall joint damage stage,and ultimate joint damage stage,and the initial load of the adjacent stages is defined as the characteristic load value.After concrete cracking occurs,the bolts start to become the main load-bearing components,and the bolt stress grows rapidly in stage II.The strain development of the concrete on the outer arc is greater than the strain value of the concrete on the side due to mutual contact and extrusion.The parameters were changed for material properties,and it was found that increasing the concrete strength and bolt strength could improve the shield fragment joint bearing performance.The optimal effect of improving the mechanical properties of the shield fragment joint would be obtained when the concrete strength grade is C60,and the bolt strength grade is 8.8.Increasing the size of the axial force and bolt preload has the most obvious effect on the load-carrying capacity in the initial elastic phase.This can reduce the joint angle and thus improve joint stiffness.Meanwhile,increasing the axial force has a greater effect on the performance of the tunnel joint than the bolt preload.
基金supported by the National Natural Science Foundation of China(No.52008308)the China Postdoctoral Science Foundation(Nos.BX20200247 and 2021M692447)the Research Project from Jinan Rail Transit Group Co.,Ltd.and China Railway No.5 Engineering Group Co.,Ltd.(No.R2-ZF-2019-039).
文摘We develop assembled reinforcement structures(ARSs)composed of connection parts,connecting rods,and straight bolts to strengthen segmental joints in the lining of shield tunnels.Through full-scale bending experiments and numerical simulations,we investigate the deformation and failure characteristics of segmental joints strengthened by ARSs,and propose a novel optimization method for ARSs.The experimental results show that the ARSs can effectively limit the opening of a segmental joint,but also that separation can occur during loading if the connection between the ARSs and segments is not designed properly.Importantly,this connection can be improved by embedding anchor parts in the concrete.In numerical modeling,we investigate the failure modes of segmental joints strengthened by ARSs for both positive bending and negative bending loading cases.In the case of positive bending loading,first the concrete around the anchor parts cracks,and subsequently the concrete on the external side of the joint is crushed.The joint failure is caused by the crushing of concrete on the external side of the joint.While the un-strengthened segmental joint fails with an opening of 5.884 mm,the strengthened segmental joint only opens by 0.288 mm under the same loading,corresponding to a reduction of 95.1%.In the case of negative bending loading,the concrete around the anchor parts first cracks,and then the amount of joint opening exceeds a limiting value for waterproofing(6 mm),i.e.,the joint’s failure is caused by water leakage.While the opening of the un-strengthened segmental joint is 9.033 mm and experiences waterproofing failure,the opening of the strengthened segmental joint is only 2.793 mm under the same loading,corresponding to a reduction of 69.1%.When constructing a new shield tunnel,anchor parts could be embedded in the concrete segments in tandem with ARSs for improved resistance to joint opening.For existing shield tunnel linings,anchor parts cannot be embedded in the concrete segments;therefore,the connections between the ARSs and concrete need to be optimized to strengthen the segmental joint.
基金Hefei Municipal Natural Science Foundation,Grant/Award Number:2022009Suqian Guiding Program Project,Grant/Award Number:Z202309Suqian Traditional Chinese Medicine Science and Technology Plan,Grant/Award Number:MS202301。
文摘Quantitative analysis of clinical function parameters from MRI images is crucial for diagnosing and assessing cardiovascular disease.However,the manual calculation of these parameters is challenging due to the high variability among patients and the time-consuming nature of the process.In this study,the authors introduce a framework named MultiJSQ,comprising the feature presentation network(FRN)and the indicator prediction network(IEN),which is designed for simultaneous joint segmentation and quantification.The FRN is tailored for representing global image features,facilitating the direct acquisition of left ventricle(LV)contour images through pixel classification.Additionally,the IEN incorporates specifically designed modules to extract relevant clinical indices.The authors’method considers the interdependence of different tasks,demonstrating the validity of these relationships and yielding favourable results.Through extensive experiments on cardiac MR images from 145 patients,MultiJSQ achieves impressive outcomes,with low mean absolute errors of 124 mm^(2),1.72 mm,and 1.21 mm for areas,dimensions,and regional wall thicknesses,respectively,along with a Dice metric score of 0.908.The experimental findings underscore the excellent performance of our framework in LV segmentation and quantification,highlighting its promising clinical application prospects.
基金the National Natural Science Foundation of China(Nos.U1738114,51372261 and 51879089)。
文摘Sn/Ni-Sn/Sn sandwich joining piece was developed and applied to fabricate segmented half-Heusler/skutterudite thermoelectric joints,and high-temperature service behavior of the joints was studied.The microstructure and contact resistance of the joint before and after aging were investigated.The joints are well bonded and no cracks appear at the interfaces of the joint before and after aging,which can be attributed to the formation of high-melting point intermetallic compounds.The electrical resistance crosses the joining layer smoothly and the contact resistance is low.These results show that the sandwich joining piece is effective and flexible,and promising for the preparation of segmented thermoelectric devices.
基金supported by the National Natural Science Foundation of China (61005082, 61020106005)Doctoral Fund of Ministry of Education of China (20100001120005)+1 种基金PKU-Biomedical Engineering Join Seed Grant 2012the 985 Project of PekingUniversity (3J0865600)
文摘Passive dynamic walking has been developed as a possible explanation for the efficiency of the human gait. This paper presents a passive dynamic walking model with segmented feet, which makes the bipedal walking gait more close to natural human-like gait. The proposed model extends the simplest walking model with the addition of fiat feet and torsional spring based compliance on ankle joints and toe joints, to achieve stable walking on a slope driven by gravity. The push-off phase includes foot rotations around the toe joint and around the toe tip, which shows a great resemblance to human normal walking. This paper investigates the effects of the segmented foot structure on bipedal walking in simulations. The model achieves satisfactory walking results on even or uneven slopes.
基金support provided by the National Natural Science Foundation of China(Grant No.52278409).
文摘The mechanical properties of the steel-plate-reinforced segmental lining are generally determined by the load-bearing capacity of rein-forced joints.However,there is a lack of valid calculation methods for compression-bending bearing capacity,and researchers mainly rely on experience and analogy for the design of reinforced joints.This paper proposes an analytical model based on the deformation and stress characteristics of the joint surface to calculate the compression-bending capacity of the steel-plate-reinforced joint.After verifying the applicability of this analytical model through finite element simulations,the evalution rules of the load-bearing capacity of the rein-forced joint were attained,followed by a quantitative investigation into the influence of joint parameters on it.The results show that:(1)the bearing capacity curve of the reinforced joint under different axial forces can be separated into two parts,with the maximum ultimate bending moment found at the demarcation point,where the steel plate yielding and joint failure occur simultaneously;(2)the steel plate strength and cross-sectional area have a strong infuence on the bearing capacity of the reinforced joint when the axial force is under 0.15RFF,where RFF is the axial force at pure-compression failure;(3)the concrete strength and segment width have a prominent influ-ence on the curve when the axial force is over 0.30RFF;(4)the impact of the fictitious strain,bolt strength,bolt diameter,and bolt loca-tion on the bearing capacity is minimal in range and amplitude.
基金supported by the National Natural Science Foundation of China(Grant No.52090083)the Postdoctoral Innovative Talents Supporting Program(Grant No.BX20200247)the Shanghai Sailing Program(Grant No.20YF1451400).
文摘In circular shield tunnels bearing high inner pressure or rectangular shaped shield tunnels,as the axial force at the segmental lining decreases,the bolt load at the segmental joint increases.It is essential to adopt high-stiffness segmental joints to improve the bearing capacity and control the deformation at the joint position.When designing high-stiffness segmental joints,the selection of ductileiron joint panel is crucial.In this study,two types of segmental joints with different joint panels were fabricated,and the effects of joint panel stiffness on the mechanical properties of segmental joints were analyzed through full-scale sagging and hogging bending tests.The results showed that the failure mode of high-stiffness segmental joint was similar to that of large eccentric compression section.According to the difference of panel stiffness,the failure modes can be specified into two types.If the stiffness is sufficient,the joint failure occurs due to the yielding of bolts;otherwise,it occurs due to the large deformation of ductile-iron joint panels.As for the design requirement of segmental joint,the stiffness of joint panel should be sufficient,i.e.,the opening and failure of the joints are finally induced by the bolt deformation.Otherwise,before the plastic deformation of the bolts,the large deformation of the joint panels will occur under a bendingmoment-dominant load,and the bearing capacity of the joints will greatly decrease.
基金A part of this research was carried from financial assistance obtained from NRDMS Division Department of Science and Technology,New Delhithe assistance received from DST and thank for the support.
文摘Rocks encountered in foundations of heavy structures are invariably intersected by discontinuities(joints).In the past,several studies have been performed by researchers to incorporate the effect of fully persistent joints in the assessment of the load-carrying capacity of rocks.However,in the field,the joints are non-persistent,and an assumption of full persistency will underestimate the capacity.Recently,Shaunik&Singh have studied the influence of non-persistency,number of joint segments and discontinuity orientation on the strength behaviour of rock specimens(Shaunik and Singh,2019).Bell’s approach can be used to obtain the bearing capacity of shallow foundations placed in jointed rocks.In the present study,results of the experimental work(Shaunik and Singh,2019)conducted by Shaunik&Singh have been used to suggest expressions by extending Bell’s approach for computing bearing capacity of the foundation placed near the crown of a rock slope.Easy to use design charts are also presented for field application.Finally,a real-life problem from Indian Garhwal Himalayas is considered,and the approach suggested in this study is utilised to obtain the bearing capacity of a bridge foundation as a function of uniaxial compressive strength(UCS)of intact rock,joint friction,spacing and orientation of joint,nonpersistency and number of joint segments.
文摘Micromechanics aims mainly at establishing the quantitative relation between the macroscopic mechanical behavior and the microstructure of heterogeneous materials.
文摘This paper studies spectral density estimation of a strictly stationary r-vector valued continuous time series including missing observations. The finite Fourier transform is constructed in L-joint segments of observations. The modified periodogram is defined and smoothed to estimate the spectral density matrix. We explore the properties of the proposed estimator. Asymptotic distribution is discussed.
基金supported by the National Natural Science Foundation of China(Grant Nos.51978162 and 52278398).
文摘The emergence of curved shield tunnels poses a significant construction challenge.If the quality of the segment assembly is not guaranteed,many segment cracks and damage will result from the stress concentration.Sensing the contact stresses between segmental joints is necessary to improve the quality of segments assembled for shield tunnel construction.Polyvinylidene difluoride(PVDF)piezoelectric material was chosen for the sensor because it can convert contact stresses into electrical signals,allowing the state of the segmental joints to be effectively sensed.It matches the working environment between the segmental joints of the shield tunnel,where flexible structures such as rubber gaskets and force transfer pads are present.This study proposes a piezoelectric sensing method for segmental joints in shield tunnels and conducts laboratory tests,numerical analyses,and field tests to validate the feasibility of the method.The results indicate that the PVDF film sensor can effectively sense the entire compression process of the gasket with different amounts of compression.The piezoelectric cable sensor can effectively sense the joint offset direction of the gasket.For differently shaped sections,the variation in the force sensed by the piezoelectric cable sensors was different,as verified by numerical simulation.Through the field test,it was found that the average contact stress between the segmental joints was in the range of 1.2–1.8 MPa during construction of the curved shield tunnels.The location of the segmental joints and the type of segment affect the contact stress value.The field monitoring results show that piezoelectric sensing technology can be successfully applied during assembly of the segments for effective sensing of the contact stress.
基金financially supported by National Natural Science Foundation of China(52090083)Shanghai Committee of Science and Technology(20DZ1202600)China Railway Southern Investment Group Co.Ltd(Project No.ZTNF-2020-1).
文摘The waterproofing capacity of segmental joints is an essential indicator for the long-term service performance of shield tunnels.The segmental joints with double gaskets have been adopted to improve the waterproof performance for certain tunnels with high water pressure,especially water-conveyance tunnels.This paper presents a series of waterproofing tests on joints with different settings of double gaskets via an improved test apparatus.Four cases are investigated,including(i)double gaskets with equal high/low waterproof capacity,(ii)the outer gasket with higher waterproof capacity,and(iii)the outer gasket with lower waterproof capacity.Different joint openings are also considered.Moreover,the water pressures at two cavities are continuously monitored to highlight the waterproofing mechanism and failure pattern of double gaskets.The results demonstrate that the gasket with the higher waterproofing capacity dominates the overall waterproofing capacity of joint with double gaskets;only a little enhancement of the waterproofing capacity is found for the joint with the same double gaskets.The waterproofing capacity of joints with double gaskets decreases with the increase of the joint opening.The failure pattern depends on the arrangement of double gaskets,and four stages can be identified during the whole failure process.The advantages of double gaskets in case of joint rotation are also discussed.
基金This study was supported by the National Natural Science Foundation of China (Grant Nos. 51978019 and 52278382)the Natural Science Foundation of Beijing Municipality (No. 8222004).
文摘The integrity and bearing capacity of segment joints in shield tunnels are associated closely with the mechanical properties of the joints.This study focuses on the mechanical characteristics and mechanism of a bolted circumferential joint during the entire bearing process.Simplified analytical algorithms for four stress stages are established to describe the bearing behaviors of the joint under a compressive bending load.A height adjustment coefficient,α,for the outer concrete compression zone is introduced into a simplified analytical model.Factors affectingαare determined,and the degree of influence of these factors is investigated via orthogonal numerical simulations.The numerical results show thatαcan be specified as approximately 0.2 for most metro shield tunnels in China.Subsequently,a case study is performed to verify the rationality of the simplified theoretical analysis for the segment joint via numerical simulations and experiments.Using the proposed simplified analytical algorithms,a parametric investigation is conducted to discuss the factors affecting the ultimate compressive bending capacity of the joint.The method for optimizing the joint flexural stiffness is clarified.The results of this study can provide a theoretical basis for optimizing the design and prediciting the damage of bolted segment joints in shield tunnels.
