This paper presents the static and fatigue tests of hybrid(bonded/bolted)glass fiber reinforced polymer(GFRP)joints.Nine specimens of single-lap hybrid GFRP joints have been fabricated to study the static and fatigue ...This paper presents the static and fatigue tests of hybrid(bonded/bolted)glass fiber reinforced polymer(GFRP)joints.Nine specimens of single-lap hybrid GFRP joints have been fabricated to study the static and fatigue behaviors in the experimental campaign.The static tests of uniaxial tension loading are first conducted,from which the static ultimate bearing capacities of the joints are obtained.High-cycle fatigue tests are subsequently carried out so that the fatigue failure mode,fatigue life,and stiffness degradation of joints can be obtained.The measuring techniques including acoustic emission monitoring and three-dimensional digital image correlation have been employed in the tests to record the damage development process.The results revealed that the static strength and fatigue behavior of such thick hybrid GFRP joints were controlled by the bolted connections.The four stages of fatigue failure process are obtained from tests and acoustic emission signals analysis:cumulative damage of adhesive layer,damage of the adhesive layer,cumulative damage of GFRP plate,and damage of GFRP plate.The fatigue life and stiffness degradation can be improved by more bolts.The S-N(fatigue stress versus life)curves for the fatigue design of the single-lap hybrid GFRP joints under uniaxial tension loading are also proposed.展开更多
Cyclic load is widely adopted in laboratory to simulate the effect of train load on ballast bed.The effectiveness of such load equivalence is usually testified by having similar results of key concerns of ballast bed,...Cyclic load is widely adopted in laboratory to simulate the effect of train load on ballast bed.The effectiveness of such load equivalence is usually testified by having similar results of key concerns of ballast bed,such as deformation or stiffness,while the consistency of particle scale characteristics under two loading patterns is rarely examined,which is insufficient to well-understand and use the load simplification.In this study,a previous laboratory model test of ballast bed under cyclic load is rebuilt using 3D discrete element method(DEM),which is validated by dynamic responses monitored by high-resolution sensors.Then,train load having the same magnitude and amplitude as the cyclic load is applied in the numerical model to obtain the statistical characteristics of inter-particle contact force and particle movements in ballast bed.The results show that particle scale responses under two loading patterns could have quite deviation,even when macro-scale responses of ballast bed under two loading patterns are very close.This inconsistency indicates that the application scale of the DEM model should not exceed the validation scale.Moreover,it is important to examine multiscale responses to validate the effectiveness of load simplification.展开更多
We focused on the efflorescence induced microstructural evolution of ettringite-rich systems prepared with calcium aluminate cement(CAC)and anhydrite.The effects of anhydrite on the visible efflorescence,and the corre...We focused on the efflorescence induced microstructural evolution of ettringite-rich systems prepared with calcium aluminate cement(CAC)and anhydrite.The effects of anhydrite on the visible efflorescence,and the corresponding capillary absorption of CAC-anhydrite mortars were revealed.The composition and microstructure of efflorescence-causing substances were investigated by optical microscope,in-situ Raman spectroscopy,scanning electron microscope,energy dispersive spectrometer,thermogravimetric analysis,and differential scanning calorimetry,at multi-scales.Results indicate that,besides the calcium carbonate,ettringite is another main component of efflorescence-causing substances.Compared with the neat CAC mortars,the addition of anhydrite has a significant effect on the degree of efflorescence by acting on the composition of hydration products and pore structure.In addition,methods are proposed for the prevention of efflorescence of CAC-anhydrite binary system.展开更多
Sandstone is widely distributed in cold regions and the freeze-thaw deterioration of them has caused many geological engineering disasters.As an important and direct index of frost resistance,the strength loss of sand...Sandstone is widely distributed in cold regions and the freeze-thaw deterioration of them has caused many geological engineering disasters.As an important and direct index of frost resistance,the strength loss of sandstones under freeze-thaw actions should be investigated to provide a guidance for the stability assessment of geological engineering.In this research,the UCS(Uniaxial compressive strength)loss of six typical sandstones with different water contents after 0,20,40 and 60 freeze-thaw cycles was measured in the laboratory.The experimental results indicated that the freeze-thaw damage was more serious in sandstones containing high water contents,and the critical saturations for causing a significant loss of UCS under freeze-thaw were 60%-80%for these sandstones.Below this critical saturation,the UCS loss of the sandstones was mainly caused by water weakening rather than freeze-thaw damage.Besides,a developed strength prediction model was proposed by combining the exponential decay function and multiple linear regression method.The initial porosity,elastic modulus and tensile strength of fresh sandstones were a good parameter combination to accurately determine the decay constant in this developed model.The main novelty of this model is that it can accurately and easily estimate the UCS loss of sandstones after any freeze-thaw cycle only using the initial parameters of fresh sandstones,but it does not need to perform freeze-thaw and mechanical strength experiments.This study not only provides an accurate prediction model of UCS under freeze-thaw,but also makes a contribution to better understanding the frost resistance mechanism of sandstones.展开更多
When dynamic load is applied on a granular assembly,the time-dependent dynamic load and initial static load(such as gravity stress)act together on individual particles.In order to better understand how dynamic load tr...When dynamic load is applied on a granular assembly,the time-dependent dynamic load and initial static load(such as gravity stress)act together on individual particles.In order to better understand how dynamic load triggers the micro-structure's evolution and furtherly the ensemble behavior of a granular assembly,we propose a criterion to recognize the major propagation path of dynamic load in 2D granular materials,called the“dynamic force chain”.Two steps are involved in recognizing dynamic force chains:(1)pick out particles with dynamic load larger than the threshold stress,where the attenuation of dynamic stress with distance is considered;(2)among which quasi-linear arrangement of three or more particles are identified as a force chain.The spatial distribution of dynamic force chains in indentation of granular materials provides a direct measure of dynamic load diffusion.The statistical evolution of dynamic force chains shows strong correlation with the indentation behaviors.展开更多
The computational efficiency of the traditional serial spherical discontinuous deformation analysis(SDDA) program has limited its application in geotechnical engineering problems that need a large number of spheres. T...The computational efficiency of the traditional serial spherical discontinuous deformation analysis(SDDA) program has limited its application in geotechnical engineering problems that need a large number of spheres. The cloud computing technology is used to parallel the SDDA program for the first time in this research. The most computationally intensive portions of the SDDA program, i.e., contact detection and matrix solution, are parallelized with proposed algorithms. The accuracy of the cloud-based parallel SDDA program(CB-PSDDA) is verified first. Further efficiency tests show that significant speedup can be obtained with an 8-server configuration and the computing scale can be up to several tens of thousands of particles. The cloud-based parallelized SDDA program increases its potential in applications of deformation and failure analysis of large-scale and realistic geotechnical engineering problems.展开更多
A numerical framework was proposed for the seismic analysis of underground structures in layered ground under inclined P-SV waves.The free-field responses are first obtained using the stiffness matrix method based on ...A numerical framework was proposed for the seismic analysis of underground structures in layered ground under inclined P-SV waves.The free-field responses are first obtained using the stiffness matrix method based on plane-wave assumptions.Then,the domain reduction method was employed to reproduce the wavefield in the numerical model of the soil–structure system.The proposed numerical framework was verified by providing comparisons with analytical solutions for cases involving free-field responses of homogeneous ground,layered ground,and pressure-dependent heterogeneous ground,as well as for an example of a soil–structure interaction simulation.Compared with the viscous and viscous-spring boundary methods adopted in previous studies,the proposed framework exhibits the advantage of incorporating oblique incident waves in a nonlinear heterogeneous ground.Numerical results show that SV-waves are more destructive to underground structures than P-waves,and the responses of underground structures are significantly affected by the incident angles.展开更多
The grade crossings and adjacent pavements of urban trams are generally subjected to complex load conditions and are susceptible to damage.Therefore,in this study,a novel pavement structure between tram tracks and roa...The grade crossings and adjacent pavements of urban trams are generally subjected to complex load conditions and are susceptible to damage.Therefore,in this study,a novel pavement structure between tram tracks and roads constructed using polyurethane(PU)elastic concrete and ultra-high-performance concrete(UHPC),referred to as a track-road transitional pavement(TRTP),is proposed.Subsequently,its performance and feasibility are evaluated using experimental and numerical methods.First,the mechanical properties of the PU elastic concrete are evaluated.The performance of the proposed structure is investigated using a three-dimensional finite element model,where vehicleinduced dynamic and static loads are considered.The results show that PU elastic concrete and the proposed combined TRTP are applicable and functioned as intended.Additionally,the PU elastic concrete achieved sufficient performance.The recommended width of the TRTP is approximately 50 mm.Meanwhile,the application of UHPC under a PU elastic concrete layer significantly reduces vertical deformation.Results of numerical calculations confirmed the high structural performance and feasibility of the proposed TRTP.Finally,material performance standards are recommended to provide guidance for pavement design and the construction of tram-grade crossings in the future.展开更多
An extensive experimental-mechanistic study was conducted to reveal the relationship between the light weight deflectometer(LWD)measured deflections and the degree of compaction of pavement base materials.Both laborat...An extensive experimental-mechanistic study was conducted to reveal the relationship between the light weight deflectometer(LWD)measured deflections and the degree of compaction of pavement base materials.Both laboratory experiments and test pits experiments were performed with different types of pavement base materials.The modulus based maximum allowable LWD deflections under different structural and compaction conditions were developed for the most commonly used pavement base aggregate in Indiana.The maximum allowable deflections are based on the equivalent subgrade modulus and the thickness of the layer to be compacted.It is emphasized that the LWD deflections must be measured as soon as the material is compacted or before the moisture content decreases beyond a specified range.Therefore,the maximum allowable deflections are specified in terms of the difference between the actual moisture content and the optimum moisture content.The maximum allowable deflection values provide a sound basis for compaction quality control using LWD devices.展开更多
基金the National Natural Science Foundation of China(No.51978400)。
文摘This paper presents the static and fatigue tests of hybrid(bonded/bolted)glass fiber reinforced polymer(GFRP)joints.Nine specimens of single-lap hybrid GFRP joints have been fabricated to study the static and fatigue behaviors in the experimental campaign.The static tests of uniaxial tension loading are first conducted,from which the static ultimate bearing capacities of the joints are obtained.High-cycle fatigue tests are subsequently carried out so that the fatigue failure mode,fatigue life,and stiffness degradation of joints can be obtained.The measuring techniques including acoustic emission monitoring and three-dimensional digital image correlation have been employed in the tests to record the damage development process.The results revealed that the static strength and fatigue behavior of such thick hybrid GFRP joints were controlled by the bolted connections.The four stages of fatigue failure process are obtained from tests and acoustic emission signals analysis:cumulative damage of adhesive layer,damage of the adhesive layer,cumulative damage of GFRP plate,and damage of GFRP plate.The fatigue life and stiffness degradation can be improved by more bolts.The S-N(fatigue stress versus life)curves for the fatigue design of the single-lap hybrid GFRP joints under uniaxial tension loading are also proposed.
基金This work was supported by the NSFS(Natural Science Foundation of Shanghai)Program under grant number 21ZR1465400.
文摘Cyclic load is widely adopted in laboratory to simulate the effect of train load on ballast bed.The effectiveness of such load equivalence is usually testified by having similar results of key concerns of ballast bed,such as deformation or stiffness,while the consistency of particle scale characteristics under two loading patterns is rarely examined,which is insufficient to well-understand and use the load simplification.In this study,a previous laboratory model test of ballast bed under cyclic load is rebuilt using 3D discrete element method(DEM),which is validated by dynamic responses monitored by high-resolution sensors.Then,train load having the same magnitude and amplitude as the cyclic load is applied in the numerical model to obtain the statistical characteristics of inter-particle contact force and particle movements in ballast bed.The results show that particle scale responses under two loading patterns could have quite deviation,even when macro-scale responses of ballast bed under two loading patterns are very close.This inconsistency indicates that the application scale of the DEM model should not exceed the validation scale.Moreover,it is important to examine multiscale responses to validate the effectiveness of load simplification.
基金Funded by the National Key Research and Development Program of China(No.2022YFC3803400)National Natural Science Foundation of China(Nos.52378255,52278270)+1 种基金Shanghai Municipal Science and Technology Major Project(No.2021SHZDZX0100)the Fundamental Research Funds for the Central Universities and the Experimental Center of Materials Science and Engineering in Tongji University。
文摘We focused on the efflorescence induced microstructural evolution of ettringite-rich systems prepared with calcium aluminate cement(CAC)and anhydrite.The effects of anhydrite on the visible efflorescence,and the corresponding capillary absorption of CAC-anhydrite mortars were revealed.The composition and microstructure of efflorescence-causing substances were investigated by optical microscope,in-situ Raman spectroscopy,scanning electron microscope,energy dispersive spectrometer,thermogravimetric analysis,and differential scanning calorimetry,at multi-scales.Results indicate that,besides the calcium carbonate,ettringite is another main component of efflorescence-causing substances.Compared with the neat CAC mortars,the addition of anhydrite has a significant effect on the degree of efflorescence by acting on the composition of hydration products and pore structure.In addition,methods are proposed for the prevention of efflorescence of CAC-anhydrite binary system.
基金supported by National Natural Science Foundation of China(Nos.42072300 and 41702291).
文摘Sandstone is widely distributed in cold regions and the freeze-thaw deterioration of them has caused many geological engineering disasters.As an important and direct index of frost resistance,the strength loss of sandstones under freeze-thaw actions should be investigated to provide a guidance for the stability assessment of geological engineering.In this research,the UCS(Uniaxial compressive strength)loss of six typical sandstones with different water contents after 0,20,40 and 60 freeze-thaw cycles was measured in the laboratory.The experimental results indicated that the freeze-thaw damage was more serious in sandstones containing high water contents,and the critical saturations for causing a significant loss of UCS under freeze-thaw were 60%-80%for these sandstones.Below this critical saturation,the UCS loss of the sandstones was mainly caused by water weakening rather than freeze-thaw damage.Besides,a developed strength prediction model was proposed by combining the exponential decay function and multiple linear regression method.The initial porosity,elastic modulus and tensile strength of fresh sandstones were a good parameter combination to accurately determine the decay constant in this developed model.The main novelty of this model is that it can accurately and easily estimate the UCS loss of sandstones after any freeze-thaw cycle only using the initial parameters of fresh sandstones,but it does not need to perform freeze-thaw and mechanical strength experiments.This study not only provides an accurate prediction model of UCS under freeze-thaw,but also makes a contribution to better understanding the frost resistance mechanism of sandstones.
基金The authors are grateful to the Natural Science Foundation of Shanghai(grant No.21ZR1465400)for providing financial support for this research。
文摘When dynamic load is applied on a granular assembly,the time-dependent dynamic load and initial static load(such as gravity stress)act together on individual particles.In order to better understand how dynamic load triggers the micro-structure's evolution and furtherly the ensemble behavior of a granular assembly,we propose a criterion to recognize the major propagation path of dynamic load in 2D granular materials,called the“dynamic force chain”.Two steps are involved in recognizing dynamic force chains:(1)pick out particles with dynamic load larger than the threshold stress,where the attenuation of dynamic stress with distance is considered;(2)among which quasi-linear arrangement of three or more particles are identified as a force chain.The spatial distribution of dynamic force chains in indentation of granular materials provides a direct measure of dynamic load diffusion.The statistical evolution of dynamic force chains shows strong correlation with the indentation behaviors.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.11672360,41731284,41920104007 and 41772328)。
文摘The computational efficiency of the traditional serial spherical discontinuous deformation analysis(SDDA) program has limited its application in geotechnical engineering problems that need a large number of spheres. The cloud computing technology is used to parallel the SDDA program for the first time in this research. The most computationally intensive portions of the SDDA program, i.e., contact detection and matrix solution, are parallelized with proposed algorithms. The accuracy of the cloud-based parallel SDDA program(CB-PSDDA) is verified first. Further efficiency tests show that significant speedup can be obtained with an 8-server configuration and the computing scale can be up to several tens of thousands of particles. The cloud-based parallelized SDDA program increases its potential in applications of deformation and failure analysis of large-scale and realistic geotechnical engineering problems.
基金supported by the National Natural Science Foundation of China(Grant Nos.41922059,42177134,and 51778487)Fundamental Research Funds for the Central Universities,CHD(300102262506)Top Discipline Plan of Shanghai Universities-Class I.
文摘A numerical framework was proposed for the seismic analysis of underground structures in layered ground under inclined P-SV waves.The free-field responses are first obtained using the stiffness matrix method based on plane-wave assumptions.Then,the domain reduction method was employed to reproduce the wavefield in the numerical model of the soil–structure system.The proposed numerical framework was verified by providing comparisons with analytical solutions for cases involving free-field responses of homogeneous ground,layered ground,and pressure-dependent heterogeneous ground,as well as for an example of a soil–structure interaction simulation.Compared with the viscous and viscous-spring boundary methods adopted in previous studies,the proposed framework exhibits the advantage of incorporating oblique incident waves in a nonlinear heterogeneous ground.Numerical results show that SV-waves are more destructive to underground structures than P-waves,and the responses of underground structures are significantly affected by the incident angles.
文摘The grade crossings and adjacent pavements of urban trams are generally subjected to complex load conditions and are susceptible to damage.Therefore,in this study,a novel pavement structure between tram tracks and roads constructed using polyurethane(PU)elastic concrete and ultra-high-performance concrete(UHPC),referred to as a track-road transitional pavement(TRTP),is proposed.Subsequently,its performance and feasibility are evaluated using experimental and numerical methods.First,the mechanical properties of the PU elastic concrete are evaluated.The performance of the proposed structure is investigated using a three-dimensional finite element model,where vehicleinduced dynamic and static loads are considered.The results show that PU elastic concrete and the proposed combined TRTP are applicable and functioned as intended.Additionally,the PU elastic concrete achieved sufficient performance.The recommended width of the TRTP is approximately 50 mm.Meanwhile,the application of UHPC under a PU elastic concrete layer significantly reduces vertical deformation.Results of numerical calculations confirmed the high structural performance and feasibility of the proposed TRTP.Finally,material performance standards are recommended to provide guidance for pavement design and the construction of tram-grade crossings in the future.
基金supported in part by the Joint Transportation Research Program administered by the Indiana Department of Transportation and Purdue University。
文摘An extensive experimental-mechanistic study was conducted to reveal the relationship between the light weight deflectometer(LWD)measured deflections and the degree of compaction of pavement base materials.Both laboratory experiments and test pits experiments were performed with different types of pavement base materials.The modulus based maximum allowable LWD deflections under different structural and compaction conditions were developed for the most commonly used pavement base aggregate in Indiana.The maximum allowable deflections are based on the equivalent subgrade modulus and the thickness of the layer to be compacted.It is emphasized that the LWD deflections must be measured as soon as the material is compacted or before the moisture content decreases beyond a specified range.Therefore,the maximum allowable deflections are specified in terms of the difference between the actual moisture content and the optimum moisture content.The maximum allowable deflection values provide a sound basis for compaction quality control using LWD devices.
