Non-seismically designed(NSD)beam-column joints are susceptible to joint shear failure under seismic loads.Although significant research is available on the seismic behavior of such joints of planar frames,the informa...Non-seismically designed(NSD)beam-column joints are susceptible to joint shear failure under seismic loads.Although significant research is available on the seismic behavior of such joints of planar frames,the information on the seismic behavior of joints of space frames(3D joints)is insufficient.The 3D joints are subjected to bi-directional excitation,which results in an interaction between the shear strength obtained for the joint in the two orthogonal directions separately.The bi-directional seismic behavior of corner reinforced concrete(RC)joints is the focus of this study.First,a detailed finite element(FE)model using the FE software Abaqus,is developed and validated using the test results from the literature.The validated modeling procedure is used to conduct a parametric study to investigate the influence of different parameters such as concrete strength,dimensions of main and transverse beams framing into the joint,presence or absence of a slab,axial load ratio and loading direction on the seismic behavior of joints.By subjecting the models to different combinations of loads on the beams along perpendicular directions,the interaction of the joint shear strength in two orthogonal directions is studied.The comparison of the interaction curves of the joints obtained from the numerical study with a quadratic(circular)interaction curve indicates that in a majority of cases,the quadratic interaction model can represent the strength interaction diagrams of RC beam to column connections with governing joint shear failure reasonably well.展开更多
A conceptual model of intermittent joints is introduced to the cyclic shear test in the laboratory to explore the effects of loading parameters on its shear behavior under cyclic shear loading.The results show that th...A conceptual model of intermittent joints is introduced to the cyclic shear test in the laboratory to explore the effects of loading parameters on its shear behavior under cyclic shear loading.The results show that the loading parameters(initial normal stress,normal stiffness,and shear velocity)determine propagation paths of the wing and secondary cracks in rock bridges during the initial shear cycle,creating different morphologies of macroscopic step-path rupture surfaces and asperities on them.The differences in stress state and rupture surface induce different cyclic shear responses.It shows that high initial normal stress accelerates asperity degradation,raises shear resistance,and promotes compression of intermittent joints.In addition,high normal stiffness provides higher normal stress and shear resistance during the initial cycles and inhibits the dilation and compression of intermittent joints.High shear velocity results in a higher shear resistance,greater dilation,and greater compression.Finally,shear strength is most sensitive to initial normal stress,followed by shear velocity and normal stiffness.Moreover,average dilation angle is most sensitive to initial normal stress,followed by normal stiffness and shear velocity.During the shear cycles,frictional coefficient is affected by asperity degradation,backfilling of rock debris,and frictional area,exhibiting a non-monotonic behavior.展开更多
The evolution of microstructure and texture in Mg-3Al-1Zn-1Ca alloy sheets subjected to in-plane shear(IPS)loading was investigated using experimental techniques and viscoplastic self-consistent(VPSC)modeling.The spec...The evolution of microstructure and texture in Mg-3Al-1Zn-1Ca alloy sheets subjected to in-plane shear(IPS)loading was investigated using experimental techniques and viscoplastic self-consistent(VPSC)modeling.The specimens were deformed under varying degrees of IPS strain(γ12=0.05,0.10,and 0.15)using a customized jig.Electron backscatter diffraction(EBSD)observations revealed profuse tensile twinning(TTW)even at an IPS strain of 0.05,with its intensity continuously increased as the IPS strain increased.The TTWs progressively engulfed parent grains with increasing shear strain,evolving into an unusual deformation twin morphology.Furthermore,VPSC model predictions confirmed basal slip as the dominant deformation mode at low IPS strains,transitioning to prismatic slip dominance at higher IPS strains.The activity of the TTW mode was significantly higher during the initial stages of IPS strain and saturated to lower values at higher strains.VPSC simulation results also indicated preferential shear accumulation on a single twin system,explaining the phenomenon of a single twin variant engulfing a parent grain.Additionally,the influence of individual slip and twin modes on texture evolution was evaluated through orientation tracking of representative grains at various shear strain increments using VPSC simulation.The simulation results quantitatively highlighted the activities of basal slip,prismatic slip,and tensile twinning,establishing a correlation between texture evolution and the underlying deformation mechanisms.展开更多
Blast-loaded reinforced concrete(RC)slabs should fail under a ductile bending mechanism enabling high energy absorption capacity.Hence,brittle shear failure must be avoided.However,due to the uncertainties related to ...Blast-loaded reinforced concrete(RC)slabs should fail under a ductile bending mechanism enabling high energy absorption capacity.Hence,brittle shear failure must be avoided.However,due to the uncertainties related to the materials,geometry,and resistance models,it may be difficult to predict which failure mode will prevail.This study analytically estimated the probability of premature flexural shear failure of slender RC one-way slabs subjected to blast loading considering such uncertainties and using the Monte Carlo(MC)method.The resistance models in Eurocode 2 were adopted.Specimens with and without shear reinforcement were analyzed.Bending failure was shown to be the most likely failure mode in the studied slabs.However,the probability of shear failure developing before bending failure was still relatively high,particularly for slabs without stirrups.To increase the confidence level concerning the preferred failure mechanism,the article proposes an overstrength factor to magnify the shear demand of the blast-loaded RC slab.Values of the overstrength factor for different target reliability levels were calculated.The study also found that the probability of premature shear failure increased with increasing amount of longitudinal reinforcement and decreasing slenderness.Likewise,greater impulse was found to enhance the risk for shear failure.展开更多
Understanding the shear mechanical behaviors and instability mechanisms of rock joints under dynamic loading remains a complex challenge.This research conducts a series of direct shear tests on real rock joints subjec...Understanding the shear mechanical behaviors and instability mechanisms of rock joints under dynamic loading remains a complex challenge.This research conducts a series of direct shear tests on real rock joints subjected to cyclic normal loads to assess the influence of dynamic normal loading amplitude(F_(d)),dynamic normal loading frequency(f_(v)),initial normal loading(F_(s)),and the joint roughness coefficient(JRC)on the mechanical properties and instability responses of these joints.The results show that unstable sliding is often accompanied by friction weakening due to dynamic normal loads.A significant negative correlation exists between cyclic normal loads and the normal displacement during the shearing process.Dynamic normal load paths vary the contact states of asperities on the rough joint surfaces,impacting the stick-slip instability mechanism of the joints,which in turn affects both the magnitude and location of the stress drop during the stick-slip events,particularly during the unloading phases.An increasing F_(d) results in a more stable shearing behavior and a reduction in the amplitude of stick-slip stress drops.The variation in f_(v) influences the amplitude of stress drop for the joints during shear,characterized by an initial decrease(f_(v)=0.25-2 Hz)before exhibiting an increment(f_(v)=2-4 Hz).As F_(s) increases,sudden failures of the interlocked rough surfaces are more prone to occur,thus producing enhanced instability and a more substantial stress drop.Additionally,a larger JRC intensifies the instability of the joints,which would induce a more pronounced decline in the stick-slip stress.The Rate and state friction(RSF)law can provide an effective explanation for the unstable sliding phenomena of joints during the oscillations of normal loads.The findings may provide certain useful references for a deeper comprehension of the sliding behaviors exhibited by rock joints when subjected to cyclic dynamic disturbances.展开更多
A pilot study was conducted at Penn State University to determine whether the type of drywall joint compound would influence the shear strength of wood-frame stud walls sheathed with Gypsum Wall Board (GWB or drywall)...A pilot study was conducted at Penn State University to determine whether the type of drywall joint compound would influence the shear strength of wood-frame stud walls sheathed with Gypsum Wall Board (GWB or drywall). In this study, five 2438 mm by 2438 mm specimens were tested under in-plane cyclic racking loading following the CUREE loading protocol for light-frame wall systems. Three specimens were finished using non-cement based joint compound while the other two used cement based joint compound. Based on the experimental testing of the specimens, the results show that the use of cement based joint compound on drywall joints produces higher shear capacity for the wall system as compared to similar specimens finished with conventional non-cement based joint compound. The result of the study is particularly important for high seismic regions where interior stud walls in residential construction effectively take part in seismic resistance even though wood shear walls are normally used on exterior walls.展开更多
In rock engineering,the cyclic shear characteristics of rough joints under dynamic disturbances are still insufficiently studied.This study conducted cyclic shear experiments on rough joints under dynamic normal loads...In rock engineering,the cyclic shear characteristics of rough joints under dynamic disturbances are still insufficiently studied.This study conducted cyclic shear experiments on rough joints under dynamic normal loads to assess the impact of shear frequency(f_(h))and shear displacement amplitude(u_(d))on the frictional properties of the joint.The results reveal that within a single shearing cycle,the normal displacement negatively correlates with the dynamic normal force.As the shear cycle number increases,the joint surface undergoes progressive wear,resulting in an exponential decrease in the peak normal displacement.In the cyclic shearing procedure,the forward peak values of shear force and friction coefficient display larger fluctuations at either lower or higher shear frequencies.However,under moderate shear frequency conditions,the changes in the shear strength of the joint surface are smaller,and the degree of degradation post-shearing is relatively limited.As the shear displacement amplitude increases,the range of normal deformation within the joint widens.Furthermore,after shearing,the corresponding joint roughness coefficient trend shows a gradual decrease with an increasing shear displacement amplitude,while varying with the shearing frequency in a pattern that initially rises and then falls,with a turning point at 0.05 Hz.The findings of this research contribute to a profound comprehension of the cyclic frictional properties of rock joints under dynamic disturbances.展开更多
The scaled suction caisson repre sents an innovative design featuring a bio-inspired sidewall modeled after snake skin,commonly utilized in offshore mooring platforms.In comparison with traditional suction caissons,th...The scaled suction caisson repre sents an innovative design featuring a bio-inspired sidewall modeled after snake skin,commonly utilized in offshore mooring platforms.In comparison with traditional suction caissons,this bio-inspired design demonstrates reduced penetration resistance and enhanced pull-out capacity due to the anisotropic shear behaviors of its sidewall.To investigate the shear behavior of the bio-inspired sidewall under pull-out load,direct shear tests were conducted between the bio-inspired surface and sand.The research demonstrates that the interface shear strength of the bio-inspired surface significantly surpasses that of the smooth surface due to interlocking effects.Additionally,the interface shear strength correlates with the aspect ratio of the bio-inspired surface,shear angle,and particle diameter distribution,with values increasing as the uniformity coefficient Cudecreases,while initially increasing and subsequently decreasing with increases in both aspect ratio and shear angle.The ratio between the interface friction angleδand internal friction angle δ_(s) defines the interface effect factor k.For the bio-inspired surface,the interface effect factor k varies with shear angleβ,ranging from 0.9 to 1.12.The peak value occurs at a shear angleβof 60°,substantially exceeding that of the smooth surface.A method for calculating the relative roughness R_(N) is employed to evaluate the interface roughness of the bio-inspired surface,taking into account scale dimension and particle diameter distribution effects.展开更多
Dynamic disturbances certainly reduce shear strength of rock joints,yet the mechanism needs deeper explanation.We investigate the shear behavior of a rough basalt joint by conducting laboratory shear experiments.Const...Dynamic disturbances certainly reduce shear strength of rock joints,yet the mechanism needs deeper explanation.We investigate the shear behavior of a rough basalt joint by conducting laboratory shear experiments.Constant and superimposed oscillating normal loads are applied at the upper block.Meanwhile,the bottom block moves at a constant shear rate.We investigate the shear behavior by:1)altering the normal load oscillation frequency with a same shear rate,2)altering the shear rate with a same normal load oscillation frequency,and 3)altering the normal load oscillation frequency and shear rate simultaneously with a constant ratio.The results show that the oscillating normal load reduces the coefficient of friction(COF).The reduce degree of COF increases with higher shear rate,decreases when increasing normal load oscillation frequency,and keeps constant if the special ratio,v/f(shear rate divided by normal oscillation frequency),is constant.Moreover,we identify a time lag between peak normal load and peak shear load.And the lagging proportion increases with higher shear rate,and decreases with larger static COF.Our results imply that a lower creep rate with a higher normal load oscillation frequency easily destabilizes the creeping fault zones.展开更多
Under external disturbances,the shear mechanical responses and debonding failure mechanisms at anisotropic interfaces of anchoring system composed of multiphase media are inherently difficult to characterize due to th...Under external disturbances,the shear mechanical responses and debonding failure mechanisms at anisotropic interfaces of anchoring system composed of multiphase media are inherently difficult to characterize due to the concealment nature of interfacial interactions.This study establishes an equivalent shear model for a bolt-resin-rock anchoring system and conducts direct shear tests under dynamic normal load(DNL)boundary from both laboratory experiments and discrete element method(DEM)simulations.The research investigates the influence of normal dynamic load amplitude(An)and rock type on shear strength parameters,elucidating the evolutionary characteristics and underlying mechanisms of shear load and normal displacement fluctuations induced by cyclic normal loading,with maximum shear load decreasing by 36.81%to 46.94%as An increases from 10%to 70%when rock type varies from coal to limestone.Through analysis of strain field evolution,the critical impact of rock type on localization of shear failure surface is revealed,with systematic summarization of differentiated wear characteristics,failure modes,and key controlling factors associated with shear failure surface.Mesoscopic investigations enabled by DEM simulations uncover the nonuniform distribution of contact force chains within the material matrix and across the anisotropic interfaces under various DNL boundaries,clarify rock type dependent crack propagation pathways,and quantitatively assess the damage extent of shear failure surface,with the anisotropic interface damage factor increasing from 34.9%to 56.6%as An rises from 10%to 70%,and decreasing from 49.6%to 23.4%as rock type varies from coal to limestone.展开更多
Borehole pressure relief helps prevent rock bursts.However,this may change the physical and mechan-ical properties of the surrounding rock,affect the variation of the plastic zone of the roadway,and lead to the failur...Borehole pressure relief helps prevent rock bursts.However,this may change the physical and mechan-ical properties of the surrounding rock,affect the variation of the plastic zone of the roadway,and lead to the failure of roadway support,thus threatening the safety of the roadway.In this paper,the variable angle shear test of drilled specimens under the action of static and dynamic loads is used to study the evolution of mechanical parameters of the specimens and their influence on the plastic zone of the sur-rounding rock.The shear strength decreases linearly with the increase of drilling diameter.With the increase of pre-static load level and dynamic load amplitude,the cohesion first increases and then decreases,and the internal friction angle decreases.Moreover,the shear failure surface changes from rough to smooth.The reasons include that the static load enhances the tooth cutting effect and the repeated friction of cracks caused by the dynamic load.Borehole pressure relief leads to an increase in the radius of the plastic zone of the surrounding rock following a quadratic function.The research results of this paper provide a theoretical basis for designing drilling unloading parameters and supporting parameters for rock burst roadways.展开更多
Rock bolts are extensively utilized in underground engineering as a means of offering support and stability to rock masses in tunnels,mines,and other underground structures.In environments of high ground stress,faults...Rock bolts are extensively utilized in underground engineering as a means of offering support and stability to rock masses in tunnels,mines,and other underground structures.In environments of high ground stress,faults or weak zones can frequently arise in rock formations,presenting a significant challenge for engineering and potentially leading to underground engineering collapse.Rock bolts serve as a crucial structural element for the transmission of tensile stress and are capable of withstanding shear loads to prevent sliding of weak zones within rock mass.Therefore,a complete understanding of the behavior of rock bolts subjected to shear loads is essential.This paper presents a state-of-the-art review of the research progress of rock bolts subjected to shear load in three categories:experiment,numerical simulation,and analytical model.The review focuses on the research studies and developments in this area since the 1970s,providing a comprehensive overview of numerous factors that influence the anchorage performance of rock bolts.These factors include the diameter and angle of the rock bolt installation,rock strength,grouting material,bolt material,borehole diameter,rock bolt preload,normal stress,joint surface roughness and joint expansion angle.The paper reviews the improvement of mechanical parameter setting in numerical simulation of rock bolt shear.Furthermore,it delves into the optimization of the analytical model concerning rock bolt shear theory,approached from the perspectives of both Elastic foundation beam theory coupled with Elastoplasticity theory and Structural mechanic methods.The significance of this review lies in its ability to provide insights into the mechanical behavior of rock bolts.The paper also highlights the limitations of current research and guidelines for further research of rock bolts.展开更多
Investigating natural-inspired applications is a perennially appealing subject for scientists. The current increase in the speed of natural-origin structure growth may be linked to their superior mechanical properties...Investigating natural-inspired applications is a perennially appealing subject for scientists. The current increase in the speed of natural-origin structure growth may be linked to their superior mechanical properties and environmental resilience. Biological composite structures with helicoidal schemes and designs have remarkable capacities to absorb impact energy and withstand damage. However, there is a dearth of extensive study on the influence of fiber redirection and reorientation inside the matrix of a helicoid structure on its mechanical performance and reactivity. The present study aimed to explore the static and transient responses of a bio-inspired helicoid laminated composite(B-iHLC) shell under the influence of an explosive load using an isomorphic method. The structural integrity of the shell is maintained by a viscoelastic basis known as the Pasternak foundation, which encompasses two coefficients of stiffness and one coefficient of damping. The equilibrium equations governing shell dynamics are obtained by using Hamilton's principle and including the modified first-order shear theory,therefore obviating the need to employ a shear correction factor. The paper's model and approach are validated by doing numerical comparisons with respected publications. The findings of this study may be used in the construction of military and civilian infrastructure in situations when the structure is subjected to severe stresses that might potentially result in catastrophic collapse. The findings of this paper serve as the foundation for several other issues, including geometric optimization and the dynamic response of similar mechanical structures.展开更多
A theoretical rigid-plastic analysis for the dynamic shear failure of beams under impulsive loading is presented when using a travelling plastic shear hinge model which tabes into account material strain hardening. Th...A theoretical rigid-plastic analysis for the dynamic shear failure of beams under impulsive loading is presented when using a travelling plastic shear hinge model which tabes into account material strain hardening. The maximum dynamic shear strain and shear strain-rate can be predicted in addition to the permanent transverse deflections and other parameters. The conditions for the three modes of shear failure, i.e., excess deflection failure, excess shear strain failure and adiabatic shear failure are analyzed. The special case of an infinitesimally small plastic zone is discussed and compared with Nonaka's solution for a rigid, perfectly plastic material. The results can also be generalized to examine the dynamic response of fibre-reinforced beams.展开更多
The shear behavior is regarded as the dominant property of rock joints and is dramatically affected by the joint surface roughness.To date,the effect of surface roughness on the shear behavior of rock joints under sta...The shear behavior is regarded as the dominant property of rock joints and is dramatically affected by the joint surface roughness.To date,the effect of surface roughness on the shear behavior of rock joints under static or cyclic loading conditions has been extensively studied,but such effect under impact loading conditions keeps unclear.To address this issue,a series of impact shear tests was performed using a novel-designed dynamic experimental system combined with the digital image correlation(DIC)technique.The dynamic shear strength,deformability and failure mode of the jointed specimens with various joint roughness coefficients(JRC)are comprehensively analyzed.Results show that the shear strength and shear displacement characteristics of the rock joint under the impact loading keep consistent with those under static loading conditions.However,the temporal variations of shear stress,slip displacement and normal displacement under the impact loading conditions show obviously different behaviors.An elastic rebound of the slip displacement occurs during the impact shearing and its value increases with increasing joint roughness.Two identifiable stages(i.e.compression and dilation)are observed in the normal displacement curves for the rougher rock joints,whereas the joints with small roughness only manifest normal compression displacement.Besides,as the roughness increases,the maximum compression tends to decrease,while the maximum dilation gradually increases.More-over,the microstructural analysis based on scanning electron microscope(SEM)suggests that the roughness significantly affects the characteristics of the shear fractured zone enclosing the joint surface.展开更多
Custom designed and built meso shear test equipment was used to examine the shear crack propagation in gassy coal under different gas pressures.The spatial-temporal evolution of gas migration pathways in the coal duri...Custom designed and built meso shear test equipment was used to examine the shear crack propagation in gassy coal under different gas pressures.The spatial-temporal evolution of gas migration pathways in the coal during shear loading was also researched.The results show that gas pressure can hasten crack growth at the shear fracture surface,can reduce the shear strength of gassy coal,and can accelerate the shear failure process.Shear failure in gassy coal exhibits five stages:the pre-crack stage;the stable crack growth stage;the unsteady crack growth stage;the fracture stage;and,finally,the friction crack stage.The shear breaking creates two kinds of crack,shear cracks and tensile cracks.Cracks first appear in the shear plane at both ends and then extend toward the center until a shear fracture surface forms.The direction of shear crack propagation diverges from the predetermined shear plane by an angle of about 5°-10°.展开更多
A topology optimization formulation is developed to find the stiffest structure with desirable material distribution subjected to seismic loads. Finite element models of the structures are generated and the optimality...A topology optimization formulation is developed to find the stiffest structure with desirable material distribution subjected to seismic loads. Finite element models of the structures are generated and the optimality criteria method is modified using a simple penalty approach and introducing fictitious strain energy to simultaneously consider both material volume and displacement constraints. Different types of shear walls with/without opening are investigated. Additionally, the effects of shear wall-frame interaction for single and coupled shear walls are studied. Gravity and seismic loads are applied to the shear walls so that the definitions provide a practical approach for locating the critical parts of these structures. The results suggest new viewpoints for architectural and structural engineering for placement of openings.展开更多
Sheet-metal products are integral parts of engineering industries and academia research. Various testing techniques have revealed the deformation behaviors of sheet metals under complex stress states. Information obta...Sheet-metal products are integral parts of engineering industries and academia research. Various testing techniques have revealed the deformation behaviors of sheet metals under complex stress states. Information obtained from tensile and compression tests, however, are insufficient for the identification of material parameters relevant to modern constitutive laws, which require experimental setups capable of generating various loading conditions and applying great amounts of strain to sheet metals. In-plane shear testing has emerged as an important method to overcome the challenges associated with tension and compression tests and can provide additional information about deformation behaviors under large plastic strains. Materials such as Mg alloys with poor levels of both ductility and formability cannot accommodate large plastic strains. Therefore, tension and compression tests have limitations in explaining the material behaviors that occur during sheet metal forming where large plastic strains are introduced. Many studies have been conducted to explain the deformation behaviors of Mg alloys under shear deformation techniques. These include severe plastic deformation(SPD), especially the equal channel angular pressing(ECAP)and equal channel angular extrusion, rolling combined with shear deformation i.e. differential speed rolling(DSR), and also in-plane shear for sheet metals, particularly under large levels of plastic strain. These in-plane shear technique involves the Miyauchi shear test, ASTM shear test, and twin bridge shear tests. Moreover, many experimental results have revealed that the evolution of microstructure and texture during in-plane shear is closely related to the failure behavior of materials. Therefore, this review is focused on techniques for in-plane shear testing that have been reported thus far, on the effect of in-plane shear on the microstructure development of Mg alloy sheets, and on the usefulness of in-plane shear testing to evaluate the formability of Mg alloy sheets.展开更多
In order to investigate the failure mechanism of rock joint,a series of laboratory tests including cyclic direct shear tests under constant normal load(CNL)conditions were conducted.Morphology parameters of the rock j...In order to investigate the failure mechanism of rock joint,a series of laboratory tests including cyclic direct shear tests under constant normal load(CNL)conditions were conducted.Morphology parameters of the rock joint surface were precisely calculated by means of a three-dimensional laser scanning machine.All test results were analyzed to investigate the shear behavior and normal displacement behavior of rock joints under CNL conditions.Degradation of rock joint surface during cyclic shear tests was also analyzed.The comparison results of the height parameters and the hybrid parameters of the joint surface during cyclic tests show that the degradation of the surface mostly happens in the first shear and the constant normal loads imposed on the joints have significant promotion effects on the morphology degradation.During cyclic shear tests,joints surfaces evolve from rough state to smooth state but keep an overall undulation.Dilatancy of rock joints degrades with the degradation of joint surface and the increase of normal loads.The closure deformation of joint is larger than that of the intact rock,and the normal stiffness increases with the increase of shearing times.展开更多
The main objective of this study is to investigate the buckling analysis of CCSs reinforced by CNTs subjected to combined loading of hydrostatic pressure and axial compression resting on the twoparameter elastic found...The main objective of this study is to investigate the buckling analysis of CCSs reinforced by CNTs subjected to combined loading of hydrostatic pressure and axial compression resting on the twoparameter elastic foundation(T-P-EF).It is one of the first attempts to derive the governing equations of the CCSs reinforced with CNTs,based on a generalized first-order shear deformation shell theory(FSDST)which includes shell-foundation interaction.By adopting the extended mixing rule,the effective material properties of CCSs reinforced by CNTs with linear distributions are approximated by introducing some efficiency parameters.Three carbon nanotube distribution in the matrix,i.e.uniform distribution(U)and V and X-types linear distribution are taken into account.The stability equations are solved by using the Galerkin procedure to determine the combined buckling loads(CBLs)of the structure selected here.The numerical illustrations cover CBLs characteristics of CCSs reinforced by CNTs in the presence of the T-P-EF.Finally,a parametric study is carried out to study the influences of the foundation parameters,the volume fraction of carbon nanotubes and the types of reinforcement on the CBLs.展开更多
文摘Non-seismically designed(NSD)beam-column joints are susceptible to joint shear failure under seismic loads.Although significant research is available on the seismic behavior of such joints of planar frames,the information on the seismic behavior of joints of space frames(3D joints)is insufficient.The 3D joints are subjected to bi-directional excitation,which results in an interaction between the shear strength obtained for the joint in the two orthogonal directions separately.The bi-directional seismic behavior of corner reinforced concrete(RC)joints is the focus of this study.First,a detailed finite element(FE)model using the FE software Abaqus,is developed and validated using the test results from the literature.The validated modeling procedure is used to conduct a parametric study to investigate the influence of different parameters such as concrete strength,dimensions of main and transverse beams framing into the joint,presence or absence of a slab,axial load ratio and loading direction on the seismic behavior of joints.By subjecting the models to different combinations of loads on the beams along perpendicular directions,the interaction of the joint shear strength in two orthogonal directions is studied.The comparison of the interaction curves of the joints obtained from the numerical study with a quadratic(circular)interaction curve indicates that in a majority of cases,the quadratic interaction model can represent the strength interaction diagrams of RC beam to column connections with governing joint shear failure reasonably well.
基金financially supported by the National Natural Science Foundation of China(Grant No.42172292)Taishan Scholars Project Special Funding,and Shandong Energy Group(Grant No.SNKJ 2022A01-R26).
文摘A conceptual model of intermittent joints is introduced to the cyclic shear test in the laboratory to explore the effects of loading parameters on its shear behavior under cyclic shear loading.The results show that the loading parameters(initial normal stress,normal stiffness,and shear velocity)determine propagation paths of the wing and secondary cracks in rock bridges during the initial shear cycle,creating different morphologies of macroscopic step-path rupture surfaces and asperities on them.The differences in stress state and rupture surface induce different cyclic shear responses.It shows that high initial normal stress accelerates asperity degradation,raises shear resistance,and promotes compression of intermittent joints.In addition,high normal stiffness provides higher normal stress and shear resistance during the initial cycles and inhibits the dilation and compression of intermittent joints.High shear velocity results in a higher shear resistance,greater dilation,and greater compression.Finally,shear strength is most sensitive to initial normal stress,followed by shear velocity and normal stiffness.Moreover,average dilation angle is most sensitive to initial normal stress,followed by normal stiffness and shear velocity.During the shear cycles,frictional coefficient is affected by asperity degradation,backfilling of rock debris,and frictional area,exhibiting a non-monotonic behavior.
文摘The evolution of microstructure and texture in Mg-3Al-1Zn-1Ca alloy sheets subjected to in-plane shear(IPS)loading was investigated using experimental techniques and viscoplastic self-consistent(VPSC)modeling.The specimens were deformed under varying degrees of IPS strain(γ12=0.05,0.10,and 0.15)using a customized jig.Electron backscatter diffraction(EBSD)observations revealed profuse tensile twinning(TTW)even at an IPS strain of 0.05,with its intensity continuously increased as the IPS strain increased.The TTWs progressively engulfed parent grains with increasing shear strain,evolving into an unusual deformation twin morphology.Furthermore,VPSC model predictions confirmed basal slip as the dominant deformation mode at low IPS strains,transitioning to prismatic slip dominance at higher IPS strains.The activity of the TTW mode was significantly higher during the initial stages of IPS strain and saturated to lower values at higher strains.VPSC simulation results also indicated preferential shear accumulation on a single twin system,explaining the phenomenon of a single twin variant engulfing a parent grain.Additionally,the influence of individual slip and twin modes on texture evolution was evaluated through orientation tracking of representative grains at various shear strain increments using VPSC simulation.The simulation results quantitatively highlighted the activities of basal slip,prismatic slip,and tensile twinning,establishing a correlation between texture evolution and the underlying deformation mechanisms.
基金supported by Trafikverket(Swedish Transport Administration)Fortifikationsverket(Swedish Fortifications Agency)Myndigheten för samhällsskydd och beredskap(Swedish Civil Contingencies Agency).
文摘Blast-loaded reinforced concrete(RC)slabs should fail under a ductile bending mechanism enabling high energy absorption capacity.Hence,brittle shear failure must be avoided.However,due to the uncertainties related to the materials,geometry,and resistance models,it may be difficult to predict which failure mode will prevail.This study analytically estimated the probability of premature flexural shear failure of slender RC one-way slabs subjected to blast loading considering such uncertainties and using the Monte Carlo(MC)method.The resistance models in Eurocode 2 were adopted.Specimens with and without shear reinforcement were analyzed.Bending failure was shown to be the most likely failure mode in the studied slabs.However,the probability of shear failure developing before bending failure was still relatively high,particularly for slabs without stirrups.To increase the confidence level concerning the preferred failure mechanism,the article proposes an overstrength factor to magnify the shear demand of the blast-loaded RC slab.Values of the overstrength factor for different target reliability levels were calculated.The study also found that the probability of premature shear failure increased with increasing amount of longitudinal reinforcement and decreasing slenderness.Likewise,greater impulse was found to enhance the risk for shear failure.
基金funding support from the National Natural Science Foundation of China(Grant Nos.52174092,and 51904290)open fund of Key Laboratory of Safety and High-efficiency Coal Mining,Ministry of Education(Anhui University of Science and Technology)(Grant No.JYBSYS202311).
文摘Understanding the shear mechanical behaviors and instability mechanisms of rock joints under dynamic loading remains a complex challenge.This research conducts a series of direct shear tests on real rock joints subjected to cyclic normal loads to assess the influence of dynamic normal loading amplitude(F_(d)),dynamic normal loading frequency(f_(v)),initial normal loading(F_(s)),and the joint roughness coefficient(JRC)on the mechanical properties and instability responses of these joints.The results show that unstable sliding is often accompanied by friction weakening due to dynamic normal loads.A significant negative correlation exists between cyclic normal loads and the normal displacement during the shearing process.Dynamic normal load paths vary the contact states of asperities on the rough joint surfaces,impacting the stick-slip instability mechanism of the joints,which in turn affects both the magnitude and location of the stress drop during the stick-slip events,particularly during the unloading phases.An increasing F_(d) results in a more stable shearing behavior and a reduction in the amplitude of stick-slip stress drops.The variation in f_(v) influences the amplitude of stress drop for the joints during shear,characterized by an initial decrease(f_(v)=0.25-2 Hz)before exhibiting an increment(f_(v)=2-4 Hz).As F_(s) increases,sudden failures of the interlocked rough surfaces are more prone to occur,thus producing enhanced instability and a more substantial stress drop.Additionally,a larger JRC intensifies the instability of the joints,which would induce a more pronounced decline in the stick-slip stress.The Rate and state friction(RSF)law can provide an effective explanation for the unstable sliding phenomena of joints during the oscillations of normal loads.The findings may provide certain useful references for a deeper comprehension of the sliding behaviors exhibited by rock joints when subjected to cyclic dynamic disturbances.
文摘A pilot study was conducted at Penn State University to determine whether the type of drywall joint compound would influence the shear strength of wood-frame stud walls sheathed with Gypsum Wall Board (GWB or drywall). In this study, five 2438 mm by 2438 mm specimens were tested under in-plane cyclic racking loading following the CUREE loading protocol for light-frame wall systems. Three specimens were finished using non-cement based joint compound while the other two used cement based joint compound. Based on the experimental testing of the specimens, the results show that the use of cement based joint compound on drywall joints produces higher shear capacity for the wall system as compared to similar specimens finished with conventional non-cement based joint compound. The result of the study is particularly important for high seismic regions where interior stud walls in residential construction effectively take part in seismic resistance even though wood shear walls are normally used on exterior walls.
基金funding support from the National Natural Science Foundation of China(Grant Nos.52174092 and 51904290)the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20220157).
文摘In rock engineering,the cyclic shear characteristics of rough joints under dynamic disturbances are still insufficiently studied.This study conducted cyclic shear experiments on rough joints under dynamic normal loads to assess the impact of shear frequency(f_(h))and shear displacement amplitude(u_(d))on the frictional properties of the joint.The results reveal that within a single shearing cycle,the normal displacement negatively correlates with the dynamic normal force.As the shear cycle number increases,the joint surface undergoes progressive wear,resulting in an exponential decrease in the peak normal displacement.In the cyclic shearing procedure,the forward peak values of shear force and friction coefficient display larger fluctuations at either lower or higher shear frequencies.However,under moderate shear frequency conditions,the changes in the shear strength of the joint surface are smaller,and the degree of degradation post-shearing is relatively limited.As the shear displacement amplitude increases,the range of normal deformation within the joint widens.Furthermore,after shearing,the corresponding joint roughness coefficient trend shows a gradual decrease with an increasing shear displacement amplitude,while varying with the shearing frequency in a pattern that initially rises and then falls,with a turning point at 0.05 Hz.The findings of this research contribute to a profound comprehension of the cyclic frictional properties of rock joints under dynamic disturbances.
基金supported by the National Natural Science Foundation of China(Grant Nos.52371301 and 52471289)。
文摘The scaled suction caisson repre sents an innovative design featuring a bio-inspired sidewall modeled after snake skin,commonly utilized in offshore mooring platforms.In comparison with traditional suction caissons,this bio-inspired design demonstrates reduced penetration resistance and enhanced pull-out capacity due to the anisotropic shear behaviors of its sidewall.To investigate the shear behavior of the bio-inspired sidewall under pull-out load,direct shear tests were conducted between the bio-inspired surface and sand.The research demonstrates that the interface shear strength of the bio-inspired surface significantly surpasses that of the smooth surface due to interlocking effects.Additionally,the interface shear strength correlates with the aspect ratio of the bio-inspired surface,shear angle,and particle diameter distribution,with values increasing as the uniformity coefficient Cudecreases,while initially increasing and subsequently decreasing with increases in both aspect ratio and shear angle.The ratio between the interface friction angleδand internal friction angle δ_(s) defines the interface effect factor k.For the bio-inspired surface,the interface effect factor k varies with shear angleβ,ranging from 0.9 to 1.12.The peak value occurs at a shear angleβof 60°,substantially exceeding that of the smooth surface.A method for calculating the relative roughness R_(N) is employed to evaluate the interface roughness of the bio-inspired surface,taking into account scale dimension and particle diameter distribution effects.
基金Project(52474122)supported by the National Natural Science Foundation of ChinaProject(HSR202105)supported by the National Engineering Laboratory for High-speed Railway Construction,China+1 种基金Project(2025B1515020067)supported by the Natural Science Foundation of Guangdong Province of ChinaProject(2022A1515240009)supported by the Natural Science Foundation of Guangdong Province,China。
文摘Dynamic disturbances certainly reduce shear strength of rock joints,yet the mechanism needs deeper explanation.We investigate the shear behavior of a rough basalt joint by conducting laboratory shear experiments.Constant and superimposed oscillating normal loads are applied at the upper block.Meanwhile,the bottom block moves at a constant shear rate.We investigate the shear behavior by:1)altering the normal load oscillation frequency with a same shear rate,2)altering the shear rate with a same normal load oscillation frequency,and 3)altering the normal load oscillation frequency and shear rate simultaneously with a constant ratio.The results show that the oscillating normal load reduces the coefficient of friction(COF).The reduce degree of COF increases with higher shear rate,decreases when increasing normal load oscillation frequency,and keeps constant if the special ratio,v/f(shear rate divided by normal oscillation frequency),is constant.Moreover,we identify a time lag between peak normal load and peak shear load.And the lagging proportion increases with higher shear rate,and decreases with larger static COF.Our results imply that a lower creep rate with a higher normal load oscillation frequency easily destabilizes the creeping fault zones.
基金support from the National Natural Science Foundation of China(Nos.51504247,52174092,51904290,and 52074259)the Natural Science Foundation of Jiangsu Province,China(No.BK20220157)+1 种基金the Fundamental Research Funds for the Central Universities,China(No.2022YCPY0202)the China University of Mining and Technology(CUMT)Open Sharing Fund for Large-scale Instruments and Equipment(No.DYGX-2025-47)is gratefully acknowledged.
文摘Under external disturbances,the shear mechanical responses and debonding failure mechanisms at anisotropic interfaces of anchoring system composed of multiphase media are inherently difficult to characterize due to the concealment nature of interfacial interactions.This study establishes an equivalent shear model for a bolt-resin-rock anchoring system and conducts direct shear tests under dynamic normal load(DNL)boundary from both laboratory experiments and discrete element method(DEM)simulations.The research investigates the influence of normal dynamic load amplitude(An)and rock type on shear strength parameters,elucidating the evolutionary characteristics and underlying mechanisms of shear load and normal displacement fluctuations induced by cyclic normal loading,with maximum shear load decreasing by 36.81%to 46.94%as An increases from 10%to 70%when rock type varies from coal to limestone.Through analysis of strain field evolution,the critical impact of rock type on localization of shear failure surface is revealed,with systematic summarization of differentiated wear characteristics,failure modes,and key controlling factors associated with shear failure surface.Mesoscopic investigations enabled by DEM simulations uncover the nonuniform distribution of contact force chains within the material matrix and across the anisotropic interfaces under various DNL boundaries,clarify rock type dependent crack propagation pathways,and quantitatively assess the damage extent of shear failure surface,with the anisotropic interface damage factor increasing from 34.9%to 56.6%as An rises from 10%to 70%,and decreasing from 49.6%to 23.4%as rock type varies from coal to limestone.
基金supported by the National Natural Science Foundation of China(Nos.52374100,52525401,and 52304150)Outstanding Young Talent Project of Shanxi Province(No.SJYC2024301)Research Project Supported by Shanxi Scholarship Council of China(No.2023-041).
文摘Borehole pressure relief helps prevent rock bursts.However,this may change the physical and mechan-ical properties of the surrounding rock,affect the variation of the plastic zone of the roadway,and lead to the failure of roadway support,thus threatening the safety of the roadway.In this paper,the variable angle shear test of drilled specimens under the action of static and dynamic loads is used to study the evolution of mechanical parameters of the specimens and their influence on the plastic zone of the sur-rounding rock.The shear strength decreases linearly with the increase of drilling diameter.With the increase of pre-static load level and dynamic load amplitude,the cohesion first increases and then decreases,and the internal friction angle decreases.Moreover,the shear failure surface changes from rough to smooth.The reasons include that the static load enhances the tooth cutting effect and the repeated friction of cracks caused by the dynamic load.Borehole pressure relief leads to an increase in the radius of the plastic zone of the surrounding rock following a quadratic function.The research results of this paper provide a theoretical basis for designing drilling unloading parameters and supporting parameters for rock burst roadways.
基金The Project(52174101)supported by the National Natural Science Foundation of ChinaThe Project(2023A1515011634)supported by Guangdong Basic and Applied Basic Research Foundation.
文摘Rock bolts are extensively utilized in underground engineering as a means of offering support and stability to rock masses in tunnels,mines,and other underground structures.In environments of high ground stress,faults or weak zones can frequently arise in rock formations,presenting a significant challenge for engineering and potentially leading to underground engineering collapse.Rock bolts serve as a crucial structural element for the transmission of tensile stress and are capable of withstanding shear loads to prevent sliding of weak zones within rock mass.Therefore,a complete understanding of the behavior of rock bolts subjected to shear loads is essential.This paper presents a state-of-the-art review of the research progress of rock bolts subjected to shear load in three categories:experiment,numerical simulation,and analytical model.The review focuses on the research studies and developments in this area since the 1970s,providing a comprehensive overview of numerous factors that influence the anchorage performance of rock bolts.These factors include the diameter and angle of the rock bolt installation,rock strength,grouting material,bolt material,borehole diameter,rock bolt preload,normal stress,joint surface roughness and joint expansion angle.The paper reviews the improvement of mechanical parameter setting in numerical simulation of rock bolt shear.Furthermore,it delves into the optimization of the analytical model concerning rock bolt shear theory,approached from the perspectives of both Elastic foundation beam theory coupled with Elastoplasticity theory and Structural mechanic methods.The significance of this review lies in its ability to provide insights into the mechanical behavior of rock bolts.The paper also highlights the limitations of current research and guidelines for further research of rock bolts.
文摘Investigating natural-inspired applications is a perennially appealing subject for scientists. The current increase in the speed of natural-origin structure growth may be linked to their superior mechanical properties and environmental resilience. Biological composite structures with helicoidal schemes and designs have remarkable capacities to absorb impact energy and withstand damage. However, there is a dearth of extensive study on the influence of fiber redirection and reorientation inside the matrix of a helicoid structure on its mechanical performance and reactivity. The present study aimed to explore the static and transient responses of a bio-inspired helicoid laminated composite(B-iHLC) shell under the influence of an explosive load using an isomorphic method. The structural integrity of the shell is maintained by a viscoelastic basis known as the Pasternak foundation, which encompasses two coefficients of stiffness and one coefficient of damping. The equilibrium equations governing shell dynamics are obtained by using Hamilton's principle and including the modified first-order shear theory,therefore obviating the need to employ a shear correction factor. The paper's model and approach are validated by doing numerical comparisons with respected publications. The findings of this study may be used in the construction of military and civilian infrastructure in situations when the structure is subjected to severe stresses that might potentially result in catastrophic collapse. The findings of this paper serve as the foundation for several other issues, including geometric optimization and the dynamic response of similar mechanical structures.
文摘A theoretical rigid-plastic analysis for the dynamic shear failure of beams under impulsive loading is presented when using a travelling plastic shear hinge model which tabes into account material strain hardening. The maximum dynamic shear strain and shear strain-rate can be predicted in addition to the permanent transverse deflections and other parameters. The conditions for the three modes of shear failure, i.e., excess deflection failure, excess shear strain failure and adiabatic shear failure are analyzed. The special case of an infinitesimally small plastic zone is discussed and compared with Nonaka's solution for a rigid, perfectly plastic material. The results can also be generalized to examine the dynamic response of fibre-reinforced beams.
基金We acknowledge the funding support from the National Natural Science Foundation of China(Grant Nos.51879135 and 51879184)the Natural Sciences and Engineering Research Council of Canada(NSERC)through the Discovery Grant No.72031326.
文摘The shear behavior is regarded as the dominant property of rock joints and is dramatically affected by the joint surface roughness.To date,the effect of surface roughness on the shear behavior of rock joints under static or cyclic loading conditions has been extensively studied,but such effect under impact loading conditions keeps unclear.To address this issue,a series of impact shear tests was performed using a novel-designed dynamic experimental system combined with the digital image correlation(DIC)technique.The dynamic shear strength,deformability and failure mode of the jointed specimens with various joint roughness coefficients(JRC)are comprehensively analyzed.Results show that the shear strength and shear displacement characteristics of the rock joint under the impact loading keep consistent with those under static loading conditions.However,the temporal variations of shear stress,slip displacement and normal displacement under the impact loading conditions show obviously different behaviors.An elastic rebound of the slip displacement occurs during the impact shearing and its value increases with increasing joint roughness.Two identifiable stages(i.e.compression and dilation)are observed in the normal displacement curves for the rougher rock joints,whereas the joints with small roughness only manifest normal compression displacement.Besides,as the roughness increases,the maximum compression tends to decrease,while the maximum dilation gradually increases.More-over,the microstructural analysis based on scanning electron microscope(SEM)suggests that the roughness significantly affects the characteristics of the shear fractured zone enclosing the joint surface.
基金supported in part by the State Key Basic Research Program of China(No.2011CB201203)in part by the General Project of the National Natural Science Foundation of China(No.50974141)the Fundamental Research Funds for the Central Universities(No.CDJZR12240055)
文摘Custom designed and built meso shear test equipment was used to examine the shear crack propagation in gassy coal under different gas pressures.The spatial-temporal evolution of gas migration pathways in the coal during shear loading was also researched.The results show that gas pressure can hasten crack growth at the shear fracture surface,can reduce the shear strength of gassy coal,and can accelerate the shear failure process.Shear failure in gassy coal exhibits five stages:the pre-crack stage;the stable crack growth stage;the unsteady crack growth stage;the fracture stage;and,finally,the friction crack stage.The shear breaking creates two kinds of crack,shear cracks and tensile cracks.Cracks first appear in the shear plane at both ends and then extend toward the center until a shear fracture surface forms.The direction of shear crack propagation diverges from the predetermined shear plane by an angle of about 5°-10°.
文摘A topology optimization formulation is developed to find the stiffest structure with desirable material distribution subjected to seismic loads. Finite element models of the structures are generated and the optimality criteria method is modified using a simple penalty approach and introducing fictitious strain energy to simultaneously consider both material volume and displacement constraints. Different types of shear walls with/without opening are investigated. Additionally, the effects of shear wall-frame interaction for single and coupled shear walls are studied. Gravity and seismic loads are applied to the shear walls so that the definitions provide a practical approach for locating the critical parts of these structures. The results suggest new viewpoints for architectural and structural engineering for placement of openings.
基金financially supported by the Science and Engineering Research Board (SERB)a statutory body of the Department of Science&Technology (DST)+1 种基金Government of India through the Start-up Research Grant (SRG) scheme (File No. SRG/2020/000341)National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT)(NRF-2020R1A2C1010134)。
文摘Sheet-metal products are integral parts of engineering industries and academia research. Various testing techniques have revealed the deformation behaviors of sheet metals under complex stress states. Information obtained from tensile and compression tests, however, are insufficient for the identification of material parameters relevant to modern constitutive laws, which require experimental setups capable of generating various loading conditions and applying great amounts of strain to sheet metals. In-plane shear testing has emerged as an important method to overcome the challenges associated with tension and compression tests and can provide additional information about deformation behaviors under large plastic strains. Materials such as Mg alloys with poor levels of both ductility and formability cannot accommodate large plastic strains. Therefore, tension and compression tests have limitations in explaining the material behaviors that occur during sheet metal forming where large plastic strains are introduced. Many studies have been conducted to explain the deformation behaviors of Mg alloys under shear deformation techniques. These include severe plastic deformation(SPD), especially the equal channel angular pressing(ECAP)and equal channel angular extrusion, rolling combined with shear deformation i.e. differential speed rolling(DSR), and also in-plane shear for sheet metals, particularly under large levels of plastic strain. These in-plane shear technique involves the Miyauchi shear test, ASTM shear test, and twin bridge shear tests. Moreover, many experimental results have revealed that the evolution of microstructure and texture during in-plane shear is closely related to the failure behavior of materials. Therefore, this review is focused on techniques for in-plane shear testing that have been reported thus far, on the effect of in-plane shear on the microstructure development of Mg alloy sheets, and on the usefulness of in-plane shear testing to evaluate the formability of Mg alloy sheets.
基金Project(51274249)supported by the National Natural Science Foundation of ChinaProject(2015zzts076)supported by the Explore Research Fund for Graduate Students of ChinaProject(201406)supported by the Hunan Key Laboratory of Coal Resources and Safe Mining Open-end Funds,China
文摘In order to investigate the failure mechanism of rock joint,a series of laboratory tests including cyclic direct shear tests under constant normal load(CNL)conditions were conducted.Morphology parameters of the rock joint surface were precisely calculated by means of a three-dimensional laser scanning machine.All test results were analyzed to investigate the shear behavior and normal displacement behavior of rock joints under CNL conditions.Degradation of rock joint surface during cyclic shear tests was also analyzed.The comparison results of the height parameters and the hybrid parameters of the joint surface during cyclic tests show that the degradation of the surface mostly happens in the first shear and the constant normal loads imposed on the joints have significant promotion effects on the morphology degradation.During cyclic shear tests,joints surfaces evolve from rough state to smooth state but keep an overall undulation.Dilatancy of rock joints degrades with the degradation of joint surface and the increase of normal loads.The closure deformation of joint is larger than that of the intact rock,and the normal stiffness increases with the increase of shearing times.
文摘The main objective of this study is to investigate the buckling analysis of CCSs reinforced by CNTs subjected to combined loading of hydrostatic pressure and axial compression resting on the twoparameter elastic foundation(T-P-EF).It is one of the first attempts to derive the governing equations of the CCSs reinforced with CNTs,based on a generalized first-order shear deformation shell theory(FSDST)which includes shell-foundation interaction.By adopting the extended mixing rule,the effective material properties of CCSs reinforced by CNTs with linear distributions are approximated by introducing some efficiency parameters.Three carbon nanotube distribution in the matrix,i.e.uniform distribution(U)and V and X-types linear distribution are taken into account.The stability equations are solved by using the Galerkin procedure to determine the combined buckling loads(CBLs)of the structure selected here.The numerical illustrations cover CBLs characteristics of CCSs reinforced by CNTs in the presence of the T-P-EF.Finally,a parametric study is carried out to study the influences of the foundation parameters,the volume fraction of carbon nanotubes and the types of reinforcement on the CBLs.
