Laminated elastomeric bearings have been widely used for small-to-medium-span highway bridges in China, in which concrete shear keys are set transversely to prohibit large girder displacement. To evaluate bridge seism...Laminated elastomeric bearings have been widely used for small-to-medium-span highway bridges in China, in which concrete shear keys are set transversely to prohibit large girder displacement. To evaluate bridge seismic responses more accurately, proper analytical models of bearings and shear keys should be developed. Based on a series of cyclic loading experiments and analyses, rational analytical models of laminated elastomeric bearings and shear keys, which can consider mechanical degradation, were developed. The effect of the mechanical degradation was investigated by examining the seismic response of a small-to-medium-span bridge in the transverse direction under a wide range of peak ground accelerations（PGA）. The damage mechanism for small-to-medium-span highway bridges was determined, which can explain the seismic damage investigation during earthquakes in recent years. The experimental results show that the mechanical properties of laminated elastomeric bearings will degrade due to friction sliding, but the degree of decrease is dependent upon the influencing parameters. It can be concluded that the mechanical degradation of laminated elastomeric bearings and shear keys play an important role in the seismic response of bridges. The degradation of mechanical properties of laminated elastomeric bearings and shear keys should be included to evaluate more precise bridge seismic performance.展开更多
The redistribution of three-dimensional(3D)geostress during underground tunnel excavation can easily induce to shear failure along rockmass structural plane,potentially resulting in engineering disasters.However,the c...The redistribution of three-dimensional(3D)geostress during underground tunnel excavation can easily induce to shear failure along rockmass structural plane,potentially resulting in engineering disasters.However,the current understanding of rockmass shear behavior is mainly based on shear tests under2D stress without lateral stress,the shear fracture under 3D stress is unclear,and the relevant 3D shear fracture theory research is deficient.Therefore,this study conducted true triaxial cyclic loading and unloading shear tests on intact and bedded limestone under different normal stressσnand lateral stressσpto investigate the shear strength,deformation,and failure characteristics.The results indicate that under differentσnandσp,the stress–strain hysteresis loop area gradually increases from nearly zero in the pre-peak stage,becomes most significant in the post-peak stage,and then becomes very small in the residual stage as the number of shear test cycles increases.The shear peak strength and failure surface roughness almost linearly increase with the increase inσn,while they first increase and then gradually decrease asσpincreases,with the maximum increases of 12.9%for strength and 15.1%for roughness.The shear residual strength almost linearly increases withσn,but shows no significant change withσp.Based on the acoustic emission characteristic parameters during the test process,the shear fracture process and microscopic failure mechanism were analyzed.As the shear stressτincreases,the acoustic emission activity,main frequency,and amplitude gradually increase,showing a significant rise during the cycle near the peak strength,while remaining almost unchanged in the residual stage.The true triaxial shear fracture process presents tensile-shear mixture failure characteristics dominated by microscopic tensile failure.Based on the test results,a 3D shear strength criterion considering the lateral stress effect was proposed,and the determination methods and evolution of the shear modulus G,cohesion cjp,friction angleφjp,and dilation angleψjpduring rockmass shear fracture process were studied.Under differentσnandσp,G first rapidly decreases and then tends to stabilize;cjp,φjp,andψjpfirst increase rapidly to the maximum value,then decrease slowly,and finally remain basically unchanged.A 3D shear mechanics model considering the effects of lateral stress and shear parameter degradation was further established,and a corresponding numerical calculation program was developed based on3D discrete element software.The proposed model effectively simulates the shear failure evolution process of rockmass under true triaxial shear test,and is further applied to successfully reveal the failure characteristics of surrounding rocks with structural planes under different combinations of tunnel axis and geostress direction.展开更多
Cyclic shear tests on rock joints serve as a practical strategy for understanding the shear behavior of jointed rock masses under seismic conditions.We explored the cyclic shear behavior of en-echelon and how joint pe...Cyclic shear tests on rock joints serve as a practical strategy for understanding the shear behavior of jointed rock masses under seismic conditions.We explored the cyclic shear behavior of en-echelon and how joint persistence and test conditions(initial normal stress,normal stiffness,shear velocity,and cyclic distance)influence it through cyclic shear tests under CNS conditions.The results revealed a through-going shear zone induced by cyclic loads,characterized by abrasive rupture surfaces and brecciated material.Key findings included that increased joint persistence enlarged and smoothened the shear zone,while increased initial normal stress and cyclic distance,and decreased normal stiffness and shear velocity,diminished and roughened the brecciated material.Shear strength decreased across shear cycles,with the most significant reduction in the initial shear cycle.After ten cycles,the shear strength damage factor D varied from 0.785 to 0.909.Shear strength degradation was particularly sensitive to normal stiffness and cyclic distance.Low joint persistence,high initial normal stress,high normal stiffness,slow shear velocity,and large cyclic distance were the most destabilizing combinations.Cyclic loads significantly compressed en-echelon joints,with compressibility highly dependent on normal stress and stiffness.The frictional coefficient initially declined and then increased under a rising cycle number.This work provides crucial insights for understanding and predicting the mechanical response of en-echelon joints under seismic conditions.展开更多
基金Project of China International Science and Technology Cooperation under Grant No.2009DFA82480Science and Technology Project of Communications’ Construction in Western China,MOC under Grant No.2009318223094
文摘Laminated elastomeric bearings have been widely used for small-to-medium-span highway bridges in China, in which concrete shear keys are set transversely to prohibit large girder displacement. To evaluate bridge seismic responses more accurately, proper analytical models of bearings and shear keys should be developed. Based on a series of cyclic loading experiments and analyses, rational analytical models of laminated elastomeric bearings and shear keys, which can consider mechanical degradation, were developed. The effect of the mechanical degradation was investigated by examining the seismic response of a small-to-medium-span bridge in the transverse direction under a wide range of peak ground accelerations（PGA）. The damage mechanism for small-to-medium-span highway bridges was determined, which can explain the seismic damage investigation during earthquakes in recent years. The experimental results show that the mechanical properties of laminated elastomeric bearings will degrade due to friction sliding, but the degree of decrease is dependent upon the influencing parameters. It can be concluded that the mechanical degradation of laminated elastomeric bearings and shear keys play an important role in the seismic response of bridges. The degradation of mechanical properties of laminated elastomeric bearings and shear keys should be included to evaluate more precise bridge seismic performance.
基金the National Natural Science Foundation of China(Nos.52469019,52109119,and 52274145)the Chinese Postdoctoral Science Fund Project(No.2022M723408)+1 种基金the Major Project of Guangxi Science and Technology(No.AA23023016)the Technology Project of China Power Engineering Consulting Group Co.,Ltd.(No.DG2-T01-2023)。
文摘The redistribution of three-dimensional(3D)geostress during underground tunnel excavation can easily induce to shear failure along rockmass structural plane,potentially resulting in engineering disasters.However,the current understanding of rockmass shear behavior is mainly based on shear tests under2D stress without lateral stress,the shear fracture under 3D stress is unclear,and the relevant 3D shear fracture theory research is deficient.Therefore,this study conducted true triaxial cyclic loading and unloading shear tests on intact and bedded limestone under different normal stressσnand lateral stressσpto investigate the shear strength,deformation,and failure characteristics.The results indicate that under differentσnandσp,the stress–strain hysteresis loop area gradually increases from nearly zero in the pre-peak stage,becomes most significant in the post-peak stage,and then becomes very small in the residual stage as the number of shear test cycles increases.The shear peak strength and failure surface roughness almost linearly increase with the increase inσn,while they first increase and then gradually decrease asσpincreases,with the maximum increases of 12.9%for strength and 15.1%for roughness.The shear residual strength almost linearly increases withσn,but shows no significant change withσp.Based on the acoustic emission characteristic parameters during the test process,the shear fracture process and microscopic failure mechanism were analyzed.As the shear stressτincreases,the acoustic emission activity,main frequency,and amplitude gradually increase,showing a significant rise during the cycle near the peak strength,while remaining almost unchanged in the residual stage.The true triaxial shear fracture process presents tensile-shear mixture failure characteristics dominated by microscopic tensile failure.Based on the test results,a 3D shear strength criterion considering the lateral stress effect was proposed,and the determination methods and evolution of the shear modulus G,cohesion cjp,friction angleφjp,and dilation angleψjpduring rockmass shear fracture process were studied.Under differentσnandσp,G first rapidly decreases and then tends to stabilize;cjp,φjp,andψjpfirst increase rapidly to the maximum value,then decrease slowly,and finally remain basically unchanged.A 3D shear mechanics model considering the effects of lateral stress and shear parameter degradation was further established,and a corresponding numerical calculation program was developed based on3D discrete element software.The proposed model effectively simulates the shear failure evolution process of rockmass under true triaxial shear test,and is further applied to successfully reveal the failure characteristics of surrounding rocks with structural planes under different combinations of tunnel axis and geostress direction.
基金funded by the China Scholarship Council(CSC.202006220274).
文摘Cyclic shear tests on rock joints serve as a practical strategy for understanding the shear behavior of jointed rock masses under seismic conditions.We explored the cyclic shear behavior of en-echelon and how joint persistence and test conditions(initial normal stress,normal stiffness,shear velocity,and cyclic distance)influence it through cyclic shear tests under CNS conditions.The results revealed a through-going shear zone induced by cyclic loads,characterized by abrasive rupture surfaces and brecciated material.Key findings included that increased joint persistence enlarged and smoothened the shear zone,while increased initial normal stress and cyclic distance,and decreased normal stiffness and shear velocity,diminished and roughened the brecciated material.Shear strength decreased across shear cycles,with the most significant reduction in the initial shear cycle.After ten cycles,the shear strength damage factor D varied from 0.785 to 0.909.Shear strength degradation was particularly sensitive to normal stiffness and cyclic distance.Low joint persistence,high initial normal stress,high normal stiffness,slow shear velocity,and large cyclic distance were the most destabilizing combinations.Cyclic loads significantly compressed en-echelon joints,with compressibility highly dependent on normal stress and stiffness.The frictional coefficient initially declined and then increased under a rising cycle number.This work provides crucial insights for understanding and predicting the mechanical response of en-echelon joints under seismic conditions.
