Regarding the freezing damage of high-grade highway subgrade in seasonally frozen area,the thesis explores the effect on the dynamic behavior of subgrade soil under freeze–thaw cycles and draws the change law of para...Regarding the freezing damage of high-grade highway subgrade in seasonally frozen area,the thesis explores the effect on the dynamic behavior of subgrade soil under freeze–thaw cycles and draws the change law of parameters(including dynamic strength,dynamic cohesion,and internal friction angle;and dynamic elastic modulus)of high-grade highway-subgrade soil with the number of freeze–thaw cycles.It aims to provide the reference for operation and maintenance of a high-grade highway.Conclusions:(1)Dynamic strength tends to decline evidently after freeze–thaw cycles,with 60%~70%decline after three cycles,and remains stable after five to seven cycles.(2)With the number of freeze–thaw cycles increasing,the internal friction angle fluctuates within a certain range without an obvious change law,only presenting the tendency of dropping off.The dynamic cohesion declines obviously,about 20%~40%after seven freeze–thaw cycles,and then tends to be stable.(3)With the number of freeze-thaw cycles increasing,the dynamic elastic modulus and maximum dynamic elastic modulus are inclined to decrease distinctly.After five freeze–thaw cycles,the former declines 30%~40%and then remains stable.Meanwhile,the latter falls 20%~40%.展开更多
Bamboo is a unique fiber-reinforced bio-composite with fibers embedded into a parenchyma cell matrix.We conducted axial compression tests on bamboo blocks prepared from bottom to top,and from inner to outer portions o...Bamboo is a unique fiber-reinforced bio-composite with fibers embedded into a parenchyma cell matrix.We conducted axial compression tests on bamboo blocks prepared from bottom to top,and from inner to outer portions of the culm.The apparent Young’s modulus and compressive strength of whole thickness bamboo blocks exhibited slight increases with increasing height along the culm,due to slight increases of fiber volume fraction(Vf)from 28.4 to 30.4%.Other blocks showed a significant increase in apparent Young’s modulus and strength from the inner to outer part of the culm wall,mainly owing to a sharp increase of Vf from 17.1 to 59.8%.With a decrease of fiber fraction volume there was a transition from relatively brittle behavior to very ductile behavior in bamboo blocks.Results indicated that stiffness and strength of bamboo was primarily due to fiber in compression,and ductility of bamboo was provided by the parenchyma cell matrix acting as a natural fiber-reinforced composite.展开更多
In this paper, an experimental and analytical study of two half-scale steel X-braced flames with equal nominal shear strength under cyclic loading is described. In these tests, all members except the braces are simila...In this paper, an experimental and analytical study of two half-scale steel X-braced flames with equal nominal shear strength under cyclic loading is described. In these tests, all members except the braces are similar. The braces are made of various steel grades to monitor the effects of seismic excitation. Internal stiffeners are employed to limit the local buckling and increase the fracture life of the steel bracing. A heavy central core is introduced at the intersection of the braces to decrease their effective length. Recent seismic specifications are considered in the design of the X-braced frame members to verify their efficiency. The failure modes of the X-braced frames are also illustrated. It is observed that the energy dissipation capacity, ultimate load capacity and ductility of the system increase considerably by using lower grade steel and proposed detailing. Analytical modeling of the specimens using nonlinear finite element software supports the experimental findings.展开更多
A nonlinear finite element method is applied to observe how inclusion shape influence the thermal response of a ceramic-metal functionally graded material (FGM). The elastic and plastic behaviors of the layers which a...A nonlinear finite element method is applied to observe how inclusion shape influence the thermal response of a ceramic-metal functionally graded material (FGM). The elastic and plastic behaviors of the layers which are two-phase isotropic composites consisting of randomly oriented elastic spheroidal Inclusions and a ductile matrix are predicted by cc mean field method. The prediction results show that inclusion shape has remarkable influence on the overall behavior of the composite. The consequences of the thermal response analysis of the FGM are that the response is dependent on inclusion shape and its composition profile cooperatively and that the plastic behavior of each layer should be taken into account in optimum design of a ceramic-metal FGM.展开更多
基金funded by the National Natural Science Foundation of China (No. 51378057)
文摘Regarding the freezing damage of high-grade highway subgrade in seasonally frozen area,the thesis explores the effect on the dynamic behavior of subgrade soil under freeze–thaw cycles and draws the change law of parameters(including dynamic strength,dynamic cohesion,and internal friction angle;and dynamic elastic modulus)of high-grade highway-subgrade soil with the number of freeze–thaw cycles.It aims to provide the reference for operation and maintenance of a high-grade highway.Conclusions:(1)Dynamic strength tends to decline evidently after freeze–thaw cycles,with 60%~70%decline after three cycles,and remains stable after five to seven cycles.(2)With the number of freeze–thaw cycles increasing,the internal friction angle fluctuates within a certain range without an obvious change law,only presenting the tendency of dropping off.The dynamic cohesion declines obviously,about 20%~40%after seven freeze–thaw cycles,and then tends to be stable.(3)With the number of freeze-thaw cycles increasing,the dynamic elastic modulus and maximum dynamic elastic modulus are inclined to decrease distinctly.After five freeze–thaw cycles,the former declines 30%~40%and then remains stable.Meanwhile,the latter falls 20%~40%.
基金supported by Basic Scientific Research Funds of International Center for Bamboo and Rattan(1632016007)the National Science Foundation of China(31400519)
文摘Bamboo is a unique fiber-reinforced bio-composite with fibers embedded into a parenchyma cell matrix.We conducted axial compression tests on bamboo blocks prepared from bottom to top,and from inner to outer portions of the culm.The apparent Young’s modulus and compressive strength of whole thickness bamboo blocks exhibited slight increases with increasing height along the culm,due to slight increases of fiber volume fraction(Vf)from 28.4 to 30.4%.Other blocks showed a significant increase in apparent Young’s modulus and strength from the inner to outer part of the culm wall,mainly owing to a sharp increase of Vf from 17.1 to 59.8%.With a decrease of fiber fraction volume there was a transition from relatively brittle behavior to very ductile behavior in bamboo blocks.Results indicated that stiffness and strength of bamboo was primarily due to fiber in compression,and ductility of bamboo was provided by the parenchyma cell matrix acting as a natural fiber-reinforced composite.
文摘In this paper, an experimental and analytical study of two half-scale steel X-braced flames with equal nominal shear strength under cyclic loading is described. In these tests, all members except the braces are similar. The braces are made of various steel grades to monitor the effects of seismic excitation. Internal stiffeners are employed to limit the local buckling and increase the fracture life of the steel bracing. A heavy central core is introduced at the intersection of the braces to decrease their effective length. Recent seismic specifications are considered in the design of the X-braced frame members to verify their efficiency. The failure modes of the X-braced frames are also illustrated. It is observed that the energy dissipation capacity, ultimate load capacity and ductility of the system increase considerably by using lower grade steel and proposed detailing. Analytical modeling of the specimens using nonlinear finite element software supports the experimental findings.
基金Funded by National Science Foundation of China(Grant:1987205).
文摘A nonlinear finite element method is applied to observe how inclusion shape influence the thermal response of a ceramic-metal functionally graded material (FGM). The elastic and plastic behaviors of the layers which are two-phase isotropic composites consisting of randomly oriented elastic spheroidal Inclusions and a ductile matrix are predicted by cc mean field method. The prediction results show that inclusion shape has remarkable influence on the overall behavior of the composite. The consequences of the thermal response analysis of the FGM are that the response is dependent on inclusion shape and its composition profile cooperatively and that the plastic behavior of each layer should be taken into account in optimum design of a ceramic-metal FGM.
