The dynamic mechanical property of concrete is one of the key parameters,which greatly influences durability of infrastructures subjected to continuous heavy loading,such as girder and track slab of high-speed railway...The dynamic mechanical property of concrete is one of the key parameters,which greatly influences durability of infrastructures subjected to continuous heavy loading,such as girder and track slab of high-speed railway foundation structure.This paper reports serials of experiments designed to investigate the deterioration of dynamic mechanical properties of different concretes under fatigue loading condition.Four parameters including relative dynamic elastic modulus(RDEM),relative dynamic shear modulus(RDSM),relative compressive strength(RCS)and water absorption(WA)of concrete were evaluated to assess the dynamic properties and microstructures of concretes.Results show that the fatigue stress levels and fatigue cycle durations significantly influence the dynamic mechanical properties of concrete including dynamic elastic modulus and dynamic shear modulus.Addition of proper mineral admixture can improve the dynamic mechanical characteristics of concrete and increase its resistance against the fatigue loading effect.Keeping the amount of mineral admixture in concrete constant,its dynamic mechanical property with fly ash is lower than that with fly ash and silica fume.The water absorption in concrete,which is an indirect parameter reflecting capillary porosity,increases evidently after bearing fatigue-loading.There is a close correlation between the deterioration of dynamic mechanical property and the increasing of water absorption of concrete.This indicates that the damage of microstructure of concrete subjected to fatigue loading is the indispensable reason for the decay of its dynamic mechanical performance.展开更多
Significant research interest has recently been attracted to the study of bipedal robots due to the wide variety of their potential applications.In reality,bipedal robots are often required to perform gait transitions...Significant research interest has recently been attracted to the study of bipedal robots due to the wide variety of their potential applications.In reality,bipedal robots are often required to perform gait transitions to achieve flexible walking.In this paper,we consider the gait transition of a five-link underactuated three-dimensional(3 D)bipedal robot,and propose a two-layer control strategy.The strategy consists of a unique,event-based,feedback controller whose feedback gain in each step is updated by an adaptive control law,and a transition controller that guides the robot from the current gait to a neighboring point of the target gait so that the state trajectory can smoothly converge to the target gait.Compared with previous works,the transition controller is parameterized and its control parameters are obtained by solving an optimization problem to guarantee the physical constraints in the transition process.Finally,the effectiveness of the control strategy is illustrated on the underactuated 3 D bipedal robot.展开更多
基金supported by the National Basic Research Program of China("973"Project)(Grant No.2013CB036201)
文摘The dynamic mechanical property of concrete is one of the key parameters,which greatly influences durability of infrastructures subjected to continuous heavy loading,such as girder and track slab of high-speed railway foundation structure.This paper reports serials of experiments designed to investigate the deterioration of dynamic mechanical properties of different concretes under fatigue loading condition.Four parameters including relative dynamic elastic modulus(RDEM),relative dynamic shear modulus(RDSM),relative compressive strength(RCS)and water absorption(WA)of concrete were evaluated to assess the dynamic properties and microstructures of concretes.Results show that the fatigue stress levels and fatigue cycle durations significantly influence the dynamic mechanical properties of concrete including dynamic elastic modulus and dynamic shear modulus.Addition of proper mineral admixture can improve the dynamic mechanical characteristics of concrete and increase its resistance against the fatigue loading effect.Keeping the amount of mineral admixture in concrete constant,its dynamic mechanical property with fly ash is lower than that with fly ash and silica fume.The water absorption in concrete,which is an indirect parameter reflecting capillary porosity,increases evidently after bearing fatigue-loading.There is a close correlation between the deterioration of dynamic mechanical property and the increasing of water absorption of concrete.This indicates that the damage of microstructure of concrete subjected to fatigue loading is the indispensable reason for the decay of its dynamic mechanical performance.
基金Project supported by the National Natural Science Foundation of China(Nos.91748126,11772292,and 51521064)
文摘Significant research interest has recently been attracted to the study of bipedal robots due to the wide variety of their potential applications.In reality,bipedal robots are often required to perform gait transitions to achieve flexible walking.In this paper,we consider the gait transition of a five-link underactuated three-dimensional(3 D)bipedal robot,and propose a two-layer control strategy.The strategy consists of a unique,event-based,feedback controller whose feedback gain in each step is updated by an adaptive control law,and a transition controller that guides the robot from the current gait to a neighboring point of the target gait so that the state trajectory can smoothly converge to the target gait.Compared with previous works,the transition controller is parameterized and its control parameters are obtained by solving an optimization problem to guarantee the physical constraints in the transition process.Finally,the effectiveness of the control strategy is illustrated on the underactuated 3 D bipedal robot.
