To better design and analyze concrete structures, the mechanical properties of concrete subjected to impact loadings are investigated. Concrete is considered to be a two-phase composite made up of micro-cracks and sol...To better design and analyze concrete structures, the mechanical properties of concrete subjected to impact loadings are investigated. Concrete is considered to be a two-phase composite made up of micro-cracks and solid parts which consist of coarse aggregate particles and a cement mortar matrix. The cement mortar matrix is assumed to be elastic, homogeneous and isotropic. Based on the Moil-Tanaka concept of average stress and the Eshelby equivalent inclusion theory, a dynamic constitutive model is developed to simulate the impact responses of concrete. The impact compression experiments of concrete and cement mortar are also carried out. Experimental results show that concrete and cement mortar are rate-dependent. Under the same impact velocity, the load-carrying capacity of concrete is higher than that of cement mortar. Whereas, the maximum strain of concrete is lower than that of cement mortar. Regardless of whether it is concrete or cement mortar, with the increase in the impact velocity, the fragment size of specimens after experiment decreases.展开更多
The effects of concrete's time-variant elastic modulus,casting structural components,assembling temporary shoring framework system,and shock by operating construction equipment on dynamic behavior of the reinforce...The effects of concrete's time-variant elastic modulus,casting structural components,assembling temporary shoring framework system,and shock by operating construction equipment on dynamic behavior of the reinforced concrete frame structure during construction were investigated. The dynamic tests of an eight-storey reinforced concrete frame structure during full-scaled stages of the sixth storey construction cycle were carried out by ambient vibration. Natural frequencies,corresponding mode shapes and damping ratio were determined by power spectrum processing the tested signal data in frequency domain. The changes of frequencies,mode shapes and damping ratios at different construction stages were given. The results show that natural frequencies and modal damping ratios reach the maximum at stage of casting fresh concrete,especially for higher modes. Modal damping ratios at each construction stage are less than 5% of those during usage.展开更多
With the increase of capacity and size of the hydro-generator unit, the spiral case becomes a more super-giant hydraulic structure with very high HD value, where H and D denote water head and maximum intake diameter o...With the increase of capacity and size of the hydro-generator unit, the spiral case becomes a more super-giant hydraulic structure with very high HD value, where H and D denote water head and maximum intake diameter of spiral case, respectively. Due to the induced lower stiffness by the more giant size and adverse operation conditions, dynamic performances of the powerhouse and the supporting structure for the giant units have become more important and attracted much attention. If the manner of steel spiral case embedded directly in concrete is adopted, on some locations of the concrete surrounding the spiral case, distributed and concentrated cracks will emerge due to high tensile stress. Although the concrete is reinforced well to control the maximum crack width, definitely these cracks will reduce the local and entire stiffness of the powerhouse. Under dynamic loads such as hydraulic forces including water pressure pulsation in flow passage acting on the structure, effect of the cracks on the dynamic characteristics of the local members and entire structure needs to be evaluated. However, research on this subject is few in hydroelectric engineering. In this paper, Three-Gorge Project was taken as an example to evaluate effect of such cracks on natural frequencies and the vibration responses of the powerhouse under hydraulic and earthquake forces in detail. Results show that cracks only reduce the local structural stiffness greatly but have little effect on the entire powerhouse especially the superstructure; vibrations of powerhouse with cracks in concrete surrounding the spiral case are still under the design limits. Results in this paper have been verified by practice of Three-Gorge Project.展开更多
Vertical shaft is main form of drivage in deep mineral depoist. They also serve as the entrance into and the exit from the underground mine. The main problems in shaft and tunnel engineering is to solve the contradict...Vertical shaft is main form of drivage in deep mineral depoist. They also serve as the entrance into and the exit from the underground mine. The main problems in shaft and tunnel engineering is to solve the contradiction between drivage and lining. The measurement of blasting vibration affecting concrete lining strength of vertical shaft is carried out in experiment and theory in this paper.展开更多
A viscoelastic micromechanical model is presented to predict the dynamic modulus of asphalt concrete （AC） and investigate the effect of imperfect interface between asphalt mastic and aggregates on the overall viscoe...A viscoelastic micromechanical model is presented to predict the dynamic modulus of asphalt concrete （AC） and investigate the effect of imperfect interface between asphalt mastic and aggregates on the overall viscoelastic characteristics of AC. The linear spring layer model is introduced to simulate the interface imperfection. Based on the effective medium theory, the viscoelastic micromechanical model is developed by two equivalence processes. The present prediction is compared with available experimental data to verify the developed framework. It is found that the proposed model has the capability to predict the dynamic modulus of AC. Interface effect on the dynamic modulus of AC is discussed using the developed model. It is shown that the interfacial bonding strength has a significant influence on the global mechanical performance of AC, and that continued improvement in surface fimctionalization is necessary to realize the full potential of aggregates reinforcement.展开更多
基金The National Natural Science Foundation of China(No. 11162015)the Natural Science Foundation of Ningxia Hui Autonomous Region (No. NZ1106)
文摘To better design and analyze concrete structures, the mechanical properties of concrete subjected to impact loadings are investigated. Concrete is considered to be a two-phase composite made up of micro-cracks and solid parts which consist of coarse aggregate particles and a cement mortar matrix. The cement mortar matrix is assumed to be elastic, homogeneous and isotropic. Based on the Moil-Tanaka concept of average stress and the Eshelby equivalent inclusion theory, a dynamic constitutive model is developed to simulate the impact responses of concrete. The impact compression experiments of concrete and cement mortar are also carried out. Experimental results show that concrete and cement mortar are rate-dependent. Under the same impact velocity, the load-carrying capacity of concrete is higher than that of cement mortar. Whereas, the maximum strain of concrete is lower than that of cement mortar. Regardless of whether it is concrete or cement mortar, with the increase in the impact velocity, the fragment size of specimens after experiment decreases.
基金Project(50678064) supported by the National Natural Science Foundation of China
文摘The effects of concrete's time-variant elastic modulus,casting structural components,assembling temporary shoring framework system,and shock by operating construction equipment on dynamic behavior of the reinforced concrete frame structure during construction were investigated. The dynamic tests of an eight-storey reinforced concrete frame structure during full-scaled stages of the sixth storey construction cycle were carried out by ambient vibration. Natural frequencies,corresponding mode shapes and damping ratio were determined by power spectrum processing the tested signal data in frequency domain. The changes of frequencies,mode shapes and damping ratios at different construction stages were given. The results show that natural frequencies and modal damping ratios reach the maximum at stage of casting fresh concrete,especially for higher modes. Modal damping ratios at each construction stage are less than 5% of those during usage.
基金National Natural Science Foundation of China (No.50679009)Foundations for Young Teachers in Dalian University of Technology(No.893219)
文摘With the increase of capacity and size of the hydro-generator unit, the spiral case becomes a more super-giant hydraulic structure with very high HD value, where H and D denote water head and maximum intake diameter of spiral case, respectively. Due to the induced lower stiffness by the more giant size and adverse operation conditions, dynamic performances of the powerhouse and the supporting structure for the giant units have become more important and attracted much attention. If the manner of steel spiral case embedded directly in concrete is adopted, on some locations of the concrete surrounding the spiral case, distributed and concentrated cracks will emerge due to high tensile stress. Although the concrete is reinforced well to control the maximum crack width, definitely these cracks will reduce the local and entire stiffness of the powerhouse. Under dynamic loads such as hydraulic forces including water pressure pulsation in flow passage acting on the structure, effect of the cracks on the dynamic characteristics of the local members and entire structure needs to be evaluated. However, research on this subject is few in hydroelectric engineering. In this paper, Three-Gorge Project was taken as an example to evaluate effect of such cracks on natural frequencies and the vibration responses of the powerhouse under hydraulic and earthquake forces in detail. Results show that cracks only reduce the local structural stiffness greatly but have little effect on the entire powerhouse especially the superstructure; vibrations of powerhouse with cracks in concrete surrounding the spiral case are still under the design limits. Results in this paper have been verified by practice of Three-Gorge Project.
文摘Vertical shaft is main form of drivage in deep mineral depoist. They also serve as the entrance into and the exit from the underground mine. The main problems in shaft and tunnel engineering is to solve the contradiction between drivage and lining. The measurement of blasting vibration affecting concrete lining strength of vertical shaft is carried out in experiment and theory in this paper.
基金Project(51408173)supported by the National Natural Science Foundation of China
文摘A viscoelastic micromechanical model is presented to predict the dynamic modulus of asphalt concrete （AC） and investigate the effect of imperfect interface between asphalt mastic and aggregates on the overall viscoelastic characteristics of AC. The linear spring layer model is introduced to simulate the interface imperfection. Based on the effective medium theory, the viscoelastic micromechanical model is developed by two equivalence processes. The present prediction is compared with available experimental data to verify the developed framework. It is found that the proposed model has the capability to predict the dynamic modulus of AC. Interface effect on the dynamic modulus of AC is discussed using the developed model. It is shown that the interfacial bonding strength has a significant influence on the global mechanical performance of AC, and that continued improvement in surface fimctionalization is necessary to realize the full potential of aggregates reinforcement.
