Study On Dynamic Mechanical Properties And Mechanism Of Concrete In Water Environment

Under the strong earthquake,the dynamic response and the failure process of the concrete dam are extremely complicated.Whether the seismic design of the dam structure is sae and reasonable depends not only on the correctness of the structural design and analysis method,but also the dynamic mechanical properties of concrete materials used for the dam.In the seismic design of the dam structure,the selection of the suitable dynamic parameters of the concrete material is the prerequisite to ensure the seismic safety of the dam and prevent the earthquake disaster,performance and mechanism of concrete materials under diferent environmental conditions become the key scientific problems in seismic design of the dam safety.In the atmospheric environment,the study of dynamic mechanical properties of concrete materials is lfruitful,which provides valuable data and a solid foundation for seismic design and safety assessment of concrete dams.But the dam structures service in the water pressure environment over a long period of time the dam structures sustain not only external water pressure,but also bear the common effect of pore water pressure and scous stress,the stress state is different from that in atmospheric environment.Moreover,dam structures also were suffered the historical load and low-temperature effect,which cause reversible damage to the concrete materials,and leading to more complex impact by those factors.It is extremely important and urgent to study the dynamic mechanical properties of concrete under the coupling effect of the water environment and other factors in order to scientifically and reasoably evaluate the true seismic safety of concrete dams.Based on the characteristics of concrete dams service in different water environment and may suffer from dynamic load,tests and mechanical analysis of concrete under water environment are carried out The main research work is summarized as follows.(1)The experiments were conducted to study the water content of the long dry concrete and air saturated concrete under water pressure environment,the water content of concrete was obtained under different water pressure variation with time,and the influence of water pressure on the water content of the concrete was analyzed,and the variation on water content of drying concrete was studied after unloading water pressure.(2)Two kinds of concrete pore model were introduced,and the influence of water content and pore water distribution characteristics under different water pressure was discussed based on the meso pore network model and the principle of mercury intrusion porosimetry.Moreover,the factors affecting the water content of the concrete were analyzed from the meso and macro level.(3)According to the characteristic concrete dam which in a dry state during construction period and under high water pressure during operation period,the dynamic compression tests were carried out for long dry concrete,the stress-strain curve,strength and elastic modulus were obtained under the different water pressure,and the dynamic increase factor and pressure enhancement factor were studied for strength and elastic modulus of concrete,and the calculation formulas were proposed for concrete strength with strain rate increases and water pressure changes,and then empirical constitutive model was established for the dynamic strength of concrete in water pressure environment.Furthermore,combining with the results of water content under the water pressure environment,the effect of water content on the strength and elasticity modulus of concrete was analyzed and discussed.(4)Summarize the in vitro free water,pore water and crack tip of free water,mechanical mechanism and concrete saturation or dehydration process of concrete effect.Based on the analysis of the test results,the mechanical properties of concrete under water environment should not only consider the factors of water environment,also need to consider the characteristics of pore structure of concrete material itself.And the effect of confining pressure and water splitting effect in vitro with water pressure;the water content and pore structure of concrete,discusses the differences in pore water caused by loading the excess pore pressure force and viscous stress,explain the excess pore water pressure and viscous stress interaction on the failure modes and strength characteristics of concrete.(5)The dynamic compression strength of concrete which undergone cyclic loading and subjected to water pressure was carried out,the stress strain curve and strength of concrete are obtained,and the formula was obtained for concrete strength with strain rate,water pressure and cycle number increases.Furthermore,considering the pore micro scale of concrete,the mechanical mechanism of concrete strength with the load cycle number changing was analyzed based on the meso pore network model and the principle of mercury intrusion porosimetry.(6)The experiment was carried out to study the dynamic mechanics for withstanding freeze-thaw deterioration and historical load damage of concrete in the atmospheric environment.The strength,deformation properties,elastic modulus and stress-strain curve of concrete was obtained analysis,and the effect of strain rate,historical load amplitude and freeze-thaw cycles time on the mechanical parameters of concrete was analyzed.Moreover,failure modes and mechanical mechanism of concrete by freeze-thaw deterioration were discussed.