Study On Damage Mechanism Of Concrete And Mechanical Property Of Saturated Concrete

Comparing with the booming background of the engineering application of concrete,the research on the concrete science and especially the constitutive relation of concrete couldn't satisfy the need of the development of the concrete engineering.Correct and rational understanding of the damage and failure mechanism of material is the key point to the development of concrete damage mechanics.With the progress of Grand Western Development Program,West-East Power Transmission program and South-to-North Water Diversion,quite a few high darn hydropower projects are being or will soon be constructed in the Western.The Western of China is the frequently-occurring earthquake area,and the most concrete regions of high dam are in the deep water,high pressure and saturated state,so the study on the influence of the pore water pressure on the static and dynamic mechanical properties of concrete material has important realistic meaning.With the support from National Nature Science Foundation of China under grants No.90510018 and 50679006,in-depth research was conducted regarding the meso-damage evolution mechanism of concrete and mechanical properties of saturated concrete.1.By comparing the basic theories of Continuum Damage Mechanics and Statistical Damage Mechanics,the defects and shortcomings of the existing damage mechanical models are pointed out.The influence of the meso-damage mechanism on the macroscopic mechanical properties of concrete materials is newly summarized into two aspects,rupture damage and yield damage.Based on the parallel bar system,combining with the synergetic method,the catastrophe theory and also the acoustic emission test,two new activated statistical damage models for quasi-brittle solid are developed,which could simulate the whole damage and fracture process of material when exposed to quasi-static uniaxial tensile traction.The whole damage course is newly divided into the statistical even damage phase and the local breach phase.The two characteristic states,the peak nominal stress state and the critical state are distinguished,and emphasize the critical state plays a key role during the whole damage evolution course.A physical mechanism existing in the fracture process zone during the local breach phase was assumed.The critical state is proposed as the final failure point in the compressive constitutive model.2.The failure process of solid is the trans-scales problem,for which the mechanics workers and the solid physicists have struggled for three and half centuries.To reveal the damage and failure mechanism of material is the persevering aim for the researchers both at home and abroad during the past several decades.Based on the damage evolution process of concrete under uniaxial tension described by the statistical damage model in this paper,a novel material failure theory,i.e.the exerting mechanism of internal mechanical capability of material is proposed.Combining with the viewpoint of the synergetic theory,the quasi-brittle material is regarded as the complicated system with the characteristics of active and self-organization behavior.The essence of the deformation and failure of solid materials is the self-organization behavior process to adapt the changes of the external load environment by the exerting and release of the potential mechanical capabilities the material owns by itself,at the cost of "damage",and the self-organization behavior obeys the exerting mechanism of intemal mechanical capability.By comparing the processes of the material damage evolution, the social advancement and the biological evolution which are the three typical nonlinear motion forms in the objective world,the correctness and rationality of this new fracture theory is proven.3.The dynamic mechanical properties of concrete material is remarkable different from the static state.The physical mechanism of the dynamic strain rate effect is usually divided into two aspects,the inertial effect and the viscous effect.The traditional phenomenological damage models couldn't reflect the complicated meso-damage evolution mechanism,so they can't describe the influence of the dynamic strain rate effect on the meso-damage evolution mechanism.The dynamic statistical damage models under uniaxial tension,which consider the inertial effect for dry concrete and the inertial and viscous combinated effect for the saturated concrete are proposed respectively.The result of the inertial effect leads to the change of the fracture form and the evolution process of the damage accumulation,and be simulated by adjusting the characteristic parameters of the evolution process of the two damage modes.The viscous effect of the pore water leads to the adjustment of the loading condition of the matrix,and be simulated by paralleling a damper with the static statistical damage model.The proposed models lively and vividly describe the damage evolution mechanism of dry and saturated concrete under dynamic loading case from the macroscopic-microscopic viewpoint.4.The failure of concrete specimen under uniaxial compression mainly contributes to the nucleation and growth of microcracks due to local tensile strain caused by the poisson effect. The traditional phenomenological damage models couldn't reflect the tensile damage evolution mechanism in meso-scale.Based on the statistical damage model under uniaxial tension,a statistical damage model under uniaxial compression is further proposed.The damage evolutional law in the compressive direction is confirmed by the tensile damage evolution process of the lateral deformation due to the poisson effect,and then the compressive stress-strain relationship is defined.The comparisons between the theoretical results and the experiment results preliminarily verify the rationality and feasibility of understanding the failure mechanism of concrete through the statistical damage constitutional law.5.Most of the researches on the mechanical property of wet or saturated concrete are the description of the macroscopic phenomenon based on the experiment,but the influence mechanism of the pore water pressure has been seldom reported.Concrete is a porous material with two pore types,active pore and entrained non-active pore,and the former will be filled with water in moisture environment.Based on the effective inclusion theory,a double pore inclusion model is proposed to predict the influence of the pore and the pore water on the initial elastic modulus of moisture concrete.The two types of pore and the mortar are regarded as the equivalent matrix,the aggregate as the inhomogeneous inclusion,a kinds of double inclusion model is proposed;and an united compressive strength expression is established combining with the fracture mechanics method,which could consider the influence of the different volume fraction of kinds of phases,pore rate and the water saturation.The Terzaghi's effective stress principle is introduced into the study of the mechanical properties of saturated concrete,and the specific expression of effective stress principle applicable to saturated concrete is established to investigate the influence mechanism of pore water pressure on the strength of concrete under complicated stress states. The relationship between strength,initial elastic modulus and saturation,loading rate of wet concrete are studied based on lots of test results in the literature.Combining with the constitutive relation of concrete suggested by the specification,the practical constitutive equations for wet concrete under static and dynamic uniaxial tension and compression are established,which considers the influence of the water content on the strength and the initial elastic modulus of concrete.