Study On Compressive Mechanical Behavior Of Concrete Based On Nonlinear Theory

Concrete is a multi-phase,multi-component and multi-defect composite,composed of cement,coarse aggregate,fine aggregate and water.Nonlinearity is one of the basic characteristics of its mechanical behavior.How to reflect the characteristic and essence of concrete mechanical behavior scientifically,and how to design and control it effectively with the knowledge of this essence,is still a huge challenge for researchers and engineers.Based on the nonlinear theory of Fractal,chaos and power law,the mechanical behavior of concrete under uniaxial compression is studied.The fractal characteristics of concrete under uniaxial static compression are analyzed.The chaotic law of damage evolution of concrete under uniaxial compression is revealed.The power law behavior of short-time creep damage of concrete under uniaxial compression is evaluated.It can provide basis and reference for controlling the composition of concrete.The research of concrete mechanical behavior,safety evaluation of concrete structure and application of nonlinear theory in concrete field are enriched.Based on the basic fractal theory,a fractal dimension calculation model for the mechanical behavior of concrete under uniaxial static compression is established by the experimental data.The damage process and failure modes of concrete specimens under uniaxial static compression are evaluated.The characteristics of concrete under uniaxial static compression are analyzed.The stress-strain constitutive equations of concrete under uniaxial static compression are constructed,and the fractal behavior of concrete under uniaxial static compression is studied.The range of fractal dimension of uniaxial static crushing is given.The relationship between the fractal dimension of uniaxial static compression and several factors are discussed,such as the diameter of coarse aggregate,the shape of specimen,the peak stress,the peak strain,the energy absorbed per unit volume,etc.It can provide the basis and reference for the preparation of concrete and the analysis of mechanical behavior of concrete under uniaxial static pressure.Based on the basic theory of chaos and the hypothesis of damage evolution equation,the formula of concrete generalized damage variable is deduced,and the chaos model of concrete generalized damage variable evolution is constructed.The damage evolution equation and damage constitutive equation of concrete are established.The chaotic characteristics of the generalized damage variable evolution are analyzed,and the critical bifurcation and the maximum generalized damage variable of the critical chaos are calculated.The relations between maximum generalized damage variable for critical bifurcation and several factors are discussed,such as coarse aggregate size,mix ratio,compressive strength of concrete,peak strain of concrete,energy absorbed per unit volume,maximum damage degree,etc.It can provide a reference for the study of damage and failure mechanism of concrete under uniaxial compression.Based on the power law,the short-time creep failure behavior of concrete under uniaxial compression is studied,and the evolution characteristics of short-time creep deformation,strain rate and strain acceleration of concrete under uniaxial compression are analyzed.The short-time creep failure modes of concrete under uniaxial compression are evaluated.A nonlinear viscoelastic-plastic six-element creep theoretical model of concrete is established.Based on the short-time creep test data of concrete under uniaxial compression,the nonlinear viscoelastic-plastic six-element creep theoretical model of concrete is fitted.According to the power-law model of the whole creep process of quasi-brittle materials and the power-law model of the creep acceleration stage,the power-law behavior of the whole creep failure process and the power-law characteristics of the creep acceleration stage of concrete under uniaxial compression are studied.The value range of the power exponent is determined.The relationships between power index and several factors are discussed,such as specimen shape,mixture ratio,coarse aggregate particle size,peak stress under uniaxial compression,Brittle Index,creep failure strength and unit volume absorption energy of concrete,etc.It can provide basis and reference for the research of concrete creep behavior under uniaxial compression.