Fatigue Failure Criterion For Concrete Materials Research

In this paper the fatigue properties of plain concrete material is studied, the emphasis is focused on the problem of establishing fatigue failure criterion. The author clearly presents the concepts of fatigue failure criterion based on stress space and strain space, and establishes fatigue failure criterion of stress space and strain space under complex stresses state respectively; Found non-linear fatigue damage equation and fatigue failure criterion of concrete under variable amplitude load, and analyze the influence of loading sequence on total fatigue life; Discuss experimental techniques of concrete under multiaxial fatigue load, and carry out uniaxial fluctuating compression fatigue experiments of concrete specimens; Finally, complete experiments of 63 concrete specimens under four lateral confinement stress levels and four loading rates. The content of each chapter is as follows:Chapter 1 is introduction: the background, significance and researching status quo about concrete fatigue are introduced, and some concepts and terms are explained. Chapter 2: discuss experimental techniques of concrete under multiaxial fatigue load, carry out concrete uniaxial fluctuating compression fatigue experiments and analyze the experiment results. Chapter 3: discuss the problem of fatigue failure criterion based on stress space. The S-N curve of unified double straight line is established, and the flaw of S-N curve is analyzed quantificationally. Chapter 4: the rule of the developing of fatigue deformation is discussed and fatigue failure criterion based on strain space is established. On the basis of experiment, a three-stage-model is proposed for describing ultimate strain and residual strain of concrete under fatigue loading. A method of using failure criterion under static load to describe fatigue failure criterion is suggested so that failure criterion under static load, fatigue load, uniaxial load, multiaxial load, constant amplitude and variable amplitude load is unified. Chapter 5:analyze the applicability of Miner's rule to variable amplitude fatigue of concrete materials. Based on the concepts of normal stress ratio and actual stress ratio, a damage variable is defined, and non-linear fatigue damage accumulation criterion is established. Chapter 6: carry out compression tests of concrete specimens under different loading rates with different lateral confinement in one direction, and establish dynamic failure criterion under complex stress state considering the effect of loading rate and lateral confinement level. Chapter 7 is conclusion and prospect.