Study On Failure Criterion Of Plain Concrete Under Multiaxial Fatigue Loading

This dissertation is a part of the project of The State Natural Science Foundation-Failure Criterion of Plain Concrete Under Multiaxial Fatigue Loading. Fatigue deformation and fatigue strength of plain concrete under constant and variable amplitude biaxial and triaxial stress state is studied as followed.Chapter 2 is devoted to presentation of multiaxial fatigue experiment system for concrete. Relevant key experiment techniques, including experiment design and operation of the system, are also discussed according to the author's experience from practical experiment.In chapter 3, experimental studies of fatigue loading spectrum are conducted. Tremendous dynamic data of working crane RC beams are acquired by dynamic data recorder EDX-1500A. On the bases of these data, an effect spectrum of crane loads is established, and fuzzy optimum selection is used to identify the best statistic distribution of the spectrum. The result indicates that the amplitude value and peak value of the cyclic load of crane beam are in normal distribution.Chapter 4 is concerned with studies of uniaxial fatigue of concrete. Tests of abnormal value and variance, analysis of variance, fuzzy optimization are introduced into statistical analysis of concrete fatigue life. A new statistical model for fatigue life distribution of concrete is proposed and statistic test for the model is conducted.Chapter 4 and chapter 5 are concerned with experimental studies of concrete fatigue in biaxial tension-compression and triaxial tension-compression-compression loading cases. Fatigue strength in such stress states are discussed, and corresponding fatigue strength envelopes are presented. Three stages of fatigue strain of concrete are summarized; equations of fatigue strain and its increasing rate in the second stage are given. Equations of deformation modulus of concrete are obtained.In chapter 7, experimental studies of two and three grade variable-amplitude fatigue in biaxial tension-compression and triaxial tension-compression-compression loading cases are carried out and fatigue damage analysis is presented. The residual strain of concrete is studied, relative residual strain is defined as damage variant. The damage evolution equation is established, by which, damage analysis and prediction of fatigue life are carried out. Tests carried out in chapter 5,6,7 fill the blank of constant and variable amplitude fatigue in tension-compression and tension-compression-compression multiaxial loading cases.