Song Yu-pu

Fatigue properties of plain concrete under triaxial constant-amplitude tension-compression cyclic loading

Fatigue tests were conducted on tapered plain concrete prism specimens under triaxial constant-amplitude tension-compression cyclic loading. The low stress of the cyclic loading was taken as 0.2fc and the upper stress ranged from 0.20ft, to 0.65ft. Three constant lateral pressures were 0. 1fc, 0.2fc and 0.3fc respectively. Based on the results, the three-stage evolution rule of the fatigue stiffness, maximum(minimum) longitudinal strain and damage were analyzed, and a unified S-N curve to calculate fatigue strength factors was worked out. The results show that the fatigue strength and fatigue life under triaxial constant-amplitude tension-compression cyclic loading are smaller than those under uniaxial fatigue condition. Moreover, the secondary strain creep rate is related to the fatigue life, a formula for describing their relation was derived. The investigation of this paper can provide information for the fatigue design of concrete structures.

Endochronic damage constitutive model for fully-graded aggregate mass concrete

The behavior of deformation and strength of a fully-graded aggregate concrete under complex stress state is the basis of the nonlinear analysis and design for mass concrete structures such as concrete dams. In this paper, based on the combined endochronic theory with damage mechanics and on the quantities of experimental data, an endochronic damage constitutive model suitable for various aggregate grade concrete is proposed. This model takes into consideration the scale effect and the effect of wet screen sieve of aggregate in which the concept of yield surface is not needed and the difference of damage evolution rule of various graded aggregate concrete is a concern. The proposed model is used to analyze the deformation and strength of fully-graded aggregate mass concrete and the wet screened aggregate concrete specimens. The calculated results are in good agreement with experimental data, which can be used as a guide for the design of arch dams and other mass concrete structures.

Biaxial tensile-compressive experiment of concrete at high temperatures

Biaxial tension-compression experiments of concrete of five stress ratios at high temperatures were carried out using the large static-dynamic triaxial test system in the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology. The stress ratios σ1/σ3 are 0, 0.1, 0.25, 0.50, and 0.75. The temperatures are 20°C, 200°C, 300°C, 500°C, 600°C. The mechanical behavior of concrete under biaxial tension-compression at high temperatures is analyzed. It is found that both the tensile strength and strain diminished with the increase in temperature under each stress ratio. Based on the test results, the relationship between tensile strengths and stress ratios and temperature is proposed. In addition, the failure criterion of concrete under biaxial stress state of tension-compression at high temperatures is established.

Numeric simulation for structure's damage identification of space truss

Damage detection by using the changes of dynamic parameters is a conventional damage diagnosis method, however, some indices are not sensitive enough to the most structural damages. In this study, the analytical data of displacement modes of truss structure are obtained by using the finite element analysis soft—ANSYS. The mode analysis technique for the axial strain change of any stick is used to detect the steel trusses with different damages. The analytical results show that the damage location and degree of the truss stick can be effectively diagnosed by means of the axial strain change.

Experimental study on performance of plain concrete due to triaxial variable-amplitude tension-compression cyclic loading

An experimental study on performance of plain concrete under triaxial constant-amplitude and variable-amplitude tension-compression cyclic loadings was carried out. The low level of the cyclic stress is 0.2fc and the upper level ranges between 0.20fc and 0.55fc, while the constant lateral pressure is 0.3fc. The specimen failure mode, the three-stage evolution rule of the longitudinal strains and the damage evolution law under cyclic loading were analyzed. Furthermore, Miner’s rule is proved not to be applicable to the cyclic loading conditions, hereby, a nonlinear cumulative damage model was established. Based on the model the remaining fatigue life was evaluated. The comparison with the experiment results shows that the model is of better precision and applicability.