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Deformation and failure of coal is a complex process with damage evolution, so it's important to study the energy mechanism during coal damage process under all kinds of loading conditions. A serial of cyclical loading and unloading tests of coal were conducted under different confining pressures by means of an advanced conventional triaxial compression testing system. The damage process of coal under confining pressure was discussed carefully. Experimental results show that hysteresis loops of coal occurs under cyclical loading and unloading conditions and correspondingly damage dissipation energy increase with increasing stress. Elastic modulus of coal would decrease with increasing cyclical stress under low confining pressure or uniaxial compression, but it would not decrease with increasing cyclical stress under high confining pressure. It indicates that damage mechanism changes due to the effect of confining pressure. So a new definition of coal damage variable was suggested based on energy analysis and the corresponding damage evolution regular was given. Such definition avoids the default of traditional definition of damage variable based on elastic modulus and can well describe the damage content of coal under different confining pressures. [ABSTRACT FROM AUTHOR]

In order to investigate the compressive behavior of high-strength concrete confined with high-strength stirrups, high-strength concrete prism specimens confined with high-strength stirrups were tested under axial compression. The effects of three variables such as stirrup ratio, stirrup yield strength and stirrup configuration were analyzed. It is shown that high-strength stirrups do not yield at peak stress of confined concrete. The calculation method for effective lateral stress and actual stirrups stress were suggested based on the stress mechanism. The high strength stirrups can provide more effective lateral stress after the peak stress, which makes the descending section more gentle for stress-strain curve of confined concrete. Based on test results and theoretical analysis, the equations for calculating the strength and strain of confined high-strength concrete were proposed, the formula of stress-strain curve were suggested. It is shown that the theoretical stress-strain curves are in good agreement with the experimental curves. [ABSTRACT FROM AUTHOR]