Triaxial experimental study of concrete with control of one stress and two strains

Abstract

The behaviour of cubic concrete specimens (100 × 100 × 100 mm) subjected to a mixed path of both stress and strain loading was investigated. The specimens were statically loaded in a true triaxial apparatus. Three different values of the minimum principal stresses were chosen (10, 15 and 20 MPa). In addition, for each value of the minimum principal stress, three or four strain rate ratios between the x-axis and the y-axis were used (0·25, 0·5, 0·75 and 1·0). The first and second peak stresses occurred in the maximum principal strain axis (y-axis) and the intermediate principal strain axis (x-axis), respectively. The maximum principal stress and the intermediate principal stress did not always exist in a fixed axis, which is related to the strain rate ratios. Some damage formed due to previous load histories, including the peak stress of the y-axis, results in a decreased load carrying capacity in the x-axis. Therefore, the peak stress of the intermediate principal strain axis (x-axis) was lower than that of the maximum principal strain axis (y-axis). Moreover, the y-axis strain corresponding to the first peak stress and the x-axis strain corresponding to the second peak stress were essentially equal. It was found that there is a limit state in concrete: if the strain difference between y- and z-axes and between x- and z-axes is large enough, the load carrying capacities of the y- and x-axes are the same, with the value related to the minimum principal stress and independent of the strain rate ratio.