Stress Tensor Gauge
It is suggested to place a small, simple and determinate structural system at the point where stress components are to be determined inside a concrete body. This structural system can be arranged so that measured strains of its members may provide sufficient information for determination of the state of stress. In the present pilot study, a determinate space truss defining a regular tetrahedron is proposed to be placed in a spherical cavity for the general case of three-dimensional state of stress. For the particular case of two-dimensional state of stress however, a simple plane truss defining an equilateral triangle to be placed in a circular hole can be recommended. In each case, the set of longitudinal strains measured along each bar can directly be transformed into a stress matrix, provided that the gauge had been carefully calibrated under various well defined states of stress before casting.
The proposed gauge may be considered as a special piece of aggregate which does not badly violate continuity of stress distribution in a rather non-homogeneous material like concrete. Besides, a numerical investigation of disturbance level for the case of plane stress, produced rather encouraging results in this respect.
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