Central Water and Power Research Station, Poona.
For the measurement of stresses at various locations in concrete dams strain gauge of Carlson type are embedded in concrete. The strains measured by these gauges are developed not only on account of loads on the structures but are also due to temperature, moisture movement and chemical action in concrete. Hence to isolate the effect of strains due to loads, from those due to other factors it is usual to employ a ‘no stress meter’. This strain meter is isolated from the stress field by means of a groove. Using photoelastic method for two dimensional analysis the distance from, the face up to which the isolated portion could be considered free from stress was determined. To get quantitative estimate, of this distance, the criterion adopted was that the stresses should not be more than one per cent of the average at the end. A general relation is suggested for finding out the depth to which the groove is to be taken.
