A gauge for measuring long-term cyclic strains on concrete surfaces

The theory and construction of a gauge for measuring long-term cyclic strains on concrete surfaces is presented. The gauge transforms axial concrete strains to smaller bending strains by means of a formed metal strip. Four e.r.s. foil gauges are used to sense the central bending strain in the strip. Calibration of the gauge shows that it is capable of reducing the concrete strains by a factor of about 25 and that the gauge factor is about 2·5 microstrain per microvolt. The gauge performs in a stable manner and an application to long-term strain measurement on a number of concrete beams repeatedly loaded at 1Hz during a period of about two years is described.