Development of a vibrating wire strain gauge for measuring very small strains in concrete beams

A vibrating wire strain gauge capable of measuring strains in concrete elements to an accuracy of better than 0.5 is presented. This offers some advantages over conventional electrical resistance gauges, the quoted accuracy of which is typically 3 , and which are often considered unsuitable for concrete because of their inability to span cracks. While vibrating wire gauges are potentially more accurate, they are prone to significant errors because of temperature changes. In the purpose-built gauge described here, temperature correction is achieved using an unstrained reference gauge. The vibration data are analysed using a moving-window Fourier transformation in order to identify and remove the geometrically nonlinear portion of the response. The resulting system is accurate, economical and easy to use. The gauges have been used to study the behaviour of cracked concrete specimens. Typical results are presented and discussed.