Summary
A technique has been developed at the Road Research Laboratory for automatically recording the load-strain curves in flexural tests of concrete beams at the standard rate of loading specified in B.S. 1881. The new technique almost completely eliminates the noise and electrical pick-up associated with the resistance strain gauges previously used, and overcomes the undesirable drying-out of the concrete beams resulting from the employment of epoxy resin adhesives to attach the resistance strain gauges. Strains were measured by an inductive transducer combined with an oscillator and ademodulator, the output of which drives the Yinput of an X- Y plotter. The load applied to the specimen is measured by the distortion of a large spring with a travel of 4 in. A linear potentiometer attached to the spring is fed with a direct supply of 500 m V. The output from this potentiometer drives the X input of the X- Y recorder. The apparatus takes only about five minutes to prepare and thus expedites the work of testing concrete beams.
