Design, Installation and Calibration of a Strain Gauge Structural Monitoring System for a Timber Windmill

The paper describes the solution to a problem of measuring loads in the structure of an ancient timber windmill during periods of high wind. For reasons of cost and expediency this was done using resistance strain gauges on the surfaces of the main supporting timbers, using them effectively as large compressive load cells. In view of the impossibility of determining the static load carried by these timbers, and so calibrating the load cells directly, an indirect calibration method was devised and this is described. Finally, results are given for measurement during a 12-h period of high wind with a brief analysis of the implications of the measured loading on the stability of the windmill.