Flexural strain and crack width measurement of steel-fibre-reinforced concrete by optical grid and electrical gauge methods

A research programme is discussed, which has investigated the fracture of steel-fibre-reinforced sprayed concrete under flexural loading, with the aim of developing a stress-block model to predict flexural behaviour in the form of a load–deflection response. This paper reports the work associated with establishing the strain and crack width profiles in relation to mid-span beam deflection. A strain analysis technique is described, which combines the use of electrical strain gauges with a semiautomated grid method (using digital image processing) for measuring and monitoring the strain and crack width profile over the depth of a fibre-reinforced beam during a flexural test. This novel strain analysis technique has established strain/crack width data, which forms a key part of a stress-block approach for predicting residual flexural strength, an essential requirement of a much needed design rationale for steel-fibre-reinforced concrete.