Longitudinal strains and stiffness of RC beams under load as measures of corrosion levels

Structural engineers rely on measurable parameters of corroding RC structures to predict their residual load-bearing capacities. The most widely used parameter is cracking of the cover concrete. This paper looks into the potential of using longitudinal strains and stiffness of corroding RC beams to predict the level of steel corrosion in the beams. It is based on results from an extensive research where 20 quasi-full-scale RC beams (153 × 254 × 3000 mm) were corroded under various levels of sustained loads. Longitudinal strains were found to non-uniformly vary across the depth of a corroding beam. Moreover, their maximum did not coincide with the location of maximum loss of steel. It was therefore recommended to avoid using them as an indicator of the level of steel corrosion or as an indicator of the structural integrity of corroding RC structures. Stiffness of corroding RC beams from deflections was found to decrease sharply at corrosion levels between 5% and 8% by mass loss of steel. For corrosion levels above 8%, stiffness was found to remain constant despite a continued increase in the level of steel corrosion. It was therefore concluded that there is merit in using stiffness to indicate level of steel corrosion at early corrosion stages but there is little value in measuring stiffness of heavily corroded RC structures.

► Longitudinal strains on corroded beams under load are controlled by crack patterns.
► Longitudinal strains at a point are poor indicators of level of steel corrosion.
► Stiffness on beams corroded under load indicates corrosion levels below 8%.