Assessment of the Flat-Jack Test for evaluating in-situ stress in post-tensioned concrete

This study investigates the use of flat-jacks for estimating residual prestress in post-tensioned concrete elements. Experimental tests were conducted on three concrete slabs in a controlled laboratory environment, where an axial load was applied to induce a known axial stress. Two flat-jacks of different sizes were evaluated to assess their accuracy and reproducibility. The results indicate that the Flat-Jack Test provides consistent stress estimations, with accuracy influenced by flat-jack size. Despite some variability, especially for the smaller device, the findings confirm that the Flat-Jack Test is a promising technique for assessing residual stress in post-tensioned concrete bridges. Further research is recommended to refine the methodology and validate its applicability across a broader range of structural conditions.