An Explorative Investigation of the Flat-Jack Test for Prestress Assessment in Post-Tensioned Concrete Structures

This preliminary study explores the feasibility of using the flat-jack test to assess residual prestress in post-tensioned concrete elements. Experimental testing was conducted on three concrete slabs under controlled laboratory conditions, with known stress states induced by axial loading. Two flat-jack sizes and two gage lengths were considered, and a tailored calibration procedure was implemented to reflect expected field conditions. The test produced acceptable stress estimations, with accuracy influenced by both the gage length and the jack size. The results are discussed within the broader context of prestress assessment, including a comparison between the flat-jack test’s performance in concrete and masonry and its positioning relative to alternative methods. The experimental design, result presentation, and theoretical analysis in this study are intentionally simple and not yet sufficiently mature to support practical application. Nevertheless, the findings offer promising initial insights and practical inspiration for practitioners and researchers exploring alternative methods for residual stress assessment in prestressed concrete structures, underscoring the need for further research to refine the methodology and validate its broader applicability.