PSI - Issue 78

Available online at www.sciencedirect.com

ScienceDirect

Procedia Structural Integrity 78 (2026) 98–104

© 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of XX ANIDIS Conference organizers Keywords: Flat-Jack Test, post-tensioned concrete bridges, residual prestress, structural assessment, test accuracy. Abstract 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. 1. Introduction After World War II, the technology of prestressed concrete experienced a rapid development in Europe. This was due to its structural efficiency and cost-effectiveness in both design and construction phases (Gupta, 2006). However, today, decades after their construction and often at the end of their service life, many prestressed concrete bridges have shown significant signs of deterioration, seriously affecting their safety and functionality. Recent collapses have XX ANIDIS Conference Assessment of the Flat-Jack Test for evaluating in-situ stress in post-tensioned concrete Dalila Rossi a *, Carlo Pettorruso a , Sara Cattaneo a , Virginio Quaglini a Department of Architecture, Built Environment and Construction Engineering (ABC), Politecnico di Milano, Piazza Leonardo da Vinci 32, Milano 20133, Italy

* Corresponding author. Tel.: +39-340-1942783. E-mail address: dalila.rossi@polimi.it

2452-3216 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of XX ANIDIS Conference organizers 10.1016/j.prostr.2025.12.013