PSI - Issue 62

Available online at www.sciencedirect.com Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2022) 000 – 000 Available online at www.sciencedirect.com ScienceDirect

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Structural Integrity Procedia 00 (2022) 000 – 000

ScienceDirect

Procedia Structural Integrity 62 (2024) 315–322

II Fabre Conference – Existing bridges, viaducts and tunnels: research, innovation and applications (FABRE24) Evaluation of the residual prestressing force in reinforced concrete elements by means of prestress release tests Alessandro Bellini a, *, Claudio Mazzotti b a CIRI Buildings and Construction (CIRI-EC), University of Bologna, Via del Lazzaretto 15/5, 40131, Bologna, Italy b Department of Civil, Chemical, Environmental and Materials Engineering (DICAM), University of Bologna, Viale Risorgimento 2, 40136, Bologna, Italy Abstract Prestressed reinforced concrete elements can be subjected to relevant stress variations over time because of steel stress relaxation and concrete time dependent deformation, often amplified in case of possible steel strands failure, caused by progressive material degradation. This will lead to a significant reduction of the overall prestressing force. The age of the majority of Italian bridges, originally designed without particular attention to durability, is quickly approaching their design service life. In this framework, the need to periodically evaluate the deterioration level of the materials becomes of paramount importance, in particular for prestressed steel strands; this will allow the attainment of a reliable estimation of the residual prestressing force in prestressed reinforced concrete beams (common in bridges and viaducts). The present paper aims at evaluating the reliability of a semi-destructive technique which can be used for performing prestress release tests on reinforced concrete elements by means of the removal of small portions of concrete, often involving only a portion of the concrete cover. Tests were performed on reinforced concrete columns subjected to a predefined compressive axial load, in order to have a direct comparison between the experimental deformation, measured by means of strain gauges, and the effective axial stress, applied through the experimental set-up. Different parameters have been considered during the tests, such as the geometric sawing configuration and the order of the steps performed before the removal of the concrete sample, evaluating their effect on the strain release, with the aim of proposing a reliable procedure easily applicable during in-situ tests. © 2024 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 Scientific Board Members II Fabre Conference – Existing bridges, viaducts and tunnels: research, innovation and applications (FABRE24) Evaluation of the residual prestressing force in reinforced concrete elements by means of prestress release tests Alessandro Bellini a, *, Claudio Mazzotti b a CIRI Buildings and Construction (CIRI-EC), University of Bologna, Via del Lazzaretto 15/5, 40131, Bologna, Italy b Department of Civil, Chemical, Environmental and Materials Engineering (DICAM), University of Bologna, Viale Risorgimento 2, 40136, Bologna, Italy Abstract Prestressed reinforced concrete elements can be subjected to relevant stress variations over time because of steel stress relaxation and concrete time dependent deformation, often amplified in case of possible steel strands failure, caused by progressive material degradation. This will lead to a significant reduction of the overall prestressing force. The age of the majority of Italian bridges, originally designed without particular attention to durability, is quickly approaching their design service life. In this framework, the need to periodically evaluate the deterioration level of the materials becomes of paramount importance, in particular for prestressed steel strands; this will allow the attainment of a reliable estimation of the residual prestressing force in prestressed reinforced concrete beams (common in bridges and viaducts). The present paper aims at evaluating the reliability of a semi-destructive technique which can be used for performing prestress release tests on reinforced concrete elements by means of the removal of small portions of concrete, often involving only a portion of the concrete cover. Tests were performed on reinforced concrete columns subjected to a predefined compressive axial load, in order to have a direct comparison between the experimental deformation, measured by means of strain gauges, and the effective axial stress, applied through the experimental set-up. Different parameters have been considered during the tests, such as the geometric sawing configuration and the order of the steps performed before the removal of the concrete sample, evaluating their effect on the strain release, with the aim of proposing a reliable procedure easily applicable during in-situ tests. © 2024 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 Scientific Board Members © 2024 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 Scientific Board Members 1. Introduction Large part of the Italian road network was designed between the post-war period and the early 1970s, therefore infrastructures are quickly approaching or have already exceeded their design service life; for this reason, bridges and viaducts, in particular, show today a widespread state of degradation, also because they were designed without paying too much attention to durability and often not planning an adequate maintenance plan over the years. 1. Introduction Large part of the Italian road network was designed between the post-war period and the early 1970s, therefore infrastructures are quickly approaching or have already exceeded their design service life; for this reason, bridges and viaducts, in particular, show today a widespread state of degradation, also because they were designed without paying too much attention to durability and often not planning an adequate maintenance plan over the years. Keywords: existing bridges; residual prestressing force; prestress release; saw-cut testing; in-situ tests Keywords: existing bridges; residual prestressing force; prestress release; saw-cut testing; in-situ tests

* Corresponding author. E-mail address: alessandro.bellini5@unibo.it * Corresponding author. E-mail address: alessandro.bellini5@unibo.it

2452-3216 © 2024 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 Scientific Board Members 10.1016/j.prostr.2024.09.047 2452-3216 © 2024 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 Scientific Board Member s 2452-3216 © 2024 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 Scientific Board Member s