Findings from in-situ survey of post-tensioned precast and segmental post-tensioned bridges

During 2019 and 2020, several segmental post-tensioned bridges or footbridges collapsed in the Slovak Republic. As a result of this sequence of bridge collapses, an inspection of a large number of segmental post-tensioned structures has been carried out since 2022 in order to determine their condition and risk rating. The inspections were carried out by Slovak universities and private companies. The findings obtained from the targeted bridge diagnostics carried out by the Department of Concrete Structures and Bridges of the Slovak University of Technology in Bratislava are presented in this paper in the context of published international findings and reports. One of the main objectives was to investigate the post-tensioned tendons and to determine the possible absence of grouting, which has an impact on the determination of the risk rating of the bridges. The data obtained so far from Slovak bridges show that half of the inspected old post-tensioned bridges (built in the 1960s, 70 s and 80 s) have some percentage of tendons, which are only partially or, in some cases, completely ungrouted. As a result of these findings, in some cases, it was necessary to reduce the number of traffic lanes or the maximum permitted load of vehicles on the bridge. Even before the late stage of corrosion, visible phenomena on the concrete surface have been observed, showing the possibility of ungrouted and corroded tendons in the bridge. This paper summarises some of the problems of post-tensioned bridges and the state-of-the-art in prestress control. Following the brittle collapses of bridges that have occurred in Slovakia, the article complements some of the knowledge gained during the targeted diagnosis of post-tensioned segmental bridges also in the context of demolitions of some high-risk bridges that have been carried out.