Jännepunosvaurion vaikutus betonisen sillan rakenteelliseen turvallisuuteen: Esiselvitys

    Research output: Book/ReportCommissioned reportProfessional

    Abstract

    In this preliminary study common causes for tendon corrosion and wire breakages are
    examined by literature research. The research focuses on risks of typical Finnish post
    tensioned and post-grouted bridges due to wire breakage. The preliminary study
    prefaces the research project in which the structural safety of post-tensioned bridge in
    case of tendon wire breakages is assessed.



    In Finland, the number of prestressed bridges is low in copmparison to other types of
    bridges. Still, if comparison is made by comparing total lengths or deck areas, the post
    tensioned bridges form a majority of bridge stock. The prestressed bridges can be
    prefabricated with prestressing or cast in place and post-tensioned. This study focuses
    on latter. In Finland a typical post-tensioned bridge is cast-in-place with post-grouted
    interior tendons. A typical number of spans of this kind of bridge is two and span length
    usually varies from 20 to 30 meters.



    The deterioration mechanism for post tensioning tendons is mainly due to defects in
    post grouting. The trapped air and water in grout in tendon duct causes a break on
    corrosion protection of tendons and tendon corrosion in duct is therefore possible. In
    anchoring zone at the end of the bridge, a leaking joints and poor detailing can allow
    water and chlorides from de-icing salts to flow in tendon ducts and anchors. In
    permanently moist conditions, corrosion initiates and progresses.



    In favourable conditions the corrosion progresses, which leads the reduction of tendon
    area and increase of tendon stress. Corrosion in tendons causes also crack initiation
    on tendon wires. Some steel grades are prone to hydrogen embrittlement due to
    corrosion, which means the ultimate behaviour of strand is brittle. As wire or strand
    breaks, the forces redistribute to adjacent tendons or strands and, depending on
    structure, to another load bearing structures.



    The bond between the strand and postgrouting plays significant role in structural
    robustness of bridge. In case of bondless tendon, the break anywhere along its length
    causes the lost of the function of entire unit. With bond, the broken tendon can re-
    anchor on grout and still function in other cross-section away from breaking point.
    From point of structural robustness, it is beneficial that concrete structure cracks as
    tendon area reduces. Still, the structure should have sufficient capacity left and ductile
    behaviour after concrete cracking.



    In this study, calculations are made by method with which the ductitility of cross-
    section in case of tendon break was assessed. As a result of calculations was observed
    that the bridges in this case have sufficient robustness and ductile behaviour in case of
    tendon loss. The calculation method seems to be reliable, still calibration is needed for
    adequate target reliability level for bridges.
    Translated title of the contributionThe effect of tendon breakage on the structural safety of post-tensioned concrete bridge
    Original languageEnglish
    Place of PublicationHelsinki
    PublisherLiikennevirasto
    Number of pages60
    Volume2017
    Edition51
    ISBN (Electronic)978-952-317-469-6
    Publication statusPublished - 21 Nov 2017
    Publication typeD4 Published development or research report or study

    Publication series

    NameLiikenneviraston tutkimuksia ja selvityksiä
    PublisherLiikennevirasto
    ISSN (Print)1798-6664

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