Szukana fraza: [Abstrakt = "Contemporary multi\-span continuous bridge structures are made from prestressed post\-tensioned concrete. In the case of long spans single\-cell box girders and sliding assembly technique are used. Such structures were built as trestle bridges approaching main bridge structure crossing the Warta river in Konin. After 10\-year service in one of the trestle bridges a failure of a multi\-strand prestressing cable was found, namely breaking of all cable strands. The following research was carried out\: testing in situ, study of design and erection documentation, laboratory tests of prestressing steel and grout, static\- strength analysis. It was found that pitting was the direct reason of the failure. It was caused by inappropriate prestressing technology, namely\: usage of bad quality grout that was too reach in airing admixture, incomplete filling of cable ducts with grout and insufficient number and inappropriate layout of ventilation ducts. On the basis of in situ inspection it was concluded that occurrence of similar failure is probable also for other cables in the trestle bridge. Based on the static\-strength analysis it was established that similar failure of a cable concerning the same span poses a serious threat to the safety of the structure. The described case of prestressing cable failure shows the significance of correct cable duct grouting for protection of cables against corrosion."]

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