Wojciech Siekierski

Awaria kabla sprężającego estakady drogowej. Przyczyny i skutki

Wspolczesne wieloprzeslowe ustroje ciągle wykonywane są czesto z betonu sprezonego.W przypadku duzych rozpietości przesel stosuje sie dźwigary skrzynkowe jednokomorowe,a montaz odbywa sie poprzez nasuwanie podluzne. W taki sposob wykonanoestakady dojazdowe do mostu przez rzeke Warte w Koninie. Po 10 latach eksploatacjiw jednej z estakad stwierdzono awarie wielosplotowego kabla sprezającego polegającąna zerwaniu wszystkich splotow. Przeprowadzono badania konstrukcji, przegląd dokumentacjiprojektowej i powykonawczej oraz badania laboratoryjne stali sprezająceji iniektu oraz analize statyczno-wytrzymalościową. Stwierdzono, ze bezpośrednią przyczynązerwania kabla byla korozja wzerowa. Przeprowadzone badania wykazaly, ze jejprzyczyną byla technologia sprezania (zabezpieczenie kabla przed korozją). W szczegolnościbyly to: zastosowanie zlej jakości iniektu, z duzą ilością dodatku napowietrzającego,niecalkowite wypelnienie iniektem kanalow kablowych oraz niewystarczającaliczba i źle rozmieszczone wentyle odpowietrzające. Na podstawie przeprowadzonychbadan sformulowano wniosek, ze wystąpienie podobnej awarii prawdopodobne jestw odniesieniu do pozostalych kabli uzytych do budowy estakady. W oparciu o przeprowadzonąanalize statyczno-wytrzymalościową ustalono, ze ewentualna awaria innegokabla dotycząca tego samego przesla stworzy zagrozenie katastrofą. Opisany przypadekawarii kabla sprezającego wskazuje na kluczową role prawidlowej iniekcji kanalowkablowych w celu zabezpieczenia kabli przed korozją.

Determination of Defect Factors for a Road Bridge Made of Prestressed Concrete

Abstract The paper concerns determination of defect factors for a road bridge made of prestressed concrete. Cracking and permanent deformations of the continuous triple-span road bridge made of prestressed concrete were reported by road administration. Inspection of the bridge was carried out. Bridge design and erection documentation were researched. Hypotheses concerning defect factors were put forward. Parametric analysis of the bridge was carried out. The analysis showed that the cause of observed defects was faulty design of prestressing, namely: underestimation of prestressing force losses, underestimation of the influence of concrete shrinkage, and inappropriate tendon layout which introduced rapid changes to prestressing force. The general conclusions are: (a) symmetric prestressing of continuous main girders should be applied in zones where sagging and hogging bending moments occur in turns, (b) long prestressing tendons should be applied with care due to substantial prestressing force losses that may occur, (c) anchoring numerous tendons at the same crosssection should be avoided since it results in rapid variation of prestressing force, (d) variations of structure deformations due to prestressing should be recorded and checked against the predicted ones.

A plane-frame model for the analysis of cross beams in open-deck railway bridges

This paper shows how to establish a plane-frame computational model for the analysis of a cross beam in an open-deck railway bridge. The model consists of the analysed cross beam, parts of the main girders, as well as transverse and wind-bracing struts. The model is used to examine the behaviour of cross beams in two different types of open-deck spans: a plate girder span and a truss girder span. The modelling technique is particularly useful when an immediate assessment of the service load that can be borne by particular structural component is necessary. For instance, in emergency situations or when the technical condition of one structural component is much worse than any other component. The latter situation may occur in the case of open-deck bridges where the condition of the deck’s components is usually very poor. The stress levels in test-loaded cross beams are computed using the proposed plane-frame modelling approach. The computational results are compared to stress values based on strains recorded during actual test loading of bridges. It is shown that the plane-frame modelling of a cross beam with adjacent structural components overestimates normal stresses in the top flange of the cross beams by between 15 and 30%, whereas a simply supported beam model gives an overestimation of over 100%. Rotational restraint of the cross beams at their connection to the main girders is also investigated. The plane-frame modelling approach underestimates the restraint by between 13 and 23%. This is acceptable as long as the bending moment at the mid-span position governs the load-carrying capacity. This is usually true for open decks.

An analytical method to estimate the natural bending frequency of the spans of railway through truss bridges with steel-and-concrete composite decks:

The Eurocode 1 standard requires railway bridges to be checked against the hazard of resonance. To perform this task, the first natural bending frequency of a bridge span has to be computed. The analytical method based on the single-beam analogy is sufficiently accurate for simply supported beam-girder bridges. This paper proves the applicability of the method for through truss bridge spans with steel-and-concrete composite decks; this is despite the fact that the spans do not strictly comply with the assumptions of this method. The flexural stiffness of the bridge span is computed taking into account the joint action of the truss girders and the composite deck; the limited extent of span shear stiffness due to diagonal bracing is also considered. A uniform distribution of the span mass over the span length is assumed. The mass is computed based on geometrical characteristics of truss and deck members, taking into account gusset plates, stiffeners, connectors and fittings. The analytical method and finite element method are applied to find the natural frequencies of two through truss bridge spans with composite decks. Computed results are compared with frequencies recorded during bridge testing. Taking into consideration the joint action of the truss girders and the composite deck, as well as the limited shear stiffness provided by diagonal bracing, significantly improves the accuracy of the assessment provided by the analytical method. The natural bending frequencies computed for the two bridge spans fall within the range of 0.95–1.05 of the recorded values.

Structural aspects of railway truss bridges affecting transverse shear forces in steel-concrete composite decks

Abstract At the steel-concrete interface, the horizontal shear forces that are transverse to cross beams occur due to joint action of the steel-concrete composite deck and the truss girders. Numerical analysis showed that values of the forces are big in comparison to the longitudinal shear forces. In both cases extreme force values occur near side edges of a slab. The paper studies possibilities of reduction of these shear forces by structural alterations of the following: rigidity of a concrete slab, arrangement of a wind bracing, arrangement of concrete slab expansion joints. An existing railway truss bridge span has been analysed. Numerical analysis shows that it is possible to reduce the values of shear forces transverse to cross beams. It may reach 20% near the side edges of slabs and 23% in the centre of slab width.