<p>Orthotropic deck structures are used in many steel bridges. Due to the typical detailing applied as around 1970, a significant number of deck structures constructed in that period suffer from fatigue damage. In many countries cracks have been detected, in particular in the weld between the deck plate and the trapezoidal stiffener. These cracks tend to grow relatively slowly, but are difficult to detect at an early stage because they initiate from inside the trapezoidal stiffener.</p><p>This paper presents a model with which the growth of these cracks can be predicted. The model is aimed at the growth rate prediction of through-thickness cracks that can be detected by visual inspection, but that do not have a risk of fracture, which would affect the traffic safety. Stresses are extracted from a detailed finite element model of the entire deck. A second, local finite element model including the crack is used as the basis of a fracture mechanics model. The growth rate determined with the model is calibrated and validated with measured cracks in various bridges.</p><p>The novel model can be used in daily engineering practice. It can serve to determine inspection intervals for orthotropic bridge decks. It can also serve to support decisions of repairing detected cracks or to determine the effectiveness of strengthening measures such as the addition of a high strength concrete overlay. The model has been successfully applied to 6 large existing bridges in The Netherlands.</p>
<p>Managing Contractor has carried out the design of the replacement of the existing cables stays at Ewijk Bridge. Replacement of the existing cables is one component of the renovation works necessary to extend the design life of this large steel bridge by at least 30 years.</p>
Worldwide, the design life of bridges can be extended by delivering repair and strengthening projects while meeting the challenge of keeping the bridge in service. Although this is a common characteristic of such international projects, there are significant differences between countries with regard to types of bridges and maintenance approaches. VSL International is active in the field of bridge repairs and strengthening in a worldwide capacity and adopts a variety of solutions to accommodate these to local conditions. This article will describe lessons learnt from a variety of projects which deal with the repair and strengthening of steel bridges, particularly cable-supported structures. Several international examples are described, in Mexico, Canada, the USA and France, where innovative solutions have been applied. These innovations focus on the unique combination of specialised temporary works, method of construction and cable technology.
<p>Cable replacement projects are highly specialized as the cables are a critical tension member of the structural system of these type of bridges and often, the traffic on the bridge cannot be disrupted during the cable replacement works. The new cables also need to fit within the existing bridges and the detailing needs to be adapted to the existing situation. Experience of the design of cable supported structures, the knowledge of cables, the methods of installation, the design of specialized temporary works and detailing around anchorages needs to be combined. This article will cover the different aspects of cable replacement, the experience of suspension bridges and cable-stayed bridges and will describe two case studies in North America.</p>
<p>Decks of cable stayed bridges are supported by cables transferring the reaction loads to the pylons.</p><p>Toe cables are either terminated in an anchorage or the main tensile element is continuous, crossing through the pylon, guided by means of saddles.</p><p>In a continuous effort to optimise structures, designers have privileged pylon presenting a plain body, with no inner cavities needed for the installation of cable anchorages. Such plain pylon bodies prompt the use of saddle to guide a continuous tendon across, or, alternatively, push the connection of the stay cable on the outside, using structural tensile components such as steel links, to obtain the transfer of the stay cable loads to the pylons.</p><p>Toe multiaxial loading of the stay cable on the pylon connection, as well as functional needs associated to stay cable operations, compelled establishment of numerous criteria to achieve the design of such devices.</p><p>Today, engineers have gained experience in the design, manufacture and installation of pylon connections including associated stay cable system. This paper aims to compile key criteria in the design of pylon connections for plain body pylon and highlighting particularities of both families of applied solutions: structural steel links and guiding friction saddles.</p>
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