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Restoration and strengthening strategies for 19th century iron pedestrian suspension bridges

Boekbijdrage - Boekhoofdstuk Conferentiebijdrage

The history of mainland Europe's oldest suspension bridges dates back to the beginning of the first half of the 19th century. The two World Wars as well as continued renovations to these bridges make that the earliest suspension bridges in central Europe (Belgium, France and Germany) can only be physically documented by decorative private suspension bridges. Europe's second oldest surviving suspension bridge (1824,Wissekerke, Belgium) is used to illustrate a particular restoration and strengthening approach used to make these bridges comply with current concepts of safety. The initially private pedestrian bridge spanning 21m across the castle's moot, is at present part of a public park. Due to ill-maintenance and deterioration over decades as well as a function shift (from private to public), the bridge does not fore fill the current European norm for pedestrian bridge design. Two options offer themselves: the bridge is closed to the general public (with limited private access), restored and kept as an "architectural" object or the bridge is strengthened ensuring maximum public utility with minimum loss of authenticity. Six different strengthening strategies are briefly presented. These strategies include the addition of extra support to reduce the span, the addition of a structure under the deck (ex. beams, truss, arch), the addition of a structure in the deck (ex. pre-stressing cables, girder), the addition of a structure above the deck (ex. truss along hand rail ), strengthening of the suspension cable and finally strengthening through cable stays. The architectural and engineering advantages and disadvantages of these strategies are highlighted. One option is selected on the basis of maximum public use, (and thus compliance with current European norm), optimal preservation, least visual impact and easy future maintenance. This strategy preserves and restores most of the authentic elements (being the cast iron mast, the suspension chain, the back stay and the railing) and replaces the structurally inadequate and non authentic deck with a steel girder with timber deck. In this solution the suspension structure thus solely carries its own weight. Connection details between authentic suspension structure and the new main load bearing steel girder are newly designed and discussed. The new girder designed for strength and stiffness carries dead loads and live loads laid down in the European Norm. The authentic cast iron railing in its deformed current state poses a challenge as it cannot be demounted and also does not comply with the European Norm. A solution is worked out that preserves, restores and strengthens the railing. Based upon this representative case study, general conclusions are given for restoration and strengthening strategies of 19th century iron pedestrian bridges.
Boek: Proceedings of International Conference on Structural Analysis of Historical Construction
Volume: 2
Pagina's: 1175-1180
Aantal pagina's: 6
ISBN:978-0-415-46872-5
Jaar van publicatie:2008
Trefwoorden:restoration, strengthening, wrought iron, iron, cast iron, suspension bridge
  • ORCID: /0000-0003-3282-5106/work/79706654
  • Scopus Id: 79952341969