2This paper presents a case study of an economical intervention on an early prestressed post-tensioned concrete structure.Built in 1960, a 60 m span concrete railway bridge at Clabecq in Belgium had a simply supported two-cell box girder. It was post-tensioned with one of the last applications in Belgium of the Blaton-Magnel 'sandwich' system. The cables were external to the concrete and only protected from corrosion by cement grout. Maintenance inspections in the 1990s revealed that corrosion of the tendons was so severe that the future safety of the bridge was compromised. The owner decided to replace all existing cables with new tendons placed in high-density polyethylene ducts, with each tendon composed of 15 monostrands. This paper describes the assessment of the existing structure, attempts to estimate the residual pre-stressing force and the design and implementation of the repair. It also discusses problems encountered and lessons learned.
The paper will illustrate the contribution of research into Construction History in condition assessment or residual carrying capacity situations for three old types of concrete constructions. We will address: -the problem of assessing the actual carrying capacity of "Hennebique" reinforced concrete type beams with their characteristic reinforcement system, widespread in many countries before the First World War.-the replacement of the external post-tensioning tendons within a hollow box girder railway bridge built in the early 1960s with the "Blaton-Magnel" anchorage system developed in Belgium from 1941 onwards, and used until the early 1960s, in Belgium and abroad.-the structural assessment of thin concrete hyperbolic paraboloid shells, which were highly popular with architects and engineers in 1950s-1960s.
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