Reliability and failure resistance of the stone bridge structure of charles bridge during floods

Abstract

The most frequent damage and collapse of some of the spans of Charles Bridge during floods occurred namely in its central part which was exposed to an intense flow of backwater and erosion of the bridge pier footing bottom, which the originally relatively shallow foundations of the piers on boxes were not able to resist for a longer time (the floods of 1432, 1496, 1784, 1890). The stone vault bridge structure was damaged due to scouring of the bridge piers foundations, their successive tilting and settlement accompanied by degradation, and finally collapse of the adjoining bridge vaults. The foundation of piers on caissons and execution of caisson rings in 1892 and 1902 to 1904 in this part of the bridge, together with measures avoiding the piling up of objects in front of the bridge, enabled the bridge to withstand the impact of more than a hundred-year flood during the events of August 2002. The numerical analysis proved an extreme sensitivity of the stone vault bridge structure to the effects of changes in the footing bottom shape. Due to the changes in the footing bottom (angular rotation, subsidence, shifting), normal and shear stresses arise in the stone vault bridge structure, and exceed the load-bearing capacity of the masonry causing its disintegration. The fundamental measure to prevent the bridge vaults from failure due to the changes in the footing bottom shape is to secure reliably the bridge piers foundations. The increased rigidity of the stone bridge structure achieved by the interaction with the additionally inserted reinforcing structure and by bracing the bridge body filler does not ensure the reliability and safety of the bridge structure from flood-related failures.