ABSTRACT
The paper presents two cases of prestressed concrete and steel old bridges damaged by corrosion in natural environment with high humidity. Investigation of the damage state of bridges, on site and laboratory, showed major damages due to corrosion of structural elements which affects the resistance, stability and durability of bridges.
The prestressed concrete bridge ensures the passing of a national road over a river in a hill area and was built in the 1950’s, being one of the first prestressed concrete bridges in Romania. It has a single span of 30 m, the carriageway is 6.80 m wide (two lanes) and there are two sidewalks of 0.90 m each. The superstructure consists of eleven precast prestressed concrete adjacent beams, 1.50 m high. The prestressing steel used for all the beams were four tendons of ø 5 mm steel wires. After the assemblage of the beams, some cracks were found on the lower face of the beam, due to the unfulfilment of the necessary prestressing degree as a cause of the slippage of the tendons in the anchors and the deformation of the anchorages. To remedy this situation, an additional prestressing was performed with external non-bonded tendons placed in the spaces between the beams, two on each lateral side of the beams. The protection of the external tendons was provided by applying a textile fabric, a cement paste layer, a steel mesh and a new cement paste layer. The existing damage mainly consists in advanced corrosion of external tendons used for strengthening of prestressed concrete beams by additional prestressing. At some tendons, the prestressing steel wires are broken due to generalized corrosion, with tendons split off. The corrosion-induced damage has been caused by deterioration of initial protection system of external tendons, which allowed the access of water and oxygen to the surface of prestressing steel wires components.
The steel bridge ensures the passing of a national road over a lowland river and was built by a French company in the 1930’s. The bridge is a five-span steel lattice girder bridge with a total length of 315 m and a carriageway 5.50 m wide. The superstructure is made of simply supported steel decks, each composed of two main steel lattice girders, connected at their lower part with cross-girders and wind bracings, and at their upper part with wind bracings. The steel elements are made of structural shapes (angle, I section and plates), joined by riveting. The corrosion protection of the steel elements is provided by painting. The existing damage mainly consists in localized corrosion with a significant reduction of the cross-section of the steel girder profiles (diagonals and verticals), above the embedded area in the concrete slab of the bridge carriageway. In some elements, the steel profiles were penetrated (sectioned) up to 7 mm thickness, due to the penetration of the entire metal section caused by electrochemical corrosion by differential aeration macro-cell.
Taking under consideration the advanced corrosion damage state of the structural elements, which affects the resistance and stability of the bridges, correlated with their age and current functional requirements, it was decided to close the two bridges and replace their superstructure.
