The effect of chloride induced corrosion in post-tensioned concrete bridges - A case study of the Gjøsund bridge in Norway

Abstract

In this thesis, a case study of the post-tensioned concrete Gjøsund bridge (Gjøsundbrua) in Norway is conducted. A load analysis of the load actions and capacity calculation of the bridge has been performed using hand calculations. The effect of corrosion in ordinary and prestressing reinforcement on the moment capacity has been studied. The impact of corrosion on the moment capacity is based on the percentage loss of the reinforcement. The bridge was built in 1973 and is located in a coastal area of Norway. The bridge is a post-tensioned concrete beam plate type and it is simply supported with a span length of 22.6 m. The concrete cover of the Gjøsund bridge is lower than today’s requirements. Previous investigations of the bridge indicated that the ordinary reinforcement is heavily corroded. The condition of prestressing reinforcement in the ducts is not known. According to the calculations in this thesis, the prestressing reinforcement has residual flexural capacity of the external loads when the ordinary reinforcement has 100% corrosion. Based on this, the prestressing reinforcement is the critical factor for the moment capacity of the bridge. Consequently, the prestressing reinforcement must not be corroding. The calculations show that moment capacity does not hold the external loads at the midspan with 34,9 % corrosion of the prestressing reinforcement. KEYWORDS: Chloride induced corrosion; Post-tensioned concrete bridge; Prestressing tendons; Load analysis; Flexural capacity.