Design of Slender Aesthetical Concrete Bridges – Challenges and Considerations

Reinforced concrete (RC) has the advantage that the material can be freely shaped to accommodate architectural design with complex curved surfaces and slender elements resulting in elegant bridges with high focus on aesthetics. It is very common that midrange to major bridges are designed together with architects which may challenge the design engineer due to the key role of the visual appearance of the bridge.

The consulting engineering company COWI has designed several midrange RC box girder bridges and cable-stayed bridges, e.g. Aarsta Bridge, Sweden created by the architect Sir Norman Foster (opened in August 2005 by His Majesty King Carl XVI Gustaf) and recently a cabled-stayed bridge in Constantine, Algeria (Constantine Viaduct, also known as Viaduc Transrhumel, currently under construction) designed together with the architects from Dissing+Weitling. Common to both Aarsta Bridge and the Constantine Viaduct are the throughout use of cross-sections consisting of curved lines. For the Aarsta Bridge, a very slender girder with double curved soffit was a structural challenge. For the Constantine Viaduct, a slender bridge deck with curved soffit and rib structure required increased need for analyses and reinforcement detailing. In addition, the pylons have been made slender with the lower part designed with corbels embracing the deck. This has resulted in harmonic, beautiful and elegant pylons.

With the Aarsta Bridge and Constantine Viaduct Bridge as case studies, this paper presents the main challenges in the design of slender bridges where aesthetical requirements governed the design. Careful attention has to be given to the arrangement of post-tensioning and the reinforcement details in connection with the slender elements.