Doubling the width of the platform of the San Pedro bridge in Spain

Abstract

This article describes how the San Pedro Bridge, which has six spans and is 750 m (2,460 ft) long, 88 m (290 ft) high, 12 m (39 ft) wide, and curved with a radius of 700 m (2,300 ft) was originally constructed in 1993 using the cantilever method. Its superstructure is a prestressed concrete box girder with main spans of 150 m (490 ft). The article shows how the width of the platform was enlarged to 23 m (75 ft) using five movable sets of scaffolding in 2008 and 2009. The bridge remained open to traffic during construction. The original platform was widened 6 m (20 ft) on each side by connecting a new lightweight concrete cantilever to the original upper slab. These cantilevers were supported by steel struts. The tie into the upper slab was made with new transverse post-tensioned tendons and the original superstructure was strengthened to resist the additional dead load of the expansion and live loads of the extra traffic. An additional new central web and a composite concrete-steel section were constructed and connected to the concrete box and central web using vertical high-strength post-tensioning bars. Also, external post-tensioning cables were implemented. The article describes how it was also necessary to strengthen the connection of the original concrete box section to the piers. Detailed calculations were performed to evaluate the load distribution transmitted to the piers by the webs and by the original inclined concrete walls of the box girder. Finally, a detailed second-order-analysis of the complete structure was made to guarantee the resistance of the piers compared with actual loads.