On 2 December 2005 the City Airport extension to the Docklands Light Railway (DLR) network was opened to the public, two weeks ahead of schedule. Halcrow were the designers for the civil, structural, rail, and communications systems on the project.

The existing light railway provides an integral transportation network around the central business district of London, UK. The extension provides a vital link to the rail network by connecting it with City Airport, located 10km from the heart of the City. This connection will improve national and international communications, as well as the development of communities along the route.

The extension consists of a 3km of elevated post-tensioned segmental concrete box viaduct with external tendons, and has been designed for two tracks of standard DLR railway loading. The spans were erected using an overhead gantry to support the 3.1m long segments prior to stressing the tendons.

SAM-LEAP5 has been successfully used by Halcrow on many projects and for many years, and so was the natural choice as the standard design tool on this project. Its integration with CAD packages, loading and section modules and improvements to problem definition and solution process mean that complicated problems can be tackled efficiently and with confidence.

The section, stress check, prestressed element and temperature difference modules were used to design the post-tensioning and reinforcement in the elevated viaduct. The ease of operation then meant that SAM-LEAP5 could be used to further value-engineer the post-tension design to suit the various span configurations and loadings.

SAM-LEAP5 stress check modules were also used for the design of the reinforced concrete piers, pilecaps and piles. The biaxial bending assessment module was of particular use when assessing the effect of construction stage loadings from the erection gantry on the piers.