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The Dubai Metro light rail scheme is a flagship project in the United Arab Emirates which is currently one of the largest civil engineering projects under construction and, when completed, will be the longest fully automated rail system in the world. The first section of the rail system is due to be opened in September 2009. This paper describes the scheme outline and contractual setup for the viaduct design and discusses the design and construction of the viaduct substructure. In particular, the design methodologies used for the piled foundations, single reinforced concrete columns and prestressed concrete pier heads are discussed as well as the design of elastomeric bearings that were used extensively for most of the viaduct spans. Seismic loading governed the design of many of the foundations and the seismic analysis and design methodology adopted is discussed, together with specific reinforcement detailing requirements. Railstructure interaction analysis and design is also covered. Other critical design issues resolved included the fatigue performance of cranked reinforcement and the treatment of the onerous construction loading from overhead gantries used to erect the precast deck segments. Bridge Engineering 162 Issue BE2 Design of the Dubai Metro light rail viaducts-substructure Smith N Hendy

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The bridge discussed in this paper was completed in 1985 and is part of a vital sea crossing. The main cable-stayed bridge has a span of 225 m with side spans of 107?5 m. The bridge carries two three-lane carriageways. The bridge cables comprise lengths of coupled high-yield bars within a grouted steel tube. An assessment of the structure in 1996-1999, using modern design standards, identified large overstress in the shortest cables anchored close to the pylons. Other cables were also found to be overstressed, but to a lesser degree. Bearings were thus installed at the piers to relieve load from the shortest cables and the second shortest sets of cables were replaced. An acoustic monitoring system was also installed on all cables to detect any problems. Since then, two bar breaks were detected in other cables, which have been replaced. Inspection and testing showed fatigue of the couplers to be responsible for the breaks. Following the first bar break detected in December 2004, an additional assessment was completed by Atkins. This paper describes the assessment of the bridge cables, examines the consequences of cable failure and discusses the reasons why the decision to replace all the cable stays was made. It also describes the specification for the new replacement stay system and its advantages over the old system. BACKGROUNDThe bridge considered in this paper was completed in 1985 and is part of a vital sea crossing. The overall length of the viaduct is approximately 13?5 km, mostly consisting of 40 m span posttensioned beams. The main cable-stayed bridge has a span of 225 m with side spans of 107?5 m. The bridge carries two carriageways, each with three lanes. The bridge is shown in Figure 1 and the numbering system for the cables is shown in Figure 2.The bridge cables comprise lengths of coupled high-yield bars within a grouted steel tube. Using modern design standards, the bridge was assessed in 1996-1999. Large overstress was identified in the shortest cables (M1 and E1), anchored close to the pylons, and other cables were also found to be overstressed, but less so. As a result, bearings were installed at the piers in order to relieve load from the shortest cables and the second shortest sets of cables were replaced. At that time, an acoustic monitoring system was also installed on all cables to detect any further problems. Two bar breaks were subsequently detected in other cables, which led to their replacement. When the first of these cables was removed, an additional three bars were found to be broken at couplers. Testing of the couplers showed that some were showing signs of fatigue damage, and fatigue was found to be the cause of the three broken couplers.Following the first bar coupler break detected in December 2004, an additional assessment was carried out by Atkins. This identified that many of the current cables were significantly overstressed in accordance with current standards. The predicted overstress in the cables, combined with the history of coupler breaks, led to the decision to replace ...

2 3Quantifying civil engineering projects in terms of sustainability and meeting carbon dioxide reduction targets is a new challenge for the civil engineering industry. While the development of carbon accounting tools has helped to identify areas of bridge design and construction which have the greatest carbon dioxide emissions, quantifying sustainability overall has been less well studied. The sustainability index for bridges described in this paper is a significant step towards facilitating systematic quantification of the sustainability of schemes through a simple, graphical tool. The output identifies where improvements can be made on a design and allows comparison of alternatives. It can be used throughout the design process to monitor decisions, the success of design changes and to inform decisions on future projects, thereby improving the sustainability of designs. The overall sustainability index rating enables targets to be set for the desired sustainability performance of bridges produced by an organisation. The methodology can be adopted by clients so that, once the key attributes are set and weighted accordingly, designs can be benchmarked across their whole bridge stock. This paper presents the background to the development of the sustainability index,its key features and examples of its use and benefits. Proceedings of the Institution of Civil Engineers Bridge Engineering 165 June 2012 Issue BE2 Pages 81-89 http://dx.