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Concrete In Australia : December 2011
28 Concrete in Australia Vol 37 No 4 1.0 INTRODUCTION Queensland Motorways Limited (QML) owns and operates the Gateway Motorway, a major national highway and urban motorway running north-south on the eastern side of Brisbane. e Gateway Upgrade Project comprised the upgrading of 24 km of motorway, including the duplication of the Gateway Bridge over the Brisbane River. e Existing Gateway Bridge (EGB) is a concrete box girder with a main span of 260 m, a world record span when completed in 1985. e New Gateway Bridge (NGB), which is the subject of this paper, was completed in 2010. It appears to be a twin of the first bridge, but in a structural sense has many differences and is notable for the extended design life of 300 years. e Gateway Upgrade Project contractor was Leighton Abigroup Joint Venture (LAJV) whose designer was the AECOM/SMEC Joint Venture. Construction of NGB was by the Gateway Bridge Alliance comprising LAJV and VSL, with design by AECOM and subconsultant Cardno. Concrete supply was by Boral. On completion of NGB in 2010, both bridges were renamed as the Sir Leo Hielscher Bridges. For the purpose of this technical paper where the individual bridges must be identified, the contractual nomenclature of EGB and NGB is used. e intent of this paper is to describe the various ways in which concrete material behaviour influenced the conceptual and detailed design, construction, and maintenance of the new bridge. e paper is written primarily from the point of view of a bridge designer, working in a design-and-construct team, with access to construction and specialist concrete materials advice. 2.0 CONCEPT DESIGN In the tender documents, QML envisaged a bridge of the same form and appearance as the EGB. However, while the NGB has six traffic lanes like the EGB, it was also to carry a 4.5 m wide shared path, and traffic loads had increased and design standards had changed since EGB was designed. ere was also the requirement for an exceptional design life and construction methods and plant had also progressed. e design outcome from the study of options during the tender period is shown in Figure 1. ere were a number of significant differences from EGB, as summarised in Table 1. e span lengths were changed to accentuate the speed and economy of balanced cantilever construction of the approach spans by shortening the 88 m spans used in EGB and avoiding the need for temporary piers. e articulation was changed to greatly reduce the number of bearings to minimise the scale of and difficulty of future bearing replacements, particularly given the extended design life. Table 1. Selected comparison of Existing Gateway Bridge (EGB) and New Gateway Bridge (NGB). Design or Construction Aspect EGB NGB Main spans lengths 145m,260m,145m 162m,260m,162m Main spans cross section Single cell box with 12 m wide bottom flange Two cell box with 15 m wide bottom flange Bridge width 23m 28m Main spans construction method Cast-in-place balanced cantilever Cast-in-place balanced cantilever Approach spans lengths 60 m (abutment end) 71 m (typical internal) 88 m (adjacent to main spans, requiring temporary pier) 60 m (abutment end) 71 m (remainder) Approach spans cross sections Twin-cell precast box with wide, reinforced cast-in-place joints. Two single cell match-cast precast boxes with epoxy joints and a longitudinal stitch pour. Approach spans construction method Span-by-span construction Balanced cantilever Longitudinal fixity Abutments and river piers All piers Movement joints 2 No. (in main side spans) with load transfer by steel needle beams) 5 No. (at abutments and in 3 No., approach spans) with load transfer through halving joints. Bearings Abutments, top and base of all approach piers, needle beams) Abutments, halving joints