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Concrete In Australia : June 2013
50 Concrete in Australia Vol 39 No 2 FEATURE: BRIDGES of the bridge required the use of an extensive design review and management process throughout the project. Australian Standards 1 were used in the design with durability the main focus. e superstructure was modelled in two dimensional grillages, due to the staged construction of the bridge, following generally accepted methods outlined by Hambly 2. e first grillage modelled the aqueduct segments during the launching process and the second modelled the entire bridge for the permanent condition. e aqueduct was designed for T44 maintenance truck. An allowance of 12 mm differential settlement between supports was also considered in design. At permanent stage, the aqueduct (half symmetric) was modelled using Strand 7, a 3D finite element software, with concrete as "brick" elements to check the stresses of the anchorage zone (Figure 3). e finite element model enabled aqueduct reinforcement to be detailed for the tensile stresses identified at the anchorage zone, as shown in Figure 4. e maximum shear at the 12 m cantilever and the tensile stresses developed at the anchorage zone required extensive reinforcement at the bridge ends to comply with both the strength and serviceability criteria specified in AS 5100.5. Arranging this reinforcement within the 300 mm web was difficult. However, careful detailing and the use of couplers enabled the successful integration of the final layout of the reinforcement within the aqueduct, as shown in Figure 5. 4.2 HDPE Liner A major challenge for the aqueduct was the concrete durability given the aggressive environment within the sewer pipe. e latest technology for sewer protection was investigated by the project team to ensure the long term durability of the structure. An HDPE anchored liner proved to be the most effective system and was more resistant to hydrogen sulphide (H2S) than other options. e comparatively new lining system involved mechanical bonding with the concrete through conical anchor studs on the rear of the liner. e 5 mm thick lining sheets were placed on the internal formwork upside down and cast in with the concrete. International standards and codes were used in the design and specification of HDPE liner. Casting the liner into the aqueduct presented challenges, including: • Adequate restraint to movement as temperature varied around it. Figure 2. Tendon coupler at the end of the segment. Figure 3. Strand 7 model of half bridge. Figure 4. Strand 7 output -- anchorage.