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Concrete In Australia : June 2013
54 Concrete in Australia Vol 39 No 2 FEATURE: BRIDGES e launch bay was in the form of a "U" beam with the bottom flange in between the rail beams supporting the bottom soffit formwork for the aqueduct segments. e top 100 mm of the 600 mm wide rail beams were finished with 19 mm thick plywood strip to facilitate the launching and reduce friction. e central panel between rail beams consisted of drop panels on hydraulic ram. e drop panels contained specially designed steel beams supported by pairs of jacks to support the internal soffit formwork. 7.2 Launching nose A 21m long launching nose was a fabricated steel plate girder with cross bracing, modified from a previous job and weighed 55 t. e nose was used to guide the concrete segments onto the piers, as shown in Figure 14, and served as a relatively light cantilever section to reach the next pier. e nose reduced bending stress in the aqueduct segments and ensured clearance with the next pier. 7.3 Launching bearings e aqueduct bearings were designed for both the launching and permanent load conditions, and used in preference to temporary bearings at piers. ese special pot bearings consisted of a profiled top plate and stainless steel "launch over" sliding surface for launching, and avoided the need to substitute permanent bearings for the temporary ones after completion of the launch. in low friction Teflon pads were placed on top of each bearing to reduce the friction during launching. e Teflon pads moved with the superstructure over the bearing and required a construction crew to be stationed at bearing locations at the interface of the moving superstructure and the bearing to pick up the sliding pads for reuse. e launching bearings were added to the next pier after the completion of the first segment launch in preparation for the next segment launching. e same process was continued until the end of launching of all segments. 7.4 Modelling of launching stages A detailed model of the launching steps along with the casting yard and launching nose was created using the ACES incremental launching module software to check the longitudinal launching forces and pier reactions, both at permanent and launching stages, as shown in Figure 15. Every part of the superstructure was exposed to a large variation of reversal bending moments during the incremental launching of a bridge. e ACES launching module was used to determine the magnitude of these moments and allow design of the aqueduct segments and the substructure for the temporary launching condition. e starting point for the analysis was when the aqueduct segments were in the launching bay, 14 m away from the first pier, passing over three supports with the launching nose attached in the front. All the moments and shear along the bridge were calculated at each step and compiled in an envelope. e aqueduct segments, substructure, the casting yard and launching nose were then designed to comply with the envelope during the launching stages. 7.5 Launching method and progress e control system and anchorage point to launch the aqueduct was located on Pier 3. Four VSL launching jacks were placed in front of the Pier 3 permanent bearings. A launching operator on the working platform in front of Pier Figure 13. Casting yard. Figure 14. Launching nose and pier lateral guide. Figure 15. ACES incremental launching analysis -- on completion of final launch.