GENERAL OVERVIEW OF WORKS
BECK HILL BRIDGE CONSTRUCTION
Beck Hill Bridge was designed by the council designers as an integral bridge. This means that the bridge was not split into the two abutments, with the bridge deck inserted between, sat on bearings that allow movement without articulation joints. The integral bridge was designed as a monolithic structure that can accommodate the forces associated with expansion and contraction of the members.
The design raised significant issues as to how this integral bridge could be constructed as designed. The challenges the integral bridge design raised were that no kicker was allowed to be poured, to prevent a visible construction joint. Kickers are important as they provide an initial first pour to start the concrete structure off in the correct position and a bottom edge for the concrete shutters to be fixed against.
Due to the requirement for a continuous pour each abutment had to be poured in one complete and continuous pour from the narrow pinch point at the top of the abutment where the high quantity of re-bar prevented adequate access for tremie pipes and pokers to vibrate the concrete. The abutment also required a sloping profiled formwork front face, which presented problems in how the concrete could be poured and compacted in one continuous operation, from the top pinch point, to the bottom from face of the sloping face, without potentially having visible honeycombing of the concrete on the patterned face due to lack of vibration.
SOLUTIONS TO THE CHALLENGES
To overcome these construction challenges PBS carried out research into the available shutter support systems and concrete compaction equipment and how this could be adapted to suit our scheme. PBS designed an in-situ concrete shutter foundation system to support the shutters self-weight, as well as that of the concrete, and to allow the setting out of the shutters in the correct location. PBS also designed a grid system of tubes, both horizontal and vertical which would allow the pokers to be dropped from the top of the abutment and inserted from the sides, giving vibration to all required areas of the abutment including the sloping front face. These tubes were designed and installed to not conflict with the specified reinforcement and were installed at the same time as the re-bar.
PBS designed and fabricated rigid extension handles onto the concrete pokers so that they could be guided into the far reaches of the abutment in the tubes and removed safely. During the pour as the depth of the concrete rose up the shutter the plastic tubes were raised/removed at strategic points so that they did not end up being cast in with the abutment. PBS had an independent structural engineer assess the concrete pour on completion and the engineer commented in the report that he was very impressed with PBS’ ingenuity in overcoming these challenges.
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