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Bridge cantilever construction - in-situ
Balanced cantilever construction is an economical method when access from the below is expensive or practically impossible. Segments may be cast in-situ or precast concrete normally with a box shape cross-section. Construction starts from the top of a pier, with the segment normally fixed to the pier either permanently or temporarily during the construction. (Construction can be carried out from an abutment provided there is a balancing weight to counteract the segments in the span).
For in-situ balanced cantilever construction, the formwork is suspended from the end of the last segment. The new segment is cast, and once the concrete has developed a predetermined strength, the section is post-tensioned to the rest of the bridge. The figures show the construction sequence of this type of construction. Segments are often cast and stressed in pairs, one each side of the pier
For further information see Concrete Society Current Practice Sheet 153, Balanced cantilever bridges, published in CONCRETE in November 2007. Copies of the Current Practice Sheet may be downloaded from the Members’ Area of the Concrete Society web site or from the Concrete Bridge Development Group (CBDG) website.
Acknowledgement:
Gifford Consulting
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