Bridge 1 at Rapahoe and Cobden Rail Bridge
1Located on the West Coast of the South Island, bridge one at Rapahoe was something of a historical engineering curiosity – constructed by hand between 1896 and 1899. The original bridge was a triumph of kiwi engineering in a very different time, when technology and methodologies were primitive by today’s standards. We were delighted to get the chance to have a look at the bridge and its design close up, undertaking a comprehensive assessment of the original timber truss railway bridge.
2Our job was to determine the remaining service life, identify remedial options and evaluate options for retaining the original bridge. It was an interesting process, applying the advanced technology of today’s world of engineering to a structure that was designed and built more than a hundred years ago. Unfortunately, the historic timber bridge ultimately wasn’t fit to continue its functional life, and the decision was made to replace it with a modern bridge, which also offered an opportunity to improve rail operations at the same time. During construction of the new bridge, train operations were to remain uninterrupted, necessitating remedial work and ongoing monitoring of the old bridge.
3The new 290m long bridge incorporated 27.5m span precast post-tensioned beam components. In close collaboration with the contractor, we reanalysed and re-detailed the superstructure to allow precast post-tensioned L-shaped components to form the major components of the final U-shaped bridge superstructure – helping them streamline the construction process.
The entire Bridge 1 Rapahoe renewal project was completed within programme and budget. In 2008, the project received an ACENZ Award of Merit – recognition of the great solution our bridging engineers were able to help deliver.