Civil Engineering November 2022 | Vol 30 No 10

Civil Engineering November 2022 23 such as post tensioning systems, arch stay cables, anchor plates and support bearings. On completion of the project, a total of 42% of the contract value would have been allocated to the creation of economic opportunities and entrepreneurial capacity in the sur- rounding areas over a period of more than seven years. ROAD UPGRADING The road upgrading took cognisance of heritage and other as- pects such as fauna and flora, landscaping and flood risk. The primary objective of this project was to reconstruct the roadway to a higher standard to improve traffic and pedestrian safety, as well as improve flood capacity of bridges and prevent overtopping of the road during floods over the complete 14 km of road. With the main part of the route being constructed in the Cogmanskloof Gorge between a river and high mountains, three new bridges and seven retaining walls were required to facilitate the upgrading. THE NEW ASHTON ARCH BRIDGE The greater Ashton-Montagu region, and Cogmanskloof Pass in particular, has experienced substantial flood damage on several occasions over the years. This resulted in multiple road closures and significant operational disruptions, with adverse impacts on the local economy. A key consideration of the bridge was to minimise flow restric- tion and improve the available free board within the restrictions of adjacent properties and road alignment levels. Through an economic analysis, the technical options for the river crossing and construction strategy were evaluated with due consideration of the impact of construction strategy on road user costs. The bridge concept, which was finally adopted for the main river crossing in Ashton, consists of a single span (110 m) con- crete tied arch solution with a deck suspended by hanger cables which accommodates four traffic lanes and pedestrian walkways. This largely eliminated the possibility of debris build up against the supports and provided the shallowest deck depth solution. To minimise traffic disruption, it was constructed adjacent to the existing bridge while maintaining traffic over it. After completion, the new bridge was used as temporary bypass while the existing bridge was demolished, and new abutments built. The new concrete tied arch bridge was then jacked transversely into its final position in less than 12 hours. The typical cross-section of the arch bridge deck provides for four 3.4 m traffic lanes and two 2.4 m sidewalks. The overall height of the arches is 23 m, and the twin parallel arch ribs are connected via five 15.5 m wishbone beams that provide lateral stability to the arch ribs. Post-tensioned tie-beams complete the arch structural form. Post-tensioned longitudinal and transverse beams support the integral deck road slab and transfers load to the tie-beam, while 24 fully-locked coil strand-type hangers connect the arch rib and tie-beam by cast steel fork sockets to structural steel anchor brackets fixed with high-strength stress bars.  Leading the change towards a more sustainable future Everything we do is designed to deliver a better world. Uplifting communities, improving access, sustaining our planet – we partner with clients to turn ambitions into actions.