Civil Engineering November 2022 | Vol 30 No 10

viable to upgrade this bridge in a sustainable manner. A holistic approach was followed to find a solution that would create an enduring structure that would maintain and improve the main access route for the communities around the area. SUSTAINABILITY AND SAFETY The initial key issues were whether the bridge should be repaired, and how, or whether it should be completely demolished and rebuilt. Ultimately, the design team for- mulated an option that entailed demolishing and rebuilding severely damaged portions of the structure, repairing other less critical elements, and upgrading the deck design to address the safety issue for pedestrian users. The foundation of the bridge is on piles, and the team realised that the weight of an up- grade was critical, as additional piles would be very expensive. The combined repair/rebuild solution, though more complex to design and construct, was deemed to be the most sustainable and cost-effective method and included: Q Q Demolishing and replacing the pier and abutment seating beams, the approach slabs, the deck and the barriers. Q Q Retaining the piles, pile caps, pier columns and abut- ments, with minor repair work for these elements. Since the deck would be demolished as part of the rehabilitation of the bridge, the team also designed the new structure so that its structural configuration could be changed from simply supported to continuous – a technique not frequently used in bridge repairs. The change allowed the number of joints to be reduced, thus limiting the points of potential water ingress to the sub- structure elements. This required a deep understanding of the technical requirements and limitations when changing a bridge’s configuration. Lastly, the team adopted several durability measures to enhance the adaptability of the structure to the harsh environmental condi- tions. These measures included using cathodic protection to control the electrochemical reaction leading to corrosion of the steel reinforcement (a method rarely used in Africa), implementing an extensive gutter system to drain water away from the bridge elements, and installing waterproofing in key locations. NEW CONFIGURATION Changing the bridge’s configuration from its existing simply supported deck to continuous was structurally possible, as there were originally two rows of bearings on each of the piers. This system was replaced by one row of bearings on the centreline of the piers for a continuous deck. Civil Engineering November 2022 41 Spalled concrete at faces near joints Spalled concrete at the end of a pier seating beam Severely damaged portions of the structure were demolished and rebuilt