Civil Engineering November 2022 | Vol 30 No 10

42 November 2022 Civil Engineering Reconfiguring the structure of the existing bridge while still maintaining the substructure elements required careful technical assessment of the loads acting on the existing piers. A continuous deck imposes higher movements on the piers, as there are no mechanical joints to accommo- date these horizontal movements. Since the piers were not going to be reconstructed, the design team had to assess whether these increased movements could be supported by the existing piers. The option to use a single row of bearings on the centreline of the piers enabled the previously eccentric loads from the deck to be removed, allowing sufficient structural capacity in the piers to accommodate the larger movements. These changes in forces from the initial design to the proposed design were meticulously assessed by the design team. The idea to change the bridge’s struc- tural configuration from simply supported to continuous is not a method typically adopted when restoring a bridge. However, doing it allowed the number of joints to be reduced by over 70%, and the number of bearings to be reduced by 20%. Reducing the number of joints and bearings substantially increased the durability of the structure. A specified construction sequence for placing the beams and casting the in-situ deck was followed to limit the horizontal movements of the beams. The beams had to reach a certain age before the deck was made continuous, and a specific, optimised sequence for the order of the different span construction was required. DIGITAL SOLUTIONS Advanced digital analysis tools were em- ployed for the upgrading of the Omaruru River Bridge throughout the various project phases. Design The analyses of the bridge were conducted in MIDAS Civil, a bridge-specific struc- tural analysis package. The design team had to prepare a workflow in this software which would allow the model to be quickly updated during the construction process. It was considered necessary since the contractor would provide real-time data of the beams to the design team to assess the deck movements and pier stresses, due to concrete creep and shrinkage, at each of the subsequent construction stages. The design team required the precast beam ages for each span as construction continued to input the parameters in the MIDAS Civil models and ensure that the construction process was aligned with the design. This required digital prowess and a deep understanding of the software to be able to rapidly update the analysis models while construction was ongoing. Modelling The Omaruru River Bridge was modelled in 3D, in its correct geographical location, using Revit elements from a database of structural elements created over the years by Zutari’s bridge team. This 3D model was used to generate the drawings that were issued for construction and could also be used to ensure that the different elements fitted together with sufficient construction tolerances. Construction Photographs were taken and video footage was captured using a drone to obtain aerial views of the bridge at the different construction stages. These images and videos allowed the design team to gain an understanding of how the construction process was progressing. The construction was carried out during the Covid-19 restriction period when the design team was prevented from conducting in-person site inspections. This restriction was overcome with frequent photographs of progress, emails, and discussions to clarify technical details. COLLABORATION Collaboration within Zutari The design team of the Omaruru River Bridge was based in Tshwane, South Africa, whereas the site team was based in Namibia. There were regular communica- tions between these teams to ensure that the construction of the bridge was aligned to the design solution for the structure, which included: Q Q The ages of the precast beams were communicated from the site team to the design team on a regular basis in order to update the analysis models and to assess the deck movements and pier stresses. Q Q The proposed products and construc- tion methodologies for the bridge bearings, concrete mix designs, con- struction sequence, drainage systems, epoxies for grouting, handrails, stress bars and waterproofing systems were communicated from the site team for approval by the design team as they were made available by the contractor. Collaboration with contractor The contractor appointed for the construc- tion and repair of the Omaruru River Bridge played a role in determining the construction method to best suit their experience and equipment. Zutari’s initial design was that of a simply supported, cast- in-situ deck. However, the contractor pro- posed an alternative design, replacing this in-situ deck with precast beams and only an in-situ slab for the following reasons: Q Q The contractor did not have a concrete batching plant in nearby Henties Bay. The only batching plants available were in Swakopmund (75 km) and Walvis Bay (110 km). These would have resulted in long hauling distances for the concrete, which would likely have influenced the quality of the concrete work. Q Q Additional mixing trucks would have been required to cast the volume of the in-situ deck continuously. Q Q There was a concern relating to the settlement of formwork in the river sand of the Omaruru River. Q Q The in-situ deck would have required substantial amounts of formwork, along with additional time to assemble and remove. Zutari evaluated the contractor’s proposed alternative design in terms of structural performance, feasibility, and construction cost. While evaluating this option of using precast beams, Zutari’s design team conceived the idea of also changing the structure’s configuration from simply supported to continuous. This alternative design of a continuous deck made up of precast beams and an in- situ slab was found to be slightly cheaper than the initial design, with a similar con- struction period. Once the client provided approval for this alternative design, Zutari reassessed it, and updated construction drawings were issued to the contractor. CONCLUSION The upgrade and rehabilitation of the Omaruru River Bridge was executed by means of a combination of concrete repair and member replacement, advanced durability measures, as well as reconfig- uring the structure. The bridge has been designed and built to adapt to the harsh environmental conditions that it will be exposed to during its design life.