Civil Engineering March 2021 | Vol 29 No 2

Civil Engineering March 2021 31 The Canelands Pipe and Pedestrian Bridge project comprises a 165 m long prestressed concrete bridge crossing the Mdloti River in Ward 58 and 60 in KwaZulu-Natal, implemented by eThekwini Municipality (client) and Naidu Consulting (consulting engineer). The project required the removal of the existing 100-year-old decommissioned SA Railways bridge and the subsequent provi- sion of a new pipe and pedestrian bridge. The existing railway bridge comprises five 33 m spans of structural steel trusses at 5.5 m deep, simply supported on reinforced concrete piers and abutments. The existing bridge supports a 400 mm diameter ductile iron sewer pipe, 350 mm diameter and 400 mm diameter steel water pipes and an open cable tray accom- modating electrical cables. In addition, the bridge currently also serves the existing community by providing a key pedestrian crossing over the Mdloti River. A condition assessment of the entire bridge confirmed that large portions of the structural steel trusses were at an advanced stage of corrosion and required immediate replacement. The existing substructure, made up of reinforced concrete, was how- ever still in good condition and showed no signs of distress. A cost benefit analysis was undertaken, and an innovative solution was proposed which included the removal and replacement of the existing superstructure only, as opposed to the complete replace- ment of the existing bridge. The new superstructure design solution comprises prestressed concrete beams launched over the existing rehabilitated substructure which would accommodate both the water and sewer infrastructure and provide a safe walkway for pedestrians. The design solution resulted in the following benefits to the client: Q Q Substructure demolition and replace- ment with new abutments, piers and piles was not necessary, which reduced the environmental impact and resulted in substantial cost savings. Q Q An Environmental Authorisation and Water Use Licence was therefore not required. Q Q The use of the existing steel trusses to launch the new bridge deck meant that no cranes were required in the river to place the precast beams between the supports. Q Q An intrusive geotechnical investigation, which would typically have negative en- vironmental impacts, was not required. Q Q Construction in the river channel, which generally has negative environmental impacts and is a huge risk for project delays during construction, was avoided. Q Q The engineer’s estimated construction period was reduced by approximately seven months because no new sub- structure construction was required. DESIGN & CONSTRUCTION A decision was taken to incorporate Building Information Modelling (BIM) principles into the project. By utilising several leading, industry-recognised software programmes, the existing and the new portions of the bridge were modelled in 3D incorporating BIM principles which provided a key visual aid to the design team to inform decisions regarding the new design, sequencing of construction, risks and limitations. Although the new bridge superstruc- ture is comparatively simple in form, the correct sequencing of the demolition and Out-the-box thinking drives innovation for bridge project The world as we know it has been turned upside down by the Covid-19 pandemic. History has shown that amidst adversity, the human race has always evolved and triumphed. That is exactly the attitude adopted by the Naidu Consulting team as it embraced the pandemic and saw an opportunity to innovate and develop new mindsets to conduct business successfully and responsibly. Josh Padayachee Pr Eng, PMP Director Bridges & Buildings Naidu Consulting josh.padayachee@naiduconsulting.com Akash Ramjee Pr Eng Sector Manager Bridges & Buildings Naidu Consulting akash.ramjee@naiduconsulting.com Daleen Stevenson BIM Lead Bridges & Buildings Naidu Consulting daleen.stevenson@naiduconsulting.com The existing Canelands Bridge