The widening of the N3 between the Westville Viaduct and Paradise Valley Interchange is one of South Africa's largest current highway infrastructure upgrades. As part of this 5.74 km capacity improvement project, Post Tensioning & Structural Solutions (PTS-S) has been entrusted with one of the most technically demanding operations in the overall scope, the installation of 127 precast bridge beams weighing approximately 66 tonnes each across the Westville (B93) and Paradise Valley (B44) viaducts.
The contract was awarded by SANRAL to the AQUA/EXR JV in May 2023, the 51-month project will increase capacity along one of South Africa's busiest freight and commuter routes. PTS-S was appointed as the specialist subcontractor responsible for prestressing the precast beams and launching them into their final positions. Supporting this operation is Struttura Consulting (Pty) Ltd who designed the temporary works system, while Greenhouse Construction manufactured the temporary chair and trestle frames. Lovemore Bros (Pty) Ltd supplied and operated the specialised gantry launching system used to place the beams safely over the live N3.
Each precast concrete beam measures approximately 33 metres long, 0.9 metres wide and 1.98 metres high, with an individual mass of around 66 tonnes. In total, 77 beams are required for the Westville Viaduct and 50 for Paradise Valley, resulting in 127 beam launches over the duration of the project. Beam placement commenced in January 2025 with the centre median structures, which have since been successfully completed at both the Westville (B93) and Paradise Valley (B44) viaducts. Operations have now progressed to the outer widening works, with the current focus on the northbound carriageway of the Westville Viaduct between Pier 1 and Pier 2 (Span 2) which nearly all launches are complete for this span. The beam placement across both locations is scheduled for completion in early 2027.
Rather than constructing bridge decks directly above live traffic, the widening is achieved by pre-casting the bridge beams off-line before transporting and launching them into position during carefully planned road closures. This approach significantly reduces disruption to the travelling public while improving safety and construction quality. Instead of months of lane closures and conventional in-situ construction above the N3, individual beam launches can be completed during controlled windows before traffic resumes normal operation.
The operation itself relies on a sophisticated combination of temporary works, heavy lifting equipment and precision surveying. PTS-S first installs steel chair and trestle frames onto the newly constructed bridge piers. Supported on temporary concrete plinths, these structures stand nearly five metres high, and each weighs up to 2.5 tonnes. Because they form the support system for the launching gantries, installation tolerances are exceptionally tight, with final levels maintained within ±5 mm. Once surveyed into position, the frames are securely clamped to the pier using tensioned high-strength stress bars to provide the support required for the launching operation.
Following completion of the temporary support system, Lovemore Bros installs gantry tracks onto the chair frames before assembling its hydraulic gantry system and 39-metre header beam. The precast beams are transferred from transport trailers onto an Assist & Self-Propelled Modular Carrier (APMC), which transports each beam beneath the gantry. Using hydraulic strand jacks mounted on the header beam, the gantry lifts the 66-tonne beam, moves it into its final position above the bridge bearings, and lowers it with millimetre-level accuracy before resetting for the next lift.
Working next to one of South Africa's busiest national highways presents numerous engineering and logistical challenges. Restricted working areas on narrow bridge decks, limited road closure windows, live traffic management, high-precision survey requirements, and the coordination of multiple specialist contractors all demand meticulous planning.
These challenges are overcome through detailed temporary works engineering, careful planning, close collaboration between all project stakeholders, and the use of highly specialised equipment. The combination of accurately designed temporary works, hydraulic lifting systems and experienced specialist personnel enables PTS-S and Lovemore Bros to safely execute complex beam launches while maintaining programme requirements and minimising disruption to the public.
With the median beam installations successfully completed and the outer bridge widening well underway, the project continues to make significant progress towards its next major milestone. Beam placement across both viaducts is expected to be completed in 2027, after which the project will move into the next phases of construction. Every successful beam launch brings the upgraded N3 one step closer to increasing capacity and improving one of South Africa's busiest transport routes. For PTS-S, the project showcases the company's expertise in temporary works engineering and post-tensioning on large-scale infrastructure projects.
