Construction World December 2017

Category A1: Civil Engineering Contractors

BRT CABLE STAY BRIDGE OVER M1 HIGHWAY There'll be a whole new generation of bus rapid transit (BRT) commuters when Rea Vaya's Sandton, Alexandra, central Joburg route starts operating in 2018 – and one of the pleasures they can look forward to is crossing the M1 highway on a spectacular new BRT-only bridge.

ensure that the cable anchors were carefully aligned with the anchors on the road-level bridge beam. Lobster-back forms were also designed for the casting of piers that support the bridge as it touches down on either side. With limited headroom across the 24 m and 27 m wide portals over the M1 north and south carriageways, Form-Scaff’s heavy capacity Super-Beams provided the only feasible answer with a low enough profile for unimpeded traffic below, while being strong enough to support the thousands of tons of construction materials above. Another advantage is that the five separate beams, each comprising four connected Super-Beams, could be preassembled offsite to save time and space on the crowded construction site. The project adopted a zero-harm policy during its execution, and a total of 771 287 hours were recorded with no lost-time injuries. Given the com- plexity of the project and the limited construction knowledge of the local community working on the project, this is a remarkable achievement. Working together, the Johannesburg Development Agency (client), Hatch (consultant), who were part of the Royal Haskoning DHV-Hatch-Malani Padayachee JV, and WBHO/Cebekhulu JV (contractor) completed this project successfully in April 2017. The BRT Cable-Stayed Bridge and associated road infrastructure for the estimated 10 000 people who walk or cycle daily between Alex and Sandton will

Rea Vaya's new route will form the backbone of Johannesburg's second new Corridor of Freedom, connecting Alexandra not only to central Joburg but also to its historically segregated, disproportionately wealthy neighbour, Sandton. The multi-million rand BRT bridge recently built between Alex and Sandton, forms part of the Rea Vaya Bus Rapid Transport (BRT) network, one of the largest projects ever undertaken by the City of Johannesburg. The bridge was built in partnership with the Johannesburg Development Agency (JDA). The 271 m long structure extends from Katherine Street in Sandton, across the M1 highway and on to Lees Street in Wynberg and incorporates eight spans. The cable- stayed section comprises a main span of 83 m crossing the M1 and a 39 m long back span provided with a central tension pier. Most remaining spans vary in length from 25-30 m. Two 52 m high slightly inclined concrete pylons, carry the cable-stayed section. Mechanically stabilised earth walls form the transition from the abutments to the roads on either side of the bridge. Two ramp bridges provide pedestrian access from either side of the highway to the 3 m wide bolt-on pedestrian walkway section

of the bridge, resulting in a 13,35 m total bridge width over the freeway. A thorough geotechnical investigation took place prior and during construction, although the decomposed granites, commonly found in this area, were mostly dense within a few metres from the sur- face. In certain sections it was found to be less competent and medium dense down to depths of 3-5 m. The heavy imposed foundation loads and bridge performance requirements necessitated the use of pile foundations. More than 1 300 tons of Form-Scaff form-and-falsework was used during the construction phase, however, the spanning of the highway without impeding workday rush hour traffic was the greatest challenge of all requiring the assistance of the country’s top structural support experts to design and the building of temporary structures to allow construction to continue unimpeded. The contractor also needed ensure that no road traffic accidents would compromise the integrity of the temporary works and subsequently designed and built concrete retaining structures to protect the supershores. Special formwork was designed to pour the towering 52 m high main pylon and

thus be catered for, but more importantly, will offer Alex residents the afford- able, convenient option of riding Rea Vaya to Sandton and back.

Winner

PROJECT INFORMATION

• Company entering: WBHO Construction • Client: Johannesburg Development Agency • Contract value: R225 701 278 (excluding VAT) • Start date: 2 March 2015 • End date: 26 April 2017 • Main contractor: WBHO Construction • Consulting engineer: Royal HaskoningDHV/Hatch/MPA JV

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