Construction World November 2016

FORMWORK AND SCAFFOLDING – ADVERTORIAL

SANDTON’S LATEST SHOWPIECE…

Client:

Johannesburg Development Agency

Main contractor: Design Engineer: Hatch Form-and-falsework: Form-Scaff Location: WBHO

Katherine Street, Sandton

Project type:

Cable Stay Bridge

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> With a span of 120 m including two bus lanes and a pedes- trian walkway, the ultra-impressive cable stay bridge will form part of the City of Johannesburg’s new generation Rea Vaya BRT route linking Alexandra to Sandton. Its span over South Africa’s busiest highway will provide safer and faster access to the central business district for thousands of commuters every day. During the construction phase however, the spanning of the highway without impeding workday rush hour traffic is the greatest challenge of all requiring the assistance of the country’s top structural support experts to design and building temporary structures to allow construction to continue unimpeded. Custom designed Chris Erasmus, Form-Scaff technical director, explains that the entire weight of the bridge needs to be supported from the time of the first concrete being laid (early last year), until the massive cable stays are More than 1 300 tons of Form-Scaff form-and-falsework is on site at the Katherine Street Bridge where WBHO is undertaking a technically challenging project to construct Sandton’s latest showpiece structure.

in place and carefully tensioned later this year. Until such time Form- Scaff’s combination of Super-Beams and Kwik-Stage will form the basis of the support for the bridge. “We also manufactured special formwork to pour the towering 52 m high main pylon and ensure that the cable anchors can be care- fully aligned with the anchors on the road-level bridge beam. Lobster- back forms were also made 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 north and south carriageways, our heavy capacity Super- Beams provide 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,” says Erasmus. Precast solution WBHO construction manager for the BRT Cable Stay Bridge, Nicol van Rensburg, says the construction starts with the Super-Beams supporting 19 pre-stressed precast concrete transverse beams spaced at 3,5 m intervals across the bridge. These 8,55 m long by 400 mm wide and 750 mm high concrete beams then provide support for 100 mm thick pre-stressed concrete planks which are in turn placed across the 3,5 m gap between the transverse beams. Casting of the main beams and slabs follows with the main beams tying into the exposed rebar of the transverse beams. At the same time the main pylon is constructed with formwork designed to reduce in plan dimension from 6 m at the base to 1,5 m at the top of the pylon.

CONSTRUCTION WORLD NOVEMBER 2016