Ebel-Abanga Bridge takes shape: first steel beam launched across the Abanga River in Gabon

The new Ebel-Abanga Bridge will be 200 metres long. With two traffic lanes and pedestrian access, it will increase the capacity and safety of National Road 2, an important transport route in Gabon that also provides connections towards Cameroon and the Republic of Congo.

The Ebel-Abanga Bridge is part of a wider programme being delivered by BESIX in Gabon with Matière and MBB for the Ministry of Public Works. The programme also includes a viaduct and four pedestrian footbridges in the capital, Libreville. At Ebel-Abanga, the bridge is based on Matière’s modular Unibridge® system, using prefabricated steel components that can be efficiently transported and assembled on site.

The central span is the most technically complex part of the structure. At 55.60 metres long, it is assembled on one bank and then launched horizontally across the river, limiting the need for heavy lifting operations directly above the water. The two side spans are simpler to install, as they can be lifted into position by crane from the riverbanks.

The first of the three longitudinal steel beams that will form the central span is now in position. The launched steel beam is 55.60 metres long and weighs 97.12 tonnes. To guide it safely during the operation, a temporary launching nose was fitted at the front and a temporary tail at the rear. Both are removed once the steel beam has crossed the river and do not form part of the permanent structure.

The entire operation was carried out over five days, alternating between assembling and pushing the girders forward. Once the girders had been assembled together with the temporary launching nose and tail, the whole assembly was pushed progressively across the river until it reached the opposite bank. The nose and tail were then removed and the steel beam was set on its bearings.

Reaching this stage also required significant work below ground. The original foundation concept had to be revised following an assessment of the actual geometry of the riverbed and the geological conditions. BESIX Engineering redesigned the foundations and optimised the pier dimensions, while Matière adapted the standard configuration of its Unibridge® system to the revised layout.

Different foundation solutions were required on each bank and were carried out by Franki Foundations, the BESIX Group subsidiary specialising in special foundation techniques. On the right bank, where the bedrock lies only three to six metres below ground level, micropiles were used. On the left bank, driven piles extend to depths of more than 30 metres to reach layers with sufficient bearing capacity. The final design therefore combines foundations tailored to the conditions on each bank, a modular superstructure and a construction method adapted to the constraints of working above the river.

The successful launch of the first steel beam makes the work carried out over recent months on the foundations, piers, temporary works and steel structure suddenly very tangible.

The next launching operations will gradually complete the central span. All three steel beams are expected to be launched by 18 November. The cross-bracing and permanent formwork will then be installed, followed by the reinforcement and the remaining formwork, before the bridge deck is concreted.

Once completed, the new bridge will provide Ebel-Abanga with a modern two-lane crossing on one of Gabon’s strategic transport routes.