Longest Bridge in Africa Strengthened using GEWI ^® Bars

Third Mainland Bridge, Lagos, Nigeria

According to historical sources, settlement on Lagos Island started as early as the 14th century. In modern times, the natural port basin continues to be an excellent starting point for trade and traffic. Situated at the gulf of Guinea, Lagos has become Nigeria’s largest city. During the 20th century, the metropolitan area extended from the island onto the mainland and onto other islands.

Today, approximately 11.6 million inhabitants live in and around Lagos, and many of them drive into the city center each day to go to work. Lagos Island is connected to the mainland and the international airport by three bridges. The longest of these bridges is the Third Mainland Bridge, which was built in two phases: the 1st phase was opened to traffic in 1980, and the 2nd phase was opened to traffic in 1991. The 11.8km long bridge is not only the longest bridge in Nigeria, but also the longest bridge in Africa. DYWIDAG Post- Tensioning Systems were used at the time the 1st phase of the bridge was constructed.

The greatly increased traffic on the bridge has lead to the deterioration of the steel parts of the sliding hinges at the cantilever ends and to vibrations in the bridge deck ends that were clearly detectable during the last few years. The condition of four expansion joints proved to be especially critical. For the repair work, the tarmac and concrete of the facing cantilever ends were removed by hydro demolition using high-pressure water, thus avoiding additional damaging vibrations to the bridge.

To repair the four expansion joints of the Third Mainland Bridge, DYWIT supplied approximately 1t of type 36 WR DYWIDAG Post-Tensioning Tendons including accessories as well as approximately 1.5t of 28mm diameter GEWI ^® Bars and accessories. The latter were partly used as a replacement for similar GEWI ^® Bars that had been removed during the demolition of the cantilever ends.

New DYWIDAG Post-Tensioning Tendons were installed for transverse reinforcement of the cantilever ends where the original tendons were removed. These tendons, as originally designed, serve to stabilize the bridge to accommodate the increasing traffic load that has become much higher than was planned when the bridge was built.

DYWIT also supplied a 110 Mp tensioning jack as well as a type 77-159 hydraulic pump. The simple handling of the easy to install, high-quality DYWIDAG Post-Tensioning Systems also helped to limit traffic obstructions caused by the unilateral blocking of the bridge during repair works to merely two months.