Second Onitsha Bridge

The Second Onitsha Bridge (also known as the Second Niger Bridge) is located between Asaba, Delta State and Onitsha, Anambra State.

Physical Specifications:

Total Length: 1,590 m

Bridge Type: Prestressed Concrete Box Girder

Major Materials: 14,000 tons of steel and 250,000 tons of concrete

Engineering Highlights ⁽¹⁾: 

Construction Start: September 1st, 2018

Construction Finish: May 23rd, 2023

Total Cost: 336 Billion Naira

Construction Methods: Cantilever Method and Incremental Launching

The Second Onitsha Bridge is also called The Second Niger Bridge. The latter is a misleading name, as the Niger runs through Nigeria. There are at least seven major bridges, including places such as Jebba and Kainji. However, between the major cities of Asaba and Onitsha, the Second Niger Bridge is an important piece of infrastructure to connect the two economies.

The bridge was completed by Julius Berger in 2023. It is a bridge of straight forward modern construction. No frills indeed. The Niger is spanned via prestressed concrete box girders. This forms the platform for its four lane road system. It is unclear how the footings were designed/constructed. The spans were put in place via the balanced cantilever method, with the girders near the shores constructed with the incremental launch method. 

Many highway bridges over land and over water utilze prestressed concrete box girders to support their roadways. Prestressed concrete are manufactured by laying a matrix of steel, fibers, or other materials in a casting bed. The material is put in tension, then the concrete is poured. When the tension is released, the is a comrpression force withing the concrete, which confers strength during service. 

The balanced cantilever method attaches sections of the bridge starting from a footing. It attaches to each side in order to balance out forces from overturning the construction. 

The incremental launch method starts with a footing and proceeds in one direction. This produces a tendancy to want to overturn in that direction. Care must be taken to ensure that this does not happen. 

1. Wikipedia - A good general descripition on the bridge and its components.<https://en.wikipedia.org/wiki/Second_Niger_bridge>

2. Julius Berger - Information from one of the major builders in Nigera. <https://www.julius-berger.com/references/second-river-niger-bridge-asaba-onitsha>