Numerical Analysis of Structural Deflection in Bridge Design: Application to the Niger Bridge, Asaba

Structural integrity assessment of ageing bridge infrastructure is a critical engineering challenge with implications for public safety and economic connectivity. This study applies numerical analysis techniques, specifically the finite element method and beam deflection equations derived from Euler-Bernoulli beam theory, to model deflection patterns in a representative span of the Niger Bridge in Asaba, Delta State, South South Nigeria. The bridge deck is discretised into 120 beam elements with material properties assigned based on published structural drawings and site inspection records from the Federal Ministry of Works. Static loading scenarios are defined to simulate standard truck axle loads, peak traffic density conditions, and the combined dead and live load envelope specified in the Nigerian Highway Bridge Design Code. The stiffness matrix is assembled and solved numerically using Gaussian elimination, yielding nodal deflection and rotation values across all load scenarios. Maximum midspan deflection under peak loading is computed as 18.7 millimetres, which falls within the allowable limit of span-length divided by 600. Parametric sensitivity analysis identifies girder cross-sectional moment of inertia and elastic modulus as the dominant design variables influencing deflection. Results are visualised as deflection profiles and compared against published field measurement data from similar bridge studies, showing agreement within 5 percent. Keywords: finite element method, bridge deflection, Euler-Bernoulli beam, Niger Bridge, structural analysis.