Structural Analysis of Culvert Performance Under Heavy Traffic Loading on Rural Roads in Kebbi State

Box and pipe culverts form essential drainage and crossing structures on rural road networks in Kebbi State within the North West geopolitical zone, yet their performance under increasing agricultural and commercial vehicle loads is rarely formally evaluated. This study analyses the structural performance of reinforced concrete box culverts on selected rural roads in Argungu, Birnin Kebbi, and Jega Local Government Areas, focusing on the effects of heavy vehicle loading on structural condition and serviceability. A field survey of eighteen culverts was conducted using visual inspection, crack width measurement, and loading response observation. Axle load data were collected at two weighbridge stations to characterise actual traffic loading relative to culvert design assumptions. Structural capacity was estimated using yield line analysis and compared against derived maximum bending moments from measured axle loads. Findings indicate that fifteen of the eighteen culverts were originally designed for loading standards below the actual traffic volumes encountered, with observed crack widths in seven culverts exceeding 0.4 mm at the culvert crown. Spalling of the roof slab was detected in four culverts, two of which showed exposed and corroding reinforcement. The load ratio analysis indicated that current peak axle loads exceeded design assumptions by a factor of 1.3 to 1.8 in the most critical cases. The study recommends the application of reinforced concrete overlay repairs to compromised slabs, weight restriction enforcement on rural routes with undersized culverts, and updated culvert design standards reflecting current agricultural vehicle loads. Keywords: box culverts, heavy vehicle loading, Kebbi State, rural roads, structural analysis.