Structural Risk Assessment of Ageing Electricity Transmission Towers in Adamawa State

Electricity transmission towers form the backbone of Nigeria's national grid infrastructure, and their structural integrity is critical to sustained power supply and public safety. This study assesses the structural risk of ageing transmission towers along a 132 kV transmission line corridor in Adamawa State in the North East geopolitical zone, focusing on towers that have exceeded their original 25-year design life. A total of sixteen towers were assessed using a field-based risk rating methodology incorporating corrosion extent grading, member deformation measurement, foundation exposure assessment, and bolt and connection condition evaluation. Structural adequacy under design wind and conductor tension loads was verified using original design documentation and current load standards. Risk scoring was performed using a modified reliability index approach, classifying each tower into low, medium, high, and critical risk categories. Findings indicate that nine of the sixteen towers received a high or critical risk classification, primarily due to extensive section loss from atmospheric corrosion and missing or corroded cross-bracing members that reduced the effective load resistance of the tower. Three towers showed measurable lean from vertical, with maximum deviations of 1.2 degrees, attributable to differential foundation settlement in waterlogged terrain. The study estimates a probability of structural failure under a 1-in-50-year wind event of approximately 22 percent for the most critical towers. Recommendations include emergency structural intervention for high-risk towers, adoption of a corrosion protection maintenance programme, and integration of drone-based inspection into the Transmission Company of Nigeria's asset management system. Keywords: transmission towers, structural risk, ageing infrastructure, Adamawa State, corrosion.