Analysis of Structural Failures in Market Shed Roofs in Onitsha, Anambra State

Market shed roof failures in Onitsha, one of West Africa's largest commercial hubs in the South East geopolitical zone, have resulted in fatalities, injuries, and significant economic disruption in recent years. This study analyses structural failures in twelve market shed roofs within the Onitsha Main Market and Bridgehead Market complexes, using post-failure investigations and structural appraisals of intact but at-risk structures. Failure investigation methodology included examination of fractured member cross-sections, review of original construction records where obtainable, and reconnaissance-level structural assessment of surrounding sheds. Key failure parameters examined include roof span, purlin and rafter sizing, connection details, roofing sheet weight, and evidence of wind uplift damage. Results indicate that overloading through accumulation of debris and additional roofing layers placed on ageing steel angle section purlins was the primary cause of structural failure in seven of the twelve cases. Wind uplift during the 2023 peak wet season contributed to roof sheet detachment and progressive collapse in four cases, with inadequate J-bolt fixings identified as the point of initiation. Roof spans in excess of 6 metres with unstiffened rafter connections were identified as a high-risk typology. The study recommends mandatory structural assessments of all market shed roofs in Onitsha exceeding 20 years of age, replacement of undersized purlins with hot-rolled steel sections, and the adoption of wind-resistant roofing fixing standards appropriate to the local wind zone. Keywords: market shed roofs, structural failure, Onitsha, wind uplift, roof collapse.