Evaluation of Failure Modes in Locally Welded Structural Frames Used in Market Sheds in Ogun State

Structural failures of metal market shed frames in Nigerian urban markets have resulted in fatalities and property destruction, highlighting the need for systematic failure analysis of locally fabricated structural steelwork. This study evaluates failure modes observed in welded structural frames used in market shed construction in Sagamu and Ijebu Ode, Ogun State. Structural inspection was conducted on 25 randomly selected market stalls, with visual assessment of weld quality, section sizes, connection details, and evidence of distress or previous repair. A sub-set of six representative frames with documented failure histories were subjected to non-destructive testing using dye penetrant inspection and magnetic particle inspection methods to characterise weld defects. Weld hardness profiles were obtained using a portable Brinell hardness tester. Results revealed that incomplete weld penetration, porosity, and undercut were the most commonly observed weld defects, present in 72 percent of inspected joints. Inadequate section sizes relative to unsupported span and roof loading were identified in 44 percent of structures. Frame failures were attributable to a combination of weld defects concentrating stress at joints and undersized members inadequate for combined dead and wind loads. The study recommends mandatory third-party structural inspection and weld quality testing for all public market infrastructure and development of simplified design guidelines for small commercial structures. Keywords: weld defects, structural failure, market shed frames, non-destructive testing, Ogun State.