Analytical Study of Lateral-Torsional Buckling in Long-Span Steel I-Section Beams Used in Industrial Building Frames in Kano State

Lateral-torsional buckling represents a critical mode of instability for steel I-section beams subjected to bending about the major axis when lateral and torsional restraint is insufficient, and is a governing failure mode in long-span industrial building frames that are often designed with minimal roof sheeting restraint. This study analytically investigates lateral-torsional buckling behaviour in long-span steel I-section beams used in industrial building frames in Kano State in the North West geopolitical zone, where manufacturing and food processing facilities increasingly employ spans of 20 to 35 metres. A parametric finite element study was conducted using ANSYS with shell element beam models incorporating geometric imperfections aligned with Eurocode 3 fabrication tolerances. Member parameters varied include span, flange width-to-thickness ratio, unbraced length between purlins, end restraint condition, and load height above shear centre. Lateral-torsional buckling resistance was compared against Eurocode 3 buckling curves and the AISC LRFD specification. Results indicate that load application at the top flange, common in purlin-to-beam connections, reduced buckling resistance by 15 to 29 percent relative to centroidal loading, an effect underestimated by the simplified Eurocode 3 beam approach. End restraint conditions provided by typical industrial column-rafter connections were confirmed to achieve an effective length factor of approximately 0.8 relative to the pin-pin case, consistent with the Eurocode 3 sway buckling mode recommendation. A design chart series is proposed for practical beam selection by Nigerian structural engineers designing industrial facilities, incorporating load height correction factors calibrated against the parametric FE dataset. Keywords: lateral-torsional buckling, steel beams, industrial frames, Kano State, Eurocode 3.