Lateral Torsional Buckling of Partially Concrete Encased Steel I Beams

In this study, the lateral torsional buckling (LTB) of a partially concrete-encased steel I beam (PCEB) is investigated numerically, and the buckling curve for laterally unrestrained PCEB is found. The concrete encasement improves the beam resistance against LTB, which benefits a steel I beam under construction. A few experimental studies on the LTB of PCEB are found in the literature. However, more studies are needed to understand PCEB behaviour comprehensively, and experiments will become expensive. Therefore, numerical studies are conducted to investigate the post-buckling behaviour of a simply supported laterally unrestrained PCEB. The torsional and warping stiffness of the PCEB is higher than the bare I steel beam, which is evident from enhanced moment capacity. In PCEB, unlike bare steel sections, thinner flanges and webs are more efficient in LTB resistance. LTB is not found in PCEB for a large slenderness range as the concrete encasement makes PCEB behave like a closed cross-section. No moment reduction due to LTB is found for non-dimensional slenderness ratios less than 0.55, whereas for bare steel I beam, this value is about 0.4. Hence, the partial concrete-encasement can shift the steel I beam’s failure mode from elastic member buckling to cross-sectional yielding.