Experimental and Theoretical Analysis for Determining the Maximum Expansion Ratio of Castellated Steel Beams

One of the efficient and cost-effective structural elements is the castellated steel beam (CSB) which can significantly lower building costs. This fact encourages studying the structural behavior of such beams and determining the castellation ability to maximize flexural stiffness while avoiding shear failure. For this purpose, experimental and theoretical investigations were carried out. The experimental work consisted of fabricating and testing six beams with span lengths of 2000 and 1038 mm and expansion ratios of 1.0, 1.25, and 1.50. Meanwhile, the theoretical part included an adopted analytical procedure that produced an unprecedented theory-based formula giving the maximum expansion ratio ( \({\psi }_{{\text{m}}}\) ${\psi }_{\text{m}}$ ), thus determining the nominal flexural strength of any castellated section. On the other hand, the experimental results, which covered a variety of mechanisms and failure modes, including overall flexural failure, shear and compression buckling of the web posts, tearing and inelastic local buckling, and compression buckling of the top tee, confirmed that \({\psi }_{{\text{m}}}\) ${\psi }_{\text{m}}$ should not be exceeded to fully utilize the flexural capacity of CSBs. The formula for \({\psi }_{{\text{m}}}\) ${\psi }_{\text{m}}$ was then graphed for design purposes, and it was found that it relies on three major parameters: loading type factor (Cc), span length (L), and properties of the root section, upon which any castellated section has a distinct ultimate flexural strength. Furthermore, the ultimate flexural strength increases as the loading type factor decreases and the span length increases.