Elastic torsional mechanical properties of ortho-octagonal steel plate web beam

Steel structures are extensively used in bridge engineering because of their exceptional performance, and bridge structures with novel appearances keep appearing. This paper proposes a new ortho-octagonal steel plate web beam similar to a cellular beam structure. The web is composed of octagonal units, which reduce the structural deadweight and support energy conservation objectives in steel bridge design. In this work, an ortho-octagonal steel plate web girder was designed and fabricated. Its stress distribution in the top and web plates was investigated using a restrained torsion test. The stress distribution pattern of the octagonal steel plate main girder was also analyzed using the finite element method. Furthermore, a parametric analysis of the finite element model was performed to investigate the effects of web spacing, plate thickness, and circular hole radius on the stresses in the top, bottom, and web plates. Based on equivalent stiffness theory, an analytical formula was developed for determining the equivalent web thickness under restrained torsion. Results demonstrate that the ortho-octagonal web serves as diagonal tension–compression members during torsion. Increasing web plate thickness and reducing circular hole radius effectively decrease stresses in the web and flanges, while enhancing the torsional moment of inertia. The proposed analytical model shows strong agreement with FEA results, with errors below 10%.