Torsional behaviour of hollow steel double web I-section beam

All across the world, there is an increasing demand for steel structures. It is used for multi-story buildings and long-span bridges. These steel materials are of certain standards of chemical composition and proper strength. This research investigates the torsional behavior of the hollow steel double web I-section beam. This research studied the effect of the depth ratio on the web or flange thickness for four beams of hollow sections. The experimental results indicated that a decrease in the depth-to-web thickness ratio (D/tw) from 63.33 to 47.5 in hollow steel sections leads to increasing in the torsional capacity by(51.2% - 52.5%), rotation angle at a rate (42.2%-43%), ductility at a rate (82.3% - 91%), and stiffness at a rate (7.2% - 7.8%), also The results indicated that reduced the depth ratio on flange thickness (D/tf) from 47.5 to 31.66 leads to very little increase in ultimate torsional strength, ultimate rotation, and ductility by (0.4% - 1.3%), (2.1% - 2.6), and (1.2% - 3.5%) respectively. This means that the increase in web thickness has a noticeable effect on the ultimate torsional capacity and rotation angle of steel tubes compared to the increase in flange thickness.