Numerical studies on large deflection behaviors of restrained castellated steel beams in a fire

• Catenary actions of restrained Castellated Steel Beams in a fire are presented.
• Compression forces in restrained CSBs are smaller than those in solid beams.
• CSBs go into catenary action at lower temperatures compared with solid beams.
• Opening shapes have little influences on the catenary action of a restrained CSB.

Large deflection behaviors of the restrained castellated steel beam (CSB) in a fire are investigated using the finite element method. Studied CSBs adopted a newly proposed fillet corner polygonal web opening shape. The capability of the finite element model is validated against verified numerical results on solid web restrained steel beams at elevated temperatures in a fire. Studied parameters of the castellated steel beam include the expansion ratio, the web opening dimension, the web opening shape, the arrangement of the web opening and the elastic axial restraint to the beam. The evolution of the end reaction force, the middle span deflection, and bending moments at critical sections of the CSB with the elevation of temperatures are presented. For the axial stiffness of a CSB is smaller than that of the original solid web steel beam, the compression force due to the restrained thermal elongation in a CSB in a fire is lower than that in the solid web beam. And the CSB goes into the catenary action phase at a lower temperature compared with the solid web steel beam. The web opening dimension, the web opening shape and the arrangement of web opening have very little influences on the catenary action behaviors of the restrained castellated steel beam in a fire.