Investigation On Web-post Buckling Behavior Of Castellated Steel Beam With The Fillet Corner Hexagonal Web Openings In Fire

Castellated steel beams are rolled steel H sections with regular circular or polygonal openings along their length. The beams are produced by cutting and re-welding rolled beam sections. An increase in beam depth provides greater flexural rigidity and strength to weight ratio. The openings allow service integration within the beams depth, which advantageously reduces, indirectly, the height of floors. The use of castellated steel beams has resulted in plant buildings, garages, bridges and longer span floors. In this paper, a novel castellated steel beam with fillet corner hexagonal web openings is proposed. Compared with castellated beams with polygonal openings, the stress concentration at the corner of the hole is reduced. Compared with castellated beams with circular openings, the manufacturing process only needs once cutting. The shear performance of the novel castellated beams is compared with that of traditional castellated beams by means of finite element method. The buckling behavior of the proposed castellated beams is slightly lower than that of castellated beams with circular openings.Different fire protected conditions can affect the temperature distributions in web-posts of castellated steel beams, thus affecting the buckling behavior of beams under shear force in a fire. Temperature distributions in web-posts of fully and partially protected castellated steel beams at elevated temperatures in a fire are investigated through the heat transfer analysis. For the partially protected beams, there are temperature gradients in web-posts along the vertical section and the horizontal section, which is due to the hole edge being left unprotected. The fire resistance time of fully protected beams increased linearly with the increase in fire coating thickness. However, for the partially protected beams, the fire resistance time cannot be effectively prolonged by increasing the thickness of fire protection when the thickness is more than 30mm.Web-post buckling behaviors of castellated steel beams with fillet corner web openings at ambient temperatures and elevated temperatures are investigated through the finite element method. A modified strut theoretical model is proposed for calculating the shear buckling capacity of castellated beams at ambient temperatures and the critical temperature at web-post buckling failure of castellated beams at elevated temperatures. The main parameters of opening distance and web thickness are studied in the present paper. The effective width and compressive force of the strut are modified based on the parametrical analyses. The modified strut model can relatively accurately calculate the critical bucking stresses of the web-post both at ambient temperatures and elevated temperatures. The design system on web-post buckling failure of castellated steel beams in a fire is be perfect, which provides evidence for design of castellated beams at ambient temperatures and elevated temperatures.