Analysis Of Web-post Buckling Performance Of Bolted Castellated Steel Beam At Normal Temperature And In Fire

Castellated steel beams are rolled H-section steel beam or I-section steel beam with regular circular or hexagonal openings along their length,the beams are produced by cutting,dislocation splicing and welding rolled beam sections.Compared with the solid web girder,the castellated steel beam increases the height of the original section,effectively improving the bending stiffness and bending capacity of the beam,while the holes in the web facilitate the arrangement of various piping systems and equipment,reducing the occupation of the building space by the pipelines and minimizing the floor height.The traditional welded castellated steel beam has some problems such as the quality of weld seam is not easy to control and welding residual deformation.In this paper,a new type of bolted castellated steel beam is proposed,avoiding the welding process.The bolting process makes the splicing process more convenient and quick,and the upper and lower T-section beams can be transported separately and assembled on site.The problem of inconvenient transportation of high-section castellated steel beams is solved.In this paper,the solid element finite element model is used to systematically study the mechanical behavior of bolted castellated steel beam at normal temperature.The parameter analysis results show that,considering the influence of the force slip of bolt connections and the pre-tightening force of bolts,in addition to the web-post buckling failure,there are two new failure modes of bolted castellated steel beams:bolt failure,bolt failure and web-post buckling joint failure.In order to avoid these two new failure modes,the number of bolts,the diameter of bolts and the size of overlap area were optimized.Compared with the traditional welded castellated steel beam,if the bolts are not destroyed,the failure mode,ultimate bearing capacity and structural deformation of bolted castellated steel beams are basically the same as those of traditional welded castellated steel beams.The two parameters of the hole spacing and the web thickness have a great influence on the web-post buckling capacity.Increasing the hole spacing or web thickness can significantly increase the web-post buckling capacity of castellated steel beam.Based on the study of mechanical properties of bolted castellated steel beams at room temperature,the mechanical properties of castellated steel beams under fire are further analyzed by finite element method.The mechanical properties of castellated steel beams with four web thicknesses at seven different temperatures are considered.The results show that the failure mode of castellated steel beams will be changed with the increase of temperature,and the overall stiffness and ultimate bearing capacity of the castellated steel beam will decrease with the increase of temperature.In addition,the existing "strut" model is used to calculate the web-post buckling capacity of bolted castellated steel beams at ambient temperature and in a fire.The theoretical calculation results are close to the results of finite element analysis.With the increase of the hole spacing and web thickness,the difference between the two gradually decreases,which verifies the applicability of the "strut" model for calculating the web-post buckling capacity of bolted castellated steel beams.