Elastic bubble augmented spline finite strip method in analysis of continuous composite beams

Local and overall instabilities of the steel beam occur in the hogging-moment region in a\ud continuous composite beam (Figure 1) and these\ud forms of buckling have been recognised to be\ud highly interactive. The overall mode of buckl\ud ing in composite steel-concrete tee-beams in\ud regions of negative bending is what is herein te\ud rmed restrained-distortio\ud nal buckling (RDB). In\ud negative bending the slab restrains the tension re\ud gion of the steel and the neutral axis is not\ud located at the mid-height of the web. The neutra\ud l axis is shifted towards the top/tension flange,\ud and in negative bending the steel region is subjected to predominantly compressive loading. In\ud addition, the web usually carries\ud proportionally higher shear loads than in ordinary steel beams.\ud The lateral-distortional buckling resistance of th\ud e steel portion in continuous composite beams is\ud therefore dependent on the extent to which the web can provide a restraining action to the\ud unstable compression flange. Although buckling of plain steel beams in both the elastic and\ud inelastic ranges of structural response has been\ud studied extensively and a great deal of research\ud work has been devoted to the understanding of their buckling modes, and codes of practice for\ud the design of structural steelwork contain relevant\ud clauses that presently are considered to be\ud quite accurate, buckling of the steel component in\ud composite beams still repr\ud esents a grey area in\ud structural engineering research and is much less well documented. The bubble augmented spline\ud finite strip method of analysis, developed by the authors, is thus employed herein to study\ud extensively the issue of RDB in composite tee-beams in hogging bending regions