Lateral-torsional buckling strength of castellated beams
A review of the research carried out on the subject of castellated beams revealed that one subject had remained largely untouched — lateral stability. This was despite the fact that the fabrication process had increased their strength and rigidity about the , plane of loading at the expense of lateral stiffness. This emphasis on in—plane behaviour stemmed from the need to catalogue the failure modes particular to castellated beams. However because of the high number of parameters necessary to describe a castellated beam and their high degree of internal redundancy, little that can be regarded as firm design recommendations and no provisions against lateral buckling have been included in national codes of practice, particularly in the present British codes. This is why the draft of the new British code for structural steelwork 8/20 to be published as BS 5950 suggests the use of the simple Vierendeel analogy for in—plane behaviour and has adopted the conservative approach of 0..11.3.2 to the prevention of lateral buckling in which the contribution of the web and tension flange are ignored. The work undertaken herein had the aim of mainly providing the missing quantitative data on the lateral —torsional buckling strength of castellated sections currently available in the U.K. Eight full size castellated beams were tested. The results of these plus the few cases reported in the literature were used as a basis for a critical evaluation of several design approaches. Comparisons between the test results and the strength predicted by B/20 were found to be generally acceptable provided cross— sectional properties at a castellation were used in the calculations. Similar results were obtained for the two — stage procedure of BS 449 and BS 153 whereas the use of Table 3 in the former was shown to lead to rather low load factors. A preliminary test programme on small scale beams showed the negligible effect that the holes had on lateral buckling behaviour. Finally a computer program which was used to calculate a value of elastic critical load confirmed that the web post did not distort when the beams failed.