Lateral-torsional buckling of haunched members in portal frames : an assessment of BS 5950 (part 1)
The research described in this thesis, relates mainly to the current method of design of steel portal frame structures. The study is divided into two major parts, first being the full-scale test on a 24 metre span frame and the second deals with the problems of lateral-torsional buckling in the haunch region of the frame. Detailed accounts of the full-scale testing on the 24 metre span frame and the experimental results are given. Supplementary tests on beams cut out from the tested frame in order to establish the strain-hardening factor are also presented. A literature survey on the published material pertinent to the lateral torsional-buckling of a tapered member was undertaken. Different methods of treatment for the elastic stability of tapered members and any evidence from previous research in this area were reviewed. Details of an appropriate finite element and the corresponding computer programme are given. This section describes the assumptions and the Finite Element formulations adopted in the computer programme. The earlier work on this analysis dealt only with prismatic members and this was extended to solve tapered sections. Therefore, a full calibration of the finite element formulation for a tapered member was carried out. The stability clauses in BS 5950 are introduced systematically. Theoretical work which leads to the formulation of the clauses in Appendix G is also described. These stability clauses were assessed by the analysis of selected prismatic and tapered members using the finite element formulation. From this assessment some modifications to the clauses are proposed. The results of the modified clauses are compared with those given by the finite element analysis and the original clauses. Lastly, the modified clauses are checked with the results of the portal frame tested, to confirm its validity. This study leads to the proposal for some amendments in the clauses in Appendix G and Clause 220.127.116.11. of BS 5950.