Buckling of high-strength steel beams

Abstract

This thesis presents experimental and numerical studies on the instability of I-section beams fabricated from high-strength steel (HSS) plates having yield stresses greater than 690 MPa. The research program contains three major tests including the assessment of residual stresses in welded I-sections, the buckling of I-beams and the lateral-torsional buckling of web-tapered beams. The measurement of residual stresses was undertaken using the neutron diffraction method, based on which a unified residual stress pattern applicable for HSS I-beams is suggested. The second part presents the experiment for buckling behaviour of eight HSS I-beams under scenarios of uniform bending and moment gradient, in which the specimens developed either lateral-torsional buckling or flange local buckling. The buckling capacity so obtained significantly exceeded the predictions of EC3 and of the AS4100, while the ANSI/AISC 360-16 guidelines marginally estimated the buckling resistance of specimens. It was also found that lateral-torsional buckling initiated after partial yielding of the compression flange. The numerical studies consisted of two ABAQUS FE models, being a test simulation model and a generic representation, to facilitate extending the pool of experimental data. A parameter that is dependent on the material properties is introduced in the AS4100 beam buckling strength formula and a new curve for buckling of HSS flexural members is proposed. In the third part, a preliminary experimental study on lateral-torsional buckling of web-tapered HSS I-beams was conducted. Four tapered beams were tested in uniform bending moment and moment gradient loading conditions and all specimens failed in lateral-torsional buckling mode without tensile rupture occurring. The strength of the beams was found to be governed by the interaction of buckling and yielding (inelastic buckling) at the section whose twist displacement was greatest. The buckling moment resistance of specimens noticeably exceeded the predictions of EC3 and AS4100, especially in the case of uniform bending when the smallest tapered cross-section is taken for calculating the nominal section capacity. An ABAQUS FE model for web-tapered beams was developed and subsequent parametric studies were undertaken to elucidate the effects of the tapering topology, residual stresses and flange compactness on the buckling strength of tapered beams.