Probabilistic study and numerical modelling of initial geometric imperfections for 3D steel frames in advanced structural analysis

Abstract

Initial geometric imperfections, including member out-of-straightness and frame out-of-plumb, shall be accounted for in the system-based design-by-advanced analysis of steel frames. The effect of considering initial geometric imperfection in planar frames using advanced analysis has been studied using different methods, such as notional horizontal load and direct modelling of imperfections. However, modelling initial geometric imperfections for 3D frames presents additional challenges because the imperfection is spatial and may involve torsion, with random magnitude. This paper presents a procedure for modelling initial geometric imperfections of three-dimensional frames composed of cold-formed hollow structural sections (HSS) or hot-rolled steel I-sections. For I-section steel frames, the linear combination of buckling modes method (LCBM) is used to model the imperfections, and the appropriate number and amplitudes of elastic buckling modes are proposed for sway frames and braced frames. For HSS frames, the notional horizontal load method (NHL) is applied to sway frames, and the corresponding load factors are presented. The LCBM is applied to braced HSS frames, and the scale factors for selected buckling modes are suggested. Moreover, advanced geometric and material nonlinear analyses are conducted on illustrative examples to verify the proposed simulation approach.