Applicable Equivalent Bow Imperfections in GMNIA for Eurocode Buckling Curves – in Case of Box Sections

Abstract

The flexural buckling resistance of compressed columns is typically determined using the flexural buckling curves of EN1993‐1‐1. With advances in computing capabilities, it has become possible to obtain the flexural buckling resistance as a result of a geometrically and materially nonlinear analysis (GMNIA) using imperfections. In design practice, equivalent geometric imperfections are usually used, but their values are calibrated against GNIA analysis. In the present research work, welded box‐section columns are investigated and a proposal for relative slenderness and yield strength dependent equivalent geometric imperfection magnitudes is developed. The required equivalent bow imperfection magnitude is determined to achieve the same resistance level as the calculation according to Eurocode‐based buckling curves. GMNIA analysis are conducted on simply supported columns subjected to concentrated force. The steel grade varied between S235 and S960. Several different section geometries are studied, the relative slenderness ratio is varied between 0.3 and 2.2. Design curve is fitted to the results and recommendation is given for applicable equivalent geometric imperfection magnitudes for steel welded box‐section columns.

Imperfections for Local and Global Interaction Buckling of Welded Square High-strength Steel Box-section Columns

“…Hence, this local imperfection is used here in the parametric study. For global imperfections, the formula developed by Somodi et al [9,30] is used for the global buckling imperfection scaling factor according to Eq. ( 1).…”

“…The global imperfection used in the developed combination is L/1000, a widely agreed-upon imperfection if the residual stresses are applied [2]. Equivalent global imperfections suitable for GMNIA analysis were recently developed by Somodi et al [9] for global buckling resistance. For interaction buckling, the authors developed equivalent imperfection combinations for welded square box-sections made of normal strength steel (NSS) [10].…”

“…Somodi et al [9] calibrated equivalent global imperfections based on EN1993-1-1 [8] buckling curves using a parametric study and GMNI analysis. An equivalent imper-fection formula, denoted as L/f glob , was proposed.…”