Eurocode 3 and the in-plane stability of portal frames

Simple design rules are proposed that will enable engineers to take into account in-plane stability when designing single-storey steel portal frames plastically to Eurocode 3, without the need to resort to second-order elastic-plastic analysis software. The proposed design rules, developed from the results of a parametric study of different types of frame, are based on the Merchant-Rankine reduction method and take into account a modest amount of benefit from strain-hardening. A simple hand method for estimating the elastic critical load, required for calculating the Merchant-Rankine reduction, is also presented. From the results of the parametric study, the proposed design rules place frames into one of two categories: • Category A: Regular, symmetric and mono-pitched frames • Category B: Frames that fall outside of Category A but excluding tied portals For each category of frame, a reduction factor based on the Merchant-Rankine reduction method is proposed.