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.
J. B. P. Lim, BEng, PhD, CEng, MICE
The Steel Construction Institute
C. M. King, BSc, MSc, DIC, CEng, MIStructE
The Steel Construction Institute
A. J. Rathbone, BEng, CEng, FICE
CSC (UK) Ltd.
J. M. Davies, BSc, PhD, DSc, FREng, FIStructE, FICE
The University of Manchester
V. Edmondson, BSc, MEng, CEng, MICE
The University of Manchester