An Elastic-plastic (second order) plane frame analysis method for design engineers

The latest edition of the structural steelwork code, BS 5950-1: 20001, requires secondary forces, generated by geometrical changes to a structure under load, to be considered during the analysis and design of ‘sway sensitive’ frames. This paper discusses the fundamental steps required in developing a computerised method for the second order plane frame analyses of steel structures, at any loaded stage up to and including collapse. Design engineers with some knowledge of a personal computer programming language in addition to an understanding of matrix structural analysis, who require a better and more in-depth command of second order effects, can comfortably adopt and develop the procedure to form a useful working tool.
The load deflection characteristics including plastic hinge order and position, in addition to collapse loads, collectively obtained from this method, compare very favourably with those determined both experimentally and theoretically from previously published papers.

John Graham, PhD, BSc, CEng, FIStructE
Engineering Design, Nottinghamshire County Council