Towards a practicable GMNIA procedure in the footsteps of the Direct Design Method

Eurocode 3 permits to utilize nonlinear finite element analysis (NFEA) in design process by carrying out Geometrically and Materially Nonlinear Analysis with Imperfections (GMNIA). Design by GMNIA can consider material plasticity and redistribution of forces in a system level such that it can result in an economical design regarding the material consumption. Unfortunately, GMNIA is scarcely adopted among structural engineers, most likely due to the complexity of the method. The determination of the safety factor for GMNIA requires numerical or experimental test results which may not be available for the designed structural system. Recently, a more holistic approach, Direct Design Method (DDM), has been introduced. In DDM, structural systems are prequalified by determining the system safety factor in advance based on system level reliability studies, thus simplifying the design process for a structural engineer. This study develops a Eurocode-compliant DDM, i.e. practicable GMNIA, for Warren roof trusses. The paper presents the prequalification process based on three trusses made of cold-formed hollow sections of the steel grade S700. Additionally, modelling techniques are presented for cold-formed hollow sections such that an accurate nominal NFEA model is achieved.