Eurocode-compliant system safety factor for advanced design of hollow section Warren trusses

Abstract

Eurocode allows for the design of structural systems by advanced analysis, i.e. by Geometrically and Materially Nonlinear Imperfection Analysis (GMNIA). In GMNIA, the entire structural system is designed by carrying out a nonlinear finite element analysis and by comparing the load proportionality factor obtained from the analysis to the predetermined system safety factor. This study determines the required Eurocode-compliant GMNIA system safety factor for the ultimate limit state design of Warren-type roof trusses. The system safety factor is determined based on system-level reliability studies conducted for 15 trusses. The investigated trusses are made of cold-formed rectangular hollow sections having a nominal yield strength of 700 MPa. The determined system safety factor is then applied for comparison calculations, in which three trusses are designed both by GMNIA and the conventional EN 1993-1-1 method. This comparison reveals a need for an accurate modelling method of hollow section connections in GMNIA. Furthermore, the comparison shows that GMNIA can offer reduced material consumption compared to the conventional method even in roof trusses, in which load redistribution capabilities are very limited. This reduction is achieved due to capability of GMNIA to accurately capture the buckling capacities of continuous top chords, whereas the conventional method must rely on conservative approximations of buckling lengths.