The right choice of steel – according to the Eurocode - Economical Bridge Solutions based on Innovative Composite Dowels and Integrated Abutments - page 10

The right choice of steel - according to the Eurocode

Oliver Hechler 1 , Georges Axmann & Boris Donnay 2

Keywords: steel, production, steel grade, material properties, ductility, toughness, weldability.

Abstract: In general, the choice of the steel grade is ruled in Eurocode EN 1993-1-1.
Several requirements are specified: choice according to the material properties, ductility
requirements, toughness properties and through-thickness properties. With reference to
these requirements on the mechanical characteristics, modern hot-rolled structural sections
are produced by precise control of the temperature during the rolling process. Fine grain
steels, produced using thermomechanical rolling (delivery condition M according to EN
10025-4), feature improved toughness values which give a lower carbon equivalent and
a fine microstructure when compared with conventional or normalised steels. This paper
gives guidance on and background to the right choice of the steel grade according to the
Eurocode. Furthermore, the influence of the production process on this choice is highlighted
and the advantages of thermomechanical steels for each criterion are discussed.

1. Introduction

Eurocode 3 [1] applies to the design of buildings and civil engineering works in steel. It
complies with the requirements and principles for the safety and serviceability of structures,
the basis of their design and verification that are given in EN 1990 - Basis of structural de-
sign. Requirements are provided for resistance, serviceability, durability and fire resistance of
steel structures. These are based on the principle of limit state design, which mainly assumes
that the resistance of cross-sections and members specified for the ultimate limit states are
based on tests in which the tolerances are met according to EN 1090-2 [2], and the material
exhibited sufficient ductility to apply simplified design models. Therefore, the material prop-
erties, for steel the steel grade, have to be specified in detail to comply with the safety level
of Eurocode 3 (“Fig. 1”).
These simplified design models and the safety concept of the Eurocode are based on
tests at ambient temperature, for which ductile failure occurs as the steel is on the upper
shelf region with sufficient toughness. In Fig. 2 (left), the conclusions from testing for the
partial safety factors and the characteristic strength are shown. If brittle fracture takes place,
the assumptions for the design models and the safety concepts are no longer met (“Fig. 2”,
right). Consequently, failure against brittle fracture must be accounted for with an appropri-
ate choice of steel with sufficient toughness.