[en] The demand for sustainable constructions increases the importance of composite structures as they lead to slim and
economical solutions with a low self-weight of the structure. The determination of the moment resistance for composite
beams follows the rules stated in EN 1994-1-1. Based on the slenderness c/t of the compressed parts of the steel-section,
composite cross-sections are classified into four cross-section classes. This classification indirectly reflects the rotation
capacity and susceptibility to local buckling. For class 1 and 2 cross-sections, the plastic moment resistance of the crosssection
may be considered. Otherwise, an elastic design (for class 3) or an elastic design considering local buckling effects
(for class 4) is necessary.
If the plastic resistance of the cross-section is assumed, it is considered that each cross-section fibre may plastify without
limitation of the strain values. For normal composite beams subjected to the sagging moments and with a high plastic
neutral axis, the real moment resistance is quite greater than one obtained by the method of the plastic design. For sections
with a large compression zone, xpl, a concrete failure in the compression zone can happen before the plastic moment
resistance of the composite cross-section, Mpl,Rd, is reached. Strain limit design, therefore, becomes critical. EN 1994-1-1
provides a limitation of the plastic design resistance only for sections with steel grades S420 and S460. However, there
is no guidance given for lower steel grades or the determination of the corresponding concrete compression force.
This paper points out, that the rotation capacity of a composite section is dependent on the slenderness of steel crosssection
parts and on the behaviour of the concrete part. A comparison of plastic and strain limited moment resistances as
well as the analysis of partial shear diagram-based strain limited design results in new findings for the limits of plastic
design methods.
Disciplines :
Ingénierie civile
Auteur, co-auteur :
SCHÄFER, Markus ; University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Engineering Research Unit
ZHANG, Qingjie ; University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Engineering Research Unit
Co-auteurs externes :
no
Langue du document :
Anglais
Titre :
Particularities for plastic design of composite beams with deep plastic neutral axis
