European Association for Earthquake Engineering ( EAEE )
Abstract
The deformation performance of the base cross sections of reinforced concrete buildings is
fundamental when large seismic events occur allowing the structure to have large excursions in
nonlinear field and guaranteeing an overall ductile behaviour.
It is well known that the axial force acting on columns significantly reduces the curvature capacity of
the sections and for this reason the technical codes give design criteria stating a limitation in order to
preserve the displacement capacity. It is also recognized that when biaxial bending occur the cross
section undergo a loss in strength capacity. Starting the study of from Bresler (1960), which provided
suitable expression to predict 3D limit interaction surfaces, several numerical and analytical models
were developed to take into account the biaxial interaction in strength.
Simultaneously it is noteworthy to point out that the presence of biaxial bending also influences the
deformation capacity of sections causing in most of the cases a relevant loss of the curvature and
ductility available with respect to the one owned along the principal axes. This important issue is not
faced by technical codes and not exhaustively treated in scientific literature as it was done for strength.
Moreover nonlinear structural models based on lumped plasticity do not take into account these
interaction aspects when defining plastic hinge properties in terms of curvature capacity.
The paper presents a numerical study in which the deformation capacity of RC cross sections
subjected to axial load and biaxial bending is investigated by means of a fiber discretization.
A procedure for the numerical definition of biaxial domains of ultimate curvature, yielding curvature
and curvature ductility is provided and the sensitivity of the biaxial deformation performance to some
geometrical and mechanical parameters (aspect ratio, concrete strength and confinement efficacy) is
discussed.The deformation performance of the base cross sections of reinforced concrete buildings is
fundamental when large seismic events occur allowing the structure to have large excursions in
nonlinear field and guaranteeing an overall ductile behaviour.
It is well known that the axial force acting on columns significantly reduces the curvature capacity of
the sections and for this reason the technical codes give design criteria stating a limitation in order to
preserve the displacement capacity. It is also recognized that when biaxial bending occur the cross
section undergo a loss in strength capacity. Starting the study of from Bresler (1960), which provided
suitable expression to predict 3D limit interaction surfaces, several numerical and analytical models
were developed to take into account the biaxial interaction in strength.
Simultaneously it is noteworthy to point out that the presence of biaxial bending also influences the
deformation capacity of sections causing in most of the cases a relevant loss of the curvature and
ductility available with respect to the one owned along the principal axes. This important issue is not
faced by technical codes and not exhaustively treated in scientific literature as it was done for strength.
Moreover nonlinear structural models based on lumped plasticity do not take into account these
interaction aspects when defining plastic hinge properties in terms of curvature capacity.
The paper presents a numerical study in which the deformation capacity of RC cross sections
subjected to axial load and biaxial bending is investigated by means of a fiber discretization.
A procedure for the numerical definition of biaxial domains of ultimate curvature, yielding curvature
and curvature ductility is provided and the sensitivity of the biaxial deformation performance to some
geometrical and mechanical parameters (aspect ratio, concrete strength and confinement efficacy) is
discussed