Fiber beam-columns models with flexure-shear interaction for nonlinear analysis of reinforced concrete structures
Creators: name: Cardinetti, Filippo <1980>
Publisher: name: Alma Mater Studiorum - Università di Bologna
Year: 2011
Subjects: ICAR/09 Tecnica delle costruzioni

description: The aim of this study was to develop a model capable to capture the different contributions
which characterize the nonlinear behaviour of reinforced concrete structures. In particular,
especially for non slender structures, the contribution to the nonlinear deformation due to
bending may be not sufficient to determine the structural response. Two different models
characterized by a fibre beam-column element are here proposed. These models can
reproduce the flexure-shear interaction in the nonlinear range, with the purpose to improve
the analysis in shear-critical structures. The first element discussed is based on flexibility
formulation which is associated with the Modified Compression Field Theory as material
constitutive law. The other model described in this thesis is based on a three-field
variational formulation which is associated with a 3D generalized plastic-damage model as
constitutive relationship.
The first model proposed in this thesis was developed trying to combine a fibre beamcolumn
element based on the flexibility formulation with the MCFT theory as constitutive
relationship. The flexibility formulation, in fact, seems to be particularly effective for
analysis in the nonlinear field. Just the coupling between the fibre element to model the
structure and the shear panel to model the individual fibres allows to describe the nonlinear
response associated to flexure and shear, and especially their interaction in the nonlinear
field. The model was implemented in an original matlab® computer code, for describing
the response of generic structures. The simulations carried out allowed to verify the field of
working of the model. Comparisons with available experimental results related to
reinforced concrete shears wall were performed in order to validate the model. These
results are characterized by the peculiarity of distinguishing the different contributions due
to flexure and shear separately. The presented simulations were carried out, in particular,
for monotonic loading. The model was tested also through numerical comparisons with other computer programs. Finally it was applied for performing a numerical study on the
influence of the nonlinear shear response for non slender reinforced concrete (RC)
members.
Another approach to the problem has been studied during a period of research at the
University of California Berkeley. The beam formulation follows the assumptions of the
Timoshenko shear beam theory for the displacement field, and uses a three-field
variational formulation in the derivation of the element response. A generalized plasticity
model is implemented for structural steel and a 3D plastic-damage model is used for the
simulation of concrete. The transverse normal stress is used to satisfy the transverse
equilibrium equations of at each control section, this criterion is also used for the
condensation of degrees of freedom from the 3D constitutive material to a beam element.
In this thesis is presented the beam formulation and the constitutive relationships, different
analysis and comparisons are still carrying out between the two model presented.