Civil Engineering Reference
In-Depth Information
Materially nonlinear analysis (with or without consideration of geo-
metric nonlinearity) of metal structures is done to determine the overall
response of the bridges and bridge components. From a numerical view-
point, the implementation of a nonlinear stress-strain curve of a construc-
tion metal material involves the integration of the state of the material at an
integration point over a time increment during a materially nonlinear anal-
ysis. The implementation of a nonlinear stress-strain curve must provide an
accurate material stiffness matrix for use in forming the nonlinear equilib-
rium equations of the finite element formulation. The mechanical consti-
tutive models associated with bridge components consider elastic and
inelastic response of the material. In the inelastic response models that
areprovidedinABAQUS[1.29],theelastic and inelastic responses are dis-
tinguished by separating the deformation into
recoverable
(elastic) and
non-
recoverable
(inelastic) parts. This separation is based on the assumption that
there is an additive relationship between strain rates of the elastic and
inelastic parts. The constitutive material models used in most available
general-purpose finite element computer programs are commonly
accessed by any of the solid or structural elements previously highlighted
in
Section 5.2
.
This access is made independently at each constitutive cal-
culation point. These points are the numerical integration points in the
elements. The constitutive models obtain the state at the point under con-
sideration at the start of the increment from the material database specified
in the step. The state variables include the stresses and strains used in the
constitutive models. The constitutive models update the state of the mate-
rial response to the end of the increment.
Geometrically nonlinear analysis is a general nonlinear analysis step. The
analysis can be also called as
load-displacement nonlinear geometry analysis
. The
initial overall and local geometric imperfections, prestressing, and residual
stresses can be included in the load-displacement nonlinear geometry anal-
ysis. If the stress-strain curve of the construction metal material is nonlinear,
the analysis will be called as
combined materially and geometrically nonlinear anal-
ysis
or
load-displacement nonlinear material and geometry analysis
. All required
information regarding the behavior of metal structures is predicted from
the combined materially and geometrically nonlinear analysis. The informa-
tion comprised the ultimate loads, failure modes, and load-displacement
relationships as well as any other required data that can be obtained from
the combined materially and geometrically nonlinear analysis. Further
details regarding the materially and geometrically nonlinear analyses can
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