Civil Engineering Reference
In-Depth Information
surface fluxes; node-based film and radiation conditions; average-
temperature radiation conditions; and element- and surface-based film
and radiation conditions. In addition, mechanical loads that can be pre-
scribed to the analysis comprise concentrated nodal forces, which can be
applied to the displacement degrees of freedom (1-6), as well as distributed
pressure forces or body forces. Predefined temperature fields are not allowed
in a fully coupled thermal-stress analysis. Boundary conditions should be
used instead to prescribe temperature degrees of freedom 11, 12, 13, etc.,
in ABAQUS (Standard) shell elements. Other predefined field variables
can be specified in a fully coupled thermal-stress analysis. These values will
affect only field-variable-dependent material properties. The materials in a
fully coupled thermal-stress analysis must have both thermal properties, such
as conductivity, and mechanical properties, such as elasticity, defined. Ther-
mal strain will arise if thermal expansion is included in the material property
definition.
Coupled temperature-displacement elements that have both displace-
ments and temperatures as nodal variables are available in both ABAQUS
(Standard) and ABAQUS (Explicit). In ABAQUS (Standard), simultaneous
temperature/displacement solution requires the use of such elements; pure
displacement elements can be used in part of the model in the fully coupled
thermal-stress procedure, but pure heat transfer elements cannot be used.
In ABAQUS (Explicit), any of the available elements, except Eulerian
elements, can be used in the fully coupled thermal-stress procedure;
however, the thermal solution will be obtained only at nodes where the
temperature degree of freedom has been activated. The first-order coupled
temperature-displacement elements in ABAQUS use a constant tempera-
ture over the element to calculate thermal expansion. The second-order
coupled temperature-displacement elements in ABAQUS (Standard) use
a lower-order interpolation for temperature than for displacement (parabolic
variation of displacements and linear variation of temperature) to obtain a
compatible variation of thermal and mechanical strain.
5.7 MODELING OF INITIAL IMPERFECTIONS AND RESIDUAL
STRESSES
Most structural steel members have initial geometric imperfections as a result
of the manufacturing, transporting, and handling processes. Initial geometric
imperfections can be classified into two main categories, which are local
and overall (bow, global, or out-of-straightness) imperfections. Initial local
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