Civil Engineering Reference
In-Depth Information
on the destruction of the state of equilibrium of the residual stresses in the
cross section. In this way, the residual stresses can be measured by relaxing
these stresses. However, it is only possible to measure the consequences of
the stress relaxation rather than the relaxation itself. One of the main
destructive methods is to cut the cross section into slices and measure the
change in strains before and after cutting. After measuring the strains, some
simple analytical approaches can be used to evaluate resultant membrane
forces and bending moments in the cross sections. Although the testing pro-
cedures to determine residual stresses are outside the scope of this topic, it is
important to detail how to incorporate residual stresses in finite element
models. It should be noted that in some cases, incorporating residual stresses
can result in small effect on the structural performance of metals. However,
in some other cases, it may result in considerable effect. Since the main
objective of this topic is to accurately model all parameters affecting the
behavior and design of metal structures, the way to model residual stresses
is highlighted in this topic.
Residual stresses and their distribution are very important factors affect-
ing the strength of axially loaded structural steel members. These stresses are
of particular importance for slender columns, with slenderness ratio varying
from approximately 40 to 120. As a column load is increased, some parts of
the column will quickly reach the yield stress and go into the plastic range
because of the presence of residual compression stresses. The stiffness will
reduce and become a function of the part of the cross section that is still
inelastic. A column with residual stresses will behave as though it has a
reduced cross section. This reduced cross section or elastic portion of the
column will change as the applied load changes. The buckling analysis
and postbuckling calculation can be carried out theoretically or numerically
by using an effective moment of inertia of the elastic portion of the cross
section or by using the tangent modulus. ABAQUS [1.29] is a popular pack-
age that can be used for the postbuckling analysis, which gives the history of
deflection versus loading. The ultimate strength of the column could be then
obtained from this history.
To ensure accurate modeling of the behavior of metal structures, the
residual stresses should be included in the finite element models. Measured
residual stresses were implemented in the finite element model as initial
stresses using ABAQUS [1.29] software. It should be noted that the slices
cut from the cross section to measure the residual stresses can be used to form
tensile coupon test specimens. In this case, the effect of bending stresses on
the stress-strain curve of the metal material will be considered since the
Search WWH ::
Custom Search