Nonlinear Material Behavior of the Bridge Components - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 62

solving uncoupled quasistatic thermoplastic problems in perforated plates. In
their analysis, a transient thermal stress problem was solved for an infinite
plate containing two elliptic holes with prescribed temperature. An exten-
sive survey of the aforementioned numerical investigations was presented by
Ding [ 2.26 ] . However, to date, the effect of residual stresses on the structural
behavior and strength of the components of steel and steel-concrete com-
posite bridges was not fully understood, which is addressed in this topic.
Residual stresses and their distribution are very important factors affecting
the strength of axially loaded steel members. These stresses are of particular
importance for slender columns, with slenderness ratio varying from approx-
imately 40-120. 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 pres-
ence of residual compression stresses. The stiffness will reduce and become a
function of the part of the cross section that is still elastic. 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. Figure 2.4 shows typical residual stress distributions in hot-rolled
and built-up I-sections. It can be seen that although both cross sections are I-
shaped sections, welding and cutting of plates of the built-up sections result in
differences in the distributions of residual stresses in both sections.
2.3 NONLINEAR MATERIAL PROPERTIES OF CONCRETE
2.3.1 General
Understanding nonlinear material behavior of concrete is quite important in
designing and finite element modeling of steel-concrete composite bridges
investigated in this topic. As a material composition, plain concrete is a com-
posite material comprising a mixture of coarse and fine aggregates, cement,
water, and additions. Numerous design approaches are available in the liter-
ature that can be effectively used to provide the mix proportions that produce
plain concrete with a target strength, workability, permeability, etc. It should
be noted that explaining these design approaches is outside the scope of this
book. However, the nonlinear material properties of plain concrete required
for designing and finite element modeling of steel-concrete composite bridges
are highlighted in this topic. Plain concrete behaves completely different
when subjected to compressive and tensile stresses. Plain concrete is a brittle