Nonlinear Material Behavior of the Bridge Components - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 60

2.2.6 Weather Resistance
As mentioned previously, steel grades with the “W” suffix used in the United
States are called “weathering steels” since they are developed for increased
weather resistance, such as corrosion resistance. Weathering steels form a thin
iron oxide filmon the surface when exposed to damp environment, which acts
as a coating that resists any further rusting. Weathering steels can be used in
bridge structures without special paints. Compared to normal steel grades,
weathering steel grades provide around 3 corrosion resistance. However,
this is greatly dependent on the severity of environment conditions. In the
United States, the ASTMG101 [ 2.19 ] specification proposed a methodology
for classification of steels as weathering. The specification proposed a corrosion
index (I) based on the chemical composition of the steel. The ASTM A709
[ 2.1 ] specification indicates that steel grades with I 6 can be classified as
weathering steels indicated by the W suffix to the grade. It should be noted
that although paint coatings for normal steels are commonly used for corrosion
resistance, other options such as galvanizing steel may be effectively used. All of
the A709 bridge steels are suitable for use with any of these coating options.
2.2.7 Residual Stresses
Residual stresses are initial internal stresses existing in cross sections without
the application of an external load such as stresses resulting frommanufactur-
ing processes of metal structural members by cold forming. Residual stresses
produce internal membrane forces and bending moments, which are in static
equilibrium inside the cross sections. The force and the moment resulting
from residual stresses in the cross sections must be zero. Residual stresses
in structural cross sections are attributed to the uneven cooling of parts of
cross sections after hot rolling. Uneven cooling of cross-sectional parts is
subjected to internal stresses. The parts that cool quicker have residual com-
pressive stresses, while parts that cool slower have residual tensile stresses.
Residual stresses cannot be avoided and in most cases are not desirable.
The measurement of residual stresses is therefore important for accurate
finite element modeling of steel and steel-concrete composite bridges.
Extensive experimental investigations were conducted in the literature to
determine the distribution and magnitude of residual stresses inside cross sec-
tions. The experimental investigations can be classified into two main cate-
gories: nondestructive and destructive methods. Examples of nondestructive
methods are X-ray diffraction and neutron diffraction. Nondestructive
methods are suitable for measuring stresses close to the outside surface of cross