Nonlinear Material Behavior of the Bridge Components - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 48

are required to meet strength and ductility requirements for all structural
applications. However, bridge steels have to provide adequate service with
respect to the additional fatigue and fracture limit state. They also have to
provide enhanced atmospheric corrosion resistance in many applications
where they are used with normal protective coatings. For these reasons,
structural steels for bridges are required to have fracture toughness and often
corrosion resistance that exceed general structural requirements in building
constructions. Overall, the author aims that this chapter acts as a basis for
designing and finite element modeling of steel and steel-concrete composite
bridges.
2.2 NONLINEAR MATERIAL PROPERTIES OF STRUCTURAL
STEEL
2.2.1 General
The main component of steel and steel-concrete composite bridges inves-
tigated in this topic is structural steel. Understanding the material behavior of
the steel is quite important for designing and finite element modeling of the
bridges. As a material composition, steel contains iron, a small percentage of
carbon and manganese, impurities such as sulfur and phosphorus, and some
alloying elements that are added to improve the properties of the finished
steel such as copper, silicon, nickel, chromium, molybdenum, vanadium,
columbium, and zirconium. The strength of the steel increases as the carbon
content increases, but some other properties like ductility and weldability
decrease. Steel used for bridges can be classified as carbon steels, which come
with yield stresses up to 275 N/mm 2 ; high-strength steels, which cover
steels having yield stresses up to 390 N/mm 2 ; heat-treated carbon steels,
which cover steels having yield stresses greater than 390 N/mm 2 ; and
weathering steels, which have improved resistance to corrosion. Steels used
for bridges should have main properties including strength, ductility, frac-
ture toughness, weldability, weather resistance, and residual stresses. These
properties are briefly highlighted in the coming sections.
2.2.2 Steel Stresses
In the United States, the specifications for plate and rolled shape steels used
for bridges are covered by the ASTM A709 [ 2.1 ] and AASHTO M270
[1.23, 1.24]. Table 2.1 shows the applicable AASHTO and ASTM standards
for steel product categories, while Table 2.2 provides an overview of the
various steel grades covered by the ASTM A709 [ 2.1 ] . The number in