Nonlinear Material Behavior of the Bridge Components - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 59

Table 2.8 Example for Additional Requirement for Toughness of Base Material
Specified in EC3 [1.27]
Example

Nominal Thickness Additional Requirement

T 27J ¼ 20 C in accordance with EN 10025

1 t 30 mm

30 < t 80 mm Fine-grain steel in accordance with EN 10025,

e.g., S355N/M

t > 80 mm Fine-grain steel in accordance with EN 10025,

e.g., S355NL/ML

structure. The specification requires that no further checks against brittle
fracture need to be made if the conditions given in EN 1993-1-10 [ 2.16 ]
are met for the lowest service temperature. EC3 (BS EN 1993-2) [1.27] also
recommends that additional requirements depending on the plate thickness,
with an example given in Table 2.8 , may be adopted.

2.2.5 Weldability
Steel weldability is defined as the ability of steel to be welded to serve its
intended application. In the United States, the AASHTO/AWS D1.5 weld-
ing specifications [ 2.17 ] govern welding of bridge steels. Following the D1.5
provisions, all bridge steels in the A709 [ 2.1 ] specification can be considered
weldable. It should be noted that increasing amounts of carbon and manga-
nese, which are necessary for higher strengths, make the steel harder and
consequently more difficult to weld. Also, the elements added to improve
weathering resistance reduce weldability. In addition, the weldability of
structural steels depends on the chemical composition. Graville [ 2.18 ]
showed that the tendency of a heat-affected zone (HAZ) to crack depends
on the carbon content and the carbon equivalent (CE) calculated using
Equation (2.4) as recommended by the Bridge Welding Code D1.5, which
considers other alloying elements in addition to carbon:
CE ¼ C+ Mn + Si
6

+ Ni +Cu
15

+ Cr +Mo +V
5

ð 2 : 4 Þ

where C, Mn, etc., represent the percentage of the element concerned in the
chemical composition of the steel. To obtain higher yield stresses, the
percentage content of the various alloying elements is increased leading
to the increase of the carbon equivalent value. Therefore, welding of
higher-strength steels is more difficult compared with normal-strength
steels. Specifications sometimes limit maximum values for carbon equiva-
lent. Steels with carbon equivalent values higher than 0.53 should have spe-
cial measures in welding.