Nonlinear Material Behavior of the Bridge Components - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 57

Table 2.5 Nominal Values of Yield Strength f y and Ultimate Tensile Strength f u — cont'd

Nominal Thickness of the Element t (mm)

t £ 40 mm 40 < t £ 80 mm

f y (MPa) f u (MPa) f y (MPa) f u (MPa)

Standard and Steel Grade

S275 NH/NLH 275 370

S355 NH/NLH 355 470

S460 NH/NLH 460 550

S275 MH/MLH 275 360

S355 MH/MLH 355 470

S420 MH/MLH 420 500

S460 MH/MLH 460 530

Table 2.6 Nominal Values of the Yield Strength f yb and the Ultimate Tensile Strength
f ub for European Bolts Specified in EC3 [1.27]
Bolt grade 4.6 5.6 6.8 8.8 10.9

f yb (N/mm 2 ) 240 300 480 640 900

f ub (N/mm 2 ) 400 500 600 800 1000

2.2.3 Ductility
Steel ductility is the capacity of steel material to undergo large strains after
the onset of yielding and before fracture, which provides an advance warn-
ing of possible failure. For steel products, relative ductility is measured as the
percent elongation that occurs before rupture in a standard tensile coupon
test. The percent elongation is dependent on the test specimen geometry and
the gauge length used to measure elongation during tensile coupon test. In
the United States, for the same material, tension specimens with a 2 in.
(50.8 mm) gauge length will exhibit a lower percent elongation compared
to those with an 8 in. (203.2 mm) gauge length. The ASTM A709 [ 2.1 ]
specification specifies that structural steel for bridges has an adequate level
of material ductility to perform well in structural applications. Steel material
ductility is different from structural steel connections and overall structural
ductility. For example, a steel member may be ductile on its own; however,
if there are holes in the cross section, it may undergo brittle failure behavior.
The yield-tensile stress ratio (YT ratio) defined as YT ¼f y / f u can provide a
reasonable measure to steel ductility. However, for steels specified in the
A709 [ 2.1 ] specification, there is no need for special consideration of the
YT ratio for most bridge structural applications.