Nonlinear Material Behavior of the Bridge Components - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 81

the prestressing tendons shall have adequate ductility, as specified in EN
10138 [ 2.30 ] . Adequate ductility in elongation may be assumed if the pre-
stressing tendons obtain the specified value of the elongation at maximum
load given in EN 10138. Adequate ductility in tension may be assumed
for the prestressing tendons if f pk / f p0.lk k . The value of k specified in
EC2 is 1.1. EC2 also specifies that prestressing tendons shall have adequate
fatigue strength. The fatigue stress range for prestressing tendons shall be in
accordance with EN 10138 [ 2.30 ] . Structural analysis is performed on the
basis of the nominal cross-sectional area of the prestressing steel and the char-
acteristic values f p0.lk , f pk , and e uk . The design value for the modulus of elas-
ticity, E P , may be assumed equal to 205 GPa for wires and bars. The actual
value can range from 195 to 210 GPa, depending on the manufacturing pro-
cess. The design value for the modulus of elasticity, E P , may be assumed
equal to 195 GPa for a strand. The actual value can range from 185 to
205 GPa, depending on the manufacturing process. The mean density of
prestressing tendons for the purposes of design may normally be taken as
7850 kg/m 3 . The values given earlier may be assumed to be valid within
a temperature range between 40 and +100 C for the prestressing steel
in the finished structure. The design value for the steel stress, f pd , is taken
as f p0.lk / g S (see Figure 2.13 ). For cross-sectional design, either an inclined
branch with a strain limit e ud or a horizontal top branch without strain limit
can be utilized. The design may also be based on the actual stress-strain rela-
tionship, if this is known, with stress above the elastic limit reduced analo-
gously (see Figure 2.11 ) . It should be noted that, according to EC2, the
recommended value for e ud is 0.9 e uk . If more accurate values are not known,

s Idealized

f pk

f pk / g s

f 0.1pk

f pd = f p0.1k / g s

Design

e

e ud

f pd / E p e uk

Figure 2.13 Idealized and design stress-strain diagrams for prestressing steel specified
in EC2 [ 2.27 ] .