EUROCODE 2 WORKED EXAMPLES - Federbeton

EC2 – worked examples 6-49
Table of Content
Fig. 6.38 Relaxation losses in % at 1000 hours for Class 2
σc. : stress on concrete at level of pretensioned steel due to self weight and
permanent load;
σcpo : stress on concrete at level of pretensioned steel due to prestressing;
α �= Es/Ec: modulus of elasticity ratio;
Ap : area of prestressing steel at the considered level;
Ac : area of concrete gross section;
Ic : inertia of concrete gross section;
zcp : lever arm between centroid of concrete gross section and prestressing steel.
Time-dependent losses of prestressing should be calculated for each tendon along his
profile so that a correct value may be used for each element. As a reference, the maximum
value of prestressing losses, as percentage of initial steel tension, turn out:
longitudinal tendon: 19% at anchorage and 14% at pier axis;
transverse tendon: 18% at anchorage and 12% at midspan.
The effects of losses are taken into account with the same procedure used for the
prestressing, but as actions of opposite sign.
6.15.2 Actions
The external loads applied on the structure should be evaluated according to the provisions
of Eurocode 1.3 Traffic Load on Bridges. As vertical train load the load model LM71 plus
the load models SW (SW/0 and SW/2 respectively) have been adopted with an α
coefficient of 1.1. For the LM71, the 4 point loads have been reduced in an equivalent
uniform load by smearing their characteristic value Qvk along the influence length so that a
qvk,1 may be obtained:
Qvk = 1.1×250×φdin = 319.6 kN → qvk,1 = 319.6/1.6 = 199.75 kN/m