PSI - Issue 54

Maricely De Abreu et al. / Procedia Structural Integrity 54 (2024) 143–148 De Abreu M. et al / Structural Integrity Procedia 00 (2023) 000 – 000

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Table 1 gives the mechanical properties derived from the tensile tests, which show the steel homogeneity and exclude any alteration of the wires beyond its outer layer exposed over time to potentially aggressive environments. The tensile strength and the yield strength of the tested steel slightly exceed the respective properties of the current prestressing steel Y1770 (1770 and 1560 MPa) and approach those of the steel strand Y1860C (1860 and 1650 MPa). Likewise, the maximum uniform elongation and area reduction measured in the tests surpass the respective thresholds of 3.5% and 25% specified by prEN 10138-2 (2009). Lastly, the elastic modulus values are within the limits of the unalloyed ferritic-pearlitic steels and close to the standard data of 205 GPa that current prEN 10138-2 (2009) recommends using as a design value.

Table 1. Mechanical properties the tested strand-wires steel.

Specimen

Elastic modulus, E [GPa]

Yield strength, R p,0.2 [MPa]

Tensile strength, R m [MPa]

[%] max. uniform elongation

Area reduction, Z [%]

St 1.1 St 2.1 St 3.1

190 180 200

1630 1640 1660

1800 1790 1830

4.4 4.1 4.8

45 33 46

Fig. 2. a) Stress-strain curves of the prestressing steel; b) Load-elongation curves of steel wires tested in the as-received condition with the reference curve derived from test 2 of Fig.2.a for a damage free wire.

The three dismantled strand pieces have also allowed four central-wire specimens to be tensile tested in the as received condition. These specimens had a free length between clamps higher than 10 cm, enough to cover a representative length of surface damage, and gripping sections uniform enough in diameter to avoid premature failure. As in the aforementioned tests, a 12.5 mm resistive extensometer was used to determine the corresponding elongations. Fig. 2b shows the four load-elongation curves obtained by testing the specimens in the as-received condition together with the image of one of them, captured during testing. A fifth curve has been added as a comparative reference. This corresponds to a hypothetical damage-free central wire of 5.2 mm diameter whose stress-strain curve would be that of Test 2, plotted in Fig. 2a. The curves provided in Fig. 2b clearly illustrate the losses of rigidity, resistance and ductility that the wires experience as a consequence of the damage induced by the corrosion action. The wire diameters that can be predicted from the initial slopes of the curves assuming 190 GPa as elasticity modulus differ by less than 5% from the mean value, as measured with a profilometer. This indicates that the effect of the oxidized surface layer on the resistant cross-section of the wires is insignificant when compared with the loss produced by the corrosion products and detached as rust. The ductility losses that reflect the elongation measured at failure have distinct meanings, depending on whether failure occurs before the complete yielding of specimen or during the plastic collapse. In the first case, necking does not take place and the quotient between maximum load and the cross-section corresponding