The first operation consists in measuring the diameter of the steels to check their dimensions, their corrosion (Fig. 11.1).

Fig. 11.1
figure 1

Source Rincent BTP—Recife

Diameter measurement.

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Direct tensile tests on steel samples taken from the site are a prerequisite.

The other important issue with steels is corrosion of the tie rod. The Swiss standard SAI 267/1 (2013) defines the acceptability of a newly injected tie rod by establishing minimum resistivity values. For example, these values can be used as criteria for re-tensioning.

Extracts from the standard concerning electrical resistance measurements are attached below.

10.7.4.2 A tie rod, once injected and energized, shall have an electrical resistance RI 0.1 MΩ (Mega Ohm).

10.7.4.3 In case a certain percentage of tie rods not showing electrical resistance I is tolerated, e.g. 5–10%, an electrical resistance II (ERM II) measurement shall be carried out on the defective tie rods to prove that there is no galvanic contact between the head of the tie rod and the frames of the structure. The test shall be performed in accordance with SIA 267/1.

The electrical resistance between the head of the rod and the frames shall have an RII value of 100 Ohms (Figs. 11.2 and 11.3).

Fig. 11.2
figure 2

Source Rincent BTP—Recife

Measuring the electrical insulation of tie rods.

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Fig. 11.3
figure 3

Measurement results

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It is interesting to note that even tie rods installed over 40 years ago can meet new tie rod requirements. The quality of the initial construction is related to these results.