PSI - Issue 84

Anna Bontempi et al. / Procedia Structural Integrity 84 (2026) 1039–1046

1041

(a)

(b)

Figure 1: degradation conditions of the bridge in situ (a) and of the specimen considered in the experimental programme (b).

Figure 2a illustrates the cross-section of the specimen. It should be noted that the element is a full-scale girder with an overall length of 8.8 m and an approximate total weight of 12.4 t. All reinforcing bars were smooth. The material properties were derived from a twin beam, which was also donated to the university for research purposes and tested up to failure (Di Stefano, 2022). An extensive in-depth diagnostic investigation was carried out on this specimen in order to assess the existing cross-section’s material properties. Table 1 presents the main characteristics of the existing materials.

Table 1: existing section materials’ properties.

Existing steel reinforcement

Yielding stress [MPa] Ultimate stress [MPa] Young Modulus [GPa]

287 412 203

Existing concrete

Cylindrical compressive strength [MPa] 44

The beam considered in the experimental program was at first tested under four-point loading in its unstrengthened condition. Once yielding of the longitudinal reinforcement was overcome, the test was interrupted in order to assess the original load-bearing capacity of the member without inducing a high level of damage. Subsequently, the beam was unloaded and the strengthening technique was applied, consisting of the installation of two 12 mm carbon fiber– reinforced polymer (CFRP) bars located at the intrados of the beam, jacketed with a fiber-reinforced mortar overlay containing polypropylene fibers (FRM-PP). The overlay was 50 mm thick (Figure 2b).

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(b)

Figure 2: cross-section of the unstrengthened (a) and strengthened girder (b).