PSI - Issue 62

A. Lupoi et al. / Procedia Structural Integrity 62 (2024) 963–971 A. Lupoi, F. Romano / Structural Integrity Procedia 00 (2024) 000–000

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For what concern the cracks pattern evolution, Fig. 7 displays the opening of the full-depth pre-existing horizontal crack throughout the five cycles, measured by the two vertical displacement transducers labeled as 45 and 46 in Fig. 5. The figure points out that the crack remains stable at the increasing of the concentrated load, slightly increasing only when the collapse is attained.

Fig. 7. Opening of the pre-existing crack.

Such consideration can be generalized to the response of the entire girder, in fact the collapse occurs in a fragile manner, without the spread of significant crack patterns. In particular, the pictures in Fig. 8 display details and the location of the failure mechanism: as visible in Fig. 8 (a) and Fig. 8 (b), collapse occurred as the crush of the section top compressed concrete, followed by the web shear failure. The fragile response is probably due to the removal of top concrete slab, which implies that the section neutral axis shifts closer to the bottom section fibers, limiting the increase of steel tensile stress. The experimental test results demonstrates the effectiveness of the repair intervention: Fig. 8 (c) shows that the failure is located about 2 m to the right of the mid-span “A” frames, whereas the repaired area, which is located to the left of the mid-span section, presents no visible damage.

(a)

(b)

(c)

Fig. 8. Girder section collapse: (a) front-view; (b) back-view; (c) collapse section location.

It is worth noting that the collapse is probably due to the presence of a pre-test internal damage, not visible from the outside, because the failure section is not the one subjected to the highest internal forces, and the collapse load is lower than the expected value. In fact, the analytical collapse load due to flexural failure is computed to be F FLEX = 753 kN, occurring at the mid-span section and associated to a fragile compressed concrete failure, consistently with