PSI - Issue 78

Maria Teresa De Risi et al. / Procedia Structural Integrity 78 (2026) 1151–1158 M.T. De Risi, C. Del Gaudio, G.M. Verderame / Structural Integrity Procedia 00 (2025) 000 – 000

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softening range of behavior (i.e., after the peak load was achieved), and the softening branch became stiff only after 4% of applied lateral drift. In summary, a light shear strengthening (SL) lead to +57% strength increment; vice-versa, for higher strengthening percentage (SH), the maximum achieved load was higher (+97% with respect to the as-built condition); displacement capacity – i.e. displacement at lateral load reduction equal to 20% – significantly increased (ductility capacity was about 3 for SH test), as well. Another interesting results comes from the analysis of damage evolution obtained by the DIC technique, as shown in Fig. 6 for tests AB and SL. Such technique allowed to obtain information about cracks width evolution during the test, even where any potentiometer was physically placed, by elaborating high-definition photos of the specimen taken at regular time interval during the whole test execution. It can be easily noted from Fig. 6, that, being equal the applied lateral drift, the main cracks width is always significantly lower for retrofitted specimens with respect to the as-built condition: at the end of the as-built test (cycle 7, i.e. about 60 mm of lateral displacement), the maximum crack width in AB specimen (w max,AB ) was more than 3 cm; on the contrary, the maximum crack with for SL column at the same cycle was less than half w max,AB .

AB

SL

AB

SL

Fig.6. Comparison between specimens AB and SL in terms of evolution of the main shear cracks width

5. Experimental versus predicted shear strength Lastly, experimentally obtained shear strength values have been compared with the code-base prediction according to the Italian code prescriptions (D.M. 2018), always applied herein without any partial safety factor for sake of comparison with experimental data. The experimental peak load (V max exp ) are shown in Table 1, along with the code-based prediction, which was applied assuming the 50% reduction of f yw (V R,DM2018 (50%)) – as in Eq. (1) – or not (V R,DM2018-MOD (100%)). First of all, it can be noted that the code-prescription about shear strength assessment is a bit conservative for the as-built specimen (-12%). For what concern retrofitted specimens, instead, it is very clear from experimental-to-predicted ratios reported in Table 1 that, if D.M. prescription is applied (according to Eq. (1)), the experimental response is underestimated by 22% to 44%.