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

1157

7

On the contrary, if the shear strength of columns strengthened with pre-stressed steel strips is calculated by neglecting the 50% of reduction suggested by Italian and European code – thus with 100% of f 0.2 in Eq. 1 is used – a numerical prediction much closer to the experimental data is obtained. It is worth noting that further tests will be necessary to confirm this outcome and propose an optimization of the strengthening design, which can be more economically and environmentally sustainable even at large-scale applications.

Table 1. Experimental-versus-predicted shear strength values

V

exp / V

R,DM2018 (50%)

V max

exp / V

R,DM2018-MOD (100%)

Test

V max [kN] 115.7 181.6 226.0

exp

max

[-]

[-]

[-]

AB SL SH

0.88 1.22 1.44

0.88 0.95 1.13

6. Conclusions Three shear-critical columns have been tested under pseudo-static loading, without and with pre-stressed stainless steel strips (CAM ® technology), applied as exterior active stirrups to improve their shear strength and displacement capacity. Experimental results reveal that: • shear strength of columns can be significantly increased, even favoring the reaching of their flexural capacity; • the technique is also able to increase the displacement capacity of strengthened columns and promote a softer degrading phase with respect to relevant as-built condition; • shear crack evolution is improved, since, being equal the applied lateral drift, the main cracks width is always lower for retrofitted specimens with respect to the as-built ones. Lastly, it was observed that code prescription by Italian D.M. 2018 about the design of this kind of strengthening technique can be still improved, making it more economically and environmentally sustainable, and also a suitable option for large retrofitting plans to increase resilience of existing RC building stock against earthquake actions. Acknowledgements This work was developed under the financial support of EDIL CAM® Sistemi S.r.l., which is gratefully acknowledged. References CEN 2005. Eurocode 8: Design of structures for earthquake resistance-part 1: general rules, seismic actions and rules for buildings. Brussels: European Committee for Standardization. Chen Y, Song X, Gan Y, Ren C. Comparative experimental study on seismic retrofitting methods for full-scale interior reinforced concrete frame joints. Struct Eng Mech. 2023;86(3):385. D.M. 2018, Aggiornamento delle «Norme Tecniche per le Costruzioni» - D.M. 17/1/18. (in Italian) De Risi M. T., Di Domenico M., Manfredi V., Terrenzi M., Camata G., Mollaioli F., ... & Verderame G. M. (2022). Modelling and seismic response analysis of Italian pre-code and low-code reinforced concrete buildings. Part I: Bare frames. Journal of Earthquake Engineering, 1 32. De Risi M. T., Scala S. A., Del Gaudio C., Verderame G.M. (2023). Seismic retrofit of Italian pre- ‘70 case -study RC buildings by solving shear failures: code-compliant assessment and economic effort. International Journal of Disaster Risk Reduction, 97, 104007. Dolce M., Gigliotti R., Laterza M., Nigro D., Marnetto R., 2001. Il rafforzamento dei pilastri in c.a. mediante il sistema CAM. Atti del X Convegno ANIDIS “L’ingegneria sismica in Italia”, September 9 -13, Potenza-Matera, Italy. Paper F3-01. (in Italian) Frascadore R., Di Ludovico M., Prota A., Verderame G.M., Manfredi G., Dolce M., Cosenza E. (2015). Local strengthening of reinforced concrete structures as a strategy for seismic risk mitigation at regional scale. Earthquake Spectra, 31(2), 1083-1102. Helal Y. Seismic strengthening of deficient exterior RC beam-column sub-assemblages using post tensioned metal strip [PhD Thesis]: University of Sheffield. 2012.