PSI - Issue 64

Maria Teresa De Risi et al. / Procedia Structural Integrity 64 (2024) 959–967 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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5.2. Strengthening cost depending on codes

As-built and post-operam assessment of building capacity is significantly affected by the adopted models by codes, and, in tune, even the number of elements requiring strengthening is significantly different from code to code. As a result, the cost of the strengthening solution adopted herein can be very different from code to code, even for the same building and the same building location. For sake of example, to quantify such a difference, Italian and American shear models application is considered and two municipalities (among the about 6700 considered herein) are selected (Fig. 4): Milan and Naples. The unit strengthening cost for each beam/column/joint is derived by De Risi et al. (2023); the number of elements to be strengthened comes from Fig.2, assuming as (current) demand PGA (PGA D ) that corresponding to a return period of 475 years according to DM 2018, i.e. PGA D = 0.05g and PGA D = 0.17g for Milan and Naples, respectively. Fig. 4 shows the required strengthening cost (calculated as in De Risi et al., 2023) to reach PGA C = PGA D . Fig. 4 clearly shows that, for 2-storey building, retrofitting cost in case of ASCE code is null, since as-built PGA C,ASCE > PGA D in both sites; vice-versa, if Italian DM 2018 is applied, cost ranges between about 120 and 230 euro/m 2 (per square meter of the total plan area) moving from low-hazard to medium hazard sites. Similar remarks applied to 4-storey building, even if, in this case, as-built PGA C,ASCE < PGA D in Naples, thus requiring a retrofit intervention; however, its cost is one half of that related to DM 2018.

Fig. 4. As-built capacity in terms of (a) Sa C (T eff ) and (b) PGA C at SD LS depending on Ns; post-operam capacity in terms of (c) Sa C (T eff ) and (d) PGA C at SD LS depending on Ns. 6. Conclusions Italian, European, and American prescriptions about shear failure detections have been investigated, by means of 2 low-medium rise pre-code RC buildings, located in several Italian municipalities. The results show that capacity at Severe Damage (SD) Limit State (LS) is generally limited by joints failures. The application of shear strength models by different codes also showed a significant difference in as-built assessment of the same building, on the resulting strengthening design - assuming a strengthening technique that solves all tensile shear failures. Italian and European code resulted in more severe strengthening interventions with respect to ASCE prescriptions, and, consequently, in significantly higher retrofitting costs. Ongoing work is addressing the assessment of the incoming second-generation Eurocodes to understand if its new safety check approach – above all for columns/beams and joint shear strength (Fardis, 2020; Biskinis and Fardis, 2020) – have an impact on the presented results. Acknowledgements This work was developed under the financial support of ReLUIS-DPC 2024-2026, funded by the Italian Department of Civil Protection (DPC). This support is gratefully acknowledged. References CEN (2005) European Standard EN 1998-3:2005: Eurocode 8: design of structures for earthquake resistance. Part 3: assessment and retroftting of buildings. Comite Europeen de Normalisation, Brussels DM 2018, Aggiornamento delle «Norme Tecniche per le Costruzioni» - DM 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 ASCE SEI/41 (2017). Seismic evaluation and retrofit of existing buildings. American Society of Civil Engineers.