PSI - Issue 78

Besim Yukselen et al. / Procedia Structural Integrity 78 (2026) 1943–1950

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achieves lower losses at equal or lower installation costs. Likewise, in the EAL vs EI plot, lower-impact solutions become accessible without sacrificing resilience. Overall, these results underscore the effectiveness of combining SIRA-based initialisation with NSGA-II in achieving retrofit strategies that balance resilience, cost, and sustainability objectives. The method enables decision-makers to choose among a diverse set of optimal solutions tailored to specific project constraints or priorities.

Fig. 4. Pareto-fronts obtained for the considered objectives

5. Conclusion This study evaluated a recently proposed framework for optimising seismic retrofitting strategies, aiming to simultaneously minimise installation costs, environmental impact, expected annual loss (EAL), and downtime to re occupancy. A central feature of the approach is a stochastic iterative retrofitting algorithm (SIRA), which emulates engineering judgment in generating retrofit schemes. By producing a diverse set of feasible or nearly feasible initial solutions, SIRA effectively reduces the computational demand of the subsequent optimisation process. Such initial solutions were then refined using the Non-dominated Sorting Genetic Algorithm II (NSGA II), which targets four objectives: EAL, downtime, installation cost, and environmental impact, while also ensuring code compliance of candidate solutions. The framework was applied to retrofit, with RC jacketing, an infilled reinforced concrete residential building, typical of Portuguese construction practices in the late 1960s, without seismic design provisions. The results showed that even minimal interventions, such as introducing a seismic gap, albeit not code compliant, yield substantial performance improvements, significantly reducing both EAL and downtime. The solutions identified by SIRA alone demonstrated meaningful improvements, with EAL values as low as €374 and downtime reduced to around 5 days. Subsequent optimisation using NSGA II further enhanced these trade-offs, with final solutions reaching EAL values as low as €246 and downtimes of 4 days, while maintaining installation costs between €68.496 and €140.361 and environmental impacts ranging from 13 to 39 tonnes of CO₂ equivalent. The outcomes confirm the effectiveness of combining SIRA with NSGA-II to generate high-quality retrofit strategies that balance economic, environmental, and resilience objectives. The methodology offers a practical and flexible decision-support tool for stakeholders aiming to upgrade existing single buildings or building stocks in earthquake-prone regions. Acknowledgements This work was supported by CONSTRUCT - Instituto de I&D em Estruturas e Construções (UID/04708), the project SERENE (2022.08138.PTDC, https://doi.org/10.54499/2022.08138.PTDC), funded by Fundação para a Ciência e a Tecnologia, I.P./MCTES (PIDDAC), and by the project ReLUIS 2024 – 2026 (WP5-WP13), funded by the Italian Civil Protection Department. References Akin, A., Saka, M.P., 2015. Harmony search algorithm based optimum detailed design of reinforced concrete plane frames subject to ACI 318-05 provisions. Computers & Structures 147, 79 – 95. https://doi.org/10.1016/j.compstruc.2014.10.003 Baker, J.W., 2015. Efficient Analytical Fragility Function Fitting Using Dynamic Structural Analysis. Earthquake Spectra 31, 579 – 599.