Comparative Seismic Performance and Retrofit Guidelines for URM, CM, and RC Buildings Based on 24 Real Post-Earthquake Case Studies

Abstract

The 2019 Mw 6.4 Albania earthquake revealed considerable vulnerability encompassing a range of different structural typologies, predominantly among buildings assigned as Damage State 4 (DS-4). Numerous efforts investigate common construction typologies such as: unreinforced masonry (URM), confined masonry (CM), and reinforced concrete (RC), however, there is a gap in the ability to comparatively quantify residual seismic and retrofit response behaviours from these typologies in a common analytical framework. A comparative evaluation of 24 actual post earthquake buildings (8 URM, 8 CM, 8 RC) has been performed uniformly applying nonlinear static (pushover) procedure in the scope of Eurocode 8 – Part 3. Normalized base shear capacity (Vb/W), inter-story drifts at Damage Limitation, Significant Damage and Near Collapse limits and global ductility (μ) were obtained for each building by bilinear idealizations of capacity curves. Statistical descriptors were also calculated for each typology (mean, standard deviation, coefficient of variation), and hypothesis testing comparisons were conducted to assess if (i) residual strength capacity (at DS-4) is hierarchically ordered as RC > CM > URM, and (ii) increasing levels of ductility after retrofit are statistically significantly different among typologies. The results support a statistically significant trend in residual strength and ductility capacity, with RC systems showing a higher normalized base shear, and URM buildings receiving the greatest percentage increase in ductility after retrofit. To express retrofit performance in a similar quantitative way, a single performance indicator called the Retrofit Efficiency Index (REI) is developed that aggregates the strength and ductility ratios within one dimension. Such a performance indicator emphasizes the advantage of the typology and also establishes a useful decision making index for heterogeneous stock of buildings. The results encapsulate real post earthquake evidence into statistically, supported performance ranges, and summarises comparative guidelines. Instead of proposing a new modelling methodology, the new corpus of results provides a rigorous quantitative framework based on uniformly analysed real damaged buildings, and provides benchmark standards directly relevant for engineering evaluation and retrofit ordering in seismic regions.