This study investigates the effects of ground-motion sequences on fragility and vulnerability of reinforced concrete (RC) moment-resisting frames (MRFs). Two four-storey, four-bay RC MRFs are selected as case studies. These structures, which share the same geometry, are representative of distinct vulnerability classes in the Mediterranean region and are characterized by different material properties, cross-section dimensions, and detailing. The first case study is a ductile MRF designed according to Eurocode 8 (i.e., a special-code frame), while the second is a non-ductile MRF designed to sustain only gravity loads (i.e., a pre-code frame). The influence of masonry infills on their seismic performance is also investigated. Advanced numerical models are developed to perform cloud-based sequential nonlinear time history analyses using ground-motion sequences assembled by randomly pairing two real records via Latin hypercube sampling. Different structure-specific damage states are considered to derive fragility curves for the undamaged structures, when subjected to a single ground-motion record, and state-dependent fragility curves by considering the additional damage induced by a second ground-motion record within the sequence. Damage-to-loss models are then used to derive mean vulnerability relationships. Results of the analysis show the importance of considering the effect of damage accumulation in the pre-code frames. Moreover, the presence of infills shows an overall positive contribution to the seismic performance of both frame types. Vector-valued vulnerability relationships accounting for the damaging effect of two ground-motion records are finally presented in the form of mean vulnerability surfaces.

This study investigates the effect of mainshock-aftershock sequences on numerical fragility and vulnerability relationships of European reinforced concrete (RC) moment-resisting frames (MRFs). A four-story, four-bay nonductile RC MRF is selected for illustrative purposes. This index building is representative of a typical vulnerability class in the Mediterranean region. The influence of the masonry infills on seismic performance is also investigated. An advanced numerical nonlinear model is developed for the case-study frame and then assessed through nonlinear dynamic analysis using both real and artificial mainshock-aftershock sequences, via a 'sequential cloud' approach. The obtained seismic demand estimates allow to generate fragility functions for the undamaged frame when subjected to mainshocks only. Moreover, statedependent fragility functions are derived for the mainshock-damaged frame when subsequently subjected to aftershocks. Damage-to-loss models, specifically calibrated on Italian post-earthquake data, are used to derive vulnerability functions for this case-study structure. Preliminary results from the study show that the frame experiences severe damages states and high losses for a range of ground-motion shaking intensities, with a clear damage increase due to aftershocks. An attempt to generate vector-valued mainshock-aftershock vulnerability relationships is finally presented. The proposed vulnerability surfaces can be more easily implemented into a time-dependent risk assessment framework.

This study proposes a practical fragility-oriented approach for the seismic retrofit design of case-study structures. This approach relies on mapping the increase of the global displacement-based ratio of capacity to life-safety demand ( CDRLS) to the building-level fragility reduction. Specifically, the increase of CDRLS due to retrofitting is correlated with the corresponding shift in the fragility median values of multiple structure-specific damage states, observing that a pseudo-linear trend is appropriate under certain conditions. Accordingly, a practical approach is proposed to fit such a (structure-specific) linear trend and then use it by first specifying the desired fragility median and subsequently finding the corresponding target value of CDRLS that must be achieved through retrofit design. The validity of the proposed approach is illustrated for an archetype reinforced concrete (RC) structure not conforming to modern seismic design requirements, which has been retrofitted using various techniques, namely, fiber-reinforced polymers wrapping of columns and joints, RC jacketing, and steel jacketing.

This study investigates the improvement in the seismic performance of an archetype reinforced concrete (RC) frame due to varying structural retrofit levels. Specifically, the study attempts to map the increase of the displacement-based global ratio between capacity and life-safety demand (CDRLS) to the reduction of seismic fragility. Such a reduction is characterized by the shift of the median fragility for different structure-specific damage states (DSs). The considered structure does not conform to modern seismic design requirements, and it is retrofitted using various techniques. Advanced nonlinear models are developed for the archetype frame, accounting for potential failure mechanisms, including flexural, joint, and shear failure. Three common retrofitting techniques are investigated, namely RC jacketing, steel jacketing, and fiber-reinforced polymers (FRP) wrapping of columns and joints. Each technique is specifically designed and proportioned to achieve predefined performance objectives (i.e., performancetargeted retrofitting), thus generating many retrofit alternatives. The improvement in seismic performance for the retrofitted frames is first characterized by computing the global CDRLS, which can be obtained using nonlinear pushover analysis combined with the Capacity Spectrum Method. Subsequently, cloud-based nonlinear time-history analyses are performed to derive fragility relationships for the as-built and retrofitted configurations, monitoring the variation in the median fragility for all DSs. Finally, the global CDRLS increase due to retrofitting is correlated with the corresponding shift in the median fragility. A linear trend is found, and it is used accordingly to develop simple models that engineers can implement to provide reasonable estimates for such shift once the global CDRLS is known.

Urban disaster risk management and reduction requires the development and periodic updating of regional building inventories. However, the development of such inventories can be very cost-intensive and time-consuming, making this a challenging task, particularly for low- and middle-income countries. This article discusses a mixed-mode building inventory data collection framework using a rapid and cost-effective remote survey technique that can be deployed in various geographic contexts. A key component of the proposed approach is an inter-rater reliability analysis of data collected from traditional sidewalk surveys and remote surveys for a small subset of buildings in the considered building portfolio, which is used to assess the suitability of the remote survey for the location(s) considered. The framework is demonstrated by developing a regional database of school buildings in the Central Sulawesi region of Indonesia. The database consists of 2536 school buildings from 454 elementary and high schools in the Palu, Sigi, and Donggala regions, susceptible to earthquake-induced ground shaking, tsunami, liquefaction, and landslides. The developed database can be used in pre-event/long-term risk analysis and management, post-event/near-real-time loss estimation, and regional-level decision-making on school assets and related policies. The database has been made available for public use and can be readily harmonized with similar databases for other regions.

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