## 1 Introduction  
Earthquakes pose a significant threat to human life, infrastructure and the economy worldwide. Past earthquakes have shown how vulnerable the existing building stock is to both direct and indirect losses, with the latter being more difficult to quantify and often overlooked in damage assessments. For example, the economic losses caused by the disruption of services or the interruption of industrial production are particularly difficult to estimate. Nowadays, there is a growing interest in quantifying and assessing potential building damage using specialized methods. Accurate prediction of expected damage prior to an earthquake based on factors such as building design, building materials, seismic retrofitting and historical earthquake data is crucial for urban planning, risk mitigation strategies and insurance. Similarly, effective damage assessment that evaluates the actual damage after the earthquake plays an important role in guiding emergency response, repair efforts and reconstruction, as well as refining future predictive models. In recent decades, numerous formulations for the calculation of damage indexes have emerged that provide clear and standardized definitions for expected and actual damage. These methods cover both the prediction of damage before an event and the assessment of damage after an event. In this study, the damage indexes developed in recent decades to assess the seismic damage condition of buildings are examined in a comprehensive literature review. The indexes assessment is performed through Multi-Stripe Analyses (MSA), which take into account the variability of the seismic input for a more robust understanding of the potential damage scenarios. Specifically, the study considers six selected damage indexes and a reinforced concrete (RC) reference building with different structural configurations: a pre-code frame system, a code-compliant moment-resisting frame system and a code-compliant shear wall system. Both the bare frame and the masonry-infilled configurations are analyzed. In this context, the potential application of damage indexes in digital twins and sensor-based systems is emphasized. Through a non-linear dynamic analysis performed on digital twins, damage indexes can be calculated in near real time, allowing for a fast and accurate post-event assessment. This approach provides a robust tool for continuous structural health monitoring and facilitates the simulation of different earthquake scenarios to better understand and prepare for potential risks. Similarly, the use of the data recorded by the sensors and their elaboration, such as floor accelerations and inter-storey displacements, may enable the calculation of damage indexes without requiring a finite element model. This enables rapid quantification of damage to buildings, including structural and non-structural components, and provides information for timely decision making for emergency response and repair strategies. In this study, we provide a comprehensive overview of selected damage indexes for the assessment of seismic damage to buildings, validate their effectiveness and highlight their strengths and limitations. The main novelty of this work lies in the comprehensive evaluation of the effectiveness and reliability of damage indexes thorough Multi-Stripe Analyses (MSA) and in the proposal of specific formulations for the consideration of masonry infills. The use of MSA is particularly important to understand how each index performs in different structural configurations--such as existing buildings, code-compliant framing systems and code-compliant wall systems--and how accurately they quantify damage at different limit states. The effectiveness of the damage indexes in the analyses carried out on finite element models suggests that these indicators can also be widely applied to digital twin models. Damage indexes can be implemented in digital twin models to assess potential damage due to extreme events such as earthquakes in near real time.