This paper introduces a novel framework to define limit states for the seismic fragility assessment of circular tunnels in soil. A numerical framework is developed for this purpose, focusing on the response of tunnels subjected to ground seismic shaking in the transverse direction. New limit states are defined based on the ovaling deformation of the tunnel, corresponding to different levels of liner stiffness degradation caused by seismic shaking. The latter is evaluated via nonlinear static pushover analyses of the examined ground-tunnel configurations. Nonlinear dynamic analyses are performed to evaluate the demand of examined tunnels and develop Probabilistic Seismic Demand Models (PSDMs). The uncertainties related with the definitions of capacity and demand are thoroughly evaluated based on the results of the nonlinear static pushover and dynamic analyses, respectively. The proposed framework is applied to a 6 m diameter circular tunnel embedded in uniform clayey soil deposit at a burial depth of 15 m. Various assumptions are made regarding the thickness and mechanical properties of the liner and the soil, leading to the investigation of 27 ground-tunnel configurations. A suite of ground motions is selected to perform dynamic analyses of each examined configuration. Based on the results of the analyses new PSDMs and PGA-based fragility functions are derived. Comparisons of the proposed fragility curves with existing, empirical, and analytical fragility curves for tunnels, reveal differences, which in some cases are significant and are mainly attributed to the different definitions of Engineering Demand Parameters (EDPs) and limit states between the compared curves, as well as to different assumptions in the analytical frameworks proposed by various studies. The proposed framework may be applied to other ground-tunnel configurations to develop fragility functions for a more rigorous risk and resilience assessment of these types of systems.

This study introduces three types of multivariable fragility surfaces, integrating effective structural features to improve damage assessment. The incorporation of additional information such as building occupancies, structural responses, and underlying soil types enhances the accuracy of conventional fragility curve predictions. Additionally, three modification factors are proposed to further refine conventional fragility curves and provide more precise predictions. The multivariable fragility surfaces are developed for eccentric brace frames modeled in Opensees software which is validated by experimental results and subjected to incremental dynamic analysis with 44 far-field ground motions. The influence of soil flexibilities on structural responses is incorporated through Winkler springs, representing soil-structure interaction. Diverse occupancies, such as hospitals, museums, and residential structures, are assessed using various peak floor acceleration thresholds and story drift ratios, employing multidimensional limit state functions to consider both structural and nonstructural losses. To account for uncertainties in structural responses and a single intensity measurement, a damage-sensitive feature derived from roof acceleration response, obtained through signal processing and system identification techniques, is introduced. The results for the proposed multivariable fragility surfaces indicate that the spectral acceleration corresponding to a 50% probability of exceedance could vary between 10.2 and 89%, in comparison to the corresponding conventional fragility curves. Finally, to evaluate the application of the enhanced fragility surface and modification factors, two instrumented EBF buildings, a 4-story EBF building, and a real 5-story hospital EBF, are selected as case studies. With additional details on soil types, occupancies, and structural responses, the process of employing modification factors resulting in enhanced fragility curves is demonstrated.

This article discusses the design of reinforced concrete structures taking into account non-uniform soil conditions, as well as aspects of sustainable engineering. To achieve this, the soil-structure interaction was explicitly introduced into the numerical model of the investigated structure which meets serviceability and the ultimate limit state conditions defined in the relevant Eurocode standards. In the numerical experiment, non-uniform soil conditions, type of foundation (isolated footing, foundation plate), material parameters and size of the cross of the elements (columns and beams) were analysed. The introduced heterogeneous soil profiles, determined by defining a parametrised, in terms of mechanical properties, spatial model of the layered soil, resulted in nonuniform settlement of the investigated structure. A global analysis of the three-dimensional reinforced concrete structure was carried out taking into account geometric nonlinearity with imperfections and material nonlinearity with creep. The displacement maps of the structure and the risk of collapse due to nonuniform settlement were established. Furthermore, an environmental so called life cycle assessment was performed for each variant analysed of the investigated structure. The innovative nature of the research is based on a joint approach to the problem of soil-structure interaction and the assessment of the carbon footprint of reinforced concrete buildings. This made it possible to determine how the varying soil conditions and different types of foundation affect the amount of material consumed and the carbon footprint associated with the production of reinforced concrete structures.