Novosti Khirurgii

Abstract The detection of collapse mechanisms in masonry structures poses a critical challenge in structural engineering, particularly when dealing with complex historical buildings under seismic loading. Masonry structures exhibit highly non-linear mechanical behaviour due to their composite nature, characterized by discontinuities, weak tensile strength, and anisotropy. Accurately capturing these failure mechanisms, which include cracking, crushing, and sliding along joints, is essential for evaluating their seismic vulnerability. This paper focuses on the mechanical challenges of simulating collapse mechanisms in a masonry historical religious complex, significantly damaged during the 2016 Central Italy earthquake. Nonlinear numerical simulations are carried out to model the structure’s response to seismic loads implementing both the Finite Element Method, based on Concrete Damage Plasticity and the Distinct Element Method, studied using two different approaches: Discrete Element Method (DEM) and the Non-Smooth Contact Dynamics (NSCD). Despite their advanced properties in numerical simulation, neither method can fully capture the complexity of masonry collapse mechanisms. Instead, the combined and controlled use of both Finite and Distinct element methods enhances the predictive accuracy of the simulations. Therefore, this study aims to propose a benchmark approach for damage analysis: through a methodological cross-assessment of their respective displacement behaviours, the time-step activations corresponding to local collapse mechanisms are identified. It is then demonstrated that together, these methods offer a more comprehensive approach to detecting collapse mechanism, with reciprocal compensating for the limitations of the other. This synergistic application is essential to address the inherent complexity of masonry mechanics, including material heterogeneity and non-linear failure progression.

Abstract In transboundary areas, harmonizing risk assessment across borders is essential for effective risk management. However, differing methodologies for seismic risk assessment used by different countries can yield unequal results on either side of the border. This study presents a framework for harmonized cross-border time-based risk assessment, built upon established seismic risk assessment practices at the national level. The framework considers cross-border hazard, exposure, fragility, and consequence models, aiming to harmonize different data sources, methodologies, and models. An emphasis is given to a heuristic approach for the harmonization of fragility curves defined in the national fragility models. The proposed framework is implemented for the Italian-Slovenian cross-border region defined by municipalities near Gorizia and Nova Gorica. The results reveal differences in seismic risk levels between the building stocks on the Slovenian and Italian sides, primarily due to higher building density, seismic hazard, and vulnerability in Italy, while the seismic risk to people was observed to be nearly equal for urban centers like Gorizia and Nova Gorica. These findings can be used to design joint strategies for long-term risk management of the analysed cross-border region. However, further research is needed, particularly to overcome limitations related to the data sources of the exposure models and methodologies for fragility and consequence models, which can be addressed over a long period through systematic standardization of cross-border seismic risk assessment.

Abstract Seismic events worldwide have shown that school buildings can exhibit vulnerability levels even higher than ordinary buildings. This highlights the urgent need for reliable risk analyses to guide decision-making in the implementation of large-scale mitigation policies. Developing seismic fragility curves that accurately reflect their typological and structural features is essential to achieve this. In this context, the paper compares two different mechanical-analytical methods, namely the “DBV-Masonry” and “Firstep-M_PRO”, which have been independently developed at the University of Genoa and at the University of Trieste, respectively. Among various possible methods, the mechanical-analytical approach is chosen for its computational efficiency in assessing large portfolios and its flexibility in capturing the features of specific buildings, such as schools (i.e. significant inter-storey height and spacing between internal transversal walls). Both methods are applied to the same sample consisting of 101 unreinforced masonry (URM) schools located in the Friuli-Venezia Giulia region (Italy). One of key-goals of the paper is to provide a very comprehensive comparison of the similarities and differences between two methods for deriving seismic fragility curves which refer only to the global in-plane response. The impact of such an epistemic model uncertainty, together with the inter-building variability, is thus quantified and fragility curves are also validated against results from previous studies.

Abstract This paper has attempted to determine the weighting levels of the soil and ground motion parameters (engineering bedrock depth (EBd), average shear wave velocity (Vs30), fundamental frequency (f0), peak ground acceleration (PGA), Joyner-Boore distance (Rjb), and epicenter distance (Repi)) in reflecting the actual damage status after the 2023 Kahramanmaraş earthquakes, which have a wide impact area of 11 provinces. The analytical hierarchy method (AHP), a multi-criteria decision-making (MCDM) process, was used to analyze these parameter data sets obtained from 44 Disaster and Emergency Management Presidency of Türkiye (AFAD) stations (Gaziantep, Hatay, Kahramanmaraş, and Osmaniye). The priority order of the parameters before the analysis was systematically collected. These parameters were categorized into soil, ground motion and earthquake source-path properties. Considering the literature, these characteristics and their combined effects were systematically weighted with AHP under five groups. According to the weighted groups in the scope of the study, the actual damage data can be determined with a minimum accuracy rate of 70% (Group 1). In comparison, the best performance evaluation was 82% (Group 5). The parameter order and weights in the actual damage data evaluation are suggested as EBd-%28, PGA-%24, Vs30-%19, Rjb-%14, f0-%10, and Repi-%5 considering the very high accuracy rate of Group 5. This suggested weighting allows the rapid and effective estimation of the damage distribution after a possible earthquake only with soil, ground motion and earthquake source-path characteristics, even in cases where reliable structure data cannot be obtained.

Abstract In 2022, the Italian National Institute of Oceanography and Applied Geophysics - OGS set up a dense accelerometer network for strong-motion monitoring in Veneto (an Italian region in the north-east of the country), covering 312 sites in over 50% of the region’s municipalities. The network is primarily focused on measurements for rapid damage assessment and the prompt organization of rescue operations. Based on the latest generation of MEMS accelerometers, it is cost-effective and sensitive enough to provide useful recordings (i.e. with a good signal-to-noise ratio) of earthquakes with a magnitude down to 2.5. This feature helps to tune the recording and processing system in less critical situations than a severe earthquake. This paper describes the technical characteristics of the network, the practical solutions for its construction, the management tools currently used and some initial results. The technical and economic sustainability of the network in the long term is a key issue that was taken into account during planning and implementation and is also constantly monitored during normal operation. The aim is to extend the life of the network well beyond the five years envisaged for the original project so that similar solutions can be proposed for other regions of Italy.

Abstract Historical observations reveal that Liquid Storage Tanks (LST) have suffered significant earthquake-induced damages. The structural response of LST are sensitive to earthquakes due to dynamic fluid-tank interaction. Since designing with consideration of fluid-tank interaction in the time domain is complex, simplified calculation approaches have been developed to calculate base shear and overturning moments, but not pressure distributions. These approaches distinguish between flexible and rigid tanks, which is difficult to decide prior analysis. This paper presents a unified calculation concept that determines support reactions and pressure distributions independently of the tank’s stiffness by applying static equivalent loads. The research focuses on the distinction between rigid and flexible design approaches, review existing codes, their limitations, and challenges associated with relative acceleration response spectra. It scrutinizes varying definitions of impulsive components and superposition principles. A unified force-based design approach is suggested that integrates rigid and flexible design principles into a unified method. The approach uses standardized pressure curves of individual hydrodynamic pressure components, linked with absolute and relative spectral accelerations and appropriate superposition methods. The unified formulation is validated through a previously conducted experimental and numerical research on above-ground steel tank. The validation and application of the unified approach forms the basis for the new generation of Eurocode FprEN 1998-4 (2025), which is demonstrated for different tank geometries. The practical application is demonstrated on a squat and a slender tank using linear finite element model, and the results are compared with various approaches in the international standards and literature.

Abstract This paper investigates the seismic upgrading of existing RC frames whose design was governed by the gravity loads in earthquake-prone regions, using new hybrid energy dissipation devices with recentering capability and applying the analytical methods of the second-generation of Eurocode 8. The energy dissipation devices combine in parallel three components (viscoelastic, elastoplastic and superelastic) that control the response under frequent (viscoelastic) and severe (elastoplastic) earthquakes, and minimize the permanent deformations (superelastic). Frames representative of residential buildings having short, medium and long fundamental periods are considered. Beams, columns and joints with brittle shear failure or insufficient ductility are first upgraded, applying local measures to attain a lateral deformation capacity of 2% of story height that ensures cost-effective strengthening with the hybrid energy dissipation devices. It is shown that the RC frames seismically upgraded with the proposed approach can endure the maximum earthquake foreseen in a high seismicity region with moderate (economically feasible to repair) damage and negligible permanent deformations. It is also shown that the energy-balance-based analysis implemented in the second-generation of Eurocode 8 for displacement-dependent dampers, with elastoplastic restoring force characteristics, can be applied with some limitations to design and verify structures featuring energy dissipation devices that include a superelastic component.

Abstract Insufficient detail in the numerical modelling of reinforced concrete (RC) bridge piers can lead to oversimplification between simulated and real column behaviour under seismic loading. This paper describes the development and validation of an advanced and computationally efficient numerical model for circular RC bridge columns. First, the lateral stiffnesses, natural frequencies and damping ratios of three differently configured RC columns at various stages of degradation were evaluated by means of quasi-static cyclic and sledgehammer tests in loading cycles of increasing lateral drift amplitude. Normalised column lateral stiffness and first mode natural frequency were found to reduce nonlinearly with increasing column drift ratio. The two variables were also correlated to link RC column degradation with natural frequency reduction, which could allow rapid post-earthquake assessment of residual capacity. RC columns suffering from heavy corrosion were found to have a higher natural frequency and a tendency to fail prematurely under cyclic loading, whereas the damping ratio was generally unchanged. A set of nonlinear beam-element models employing fibre-discretised cross-sections was then developed and validated against experimental measurements. The model simulates buckling, fracturing, low-cycle fatigue, and bond-slip of vertical reinforcements, as well as nonuniform geometrical and mechanical deterioration of critical column sections. Individual fibre responses in the numerical model offered explanations for specific features of the experimental column stiffness and natural frequency reduction curves. Underlying mechanisms included the redistribution of compressive stress between concrete and rebars during cyclic loading, crushing of cover concrete, and yield of vertical reinforcements. Overall, the model accurately simulates the hysteresis response of the differently configured RC columns, without the need for column-specific adjustments.

Abstract Many European countries benefit from risk-informed mitigation and prevention tools, including seismic vulnerability models (VMs) that express the susceptibility of structures to earthquake damage. However, in the Balkan countries including Montenegro, comprehensive seismic risk investigations are still lacking, despite being a region affected by moderate seismicity. In this paper, we propose a novel heuristic approach to evaluate the VM for masonry buildings in Montenegro. Based on previous studies on the seismic exposure of Montenegro and accounting for additional vulnerability factors, we classify masonry buildings into three categories: unreinforced stone masonry (URM-St), unreinforced brick masonry (URM-Br), and confined masonry (CFM). These typologies are firstly compared with reference vulnerability models (RVMs) found in the literature for neighboring countries. The RVMs are then weighted using an expert-based approach, considering their similarities and differences with Montenegrin building classes, to create hybrid VMs for each class. These hybrid VMs are finally combined using a heuristic approach based on real damage data from two historical reports on the 1979 Montenegro earthquake.

Abstract In this paper, a rapid procedure for vulnerability and risk analysis at urban scale is presented and validated with respect to a homogeneous territorial area. The methodology is aimed at defining fast evaluations by taking advantage of a division of the territory into compounds based on historical evolution and development of the urban clusters. A compound-based taxonomy realized according to the CARTIS methodology has been adopted as exposure model. The vulnerability models have been validated with respect of recent seismic events for both masonry and RC buildings. Hence, a modified macroseismic vulnerability model for compound evaluations has been used. The simplified procedure has been evaluated with respect to a unit-based analysis where every structural unit has been specifically investigated through a macroseismic approach. The comparisons between the compound-based (CB) and the building-by-building (BB) evaluation are obtained in terms of damage scenarios through binomial distributions. The procedure has been validated by assessing two distinct urban centers located in the Garfagnana area, Tuscany (Italy). The results show that the simplified procedure matches the forecasted damage states, limiting the required information and the time of the investigation. The evaluation has been finally extended to the territorial area of Garfagnana and part of the Lunigiana, analyzing a total of 17 municipalities where the CARTIS taxonomy is available. Herein, fragility curves have been derived according to unified classes for a territorial evaluation. The research proves the effectiveness of the procedure in evaluating the seismic vulnerability of large areas, presenting a rapid tool useful for administrators and stakeholders in the management of urban stock.