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Earthquakes are often followed by higher-intensity aftershocks, which tend to aggravate the accumulated and more severe damage to building structures. The seismic vulnerability of concrete-filled steel tube (CFST) structures under major aftershocks is more complex. In this paper, a CFST frame and a frame with buckling-restrained braces (BRBs) are studied, and the finite element analysis software Midas 2022 is used to analyze the seismic vulnerability of the two types of structures under main shock and main–aftershock. The results show that the structural vulnerability of the two structures is significantly higher under the main–aftershock sequences than under the main shock alone. Compared with the CFST structure, the structure with BRBs can effectively reduce the structural displacement and the hysteretic energy, decrease the plastic deformation risk of the structural components, and improve the seismic performance. The structure with BRBs can significantly reduce the probability of structural collapse under the main–aftershock sequence and can provide a reliable guarantee of the stability of the building. [ABSTRACT FROM AUTHOR]

Conservation of the European-built heritage is nowadays closely related to interventions in masonry construction. Since a significant part of these structures are located in earthquake prone zones, designing protective measures that ensure their preservation requires the assessment of the associated seismic vulnerability and the understanding of their degradation mechanisms. However, due to the presence of discontinuities between its constituent elements, the numerical simulation of the non-linear response of masonry structures subjected to strong earthquakes is a cumbersome task, especially when performed using the traditional finite element method. As an alternative, the discrete element method is particularly suitable for the numerical analysis of such structures under large, damaging loads. By allowing discrete displacements/rotations of individual bodies, and by automatically recognising new contacts between bodies, while eliminating obsolete ones, this numerical approach can simulate the complete detachment of discrete bodies initially in contact. The present paper illustrates the use of the discrete element method to assess the seismic vulnerability of stone arches. A probabilistic approach allows to consider the variability of the seismic action and the uncertainties in the definition of the material properties. First, an un-reinforced masonry arch is considered. Based on non-linear multi-directional incremental dynamic analyses, five damage states are proposed and the respective fragility curves are elaborated. To improve the arch's seismic performance, two reinforcing solutions using steel elements are considered and analysed comparatively. [ABSTRACT FROM AUTHOR]

Several Italian cities are characterized by the presence of centuries-old historic walls, which have a cultural heritage value and, due to their structural role as a retaining wall, often influence the safety of adjacent buildings and infrastructure. Ancient urban walls are increasingly subject to instability and collapse phenomena, because the greater frequency of extreme meteoric events aggravates the static condition of the walls and of the wall–soil system. Since the seismic risk in the contexts in which the historical urban walls are located is often medium-high, it is advisable to evaluate the influence of soil moisture on the seismic response of the soil–structure system. In this paper, the seismic vulnerability of historical urban walls was examined through considering scenarios of both dry and wet soil, in order to evaluate the seismic response of the structure as a function of soil imbibition. Seismic vulnerability analyses were carried out on the case study of the historical urban masonry walls of Volterra (Italy), which have been affected by two major collapses in the last ten years. Seismic vulnerability was assessed by means of the limit equilibrium method and the finite element method, and through adopting proper soil imbibition models. The results highlight which sections of the walls are at greater seismic risk due to the presence of soil moisture, as well as the influence of soil imbibition on the structural safety and failure mechanism. [ABSTRACT FROM AUTHOR]

The paper presents a mechanical-based framework for the evaluation of local-scale seismic fragility curves. The approach is oriented to a seismic vulnerability assessment of unreinforced masonry buildings and makes use of basic exposure data easily obtained from survey or available in existing database. An efficient finite element model and static nonlinear analyses are employed to assess the structural behaviour. The mechanical-based fragility curves are evaluated using Monte Carlo simulations that allow to account for the uncertainties propagation. The proposed approach is tested on a case-study regarding the city centre of Cosenza, in southern Italy, using exposure information available from CARTIS database. [ABSTRACT FROM AUTHOR]

The need to assess the vulnerability of non-engineered residential RCC buildings in Nepal has become urgent, especially considering the ongoing modifications and additions to these structures without understanding their susceptibility to seismic events. Many residential buildings, particularly those up to three stories, did not fully comply to the guidelines outlined in Nepal Building Code NBC 105:2020. Therefore, there is a necessity to assess the seismic performance of these structures. This study aims to quantify the seismic vulnerability of such buildings by focusing on three distinct types: regular two and three-story structures, and irregular three-story structures. Using finite element modeling, the analysis of the buildings' seismic capacity was performed through pushover analysis. Subsequently, linear time history analysis is conducted to determine the seismic demand. Two software were utilized to conduct the analyses, namely SAP2000 and STERA_3D. The study also includes the matching eleven strong ground motion inputs to Nepal's site characteristics and response spectrum to ensure the relevance of the local context. Furthermore, fragility curves are constructed to compare the probability of structural failure, by first conducting the nonlinear dynamic analyses on the building specimens. The result showed that the probability of complete failure rises rapidly when an additional story is constructed with vertical irregularity, increasing from 1.8% to 5.7% in a non-engineered two-story building. The study also observes variations in top displacement across all three buildings due to differences in earthquake duration and frequency. From the findings, it is revealed that a significant increase in seismic vulnerability for vertically irregular buildings compared to regular ones. [ABSTRACT FROM AUTHOR]

• Light metal exoskeletons are used for integrated seismic-energy retrofit of existing RC buildings. • Three different solutions are applied to increase the seismic performances of an existing RC school buildings. • Seismic behaviour before and after interventions is investigated in the static non-linear field. • The comparisons among intervention techniques are made in terms of the seismic safety index provided by the Italian technical standard. • Local reinforcement interventions on RC school building columns are performed together with the applied exoskeletons to attain the minimum safety index required by the standard code for this building category. Italian built heritage is highly vulnerable due to old public and private buildings designed without recent seismic and energy regulations. In particular, school buildings represent a critical typology that should be retrofitted to guarantee safety and comfort to the users. In this framework, interventions from building outside able to avoid interruption of school activities should be required. A solution to solve this issue can be found in the retrofit solution with exoskeletons. In this scenario, the paper presents the comparison among three similar solutions of metal lightweight exoskeletons for the integrated seismic-energy retrofit of a RC school building assumed as a case study. The RC structure of the school is firstly modelled with a finite element software and then subjected to pushover analysis before and after retrofit interventions to assess the benefit of each exoskeleton solution. The comparisons among intervention techniques are made in terms of the seismic safety index (ζ E) provided by the Italian technical standard. The results show the more or less efficacy of the different inspected systems, even if integrative local interventions are needed to reach the minimum safety index (0.60) required for school buildings. As a conclusion, these novel light metal exoskeletons have proven to be efficient retrofitting systems for residential buildings or even for school buildings with regular façades and plan layouts. [ABSTRACT FROM AUTHOR]

Introduction: Masonry minarets in Old Cairo are highly susceptible to earthquake damage, particularly those not designed or updated to withstand seismic loads. Therefore, regular monitoring is necessary to ensure their safety and detect any deterioration or reduction in seismic performance. The direct loss of a minaret can lead to the collapse or severe damage to the structure itself. The cascading impacts of partial or complete minaret failure can have significant consequences for the immediate vicinity and the broader community. By studying the effects of earthquakes on minarets and developing mitigation strategies, countries can take proactive measures to protect these structures and ensure the safety of people. Objective: This study focuses on a specific type of Islamic architecture: the historic minarets in Cairo. The research aims to evaluate the seismic vulnerability of eight cultural heritage minarets in Cairo, identifying the parameters influencing their seismic behaviour and susceptibility to earthquake damage. Methods: The research utilizes empirical seismic vulnerability methods and ambient vibration measurements on eight minarets. An empirical approach compatible with the nature and style of the minarets is employed to evaluate their vulnerability using index values and curves. The method's validity is assessed, and areas of conformity and limitations are identified. Ambient vibration tests (AVTs) are also conducted using a temporary seismic network installed at various heights inside each minaret to determine their dynamic characteristics. Results: The seismic vulnerability Index (I_V) is calculated for the selected minarets based on the state of each vulnerability parameter. The contribution of each parameter to the final I_V values of the minarets are presented. Vulnerability curves are developed for each minaret, interpreting the conventional vulnerability indexes in terms of mean damage grades for seismic events with varying intensity on the EMS-98 scale. These mean damage grades can also indicate the expected damage levels of structural and non-structural minaret elements for events with different seismic intensity levels. AVTs are conducted at various heights on the selected minarets, and the dynamic characteristics are extracted from the recorded data. Variations in these characteristics are considered significant for structural health monitoring analysis. The peak-picking method is employed to directly extract each minaret's natural frequencies and mode shapes, as changes in dynamic characteristics are relevant to health monitoring analyses. Conclusions: The recent study examined the seismic vulnerability assessment of eight masonry minarets in the historic Old Cairo district. The assessment revealed vulnerability index values ranging from 10.3 to 26.1, indicating a concerning susceptibility to seismic events among these structures. Vulnerability curves were constructed for each minaret, visually representing potential damage scenarios across different levels of the EMS-98 intensity scale. These outcomes are significant as they facilitate prioritizing interventions to safeguard the most vulnerable minarets. Additionally, a novel empirical period equation was introduced to estimate the fundamental period of minarets in Old Cairo based on their heights. The equation was validated against field measurements and data from the literature. The study is limited by its focus on a specific category of minarets, specifically the historical masonry minarets in Old Cairo. Furthermore, limitations arise from the need for detailed finite element models to capture these minarets' dynamic responses accurately. Therefore, ongoing research involves the development of detailed finite element models and calibrating fundamental periods for the selected minarets. The anticipated results hold the potential to enhance our understanding of the structural dynamics of historical minarets, ultimately guiding the formulation of tailored seismic retrofitting and preservation strategies. These strategies, aimed at preserving these cherished cultural heritage assets, represent our collective commitment to ensure the endurance of these timeless landmarks for future generations. [ABSTRACT FROM AUTHOR]

The overhead gas-insulated transmission line (GIL) in ultra-high-voltage converter stations, distinct from traditional buried pipelines, demands a thorough investigation into its seismic behavior due to limitations in existing codes. A refined finite element model is established, considering internal structure, slip between various parts, and the relative displacement at the internal conductor joint. Seismic analysis reveals the vulnerability of the GIL at the corner of the pipeline height change, with two failure modes: housing strength failure and internal conductor displacement exceeding the limit. Furthermore, the acceleration amplification coefficient of the support generally exceeds 2.0. Two retrofit methods, namely increasing the fundamental frequency of all supports and fixing the connections between all supports and the housing, have been proposed. The results indicate the effectiveness of both methods in reducing the relative displacement. Fixing all the supports effectively reduces the stress, whereas the other one yields the opposite effect. The seismic performance of a GIL is determined not by the dynamic amplification of supports, but by the control of relative displacement between critical sections, specifically influenced by the angular deformation of the pipeline's first-order translational vibration mode along the line direction. Seismic vulnerability analysis reveals a reduction of over 50% in the failure probability of the GIL after the retrofit compared to before the retrofit, with the PGA exceeding 0.4 g. [ABSTRACT FROM AUTHOR]

• The seismic risk assessment of typical historical masonry churches located in the Banat region, Romania, through multilevel analysis procedures is presented. • By selecting six churches in this area, territorial scale assessments are carried out by means of LV0 and LV1 methods recommended by Italian code. • In a second step, local (LV2) and global (LV3) numerical analyses are performed on one representative church with the aim of identifying possible collapse mechanisms. • The LV2 method is applied by following a computational kinematic limit analysis approach. • In the LV3 method, modal linear and non-linear static analyses are carried out on a global finite element model. This paper aims to show some results of seismic assessment of Romanian Orthodox existing masonry churches, by extending the multi-level approach proposed by the Italian directive for seismic risk evaluation of cultural heritage. To this scope, a sample of six existing churches is examined, belonging to a church typology characterized by a single vaulted nave and a bell tower incorporated into the main façade. All churches considered in this study are located in the Banat region, which is an area with a medium–high seismic hazard. Firstly, territorial Level of Valuations (LV0 and LV1) are conducted on the churches sample examined. Afterwards, local (LV2) and global (LV3) valuations are performed on a case study, the Învierea Domnului church, assumed representative of all the churches sample under consideration. In particular, local analyses are performed on some church architectural portions with the kinematic limit analysis. Whereas, global analyses are conducted with non-linear push-over approach. Comments and comparisons of the obtained results are reported for each LV examined. [ABSTRACT FROM AUTHOR]

This paper investigates the seismic performance and vulnerability of multi-span Reinforced Concrete (RC) bridges with unequal height piers exposed to varied corrosion damage scenarios. An advanced three-dimensional nonlinear finite element modelling technique is developed and verified with available experimental results of a reference shake table test on a large-scale RC bridge. In addition to the pristine state of the reference bridge, various hypothetical corrosion scenarios, including the symmetrical and asymmetrical corrosion of piers, are considered. Several nonlinear analyses, including the pushover and Incremental Dynamic Analysis (IDA) approach, are performed to evaluate the seismic behaviour and vulnerability of hypothetical RC bridge specimens. The influence of symmetrical and asymmetrical corrosion of piers on nonlinear dynamic behaviour and failure mechanism (both in the global and local scales) of studied bridges are then discussed. Finally, the IDA results are used to develop time-dependent fragility curves. The analyses show that seismic vulnerability of a deteriorated irregular multi-span RC bridge crucially depends on the corrosion scenario of its piers, where the unbalanced distribution of seismic ductility demand might be regulated/intensified by different corrosion scenarios. Moreover, some corrosion scenarios resulted in near-synchronised failure of unequal height piers. • Modelling guidelines for advanced 3D finite element modelling of irregular RC bridges, including corrosion damage models. • Impact of various corrosion scenarios on capacity and seismic failure sequences of irregular ageing multi-span RC bridges. • Time-dependent seismic fragility analysis of corrosion-damaged multi-span RC bridges with substructural irregularity. • Influence of corrosion scenario on unbalanced distribution of ductility demands in irregular multi-span RC bridges. [ABSTRACT FROM AUTHOR]

• The corrosion effects due to the carbonation phenomenon are evaluated considering existing RC bridges. • Multi-modal pushover analysis was conducted in order to evaluate the influence of the corrosion effects on the seismic performance of existing RC bridges considering two different collapse mechanisms: the ductile collapse mechanism and the brittle collapse mechanism. • The results are summarized in terms of appropriate risk indices to highlight the evolution of the collapse mechanisms during the life of the structure. Recent collapse events of existing reinforced concrete bridges have increased the attention on the mandatory and suitable maintenance of these strategic constructions. In fact, most of these failures were due to an inadequate scheduling of maintenance interventions. One of the main issues concerning the load-bearing capacity of existing reinforced concrete structures is related to the steel reinforcement corrosion caused by carbonation phenomenon. Such aspect should not be even more overlooked considering the strategic role of infrastructures like the bridges of the Italian motorway network, mainly built around the 1960′s and widely used even right now. Consequently, reinforced concrete bridges require the execution of maintenance interventions in order to guarantee an adequate safety level under both serviceability conditions and exceptional loads, also considering that they were often designed without taking into account seismic actions. This paper investigates the seismic performance of five existing reinforced concrete bridges under several corrosion scenarios of piers steel reinforcement caused by carbonation phenomenon. In particular, three different corrosion levels (slight, moderate and high) are considered by analysing the evolution of the phenomenon effects for a structure lifetime equal to 75 years. The seismic vulnerability is evaluated by defining appropriate risk indices expressed in terms of peak ground acceleration and corresponding return period. The risk indices are determined by performing modal pushover analyses on finite element models of the bridges, considering the corrosion effects in terms of steel rebars cross section reduction. Some correlations between corrosion levels and risk indices are drawn. [ABSTRACT FROM AUTHOR]

• Novel method for simplified 2D shell modelling of one-way jack arch floors. • 2D elastic orthotropic shell properties are calibrated via an iterative procedure. • Calibration based on comparisons with detailed nonlinear 3D floor modelling. • Application to timber/steel and tile vault floors of Eixample district, Barcelona. • Seismic performance analysis of an Eixample building with two different floors. The type of floor system has a decisive role in the seismic performance of unreinforced masonry buildings. The in-plane stiffness of the floors has to be adequately represented in the numerical modelling of existing buildings, as it can influence their seismic capacity. This paper investigates the seismic behaviour of one-way arch floor systems composed of steel or timber beams, and ceramic tile vaults. The main objective of the research is to provide a numerical procedure for the simplified modelling of jack arch floor systems in the seismic assessment of unreinforced masonry buildings. The presented approach aims to provide values for the orthotropic properties of simplified floor models composed of elastic 2D shell elements. The orthotropic elastic properties are computed and calibrated by means of comparisons with detailed 3D nonlinear models of the floors. The case study is a multi-storey existing masonry building of the historical "Eixample" district in Barcelona, which includes one-way arch floor systems. The Finite Element Method has been used for the numerical simulation of the seismic performance through nonlinear static (pushover) analyses. The results of the study contribute to a better understanding of the effect of the behaviour of one-way floors with steel or timber beams and tile vaults on the seismic response of masonry buildings. This work provides indicative values for the proper modelling of these particular floor slabs. The proposed methodology is also applicable to the numerical simulation of any other one-way floor system. [ABSTRACT FROM AUTHOR]

Many existing historical masonry arch bridges used in the road and railway networks are still in service. However, most of them show a structural performance deficit due to several factors. This study deals with the seismic behavior assessment of an existing masonry three‐arched railway bridge through a nonlinear, non‐adaptive static analysis carried out by a three‐dimensional Finite Element model. Input data were collected from a variety of sources. The structural analysis showed a risk index that was not in compliance with the limit values suggested by current European Standards. In order to improve the structural reliability of the masonry arch railway bridge, a traditional structural rehabilitation was proposed and designed. The bottom faces of the arches and the piles of the masonry bridge were strengthened by reinforced concrete thin slabs and reinforced concrete jackets, respectively, all adequately connected to the existing structure by using steel bar connectors. Finally, a nonlinear analysis of the strengthened structure showed that the new risk index satisfied the seismic vulnerability verification. The proposed structural rehabilitation using traditional techniques appears to be a viable but not unique solution to improving structural reliability. [ABSTRACT FROM AUTHOR]