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Conversely, the numerical modeling of the seismic behavior of masonry structures represents a very complex problem due to the constitutive law of this structural material and its highly nonlinear behavior. Historical structures represent a significant percentage of existing constructions in numerous seismic-prone regions, and some of these are iconic monuments of their countries. Damage fragility curves were identified for typological building classes, defined by considering parameters present in both post-earthquake observations and census data with the aim of extending the results to the whole national territory. [Extracted from the article]

Unbonded posttensioned controlled rocking masonry walls (PT-CRMWs) have been increasingly studied in the last decades due to their promising results regarding seismic resilience. However, implementing posttensioning (PT) has still some drawbacks, such as construction challenges, PT losses, and yielding during a seismic event. In response, this study investigates a newly proposed energy dissipation-controlled rocking masonry wall (ED-CRMW), which eliminates the use of unbonded posttensioned bars and relies instead on gravity loads to self-center the wall to its vertical plumb while incorporating an energy dissipation (ED) device to limit seismic displacements. The study presents a design approach for the proposed system, including the influence of higher mode effects. In this respect, a multispring macro model is developed using OpenSees and validated against recent experimental results by the authors. Next, as no distinct values are yet provided in ASCE 7, the seismic response modification factor is investigated using collapse risk analysis. Specifically, using the validated model, nonlinear static and dynamic analyses are performed to 20 ED-CRMW archetypes with different design configurations. The results demonstrate that the design objectives were achieved and that a seismic response modification factor of 7 assigned to the selected design configurations meets the FEMA P695 acceptance criteria for seismic collapse risk under the maximum considered earthquake (MCE). [ABSTRACT FROM AUTHOR]

Infill walls are the most common separator panels in typical reinforced-concrete (RC) frame structures. It is crucial to investigate the influence of the infill walls on the earthquake behavior of RC frames. The load resistance of infill materials was often not taken into account in the designing phase, whereas the infill walls have significant contributions to the structural behavior under lateral and vertical loadings. A three-dimensional 4-story RC building is designed, and in order to make a realistic model, different infill walls configurations were taken into account with the openings in the infill. Four different models were created for structural analysis for infill wall effects, namely, full RC infilled frame (Model I), corner infill at ground story RC infilled frame (Model II), open ground story RC infilled frame (Model III), and bare RC frame (Model IV). Static adaptive pushover analysis has been performed for all structural models by using the SeismoStruct software. The double strut nonlinear cyclic model was used for modeling the infill walls. In this study, three different compressive strengths of infill walls are taken into consideration, and the effects on seismic design factors (namely, the response reduction factor, the ductility, the overstrength factor, and the deflection factor) are calculated. The obtained values of the response reduction factor (R) are compared with the given values in the BIS code. The results show that the R factors of all RC infilled frames are decreased when the compressive strength of the masonry infill reduces. However, the R values of bare frames are less than the corresponding values recommended in the BIS code. It is worth noting that the National Earthquake Hazards Reduction Program (NEHRP) provisions underestimate the deflection factors of the reinforced-concrete (RC) frames according to the evaluated deflection factors of the herein studied RC frames. [ABSTRACT FROM AUTHOR]

• The model update process with the TSA reduces the differences between numerical and experimental dynamic characteristics. • Using quake records explicitly prepared for the region in dynamic analyses of masonry structures provides realistic results. • The most critical areas of masonry clock towers in terms of stress are the section change zones that cause sharp transitions. • Restoration prevents masonry structures from becoming vulnerable to external factors by addressing minor issues. • If the faults pass through or close to a city, the quake performances of masonry structures in that city must be evaluated. This article presents comprehensive numerical and partial experimental studies to determine the seismic performance of the recently restored masonry clock tower in Bayburt before and after restoration. The numerical dynamic characteristics of the structure are obtained by free vibration analysis conducted on the preliminary finite element model, while the experimental ones are determined through ambient vibration testing. The ultimate finite element models reflecting the actual state of the structure pre- and post-restoration are created through a model updating process based on the principle of minimizing the differences between numerical and experimental dynamic properties via the Tabu Search Algorithm. Dynamic analyses of the models are carried out by the mode superposition method in the time domain, using eleven earthquake ground motion records selected considering the tectonic structure of the region and scaled to the design spectrum explicitly established to the site. Seismic responses are evaluated based on displacement, maximum-minimum principal stress, and maximum-minimum principal strain. The maximum principal stress value, the most critical parameter jeopardizing the safety of masonry structures, is 2.069 MPa before the restoration reaches 2.489 MPa, with an increase of approximately 20.3 % after the restoration. Since this value is less than the tensile strength of the masonry material, 3.120 MPa, it is not at a level that poses any risk to the structure. Other structural reactions also remain below the limit values. Therefore, according to today's seismic hazard analysis criteria, it can be said that the clock tower is safe. However, the North Anatolian Fault Zone, with high tectonic activity passing just south of the city, has the potential to produce severe earthquakes that may affect the region in the future. Therefore, it is necessary to periodically monitor the seismic behaviors of the historical masonry structures in Bayburt and take essential precautions based on the results. [ABSTRACT FROM AUTHOR]

The stiffness of masonry infill walls is commonly neglected in design practice of Reinforced Concrete (RC) structures. In fact, the stiffness of masonry infill wall may significantly influence seismic performance and dynamic behavior of RC buildings. In this research, influence of masonry infill walls to the structural performance of a three-story RC frame is investigated. In addition, possible application of friction-based support is also studied. Full 3D non-linear time history analysis is conducted to observe the behavior of the structure under two-directional ground motion. In the analysis, any failed elements are removed subsequently from the model to avoid numerical analysis problem. The result shows that the masonry infill walls can significantly influence the structural behavior of RC structure. Inappropriate placement of masonry wall may lead the building undergo soft-story mechanism. It is also found that the use of friction-based support can effectively improve the seismic performance of the building. [ABSTRACT FROM AUTHOR]

Multistoried masonry infilled concrete (RC) frame with open ground storey has been recognized as a serious stiffness irregularity that has led to typical soft storey collapse of many buildings in past seismic events. Present study represents extensive static and dynamic analyses to investigate the seismic behavior of masonry infilled soft storied RC buildings. Several soft storied 2D frames with variation in number of storeys, number of spans, percentage of infilled frame panels, height to horizontal extent ratio as well as randomness of infill positions have been analyzed and the behavior of frames is investigated. Effect of variation of these parameters on base shear, natural period of vibration, storey drift etc. are studied. Results show that the base shear is significantly increased in presence of structurally active infill panels as compared to static analysis while randomness in the distribution of infill shows no appreciable influence. The findings show that seismic forces obtained from static analysis leads to significantly under-designed ground storey columns in soft storey buildings and are vulnerable during earthquake. Magnification of base shear as a function of amount of infill number of storeys are presented which may act as a guideline for the engineers towards safer design of columns and other elements of buildings with open and soft ground storey in a rational manner. [ABSTRACT FROM AUTHOR]

• Seismic performance-based assessment of a masonry building in aggregate. • Definition of the Minimum Unit of Analysis (MUA) to model the "aggregate effect". • Non-linear static (pushover) analyses at global-, structural unit- and wall-level. • Target structural unit approach to define the reference configuration for the target building. • Optimal MUA has the closest seismic performance to that of the reference configuration. The seismic vulnerability assessment of unreinforced masonry buildings within historical centres is a very challenging research subject given the inaccuracy of investigating these buildings as independent structures. Indeed, these buildings are often part of complex structural systems, which may differ in geometry, building materials, construction techniques and maintenance condition, as they result from an urban continued growth phenomenon, in adjacency and continuity with the existing built environment. For this reason, when assessing the seismic vulnerability of buildings enclosed in aggregate, the reciprocal interactions with adjacent structures should be considered. However, even though several studies have been performed in recent years to address this issue, it is not yet clear how to represent these interactions in numerical models, without the need for modelling the entire aggregate. Hence, this study aims at understanding how the "aggregate effect" should be modelled for a more accurate seismic assessment of unreinforced masonry buildings located within historical centres. To this end, an innovative procedure, from now on referred to as "target structural unit approach", was developed, aiming at identifying the optimal portion of the aggregate that best represents the "aggregate effect" for the investigated structural unit, i.e., the Minimum Unit of Analysis (MUA). This procedure is based on a multi-level analysis of the seismic response of the target structural unit, investigating different modelling configurations in addition to the complete aggregate or the isolated building. The evaluation is preliminarily performed at global– and wall– level; then, the structural unit– level is introduced as additional verification level, with the aim to understand the variability of the seismic response of the case study building in function of different boundary conditions. The procedure herein proposed was employed to a case study located in the "Bairro Ribeirinho" neighbourhood in Faro (Portugal), by performing nonlinear static analyses using a software code based on the macro-elements approach. Although just some first results are shown and further investigations are needed, the proposed approach can be used for the validation of seismic assessment strategies specific for masonry buildings enclosed in aggregate. [ABSTRACT FROM AUTHOR]

Abstract The out-of-plane response is a complex and at the same time key aspect of the seismic vulnerability of masonry structures. It depends on several factors, some of which are the material properties, the quality of the walls, the geometry of the structure, the connections between structural elements and the stiffness of the diaphragms. During the last years, a wide variety of numerical methods has been employed to assess the out-of-plane behaviour of unreinforced masonry structures. Finite element macro-modelling approaches are among the most famous as they allow modelling large structures at a reasonable computational cost. However, macro-modelling approaches may result in a non-realistic representation of localized cracks and a dependency of the numerical solution on the finite element mesh. Mixed strain/displacement finite elements have been recently proposed as a remedy to the above numerical pathologies. Due to the independent interpolation of strains and displacements these finite element formulations are characterized by an enhanced accuracy in strain localization and crack propagation problems, being at the same time practically mesh independent. For these reasons, mixed finite elements are employed in this work for the out-of-plane assessment of unreinforced masonry structures, being at the same time their first real-scale application. A full-scale experimental campaign of two masonry structures, a stone and a brick one, subjected to shaking-table tests is chosen as reference benchmark. Their structural response under seismic actions is numerically assessed through nonlinear static analysis. The proposed approach is validated through the comparison of the numerical results with the experimental ones, as well as with the results obtained using standard irreducible finite elements. Highlights • Large-scale application of mixed strain/displacement finite element formulation. • Simulation of shaking table experiments on brick and stone masonry mock-ups. • The mixed formulation predicts the out-of-plane collapse mechanisms. • Mesh-dependency study using the standard and the mixed formulation. • The mixed formulation gives mesh-independent results without tracking procedures. [ABSTRACT FROM AUTHOR]

Highlights • Surveys of seismic damage show that merlons are vulnerable to out-of-plane mechanism. • Nonlinear kinematic analysis of rigid merlons on deformable walls/towers is proposed. • Effects of geometry and materials on the seismic behavior are studied parametrically. • The procedure supplies a tool for straightforward assessment of seismic vulnerability. Abstract The observation of the damage occurred to ancient masonry buildings is the necessary first step to understand the seismic behavior of the elements that compose them. Looking at the recent seismic events in Italy, a severe damage could be noticed on a wide range of historical buildings, in some cases even for low values of peak ground acceleration. In particular, the present paper focuses on ancient fortified architectures, characterizing the historic city centers and landscapes, investigating the seismic vulnerability of its most typical element: the merlon. The analysis of the observed damage on the fortified building typology, collected and catalogued in previous works, clearly points out that merlons are frequently damaged, particularly by out-of-plane mechanisms and even for low accelerations. Given the fact that these elements are particularly vulnerable and, at the same time, particularly meaningful from a historical and cultural point of view, the present work focuses specifically on the out-of-plane damage mechanisms suffered by these protruding elements, in order to better understand their behavior during earthquakes, to quantify their vulnerability and to provide simple instruments for their seismic protection. Indeed, though the collapse of merlons is rather common, it has received little attention in the literature. The present paper analyses both merlons on towers and on walls, in clay brick masonry or in stone masonry, and describes, through a parametric analysis, their behavior as the features change. A simple linear elastic model was adopted to identify the activation of the out of plane mechanisms, while the subsequent collapse was analyzed with a non-linear kinematic model. Moreover, appropriate filtering equations were chosen to modify the response spectrum at the ground, thus taking into consideration the seismic filtering effect exerted by the supporting wall or tower. The proposed procedure is discussed and validated by means of three different case studies: the San Felice sul Panaro Fortress (damaged in the Emilia 2012 earthquake), the Arquata del Tronto Fortress, and the Rancia Castle (both damaged in the 2016 Central Italy earthquake). By changing the parameters (geometries, materials, soil) between extreme but realistic values, the curves that relate the slenderness of the merlons to the PGA that leads to the activation of the mechanism (or collapse) are plotted. These graphs supply ranges of vulnerable conditions, representing a straightforward and reliable instrument, also for practitioners and public bodies in charge of heritage preservation, useful to define priority lists for interventions and to optimize the resources for the prevention of future damage. [ABSTRACT FROM AUTHOR]

Abstract Performance-based assessment (PBA) has become a matter of emphasis for multi-story unreinforced masonry (URM) buildings recently. It is however very hard to assess the performance of the multi-story URM buildings because of their complex engineering characteristics and structural performance. The primary goals of this study are to identify the seismic vulnerabilities of the URM buildings and to evaluate their structural performance based on the PBA principles. In this respect, a concept PBA layout is prepared for the URM buildings to describe better the performance assessment. In order to evaluate the structural behavior and seismic risk for the multi-story URM buildings, the study focuses on a case study of Historical Khatib School, which is located in Erzurum, Turkey, and it was assessed using the previously determined layout steps. Highlights • To evaluate the multi-story URM buildings in terms of their structural characters • To develop a layout for performance based evaluation of historical URM structures • To determine the structural behavior of URM buildings when subject to seismic load • To propose a simple numerical analysis technique for URM structures [ABSTRACT FROM AUTHOR]

Seismic protection of ancient masonry towers is a topic of great concern among the scientific community. A methodology for the seismic vulnerability assessment of all types of towers and slender unreinforced masonry structures (e.g., light houses and minarets) is presented. The approach is developed by four validated 3D FEM models representative of European towers. The models are subjected to linear elastic investigations to establish load carrying capacity and dynamic properties for validation against similar towers. Seismic simulations are developed through intensive nonlinear static pushover analyses. From the assessments, the failure modes and overall seismic response of the towers are obtained. Low tensile strength of masonry and large openings at belfries have significant influence on the seismic behavior, resulting in a quasi-brittle failure. All the towers presented an imminent high vulnerability to seismic actions. The few investigations reported in literature on the seismic behavior of towers are focused on in-plane behavior, disregarding out-of-plane behavior and toe crushing, both aspects are investigated in this paper. The more flexible towers are close to present toe crushing in both planes. The failure mechanisms are validated with reported post-earthquake observations on real damaged towers. [ABSTRACT FROM AUTHOR]

Recent earthquakes have highlighted that historical fortified masonry constructions may suffer extensive damage, even under low-to-moderate seismic actions, and corner towers may be one of the most vulnerable structural elements. An accurate assessment of the structural seismic performance is one of the most effective tools to deeply understand and identify the main structural weaknesses of such a building typology. To this aim, the need to properly simulate the dynamic behavior of large complex masonry buildings can strongly limit the application of simplified analysis methods widely used in common practice and largely presented in the literature. The objective of this study is to provide a comprehensive numerical insight into the earthquake response and seismic vulnerability of historical fortified masonry palaces with corner towers using non-linear dynamic analyses and a macro-modelling FE-based approach, which is able to take into account the complex interactions between different macro-elements and the characteristics of the seismic action. After a knowledge phase of the geometrical and constructive features of the two palaces under study, detailed three-dimensional FE models have been developed and predictive non-linear dynamic analyses have been performed to assess damage patterns and identify the most critical macro-elements. The numerical analyses highlight that the seismic response and damage distributions are significantly influenced by the geometrical features and main dynamic properties of the two palaces. A fundamental role is also played by the interactions of the different macro-elements with the adjacent structural parts. The results of the non-linear dynamic analyses point out that the two palaces are highly vulnerable to seismic actions, highlighting the onset of possible local collapse mechanisms and recurrent damage concentrations. For both the palaces, the most critical elements are the corner towers that present remarkable cracks patterns along the height, in the connection regions with the adjacent walls, in the upper part and in the vaults. Widespread damage is also observed in the macro-elements that are characterized by high slenderness, large openings and small walls thickness, and in the large vaults of the two palaces. A clear correlation between large displacements and high values of energy density dissipated by tensile damage is generally observed for the main critical macro-elements of both the palaces. The main outcomes presented in this study may also represent a useful insight to improve the knowledge and better understand the earthquake response and seismic vulnerability of similar historical fortified masonry palaces located in the same region, providing valuable information for practical applications in seismic risk assessment and mitigation at territorial scale. [ABSTRACT FROM AUTHOR]

• Seismic assessment and earthquake response of slender historical masonry bell towers. • Seismic response is affected by the main geometrical features and main vibration properties of the bell towers. • Damage distribution among the different parts of the bell towers for different PGA values. • Influence of different accelerograms on the energy density dissipated by tensile damage and maximum top displacements. • Main limitations of the simplified approach are highlighted through a comparison with non-linear dynamic analyses. Masonry bell towers represent a large portion of the Italian cultural heritage and are highly vulnerable to seismic actions mainly due to their relevant slenderness, as also observed in recent seismic events. The present study investigates the seismic vulnerability and earthquake response of five slender historical masonry bell towers, which are located in South-East Lombardia (Northern Italy), through a preliminary simplified procedure suggested by the Italian Code and advanced numerical simulations. To thoroughly study the seismic response of the bell towers, detailed three-dimensional FE models with a damage plasticity constitutive law for masonry are developed and non-linear dynamic analyses are performed using different accelerograms. The results of the non-linear dynamic analyses show that the geometrical features and the main vibration properties of the bell towers turn out to be the main parameters influencing the seismic performance of such a construction typology. Moreover, it can be noted a clear influence of the accelerograms characteristics on both the energy dissipated by tensile damage and the maximum normalized displacements of the bell towers. On the other hand, the structural geometrical characteristics play a very important role in terms of damage distribution among the different parts of the bell towers. In addition, the main limitations of the simplified approach suggested by the Italian Code for the seismic assessment of the bell towers under study are highlighted through a comparison with the results obtained from non-linear dynamic analyses. The main outcomes presented in this study may also represent a useful insight to better understand the earthquake response and seismic vulnerability of similar masonry bell towers located in the same region, providing valuable information that can be directly used in seismic risk assessment at regional scale. [ABSTRACT FROM AUTHOR]

• Discuss the performance of masonry structures after the 2017 Lesvos earthquake. • Presents the failure patterns and highlights factors that were decisive. • Examines the role of traditional construction techniques and architectural features. • Provides an insight of the performance of previous interventions. On the 12th of June 2017 an earthquake of Mw = 6.3 struck SSE of Lesvos Island, causing one human fatality and severe damage to the built environment. The traditional settlement of Vrissa was the most affected area, having masonry structures as the majority of its building stock. The objective of the present study is two-fold: to present the structural damage and failure patterns induced by the Lesvos earthquake to masonry structures; to highlight the causes and weaknesses that led to damage, or the factors that prevented it. Particular attention is paid to traditional construction techniques and architectural features that contributed to the seismic response of the structures, either having beneficial or detrimental effect. To this end, a field reconnaissance has been conducted and meaningful technical conclusions are drawn by the observations. Structural systems of both unreinforced and timber-reinforced masonry are inspected. Besides the identification of frequent cases of local, out-of-plane and in-plane mechanisms, combined global mechanisms are also pointed out. Finally, insight into the performance of past interventions is also given, assisting the challenging task of engineering practice. [ABSTRACT FROM AUTHOR]

• Geometrical survey of a 40 m height masonry bell tower by means of drone and images elaboration algorithm. • Mechanical and chemical diagnostic of existing masonry with different non destructive tests. • Seismic vulnerability assessment by means of modal, pushover and kinematic analyses. • Strengthening design against overturning of masonry bell tower. The masonry building Heritage embraces a large variety of structural typologies, including churches, bridges, arenas, theatres, portals, castles, temples, and towers. The structural behaviour of these constructions appears often complex to be understood due to the uncertainties related to the materials and internal geometry. In this paper, a complete study (i.e. from the data acquisition and elaboration to the vulnerability analysis and proposal for a non-invasive strengthening procedure) of a monumental bell tower building is reported. An extensive program of structural and geometrical surveys has been planned and performed. The main goal of the breakdown was to assess the stability and the seismic vulnerability of the bell tower. Moreover, an innovative use of the drone-based survey for the computation of the geometry of the structure is proposed, in order to significantly reduce the time-cost expenditure of the structural assessment, without any significant lack in the accuracy of the measurements. The resulting object, obtained from the drone-based digitalized survey, was inputted and set in a Finite Element Method (FEM) code for structural modelling. Moreover, a nonlinear kinematic analysis was performed to individuate the possible failure mechanisms. Finally, a non-invasive strengthening procedure, aiming to the improvement of the seismic capacity, is proposed. [ABSTRACT FROM AUTHOR]