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Many historical cities enjoy the presence of masonry buildings with inestimable historical, artistic and cultural value. Old masonry buildings often suffer structural deficiencies, design faults and materials aging process. In recent years, many researchers focused their attention on the opportunities that structural health monitoring (SHM) can ensure for the health state of existing masonry structures, where damage can be difficult to be promptly predicted, pontentially causing abrupt collapses, with high risks for the community. This paper presents an experimental study on the effectiveness of two types of stress sensor for SHM of new masonry elements. Ceramic piezoelectric sensors and capacitive sensors were installed in mortar joints of two series of specimens made of calcarenite stone masonry and clay brick masonry. All specimens were tested under uniaxial compression with displacement control, to assess the effectiveness of sensors in recording pressure variation within the different types of masonry and therefore testing their potential use for SHM applications. Even though both the ceramic and capacitive sensors were designed as stress sensors for concrete structures, their installation within mortar joints provided a good response, based on the comparison with standard measurement devices. Results demonstrate the suitability of the sensors even for SHM of masonry structures.

Structural Health Monitoring (SHM) represents a strategic solution for the preservation of cultural heritage buildings. Existing masonry structures often suffer reductions in mechanical performances due to physiological aging of material constituents, external actions, and effect of catastrophic natural events. In many cases, the prompt prediction of damage in masonry elements is difficult and it can cause sudden collapses, compromising the safety of people. The proposed experimental study examines the effectiveness of two low-cost and innovative stress sensors, i.e. piezoelectric and capacitive stress sensors, for SHM of masonry structures. To this scope, the sensors were embedded in the mortar joints of two small-scale clay brick and calcarenite masonry wall specimens consisting of three panels. Experimental tests were carried out by applying a constant vertical compressive load at the top of each specimen and simulating the damage with a progressive reduction of the cross-section of one of the panels. During the tests, the vertical stress distributions (and their variations), were monitored by the sensors. Experimental outcomes from sensor reading were then compared to that numerically provided by a refined finite element simulation of the test. Results will show that vertical stress variations in masonry structures can be effectively accounted by the adopted sensors and potentially interpreted for the early prediction of structural damage.

This paper presents a pilot study on the characterization of the high-strain rate compressive behavior of a novel concrete with two different substituted recycled plastic aggregates. A reference mix with an average compressive strength of about 55MPa is considered. Recycled PolyEthylene Terephthalate (PET) powder and recycled mixed plastic (composed of PolyPropylene (PP) and PolyEthylene (PE)) granules were adopted to substitute fine and coarse aggregates. Two different substitution strategies are employed. In the first one, the PET powder is used to substitute the fine sand by volume. In the second one, the PET powder is used to substitute the fine sand while the recycled mixed plastic granules are used to substitute the coarse sand and fine coarse aggregates by volume (50% for PET powder and 50% for recycled mixed plastic granules). Four total replacement levels (5%, 10%, 20%, and 30%) by volume were considered. The fresh concrete properties (slump and density) and quasi-static compressive behavior, are investigated. The micro-scale characterization of the material using SEM scans provided a complete understanding of the observed macro-scale behavior. Tests were performed using conventional quasi-static loading with a compressive testing machine and high-strain rate tests with a Φ80-mm Split-Hopkinson Pressure Bar (SHPB) for strain rates up to 200s−1. The dynamic tests revealed the marked strain rate dependency, although specimens with large plastic volume substitution were more sensitive to the strain rate effect. A probabilistic data-driven model for the Dynamic Increase Factor (D I F) is also proposed based on the test data. Ultimately, this study indicates that the proposed material has a good high-strain rate compressive behavior and can be a promising material to be employed for protective techniques against impact and blast loads.

The aim of this paper is to check the accuracy of analytical capacity models available for the prediction of out-of-plane strength of unreinforced masonry (URM) infill walls. The accuracy of the available models is checked by detailed comparison with the existing experimental results. In doing so, both types of capacity models are evaluated: Type I for the prediction of the strength in the undamaged state, and Type II for the prediction of strength reduction in the in-plane damaged state. Results from the calculations are discussed, and the best among the available models are recommended. Furthermore, the influence of orthotropy of the infill masonry in the out-of-plane capacity predicted by the models is discussed. The paper also highlights the prospect of using the capacity models in the cases of infill-beam gap and infill with openings. In the paper, the best pairs of models (composed by a model for the prediction of the out-of-plane strength in the undamaged state and a model for the prediction of the reduction of the out-of-plane strength in the damaged state, not necessarily provided by the same author) for URM infill walls, are suggested for the first time.

The growth of urbanization in the last decades has already created a considerable number of Construction and Demolition Waste (CDW) materials. Concrete, bricks, glass, and tiles are widely used in residential construction accounting for a large proportion of CDW. The use of CDW as aggregates in the new concrete mixture has been recognized as an attractive approach to conserve natural resources and reduce the environmental influence of the construction industry. Nowadays the application of crushed bricks as coarse aggregate has recently been a reasonable target of research. However, construction structure and material can be subjected to vehicular impacts (e.g., cars, trucks, trains, boats, aircraft, etc.) and to other complex fast varying dynamic loads during their service life. Given that response of different aggregate concrete can be quite different due to its sensitivity to strain rate effects, the high-strain rate compressive behavior of recycled bricks aggregate concrete (RBC) is with little attention yet, the availability of this data is crucial for the definition of the constitutive laws accounting for the strain rate effects and allows for the evaluation of the structural response under fast varying loads such as impacts and blasts. The dynamic compressive behavior of RBC under high strain rate is investigated by large diameter Split-Hopkinson Pressure Bar (SHPB, diameter is 155 mm) in this study. Specimens are prepared by four different substitution levels respectively, from 0% (natural plain concrete) to 100% (all coarse aggregate is substituted by crushed bricks). A total of 36 specimens (with a diameter of 150mm, and a height of 75mm) are tested under three different air pressure corresponding to three strain rates. Tests can reach a maximum strain rate of 100s−1. The stress-strain relationships and the dynamic increase factor (DIF) for RBC under different strain rates are obtained and discussed. The results show that RBC is quite strain-rate sensitive constructional material.

In reinforced concrete (RC) multi-storey buildings, the important role of the seismic interaction of structural frames with masonry infills has been revealed by several earthquakes and investigated by many authors. Recently, several innovative infill solutions have been proposed to mitigate such interaction, which could result in widespread damage in both the masonry and the RC structure and sometimes jeopardize the building stability and the occupants’ safety. One solution consists in the partitioning of the masonry infill into several sub-panels, relatively sliding along specific joints. This paper investigates the seismic assessment of this technological solution in the framework of performance based earthquake engineering. A two-dimensional five-storey RC seismic-resistant frame is selected as case study and the performance is assessed by comparing the responses of the same structure infilled with different solutions, made of sliding joints or traditional masonry, or in the bare configuration. Incremental Dynamic Analyses (IDA) is used for the probabilistic determination of fragility curves of the structures. Results show the seismic fragility and reliability of the different investigated structures, especially addressing the probabilities of occurrence of damage at different limit states and quantifying the associated expected annual loss.

A new multistrut macromodel for the analysis of the progressive-collapse response of infilled reinforced concrete (RC) frames is presented in this paper. The model consists of three struts: two outer infinitely rigid and resistant struts and one inner fiber-section strut. The inclination of the struts as well as the stress-strain response are modulated by two parameters that are obtained by means of analytical correlations provided in the paper. The latter link the geometric and mechanical properties of an infilled frame to the geometric configuration and mechanical response of the equivalent strut model. This confers the model the capability to adapt to consider different collapse configurations. The analytical correlations are obtained from an experimental data set of pushdown tests, enlarged with data from refined finite-element (FE) simulations. Validation tests are finally carried out comparing the model prediction with results of experimental and FE pushdown tests not considered for the definition of the empirical database. Results show that, because of its flexibility, the model is sufficiently reliable and, at the same time, of simple implementation in FE analysis software to perform progressive-collapse simulations.

During the last years, several mechanics-based macromodels have been proposed to assess the cyclic response of infilled RC frames. However, the uncertainties behind the assumptions on damage and failure mechanisms compromise the reliability of such approaches. For this reason, this paper proposes a new data-driven hysteresis model for the cyclic response of infilled RC frames. The infill panel is schematized as a single-degree-of-freedom element, whose constitutive law is given by the proposed hysteresis model. The model combines a degrading Bouc-Wen element with a slip-lock element, which is introduced specifically to reproduce the pinching effect due to crack openings in the masonry panel. The parameters governing the model have clear physical meanings and are calibrated on the basis of an experimental data set of cyclic responses of single-story single-bay RC infilled frames. The calibrations are carried out by means of a genetic algorithm-based optimization. Analytical correlation laws linking the model parameters with geometric and mechanical properties of the RC infilled frame are proposed and validated by blind validation tests. Results show adequate accuracy of the model in reproducing the cyclic response of infilled frames characterized by significantly different geometrical and mechanical features. The model is defined by a smooth analytical hysteresis law, with great advantages regarding numerical stability and computational effort. This makes it suitable for dynamic and stochastic simulations.

In the framework of seismic design of structures, response spectrum analysis (RSA) is the most commonly used approach in practice. The most popular combination rule is the complete quadratic combination (CQC) which is also prescribed by the most of seismic design codes and is based on the assumptions that the seismic acceleration is a white noise process and the peak factor ratios associated to the total and modal responses are unitary. Recently, the damping adjusted combination (DAC) rule has been developed for base-isolated structures to overcome the aforementioned simplified assumptions. Although it has been proved that the simplifications about peak factors lead to noticeable errors in the case of base-isolated structures, the accuracy gain of DAC with respect to CQC in the case of fixed-base structures is still unknown. Therefore, the paper presents an in-depth study on the RSA of three-dimensional frame structures, aimed to evaluate the accuracy of the above methods. Two reference classes of frame structures having different degree of complexity are considered. Average interstorey drift and floor torsion responses, obtained from a set of Time History Analyses are compared with those of the modal combination rules. Lognormal joint probability density functions of the predictive errors from CQC and DAC are finally evaluated for a reliability assessment of the two combination rules under bidirectional seismic excitations.

A brief introduction to Filippo Di Trapani's Book "Dilthey e il giovane Hegel"

Assessment of seismic vulnerability of urban areas provides fundamental information for activities of planning and management of emergencies. The main difficulty encountered when extending vulnerability evaluations to urban contexts is the definition of a framework of assessment appropriate for the specific characteristics of the site and providing reliable results with a reasonable duration of surveys and post-processing of data. The paper proposes a new procedure merging different typologies of information recognized on the territories investigated and for this reason called “hybrid.” Knowledge of historical events influencing urban evolution and analysis of recurrent building technologies are used to evaluate the vulnerability indexes of buildings and building stocks. On the other hand, a vulnerability model is calibrated by means of experimental and numerical investigations on prototype buildings representative of the most recurrent typologies. In the final framework, the vulnerability index, calculated through simplified assessment forms, is linked to the seismic intensity expressed by the peak ground acceleration and associated with an index of damage expressing the economical loss. The procedure has been tested on the urban center of Lampedusa island (Italy) providing as the output vulnerability index maps, vulnerability curves, critical PGA maps, and estimation of the economical damage associated with different earthquake scenarios. The application of the procedure can be suitably repeated for medium-to-small urban areas, typically recurring in the Mediterranean by carrying out each time a recalibration of the vulnerability model.

The assessment of the capacity of RC masonry infilled RC structures constitutes nowadays a still debated issue. Pushover based procedures for the evaluation of seismic performance, such as N2 method, are largely used in practice and in force in several technical codes. The latter has proved to be reliable for a large number of structural typologies, however in the case of infilled frames, the choices made on the modelling strategy may radically modify the outcomes observable from the capacity curves and the consequent performance levels achievable. In the paper, the extent of different modelling choices on the results of the application of N2 procedure is investigated by the deep analysis of a case study of a scholastic facility in Italy. Three modelling hypotheses are considered: neglecting of infills; equivalent strut macromodeling and equivalent strut macromodeling with prediction of additional shear demand arising because of the interaction with the infills. The impact of each on the capacity curves and then on the reliability of the overall N2 procedure is discussed pointing out the major criticalities.

The opportunity to locate and quantify the major criticalities associated to natural catastrophic events on a territory allows to plan adequate strategies and interventions by civil protection bodies involved in local and international emergencies. Seismic risk depends, most of all, on the vulnerability of buildings belonging to the urban areas. For this reason, the definition, by a deep analysis of the territory, of instruments identifying and locating vulnerability, largely favours the activities of institutions appointed to safeguard the safety of citizens. This paper proposes a procedure for the definition of vulnerability maps in terms of vulnerability indexes and critical peak ground accelerations for mid-small urban centres belonging to Mediterranean areas. The procedure, tested on the city centre of the Island of Lampedusa, is based on a preliminary historical investigation of the urban area and of the main formal and technological features of buildings involved. Moreover, the vulnerability of the constructions is evaluated by fast assessment methods (filling of evaluation forms). The vulnerability model, allowing the definition of the fragility curves, is calibrated on the basis of the results of an identification process of prototype buildings, selected to be adequately representative. Their characterizations have been provided using the results of an experimental dynamic investigation to develop high representative numerical model. Critical PGA values have been determined by pushover analyses.The results presented provided an unambiguous representation of the major criticalities with respect to seismic vulnerability and risk, of the city centre of the island, being a suitable tool for planning and handling of emergencies.

Native generalist grazers can control the populations of non-indigenous invasive algae (NIIA). Here, it was found that the simultaneous consumption of two co-occurring NIIA, Caulerpa cylindracea and C. taxifolia var. distichophylla, hinders the grazing ability of the main Mediterranean herbivorous, the native sea urchin Paracentrotus lividus. The ingestion of any of the two NIIA alone did not produce any difference in sea urchin righting time with respect to usual algal diet. In contrast, the simultaneous consumption of both NIIA, which grow intermingled in nature and are consumed by P. lividus, retarded its righting behavior. Such result reveals substantial physiological stress in the sea urchin, which resulted in reduced motility and coordination. The reported findings reveal the potential of NIIA co-occurrence to escape the supposed control exerted by the main native generalist grazer in Mediterranean sublittoral communities, which in turn can be locked in an “invaded” state.

Background: The recent seismic events in Italy have underlined once more the need for seismic prevention for historic constructions of architectural interest and in general, the building heritage. During the above-mentioned earthquakes, different masonry monumental buildings have been lost due to the intrinsic vulnerability and ageing that reduced the structural member strength. This has made the community understand more that prevention is a necessary choice for the protection of monuments. Objective: The paper aims at demonstrating a strategy of investigation providing the possibility of health judgment, identifying a computational model for the assessment of structural capacity under service and exceptional loading like/due to high-intensity earthquakes. Considering its cost, the proposed approach is applicable only for monumental buildings. In detail, activity regarding the Bell Tower of the Palermo Cathedral is described. This investigation is framed in a huge campaign aimed at assessing the health of monuments in Palermo and their capacity to resist expected seismic actions. Methods: The process of the dynamic identification of the Bell Tower of Palermo Cathedral is discussed starting from the measurement of the response by high sensitivity seismometers and the analysis of the response signals. Then, the formulation of a Finite Element (FE) model of the tower is proposed after the identification of the main modal shapes. Once the Finite Element (FE) model was assessed, it was possible to evaluate the Bell Tower safety level in service and faced with exceptional loads. Results: The structural signals recorded along the height of the tower were analyzed to recognize the variation of the frequency content varying the external environmental loads. The signals were processed to obtain the experimental modal shapes. An FE model was defined whose mechanical parameters were successfully calibrated to give the experimental modal shapes. Conclusion: The analysis of the response signals made it possible to identify the actual behavior of the structure and its compatibility with the service loads. Further, an effective structural model of the Bell Tower of Palermo Cathedral was possible for assessing its capacity level.

The paper presents the results of some full-scale tests regarding the base-isolation system of the emergency room building of the polyclinic hospital in Palermo (Italy). This building has been recently realized and its base isolation system is characterized by double friction pendulum isolators. Static lateral pushing tests were aimed at identifying fundamental mechanical properties of the whole isolation level (e.g. friction forces and stiffness) in order to verify the agreement with the design hypotheses. Further dynamic tests provided different displacements of the isolated base followed by the instantaneous release (snap-back tests), in order to verify the effectiveness, the mechanical parameter in dynamics and re-centering capacity of the isolation system. The design of both the types of test and the respective results and interpretations are illustrated in the paper highlighting a number of issues arising when arranging such kind of investigations on full scale buildings.

A new macroelement model is presented in this paper for the simulation of the in-plane (IP) and out-of-plane (OOP) response of infilled frames subjected to seismic actions. The model consists of two diagonal, one horizontal, and one vertical struts. Each strut is represented by two fiber-section beam-column elements. The model is able to capture the arching action of the wall under an OOP load as well as the interaction between the IP and OOP actions. The proposed modeling approach is sufficiently simple and efficient that it can be used for the static or dynamic analysis of an entire structural system. An experimental validation has been carried out. A further numerical study performed with the macroelement model has shown that wall damage due to IP loads can significantly reduce the OOP resistance of the wall, and this influence depends on the slenderness (height/thickness) of the wall. A more slender wall will suffer a more significant loss of OOP resistance.

Infill masonry walls in framed structures make a significant contribution to the response under seismic actions. With special regard to reinforced concrete (RC) structures, it is known that internal forces modifications caused by the frame–infill interaction may be not supported by the surrounding frame because of the additional shear forces arising at the ends of beams and columns. Such additional forces may lead to the activation of brittle collapse mechanisms and hence their prediction is basic in capacity assessment, especially for structures that disregard the details for seismic zones. In this paper a parametric study is carried out addressed to the prediction of the shear forces mentioned before. The results of this study can be used as a support when the simplified model is adopted consisting in the substitution of infill with an equivalent pin jointed concentric strut, because in this case the structural analysis fails in the prediction of the shear forces in question. Through the paper, in which existing RC infilled frames designed only for vertical loads are discussed, analytical laws, depending on the level of the axial force arising in a concentric strut equivalent to infill, are proposed, the above analytical law allowing to correct the local shear forces in the frame critical sections, which are not predictable in the case of substitution of infill with an equivalent concentric strut.

Seismic engineering is constantly looking for new strategies and methods that provide designers with the opportunity to get more and more efficient solutions both from the performance and from the economic point of view. In this context, the scientific community is called not to miss its support and to face the new challenges coming from the observation of the damage caused by the recent earthquakes. This Special Issue of “Ingegneria Sismica” collects some works focusing the theme of the seismic vulnerability, some of them specifically refer to mitigation strategies while others address modeling strategies. Obviously, for the multiplicity of aspects involving the theme of "seismic vulnerability", only a few issues have been discussed. In particular, some works deal with the theme of base isolation from the point of view of design and seismic reliability, others are focused on the theme of structural robustness considered as a further goal of seismic design. Further papers are deepening the problems of interaction between frames and masonry infills, providing simplified modeling strategies, suggesting criteria to reduce interaction effects, but above all by providing methods for the analysis of combined in-plane / out-of-plane behavior. The themes related to modeling are also addressed with particular care. Other papers in fact face the issues of model uncertainty and of the reliability of constitutive laws for normal and high strength confined concrete, being the latter of fundamental importance for the assessment of the rotational capacity of reinforced concrete structural elements under seismic actions. Moreover, the problem of the reliability of seismic vulnerability assessment methods is also discussed, with particular reference to multimodal "pushover" analysis. This Special Issues is composed of 10 paper produced by 29 authors, to whom we would like to address a special thank for the effort made during the editorial phases. Finally, the Guest Editors, Paolo Castaldo, Liborio Cavaleri e Fabio Di Trapani, wish to thank Prof. Gianmario Benzoni and Prof. Rosario Montuori for this opportunity and for their assistance.

Artificial and natural records are commonly employed by researches and practitioners to perform refined seismic assessments of structures. The techniques for the generation of artificial records and their effectiveness in producing signals which are significantly representative of real earthquakes are still debated as well as results of the consequent seismic assessment to expect from their application. The paper presents an in-depth comparative study highlighting the effect of employing different typologies of artificial ground motion records on seismic assessment results, especially addressing seismic fragility curves. Three sets of 50 stationary, nonstationary evenly modulated and fully nonstationary accelerograms are generated based on design spectrum compatibility criteria. Standard nonlinear time history analyses of 4 reference structural models of reinforced concrete (RC) structures having different degree of complexity are firstly carried out monitoring results in terms significant engineering seismic demand parameters. So far, incremental dynamic analysis (IDA) is used to derive fragility curves. Peak ground acceleration and spectral acceleration are used as possible intensity measures in order to compare results of seismic fragility assessment. The combination of structural irregularity, severe damage and input typology is finally analyzed and discussed in order to assess the degree of dependence of fragility assessments on the typology of signal adopted.

Structural frames, constructed either of steel or reinforced concrete (RC), are often infilled with masonry panels. However, during the analysis of the structural frames, it has become common practice to disregard the existence of infills because of the complexity in modeling. This omission should not be allowed because the two contributions (of infills and of frames) complement each other in providing a so different structural system. The use of different modeling assumptions significantly affects the capacity as well as the inelastic demand and safety assessment. In specific, the adoption of equivalent diagonal pin-jointed struts leaves open the problem of the evaluation of the additional shear on columns and consequently of the choice of a proper eccentricity for the diagonal struts. In this context, this paper presents the results of a real case study. The seismic performance of the RC structure of a school is evaluated by using concentric equivalent struts for modeling infills and the level of the additional shear on the columns is fixed as a rate of the axial force on them in agreement to a strong correlation obtained after a numerical experimentation. Hence, the applicability of the correlation mentioned before is shown and the form in which the results can be provided is presented. The characteristics of the new approach, first time applied to a real case, are highlighted by a comparison between the performance obtainable with different modeling detail levels of the infills. Through the paper, it is proved that the simplified evaluation of the additional shear demand produced by infills just for the base columns is sufficient to warn that a simplified model disregarding infills or based on the use of concentric struts for the infills may considerably overestimate the structural capacity. Further, by the study of a real case, the paper provides an overview of the models developed by the authors to obtain the capacity of reinforced concrete framed structure for the practical applications.

Steel jacketing of reinforced concrete (RC) columns is a common retrofitting technique used to restore bearing and deformation capacity of buildings presenting structural deficiencies. For practical reasons, steel angles are in several cases arranged leaving a gap with the end beams or slabs. Despite this disconnection, the angles are still able to support a non-negligible portion of load because of the frictional forces developed along the column-angle contact interface. In these cases, the definition of computational numerical and analytical models for the assessment of reinforced cross sections becomes more complex and must be handled with care. The actual load-carrying capacity of the angles is a function of lateral confinement pressure, cohesive strength, and the friction coefficient between the materials. This paper presents first the results of an original experimental campaign on RC column specimens with and without steel jacketing subjected to compressive axial and eccentric tests. Subsequently, a new approach is proposed to define a plane fiber-section model of the reinforced cross section accounting for the frictional action occurring along the column-angle interfaces. An equivalent stress-strain constitutive model for the angles is calibrated and validated through comparison with experimental results. Finally, a simple analytical stress-block procedure to derive continuous and simplified axial force bending moment domains is illustrated as a method for the hand-verification of reinforced cross sections.

Infill-frame interaction constitutes a still open question both in research and in practicing engineering. Computational models used to predict this interaction are, in most cases, addressing the estimation of the response of the infilled frames when subjected to actions parallel to their plane. However, the observation of the post-earthquake damage has demonstrated that infills, weakened by the in-plane actions, may fail out-of-plane increasing the risks associated to the earthquake scenarios. In spite of this, different studies have shown that infills, if properly designed and supported by the frame, exhibit a significant strength and displacement capacity when called to resist to out-of-plane actions, offering the possibility to develop an arching mechanism in their deformed configuration. The prediction of the combined in-plane out-of-plane response prefigures the new goal of the seismic assessment of masonry infilled frames. This paper presents an in-depth literature review of the capacity models developed for the prediction of the out-of-plane response of infilled frames, from the first flexural based computational models to the models implementing the arching action theory in their formulation. A comparison between the results obtainable is provided in order to compare the models reliability against the results of different experimental tests. A final discussion is devoted to the effectiveness the recent integrated in-plane/out-of-plane macromodels used in 3D structural models. A new promising approach, based on the use nonlinear fiber-section elements, is also outlined providing a numerical testing of the capacity of such elements to naturally account for the out-of-plane arching mechanism.

A common way to model infill-frame interaction is the use equivalent strut macromodels. In most cases these are compression only resistant truss elements defined with a multi-linear axial-force / axial-displacement law. The main difficulty in using this approach is to correctly calibrate such a force-displacement curve (slope of ascending and post-peak branches, critical yielding, peak and residual forces) because of the large number of variables (mechanical and elastic properties of materials) and the different possible damage mechanisms activated for the frame-infill system. Another possible way is using fiber-section elements as diagonal struts. In this case the force-displacement law is substituted by a stressstrain curve. In both cases a reliable definition of inelastic response of the strut, based on mechanical approaches, which are valid in general is not easy, as most of models provide rules valid for specific typologies of infills (e.g. weak or strong infills) and frames (e.g. concrete or steel frames). Based on this, the paper proposes the use of fiber-section diagonal struts with a concrete-type stress-strain relationship calibrated using a semi-empirical approach. The Kent-Scott-Park model, depending on four parameters, is used as reference constitutive law for the strut. Experimental data and additional numerical simulations are used to derive semiempirical correlations linking geometrical and mechanical properties of the frame-infill system to the aforementioned parameters governing nonlinear response of the diagonal. Analytical expressions of the best fitting curves are finally provided and suggested as design equation.

This chapter suggests that an extension of the capability of the traditional inplane macro-models to capture the simultaneous in-plane and Out-Of-Plane (OOP) response of infills. A new simplified macro-model for the assessment of both in plane and out-of-plane responses of infilled frames was developed and validated. The possibility to simulate the arching action is achieved by using distributed plasticity fiber-section elements, able to directly account for the coupling between axial load and bending moment. The arching action is explicitly introduced by the use of fiber-section beam-column elements, which can model the coupling between axial-load and bending moment. The model presented is able to predict simultaneously the In-Plane and OOP response explicitly accounting for arching mechanism and two-way action. The OOP tests were carried out by inflating an air bag enclosed by a reaction panel and monitoring the response in terms of force and displacement of the mid-span joint.

During the last decades, several macro-models have been proposed for the modelling of the infill panels' contribution to the lateral strength of frames. Despite all this effort, a robust model, which takes into account the influence of the vertical load, is not yet available. Furthermore, the influence of the very common case of infill walls with openings, such as windows and doors, has been neglected in all the code provisions that have been published so far. In this paper, an updated macro-model, based on the equivalent pin-jointed diagonal compressive strut, is presented. The proposed macro-model is able to represent the stiffening effect of the infill panel with openings by taking into account both the size of the opening and the vertical load acting on the frame. Detailed and in-depth parametrical investigation, based on finite element analysis, shows that the proposed mathematical macro-model can be used as a reliable and useful tool for the determination of the equivalent compressive strut width since it accounts for a large number of parameters, which are not generally accounted for by the already available models in the literature.

Axial load and biaxial bending strongly influence the deformation capacity of column cross-sections, in most cases causing a non-negligible loss of curvature and ductility with respect to the case of pure bending along principal axes, commonly assumed as the basic condition to assess the inelastic capacity. In consideration of this the paper investigates the biaxial deformation performance of RC rectangular cross-sections belonging to one-dimensional elements, focusing on the influence of some parameters as the cross-section aspect ratio and the distribution of the rebars, as well as the mechanical characteristics of concrete and steel and the impact of biaxial/axial stresses. In the paper ultimate curvature domains, yielding curvature domains and ductility domains as novel assessment tools are provided. The deformation performance of the cross-sections, represented by the above domains, is discussed through a parametric study on the sensitivity of the domain shape to the major governing geometrical and mechanical factors. Further the role of axial load in terms of capability to level out the deformation capacity associated to different planes of bending is highlighted. Finally, a definition of specific biaxial ductility indicators is provided. The latter are proposed as measures to classify the biaxial deformation capacity associated with rectangular RC cross-sections for an engineered design.

The fundamental period is one of the most critical parameters for the seismic design of structures. There are several literature approaches for its estimation which often conflict with each other, making their use questionable. Furthermore, the majority of these approaches do not take into account the presence of infill walls into the structure despite the fact that infill walls increase the stiffness and mass of structure leading to significant changes in the fundamental period. In the present paper, artificial neural networks (ANNs) are used to predict the fundamental period of infilled reinforced concrete (RC) structures. For the training and the validation of the ANN, a large data set is used based on a detailed investigation of the parameters that affect the fundamental period of RC structures. The comparison of the predicted values with analytical ones indicates the potential of using ANNs for the prediction of the fundamental period of infilled RC frame structures taking into account the crucial parameters that influence its value.

Reinforced concrete (RC) jacketing is a common method for retrofitting existing columns with poor structural performance. It can be applied in two different ways: if the continuity of the jacket is ensured, the axial load of the column can be transferred to the jacket, which will be directly loaded; conversely, if no continuity is provided, the jacket will induce only confinement action. In both cases the strength and ductility evaluation is rather complex, due to the different physical phenomena included, such as confinement, core–jacket composite action, preload and buckling of longitudinal bars. Although different theoretical studies have been carried out to calculate the confinement effects, a practical approach to evaluate the flexural capacity and ductility is still missing. The calculation of these quantities is often related to the use of commercial software, taking advantage of numerical methods such as fibre method or finite element method. This paper presents a simplified approach to calculate the flexural strength and ductility of square RC jacketed sections subjected to axial load and bending moment. In particular the proposed approach is based on the calibration of the stress-block parameters including the confinement effect. Equilibrium equations are determined and buckling of longitudinal bars is modelled with a suitable stress–strain law. Moment–curvature curves are derived with simple calculations. Finally, comparisons are made with numerical analyses carried out with the code OpenSees and with experimental data available in the literature, showing good agreement.

Following a thorough and lengthy procedure, we would like to thank all contributors for their highest calibre papers, which comprise the Special Issue on “Seismic analysis and risk mitigation of existing constructions” of the Open Construction and Building Technology Journal. The topic of the Special Issue encompasses a large number of issues spanning the design of special interventions for the reduction of the effects of earthquakes on civil structures and infrastructures, to the structural identification and assessment issues. The field of seismic engineering is continuously looking for new strategies and methods, which empower the designers and make them able to obtain more accurate response predictions. Researchers are involved in this process and are called to successfully encounter new challenges emerging from the increasing need for the assessment of existing constructions, especially when assuming strategic roles. As is also reflected by the papers presented in the Special Issue, the continuous advances of the research in this field moves across two basic directions. On the one hand, there is the direction of the robustness and the reliability of the recent nonlinear seismic assessment methods (static, dynamic, incremental dynamic). Several approaches can be followed to predict the response of structures to strong ground motions; however the results coming from each of them are in some cases conflicting and not always amenable to easy interpretation. On the other hand, the reliability of structural models still remains a major task of structural engineering and of seismic engineering in particular. Mathematical models have to reproduce the physics of structures and its evolution during complex damaging processes. Global and local models tend to reflect this by minimizing the loss of information. In the Special Issue, we are proud to present state-of-the-art research findings described in detail in 9 papers authored by 27 researchers of different universities in Italy, California (USA), Greece and United Kingdom. The papers deal with the seismic analysis and risk mitigation aiming to address different purposes by proposing numerical, analytical approaches and experimental tests.

L'incamiciatura metallica di pilastri in c.a. mediante angolari e calastrelli (steel jacketing) è una tecnica comunemente adottata, per migliorare la capacità resistente e deformativa di edifici esistenti. Nel caso in cui gli angolari non siano direttamente posti in contatto con le zone nodali (in corrispondenza di travi e solai), la definizione del modello computazionale della sezione trasversale deve essere gestita con cautela poiché differente è il regime di trasferimento degli sforzi che si instaura. Nel caso di applicazione di uno strato intermedio di malta fra acciaio e calcestruzzo, l'effettiva capacità di carico degli angolari è funzione della pressione di laterale confinamento, della la coesione e del coefficiente di attrito fra i materiali. L'attribuzione di tali parametri meccanici non è immediata e la definizione del modello computazionale richiede accorgimenti specifici. Il presente studio è dedicato all'implementazione di un modello numerico per le sezioni in c.a. rinforzate, includente gli effetti dell'interazione attritiva di interfaccia. Il modello è calibrato e validato attraverso il confronto con i risultati di una campagna sperimentale su campioni di colonne rinforzate soggette a compressione e pressoflessione. Sulla base dei risultati viene infine proposta una procedura analitica semplificata per la definizione dei domini di resistenza delle sezioni rinforzate, fornendo i parametri di taratura del legame stress-block per il calcestruzzo

In the Mediterranean Sea the co-occurring sea urchins Paracentrotus lividus and Arbacia lixula are usually considered to share the same ecological role in the formation of barren from Cystoseira canopy. However, their foraging ability may vary due to feeding behavior and species-specific morphological traits. The relative effects of P. lividus and A. lixula on Cystoseira canopy was tested experimentally both in the laboratory, at a density of about 20 ind./m 2 , and in the field by gut content analysis. Field and laboratory results show that A. lixula is unable to affect Cystoseira spp. Furthermore, these results confirmed the great ability of P. lividus to consume Cystoseira canopy, thus supporting the evidence of the major role of this species in the creation of a barren state.

Despite the fact that the fundamental period appears to be one of the most critical parameters for the seismic design of structures according to the modal superposition method, the so far available in the literature proposals for its estimation are often conflicting with each other making their use uncertain. Furthermore, the majority of these proposals do not take into account the presence of infills walls into the structure despite the fact that infill walls increase the stiffness and mass of structure leading to significant changes in the fundamental period numerical value. Toward this end, this paper presents a detailed and in-depth analytical investigation on the parameters that affect the fundamental period of reinforce concrete structure. The calculated values of the fundamental period are compared against those obtained from the seismic code and equations proposed by various researchers in the literature. From the analysis of the results it has been found that the number of storeys, the span length, the stiffness of the infill wall panels, the location of the soft storeys and the soil type are crucial parameters that influence the fundamental period of RC buildings.

The chance to locate and quantify the major risks associated to natural catastrophic events on a territory allows to plan adequate strategies and interventions by civil protection bodies involved in local and international emergencies. The seismic risk depends most of all by the vulnerability of buildings belonging to the urban areas. For this reason the definition, by a deep analysis of the territory, of instruments identifying and locating vulnerability, largely favours the activities of institutions appointed to safeguard the safety of citizens. Seismic and hydro-geological risks constitute the major component of the activities involving assistance actions carried out by civil protection bodies because of their repetitiveness and the amount of human resources needed to face the emergencies. The possible coordinate action and cooperation between different countries is fundamental importance, especially if the procedures are based on standardized rules and civil protection plans are characterized by consciousness of the territory and the associated risks. The promptness of the response is basic for the success of the operations. This feature is however not only achievable by practice exercises aimed to implement a responsiveness system to emergencies, but also through a deep understanding of the existing risks and the major exposure recognized for the urbanized contexts. The challenge for the assessment of seismic vulnerability of buildings is not easy because it involves a large amount on constructions to investigate in a reasonable time. Several researchers, based on the post processing of data coming from the observation of damaged buildings, proposed simplified relationship linking a vulnerability index with the intensity of a seismic event (Benedettini and Petrini (1984), Braga et al. (1984), Angeletti et al. (1988), Casolo et al. (1993). In other studies the interest has been addressed to the definition of fast assessment methods for the vulnerability index and the relative large scale application (Martinelli et al. (1999), Dolce et al. (2004), Dolce and Moroni (2005), Dolce and Martinelli (2005). In this summary the outputs of the activity carried out within the research project "SIMITDevelopment of an integrated cross-border Italian-Maltese civil protection network" are presented with specific reference to the assessment of the seismic vulnerability of buildings and definition of vulnerability maps in terms of vulnerability index and peak ground acceleration limit values. In agreement with the scope of the paper, the criteria adopted for the assessment of vulnerability and definition of the vulnerability maps were calibrated to provide reliable predictions for typically small urban contexts, which are largely widespread in Mediterranean area. The representative test site selected for the activities was the city centre of the island of Lampedusa. The choice was particularly suitable for the prefixed purposes because of the opportunity to operate on a large quantity of buildings concentrated in a small area with and characterized by a repetitiveness of the constructive typology. The final gaol was to develop a standard procedure for the assessment of seismic vulnerability of small urban contexts widespread in the Mediterranean. The specific research activity carried out on the island has been divided in 4 phases, characterized by a progressive level of depth of the analysis, listed below: • Historical, critical, and typological analysis of the urban centre and typical buildings; • Simplified assessment of seismic vulnerability of buildings by standard vulnerability forms; • Choice and validation of a vulnerability model; Definition of fragility functions and vulnerability maps. The historical-critical study was aimed at the recognition of the urban evolution of the city centre of Lampedusa over the time and of the regulations succeeded which have changed the constructive and typological framework of buildings. The subsequent typological analysis of the buildings, performed through several surveys, made it possible to categorize the recurring structural types within the city centre of the island and their similarities and differences in relation to periods of construction. Such preliminary activities permitted to collect fundamental information, necessary for a fast and effective assessment of the buildings vulnerability, carried out by the use of evaluation forms already known in the literature and commonly used in Italy (GNDT (1994)) for the fast assessment of the vulnerability single buildings and building aggregates. The major output coming from the use of such kinds of vulnerability evaluation forms is constituted by possibility to determine a numerical vulnerability index, suitable to be adopted for the definition of the vulnerability maps. The definition of the fragility curves, which provide a relationship between the intensity of the seismic event (synthetically represented by the Peak Ground Acceleration) and the structural damage, passes through a preliminary calibration, necessary to adapt the vulnerability model (index of vulnerability vs. PGA) to the characteristic building context. In the current study, the calibration operations were performed by an experimental dynamic monitoring campaign on two prototype buildings, followed by the realization of the numerical structural models consistent with the experimental results. The seismic assessment of the prototype buildings by static pushover analysis made it possible the determination of the critical PGA values to be linked with indexes of vulnerability previously evaluated, in order to adapt the vulnerability model to the urban context of the island of Lampedusa. The final outputs are the fragility curves and the associated vulnerability maps for the urban area of Lampedusa, presented in terms of index of vulnerability and critical peak ground accelerations.

The deformation performance of the base cross sections of reinforced concrete buildings is fundamental when large seismic events occur allowing the structure to have large excursions in nonlinear field and guaranteeing an overall ductile behaviour. It is well known that the axial force acting on columns significantly reduces the curvature capacity of the sections and for this reason the technical codes give design criteria stating a limitation in order to preserve the displacement capacity. It is also recognized that when biaxial bending occur the cross section undergo a loss in strength capacity. Starting the study of from Bresler (1960), which provided suitable expression to predict 3D limit interaction surfaces, several numerical and analytical models were developed to take into account the biaxial interaction in strength. Simultaneously it is noteworthy to point out that the presence of biaxial bending also influences the deformation capacity of sections causing in most of the cases a relevant loss of the curvature and ductility available with respect to the one owned along the principal axes. This important issue is not faced by technical codes and not exhaustively treated in scientific literature as it was done for strength. Moreover nonlinear structural models based on lumped plasticity do not take into account these interaction aspects when defining plastic hinge properties in terms of curvature capacity. The paper presents a numerical study in which the deformation capacity of RC cross sections subjected to axial load and biaxial bending is investigated by means of a fiber discretization. A procedure for the numerical definition of biaxial domains of ultimate curvature, yielding curvature and curvature ductility is provided and the sensitivity of the biaxial deformation performance to some geometrical and mechanical parameters (aspect ratio, concrete strength and confinement efficacy) is discussed.

The recent large interest in nonlinear seismic analysis methods, static and dynamic, has required proper strategies of modeling based on reliable, and at the same time easy to use, constitutive laws for the structural elements. Regarding the behavior of framed structures, special attention has to be devoted to infills because of the key role they play in modifying overall stiffness, strength and ductility under seismic excitation. Pointing out the attention on this topic the paper discusses a criteria for modeling the structural behavior of infills based on a macromodeling approach, that is to say on the substitution of infills with diagonal pin jointed struts. Is here shown how multilinear plastic link elements governed by a hysteretic Pivot model, available in different FEM codes, can be appropriately used to model the equivalent struts to perform linear or nonlinear analyses. In order to enlarge experimental knowledge on cyclic behavior of infilled frames structures and as reference for developing the above mentioned modeling strategy, an experimental campaign on single-storey, single-bay, fully infilled frames with different kinds of masonry and subjected to lateral cyclical loads, was carried out, and some others available in the literature are referred to. Validation of Pivot modeling approach was carried out comparing experimental results and computer simulations of the experimental tests. In the paper hysteresis parameters values calibrating Pivot law are also given for involved masonry infills typologies and some proposals for correlation between strength and stiffness of infilled frames and of masonry infills are provided as a tool for the quick calibration of the Pivot model in practical applications.

A statistical non linearization method is used to approximate systems modeled by the Bouc differential equa- tion and excited by a Gaussian white noise external load. To this aim restricted potential models (RPM) are used, which are suitable for an extended number of nonlinear problems as have been proved several times. Since the solution of RPM is known by the probabilistic point of view, all statistical characteristics can be derived at once with advantages by the computational point of view. Hence, this paper discusses the possibility to determine sets of parameters characterizing po- tential models that are valid for describing a hysteretic behavior. In this way the characterization of the hysteretic behavior of a system can be performed with computational efforts lower than that normally requested. Keyword: Bouc model, energy dissipation, equivalent non linearization, hysteretic behavior, response statistics, restricted potential models.

The prediction of the response of infilled frames through the simplified approach of substituting the infill with an equivalent pin-jointed strut is treated. In this framework the results of an experimental study for the mechanical characterization of different types of masonry infills having the aim of estimating strength, Young modulus and Poisson's ratio are presented. Four types of masonry were investigated and subjected to ordinary compressive tests orthogonally to the mortar beds and along the directions of the mortar beds. The experimental campaign confirmed the possibility of using an orthotropic plate model for prediction of the Poisson's ratio and Young modulus along the diagonal direction of infills (these parameters are requested by a model already known in the literature for the identification of struts equivalent to masonry infills). The experimental campaign made it possible to recognise a correlation between the Poisson's ratios and the strengths of masonries investigated along the orthotropic axes and to obtain the diagonal Poisson's ratio without specific experimental tests. Finally, the experimental responses of some infilled frames were used to test the reliability of the model proposed here. © 2013 RILEM.

In this paper the results of an experimental investigation aimed to the assessment of Young moduli, rigidity moduli and other mechanical properties for different types of masonry are shown. The mechanical characteristics predicted by models proposed by some technical codes were compared against experimental data. This study was motivated by the suggestion of the Masonry Standards Joint Committee's (MSJC) code that, while proposing the use of such models, acknowledges the lack of testing in support of their validation. The experimental investigation has included compressive tests on components (blocks and mortar), diagonal compressive tests and ordinary compressive tests (orthogonally to beds joints) on portions of masonry. The details of the experimental campaign and the prediction capacity of the above models, for the types of masonry investigated, are presented.