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The conservation and the preservation of existing masonry buildings, most of them recognized as cultural heritage, require retrofitting techniques that should reduce the invasiveness and assure reversibility and compatibility with the substrate. In this perspective, the strengthening system should be able to improve the bearing capacity of the structural member and, at the same time, to assure mechanical and material compatibility. The use of Fabric Reinforced Cementitious Matrix (FRCM) composites is now recognized to be suitable for these purposes. Indeed, the inorganic matrix has comparable properties with respect to the existing historical mortars while the fabric has relevant tensile strength. At the same time, these systems assure satisfactory level of reversibility (or at least removability). In this scenario, the present research aims to investigate the FRCM-confinement of masonry columns focusing on the influence of specific parameters, still poorly investigated, in order to deeply understand their effect on the mechanical response. In particular, the experimental variables are: the type of masonry substrate (Tuff and clay brick with lime-based mortar), the type of FRCM system (glass dry mesh + lime-based mortar and steel mesh + lime-based mortar) and the number of plies (1, 2 and 3). In addition, a detailed experimental characterization of the utilized materials has been carried out, including bond tests between the reinforcement and the substrate. The results evidenced that the FRCM is an effective solution for masonry columns confinement once a proper design is performed, taking into account all involved parameters. The different strengthening systems exhibited different failure modes. Generally, a single ply of external reinforcement produced a negligible increase of bearing capacity. Both strengthening systems applied with multi-ply strengthening schemes produced a significant increase in terms of strength and ultimate axial deformation. This benefit was observed for both Tuff and clay masonry columns. Two available design-oriented formulas, reported in the Italian CNR (National Research Council) and ACI (American Concrete Institute) guidelines have been utilized, in order to further investigate their accuracy, mostly in the case of multi-layered reinforcement. The performed comparisons highlight that the two design relationships provide similar and accurate results when referred to the GFRCM (Glass-FRCM) system in 1- and 2-layer configurations, while the predictions appear conservative when 3 layers of GFRCM are utilized, for both masonry types. Considering the SRG (Steel Reinforced Grout) system, the results predicted by the two models are more scattered, mostly when the number of layers increases. In addition, the formulation proposed by CNR appears more accurate in the case of Tuff masonry while the ACI predictions are closer to the experimental results in the case of clay brick masonry.

The Stick-IT model (Stick for Infilled frames Typologies), that is a MDOF system consisting of a series of lumped masses connected by nonlinear shear link elements, was introduced to predict the response, in terms of interstory drift ratio (IDR) and peak floor acceleration (PFA), for infilled RC building typologies. Stick model parameters can be defined starting from low level building geometrical features, easily retrievable at the large scale, such as in plan dimensions, number of stories or the percentage of infills openings and considering the infills consistency. This paper investigates the applicability of Stick-IT to predict the performance and direct economic losses for existing RC infilled frame type buildings. In the framework of a performance-based assessment, the comparison of seismic-loss outcomes provided by using either a detailed finite element model (FEM) (L1) or simplified Stick-IT structural models (L2) are illustrated and discussed. The potential of Stick-IT model is investigated referring to a real building damaged and repaired after the 2009 L'Aquila earthquake and adopting as earthquake input records registered in the proximity of the building. Story-level building damage simulated by L1 and L2 models is compared to real damage, showing satisfactory prediction. The comparison of the real repair costs with those evaluated using L1 and L2 models provides encouraging validation. The application suggests that simplified models such as Stick-IT, despite the low level of information required for its application, can be usefully applied to perform damage and loss scenarios at the large scale. Matlab code to generate the Stick-IT, as well as the example code for the present study, are openly shared through the repository https://github.com/marcogaetanidaragona/Stick-IT.

Strengthening strategies have become extremely efficient as demonstrated in recent scientific works and real field applications. The recent calamitous events focused the interest on existing masonry structures. In the common practice the strengthening strategies are performed improving the load capacity of existing structural elements. However, especially for slender masonry elements like as arches and barrel vaults, the increase of load capacity may not be the only and optimal approach. The ductility capacity represents an important aspect that should be taken into account in a strengthening strategy. A great number of applications is performed without relying on and assessing the ductility of the strengthened elements. This approach could promote deleterious effects on the structural behavior due to the brittle behavior provided by excessive amount of strengthening. Furthermore, a strengthening strategy must respect the compatibility with the masonry substrate especially for heritage applications. The present paper focuses on the out-of-plane behavior of slender masonry elements strengthened with FRP or FRCM systems. A parametrical analysis was performed and results, in terms of bending moment–curvature diagrams and ultimate curvatures were analyzed in dimensionless form. The behavior of strengthened masonry is independent on the type of stress–strain constitutive relationship of composite, depending on mechanical fiber reinforcement ratio, ω. It is very important for practical applications when an overestimation of the effective amount of reinforcement is designed. In this sense the type of composite can be optimized, especially for poor masonry, where higher ω could promote brittle behaviors. At low ω, the type of the stress–strain constitutive relationship becomes a key aspect (e.g. linear or bi-linear strongly correlated to the type of composite: FRP or FRCM). Furthermore, the impact of the axial load both on the ductility capacity and on the load capacity becomes negligible at high values of ω. The results, provided in a dimensionless form, constitute the basis for a valid support to the design of interventions using composites on masonry structures. This work represents a preliminary study to highlight some issues often overlooked in the strengthening of masonry structures, based on direct application of available design guidelines. It is the basis for future development of normalized approaches to perform targeted experimental validations and optimize the design of strengthening systems.

Existing reinforced concrete buildings were mainly designed with old code provisions. This resulted in lack of proper seismic details and, in turn, the occurrence of premature brittle failures as frequently observed in the aftermath of recent seismic events. The shear failure of the joint panel is one of the main reason limiting the seismic performance of existing structural systems. Several retrofit solutions were proposed in the recent years to improve the joint panel shear strengthening and, nowadays, composite materials are frequently used in the common design practice. The widespread use of fibre-reinforced cement composites (FRCC) and high-performance fibre-reinforced cementitious composites (HPFRCC) opened new frontiers in the design of the shear capacity of RC members. The high tensile strength, toughness, and tolerance for damage make these materials attractive for the use in earthquake-resistant structures, with emphasis on RC members with shear-dominated response. Although several experimental tests demonstrated the effectives of these materials in the seismic retrofit of existing beam-column joint a proper design formulation is still lacking. This research paper presents a novel procedure for the design of the exterior FRCC jacketing of poorly detailed on beam-column joints. A mechanical model based on the principal tensile stress approach is proposed. The model is later validated against a comprehensive database of experimental tests at global and local level. The proposed procedure allows the designers to calculate the thickness of the FRCC jacketing to avoid the joint panel shear failure and promoting a more ductile failure mode.

The cast in place floors of existing buildings realized in Italy in the ‘60–70’ years are commonly made by longitudinal beams and hollow clay bricks with a top deck without internal reinforcement. Thus, they are unable to properly guarantee the load distribution function over structural members which is strongly required in case of seismic actions. Furthermore, the deck thickness of such horizontal structures is commonly less than the minimum value given by current codes (≥40 mm) in order to assume the floor as rigid in plan. The effectiveness of an innovative system, based on the use of Fibre-Reinforced Cementitious Composite (FRCC), is investigated in the paper as a strengthening technique of these existing floors. Three point bending tests on two full scale cast in place reinforced concrete (r.c.) floors have been carried out: one specimen was tested in the ‘‘as built’’ configuration; one specimen was strengthened with a new FRCC deck, about 2 cm thickness made by fibre-reinforced, shrinkage-compensated, high-strength, high-ductility, highly-fluid cementitious mortar. The main aspects related to the application procedure of the system, the experimental test setup, as well as the experimental results in terms of crack pattern, strength and deformation of the specimens are herein presented and discussed.

Fiber Reinforced Polymer (FRP) composites have been widely used in past decades for the seismic upgrading of sub-standard reinforced concrete (RC) members and their effectiveness as a suitable strengthening technique for such kind of structural components has largely been proved. However, some concerns still arise with the effectiveness of such composite materials at high temperature, such as in the case of fire exposure. Furthermore, the use of FRPs requires a min- imum quality for the concrete substrate to avoid undesirable premature failure mechanisms. Usually, the replacement of the poor quality or damaged concrete cover of existing members with a new one is needed before the strengthening intervention. Current research is now moving towards the adoption of inorganic composite materials, such as Fiber Reinforced Cementitious Composite (FRCC), for repairing existing RC buildings and infrastructures as a replacement of the original concrete cover, due to its good durability properties and resistance to high temperature. The present study discusses the possibility of adopting such FRCC jacketing also for the seismic upgrading of existing shear critical RC columns. The experimental performance of RC columns strengthened with FRCC jacket- ing subjected to cyclic lateral loading and different axial load ratios is analyzed herein, and the experimental performance of FRCC and FRP jacketed columns is compared to point out the effectiveness of both retrofit solutions.

In many engineering applications the limit analysis theorems can be used to estimate the ultimate capacity of several structures. However, the limit analysis can be applied on structures with an adequate plastic capacity. When the goal is to evaluate the ultimate capacity of masonry structures, they could show some drawbacks. For this reason, the incremental analysis represents a valid alternative to estimate the ultimate capacity of masonry structures. These structures could show brittle failures before the hinge mechanism. It is a key aspect especially for curved masonry elements like as arches and vaults. The work focuses on the incremental analysis of masonry barrel vaults without backfill. An analytical model in the framework of the incremental analysis has been proposed. The analytical model allows to assess both the ultimate capacity and the ductility of the masonry barrel vaults. In the first part, the proposed model has been discussed. Then, parametric analysis was performed to assess the impact of physical, geometrical and mechanical parameters on the ultimate behaviour. The numerical results allow to identify some structural examples where the brittle behaviour becomes crucial. Finally, the proposed model was validated with experimental results on a full-scale masonry barrel vault.

Masonry elements are often strengthened in order to improve their structural capacity. Generalized methods to assess the behavior of confined masonry columns are not available in the technical literature. They have been usually derived from concrete confinement models. However, concrete and masonry present several crucial differences due to their physical and mechanical properties. In fact, generalized models to assess the axial capacity of masonry columns were limited by the strong variability and heterogeneity of physical and mechanical properties. However, the recent scientific researches provided relevant information on the experimental behavior of confined masonry columns. In this paper, a confinement model has been proposed to assess the axial capacity of clay brick masonry strengthened using several strengthening systems. The model has been validated by means of comparisons with experimental results. In order to assess the potential of the proposed model, the comparison was carried out also with other available mechanical models.

The increasing attention of governments and insurance companies toward the evaluation of tsunamis' impacts on coastal communities led to a renewed interest in assessing the behavior of existing buildings under onshore tsunami flows. Codes and standards regulating assessment procedures for existing structures under tsunami loading are currently missing, and only a few design codes for vertical evacuation shelters can be found. Furthermore, structural analysis methods currently assume watertight buildings for the assessment of their performance under tsunami inundation. In this work, a methodology for assessing the performance of reinforced concrete (RC) buildings that considers explicitly the progressive failure of exterior breakaway infill walls hit by tsunami flows is proposed. The effects of the progressive failure of breakaway infill walls on the overall performance of RC buildings have been highlighted on case-study buildings representative of low-, mid- and high-rise buildings built before the 1980s in the Mediterranean area, characterized by masonry infill walls with low out-of-plane (OOP) capacity. In the absence of specific guidelines for assessment, load models provided by existing tsunami design codes for evacuation buildings were adopted and opportunely modified for the case of buildings with breakaway infill walls. The explicit consideration of the failure of exterior breakaway infill walls completely changed the distributions of loads inside the structure, leading to different structural capacity and damage evolution with respect to watertight buildings. The height of the building affected the global capacity but did not influence the damage evolution. The proposed methodology can represent a suitable solution for a realistic performance assessment of frame structures with breakaway claddings.

Masonry-infilled reinforced concrete frames represent a very common construction typology across the Mediterranean countries. The presence of infills substantially modifies the global seismic performances of buildings in terms of strength, stiffness, and energy dissipation. Although several research studies focused on the overall performances of infilled reinforced concrete frames, the modeling of infill panels remains an open issue due to the complex interaction between the infill and the frame and the uncertainties involved in the definition of the problem. In the present paper, an existing masonry-infilled RC frame designed according to obsolete seismic codes is chosen as a case study. A refined three-dimensional finite element model is built for performing nonlinear static and time-history analyses in order to investigate some significant aspects related to the modeling of infills. In particular, it is investigated the effect of different infill constitutive models on the seismic performance of infilled RC building expressed in terms of engineering demand parameters such as interstory drift ratios and peak floor accelerations, and on the generation of damage fragility curves.

The present analytical work deals with the assessment of the performances of Reinforced Concrete (RC) Deck Arch Bridges under the non-seismic loading conditions required by the current mandatory Italian codes. In particular, the attention is focused on a specific RC deck arch bridge typology, better known as the “Maillart Type Arch Bridge”, which is characterized by a very stiff deck beam and a slender and wide vault. As well as other existing RC structures which were designed under only gravity loads and without specific structural details, such as lower limits for longitudinal and transverse reinforcement bars, these bridges could be damaged by loading conditions not considered at the time of design. For the evaluation of the main critical issues related to the current performance of such bridges under the current non-seismic loading conditions, it has been defined a large inventory of simulated arch bridges in accordance to the design procedures usually adopted in 1950s which considered only gravitational loads, i.e. self-weight and moving loads. Each bridge of the inventory is modelled and studied by means of a Linear Gravitational analysis implemented in the structural software SAP2000, with support of an Application Programming Interface (API), such as Matlab. Due to the differences between the current loads and those considered at the design time and to the approximations of the design strategies of the time, a performance - based analysis of the existing bridges under non-seismic loads is important for the stakeholders as much as for the decision - makers in order to plan risk mitigation programs and prioritize eventual retrofit interventions for risk reduction.

In restoring ancient timber structures, employing traditional connections would be advisable with the aim of minimal modification of the overall structural behaviour. Moreover, instead of steel connectors or adhesive resins and rods, commonly used in interventions, employing timber pegs can be an efficient solution. Nevertheless, the lack of design rules for traditional timber joints or for timber pegged connections in European codes doesn’t encourage this more conservative approach. In this study, stop-splayed scarf joints behaviour before and after reinforcement with steel pins or timber pegs is experimentally investigated, in order to understand the role of the fastener inside this carpentry joint and check the reliability of existing design methods. The experimental program has two steps: in the first one, three samples of fir scarf joints without fasteners, with timber pegs and with steel pins have been tested, trying to define the forces distribution among the different resisting elements. In the second phase, two samples of simple shear plane joints, made with the same timber and fastened with both timber pegs and steel pins have been tested to improve the analysis of fastener role in reinforced scarf joint behaviour.

The assessment of the effectiveness of strengthening interventions against the out-of-plane failure mechanisms of masonry walls requires developing a proper modelling approach. In this paper, the attention is focused on strengthening systems based on injected anchors made of carbon fibre reinforced polymer (CFRP) tubes. The resistance to corrosion and the possibility of using traditional grouts make such systems a promising alternative to steel bars in interventions on masonry structures aimed at improving poor connections between orthogonal walls. The paper introduces a modelling approach to assess the anchors contribution in the out-of-plane response of T-shaped masonry walls under horizontal actions. The approach adopts a rigid macro-block model of masonry based on the kinematic method of limit analysis. The contribution of the anchors is evaluated at the onset of the out-of-plane response of the strengthened system, defining its horizontal capacity and the crack inclination of the expected mechanism. The results obtained with the proposed model are firstly validated through the comparison with literature experimental findings. Then, parametric analyses are developed accounting for geometric and loading parameters characterizing T-shaped wall connections, and the performance of different layouts of anchors is assessed. Preliminary design indications are also provided to address the optimal balance between effectiveness, low invasiveness, and costs of such strengthening interventions.

Fabric Reinforced Cementitious Mortar (FRCM) strengthening demonstrated to be an efficient way to improve the in-plane shear capacity of masonry walls, in particular for its high compatibility with masonry substrate. Recently, Italian CNR guidelines provided two approaches to design in-plane shear strengthening interventions for masonry with FRCM system, one is very simple and practitioner oriented, but it has clear limitations in its applicability, while the second has a more complex formulation, but it is valid for a wider range of applications. The main aim of this work is to reconciliate the two approaches and to clarify the potential of FRCM systems in masonry strengthening with design charts and manipulations of the more refined available formulations, with the goal to provide a simple method to account for the refined version in a practitioner oriented approach. The focus is on the impact of material properties on the capability of strengthening. A final worked example provides a comprehensive overview of the potential of the proposed method.

Typically, panel-to-panel and panel-to-foundation connection zones in Cross-Laminated Timber (CLT) walls consist of steel-to-timber mechanical connections (hold-downs and angle-brackets) and timber-to-timber contact. While hold-downs and angle brackets are extensively studied in literature, the role of timber-to timber contact is underestimated. The platform constructional technology used for build CLT walls requires that the vertical timber panels compresses the horizontal CLT floors, engaging the orthogonal to grain timber properties in the seismic response. This paper discusses a new development concerning a theoretical sectional model for CLT panels proposed by the authors in a recent work, where strength of the panels subjected to combined axial force and bending moment was studied accounting for orthogonal to grain timber properties. As advancement, a theoretical moment-curvature model for CLT panels is proposed in this paper and the displacement capacity (i.e., ductility) is investigated. The main parameters which affect the ductile behavior of the panels have been studied by means of parametric analyses, i.e. varying cross-section dimensions, amount of axial force, and hold-downs resistance. Theoretical results have been also compared with numerical ones derived from a bi-dimensional finite element model developed by the authors and a good matching between the results has been highlighted.

A new jacketing technique consisting in a thin layer of Fibre Reinforced Cementitious Composites (light FRCC jacketing) in replacement of the original cover has been recently proposed for increasing durability and load bearing capacity of existing reinforced concrete (RC) structures. Although the advantages in terms of durability have been widely investigated, the behaviour of retrofitted columns under cyclic loading still deserves attention. This paper deals with the seismic response of RC columns retrofitted with a light FRCC jacketing. To this scope, flexural and shear critical RC columns were retrofitted and tested under load reversal. The resulting damage pattern was analysed by means of the Digital Image Correlation (DIC) technique. The cyclic response of the FRCC jacketed columns was compared with that of bare columns, to assess the suitability and effectiveness of the FRCC jacketing as a seismic retrofit technique. The experimental results demonstrated that the FRCC jacketing can represent a valid strengthening solution for shear critical members. In the case of flexural columns, the FRCC jacketing was able to provide an increase in ductility but induced a rocking behaviour. Preliminary modelling considerations for assessing the seismic response of FRCC jacketed columns have been finally provided, based on experimental evidences.

Recent devastating earthquakes pointed out the high vulnerability of existing reinforced concrete (RC) buildings and the critical role of infills. The presence of stiff infills may significantly modify the lateral response of RC moment resisting frame buildings and cause severe damage on the surrounding RC members due to seismic actions transmitted at level of beam-column joints. Furthermore, due to their brittle response, they commonly exhibited severe damage often leading to high economic losses. In this context, effective seismic retrofit strategies should aim at both increasing the shear strength of RC members and reducing the damage to infills. However only few tests are available in literature addressing the seismic strengthening of existing RC frames accounting for the infill-to-structure interaction. To fill this gap a comprehensive experimental program of pseudo-dynamic tests on full-scale two-storey infilled RC frames has been designed and is currently ongoing at the full-scale laboratory testing of the University of Napoli Federico II. This paper reports the preliminary experimental results and numerical analyses carried out by using available non-linear models accounting for the infills contribution. The comparison between theoretical predictions and experimental results provides useful insights to improve the numerical models to reproduce the infill-to-strut interaction. Finally, a retrofit strategy to improve the seismic performance of the structural system and reducing the expected damage to infills is herein outlined. © 2021 COMPDYN Proceedings.

The seismic vulnerability of masonry buildings to out-of-plane failure mechanisms is frequently related to poor connections between orthogonal walls. The effectiveness of these connections represents a necessary condition for the repartition of the horizontal action among the in-plane stressed walls, allowing a box behaviour of the whole structure. Steel injected anchors or tie rods have been widely used in the past to improve connections between orthogonal walls, but proper analytical approaches to evaluate their effectiveness are still a matter of ongoing research. On the other hand, many seismic codes nowadays require assessing the safety improvement achieved with the strengthening interventions, and the compatibility with masonry of many techniques has become a matter of debate in the light of the damage frequently caused by the same interventions. In this framework, the present paper focuses on the possibility of using injected anchors made of innovative materials, as pultruded CFRP tubes, in conjunction with traditional grout. For this purpose, a macro-block model, previously validated for the analysis of unreinforced stone masonry structures, is further developed to account for the contribution of these innovative strengthening systems in the out-of-plane response of masonry walls with T-shaped connections. The model, also considering the contributions of frictional resistances at masonry bed joints, is based on the kinematic approach of limit analysis. Literature results concerning full-scale tests of a T-shaped wall are assumed as a reference to validate the proposed approach. Then, the validated model is used to investigate the influence of some design parameters on the performance of the reinforced system and a first attempt to address the design of strengthening interventions with injected anchors is presented.

Masonry columns often exhibit a lack of load-carrying capacity that is due to overloads and do not provide any ductility or dissipation capacity under seismic forces. Column confinement has been extensively studied as an effective technique, which could mitigate these structural vulnerabilities. The confinement of masonry columns will be studied in this paper, by considering fabric-reinforced cementitious matrix (FRCM) materials as external jackets. Due to the lack of information in the scientific literature, a new analysis-oriented model (AOM) for the prediction of the axial stress-strain law will be presented and discussed in this paper. The proposed AOM consists of a system of equations that make several assumptions: crossing the predicted peak point (strength and relative strain), crossing the ultimate point (80% residual strength and relative strain), and the horizontal tangent at the peak point and the initial (linear elastic) slope derived from the geometry and mechanical properties of the materials involved. The AOM was demonstrated to be simple and accurate, based on Pearson's test (χ2); therefore, the proposed approach could be considered for future design equations. In addition, this paper will illustrate and discuss the validation of two available design-oriented models (DOMs), which could predict the axial strength of FRCM jacketed columns, by comparing the theoretical results with a database of experimental results that is available in the scientific literature. Novel formulas for the computation of both the peak and ultimate axial strains will be further proposed, as the basis for a design procedure. Their accuracy was demonstrated by considering an experimental versus theoretical comparison.

Modeling of masonry buildings subjected to seismic actions still represents an open problem in structural engineering. The equivalent frame model is the most used approach to analyze the seismic behavior of both existing and new masonry constructions but, despite this, several aspects are being researched to improve its effectiveness. Among these, modeling of spandrel panels plays a key role to correctly analyze the in-plane seismic response of unreinforced masonry walls. Actually, horizontal mono-dimensional beam-like elements provided of both strength and displacement capacity are used to schematize the spandrel panels, also according with the most of current national and international codes. In this paper an alternative strut and tie scheme to model the spandrel panels, suitable to be used within the equivalent frame approach, is presented: the compressed masonry material is schematized with an equivalent diagonal no-tension truss, whose length and effective compressed area are obtained with limit equilibrium conditions, while tensile-resistant element is represented by no-compression truss. Such model allows a more realistic representation of the mechanical behavior of spandrels because both amount of axial force within the spandrel and the reduced elastic flexural and shear stiffness due to progressive cracking of material are taken into account. Moreover, the local failures of both compressed masonry and/or tensile-resistant elements are better identified and, consequently, also the failure mechanisms of the whole equivalent frame are better detailed. The proposed schematization has been used to simulate the seismic behavior of some reference case studies of existing masonry walls, strengthened with different steel ties arrangement. These walls have been modelled with a hybrid equivalent frame model which consists of mono-dimensional beam-like element for piers, fully rigid offsets for the nodal panels and a strut and tie scheme for spandrels.

This paper deals with the experimental monotonic and cyclic behavior of masonry spandrels reinforced with Fiber Reinforced Polymers (FRP). The research is a part of a wider program, started by the authors in the last decade, regarding the analysis of the seismic behavior of masonry spandrels in historical buildings of the Mediterranean area. The paper summarizes the properties of the test units, the test set-up and the results of the experimental monotonic and cyclic behavior conducted on twenty-four scaled down H-shaped spandrels made with homogeneous material (e.g. mortar with low tensile strength). Both unreinforced and FRP-reinforced specimens with three different slenderness ratios – e.g. slender, intermediate and squat – and three different arrangements of FRP laminates have been considered for the tests. The main objective has been to verify the possibility of preventing brittle failure modes, typical of spandrels subjected to in-plane seismic actions (e.g. diagonal cracking), and of increasing their strength by applying specific reinforcement systems, so encouraging more ductile behavior characterized by toe-crushing at the ends of the spandrels itself.

The prediction of seismic performances of buildings in terms of engineering demand parameters EDP, such as interstorey drift ratios IDR and peak floor accelerations PFA, represents a fundamental step towards the assessment of potential direct economic losses. This paper proposes a simplified model for the rapid assessment of EDPs in infilled moment resisting frames subjected to seismic loadings suitable for large scale assessment studies. The proposed model, named Stick-I (Stick model for Infilled frames), is a multi-degree of freedom MDOF system consisting of a series of lumped masses connected by means of nonlinear shear link elements. The shear link behavior is suitably calibrated adopting a multi-objective Genetic Algorithm procedure that employs the results of nonlinear cyclic pushover analyses performed on refined nonlinear FEM. Based on the regression study performed on a suitably generated Stick-I model database, a more general Stick-IT model, representative of RC Infilled frame Typologies of assigned storey number and dimensions in plan, is introduced. Simplified formulas for the definition of Stick-IT model are proposed depending on low-level information data that can be easily retrieved from rapid on-site surveys or remote sensing techniques. Both Stick-I and Stick-IT models are validated comparing the results of NRHA performed on refined FEMs with the results obtained adopting the simplified models and good agreement in terms of maximum EDP values and distribution along the building height is obtained. The typological Stick-IT model, which is defined as a function of few geometric and mechanical parameters, can be easily applied for simplified evaluation of expected response for building typologies. Hence, it can also be usefully employed for assessment of direct losses at the large scale, with a significant reduction in computational burden with respect to more refined methods.

This paper investigates on the effect of story lateral stiffness variation on the maximum elastic interstory drift ratio (IDRmax) for existing reinforced concrete (RC) buildings. Several classes of existing gravity load designed RC buildings are obtained via a simulated design approach. The presence of infills in the perimeter frames as well as different opening percentages along the height are considered. A simplified elastic analysis is performed, adopting an equivalent multistory cantilever system to represent the stiffness variation along the buildings height. IDRmax is significantly influenced by the ratio of the lateral stiffness at the second and upper stories over the lateral stiffness of the first story. Such a ratio has been found dependent on a number of geometric and configuration factors, including the variation of the opening percentage ratio. Two regression formulas are proposed to estimate, given the spectral displacement at the fundamental period T, the roof displacement and IDRmax as a function of the building height and the opening percentage at first and upper stories. Suitable modification of the formulas is also introduced to account for possible cracking of RC elements and infill panels even at very low levels of lateral drift. These expressions could be used for the simplified evaluation of the expected drift demands for buildings of existing RC typologies. Finally, the proposed formulations are applied to a number of permanently monitored buildings, comparing the calculated IDRmax with the one resulting from record processing, obtaining a fair good agreement.

The lateral seismic capacity and the in-plane failure pattern of adobe masonry may be understood by performing quasi-static experimental tests on full-scale adobe walls. Information regarding the maximum lateral capacity and the displacement ductility are normally obtained during these tests. Also, information about limit states could be obtained. Along the years, universities in Europe, Asia and Latin America have performed this type of tests and the results of some of these works are summarized in this chapter.

The high vulnerability of existing Reinforced Concrete (RC) structures, even to moderate seismic events, has been confirmed from recent post-earthquake surveys. Short and wall-like RC columns are particularly prone to brittle failures, governed by concrete crushing. To reduce the vulnerability of existing RC columns, the use of externally bonded Fibre Reinforced Polymer (FRP) reinforcement has been recognized as an effective method for preventing the aforementioned brittle failure and, hence, increasing members' lateral capacity and ductility. In the first part of this study, the results of an observational analysis on columns shear failures in RC buildings severely damaged after the L'Aquila earthquake are presented. The second part of the study presents and discusses the results of an experimental program carried out on seven short RC columns governed by shear failure under load reversal and compressive axial load. Both columns in “as built” configuration and strengthened in shear with discontinuous carbon FRP (CFRP) strips have been tested. Two classes of concrete have been used, in order to simulate structures with medium or poor material quality, and different external reinforcement ratios have been investigated. The specimens' responses have been analysed in terms of failure modes, strength/deformation capacity and strain distribution in CFRP strips.

Numerous experimental programs have been conducted in recent years to understand the potential benefits of different types of external reinforcement systems aimed to reduce the seismic vulnerability of existing structures. The Fibre Reinforced Cementitious Mortar (FRCM) materials are spreading as an alternative strengthening technique to the traditional use of Externally Bonded - Fibre Reinforced Polymer (EB-FRP) systems, for both structural and non-structural members of civil and industrial buildings. The behaviour of FRCM materials depends on numerous parameters and it is, in general, more complex than what observed for the more traditional EB-FRP ones, mainly due to the presence of a cement-based adhesive. Both tensile and bond tests can help researchers and manufacturers in optimizing the strengthening system. In this framework, the potential of the Digital Image Correlation (DIC) technique for monitoring the behaviour of FCRM systems is very high. Nevertheless, the accuracy of such a monitoring technique is good enough only if sensitivity analysis and critical post-processing of results are performed. Recently, several tests were performed in a Round Robin Test (RRT) initiative involving several laboratories and concerning tensile tests on different types of FRCM systems and bond tests on the same reinforcements applied to masonry elements. The experimental results of the tests performed by two of these laboratories are compared in this paper in order to investigate the effect of set-up on both the global performance and the local bond behaviour of three FRCM systems (glass, basalt, steel). The results allow also to evidence benefits and weaknesses of using DIC technique for monitoring tests on FRCM systems.

Field surveys in the aftermath of major seismic events, laboratory tests and numerical studies outlined that existing reinforced concrete (RC) structures are likely to exhibit premature shear failures. However, a proper quantification of the shear capacity of existing members with seismic details non-conforming to current seismic code is still a challenging task. Several models based on mechanical approaches or experimental observations are available in literature, current standards and guidelines. Nevertheless, the lack of a widely accepted theory often results in the use of old formulations, mainly developed for design purposes, to assess the shear strength of non-conforming RC members. This study investigates the available shear strength formulations. Eight capacity models commonly adopted in the current practice and worldwide standards or guidelines have been assessed comparing the model predictions with a unique database of 180 experimental tests properly selected to be representative of non-conforming RC members. Members with rectangular or circular cross-section, different aspect ratio (i.e. slender or squat) and shear or flexure-shear failure mode have been investigated. Meaningful statistics have been used to quantify the accuracy and the level of safety of each formulation. Several criticisms in the use of the available formulations are herein outlined. Suggestions for the model applicability have been provided in order to drive the reader to select the most appropriate shear strength formulation for assessment purposes. Finally, corrective factors have been calibrated to allow the use of the selected models with specific levels of safety.

The effectiveness of FRP systems as a confinement technique to strengthen masonry columns has been widely investigated in the last decades. Recently, a new technique, Fabric Reinforced Cementitious Matrix (FRCM), based on the use of fibrous nets embedded in inorganic matrix, has been developed and investigated as a strengthening solution in masonry buildings. Actually, the number of experimental tests on masonry columns confined by using FRCM systems is very limited, especially for real scale specimens. To fill such gap an experimental program aimed at investigating the behaviour of full scale columns made of limestone masonry blocks confined with different FRCM systems has been carried out. The results of four uniaxial compression tests are illustrated and discussed. The used FRCM systems are made with glass and basalt dry nets embedded in a lime-based mortar. The influence of transverse confinement by using internal reinforcement in forms of pultruded GFRP bars has been also investigated. The mechanical properties of the confined specimens resulted increased in terms of load-carrying capacity and ultimate axial strain.

Aim of this work is the evaluation of FRCM capacity in repairing pre-damaged clay brick walls under out of plane loads. Full scale experimental tests have been performed damaging clay brick walls subjected to out of plane loads; then, tests are performed on damaged walls repaired with innovative composite grids with inorganic matrix (FRCM). The boundary constraints of the walls (two adjacent edges constrained and the other two free) allowed to simulate a non-uniform out of plane behaviour of the wall subjected to a pointwise normal load applied at the free corner. The aim of this study was to assess the potentiality of FRCM to recover stiffness after significant damage and to improve the lateral (out-of-plane) capacity of the repaired wall. Experimental evidences demonstrated that the externally bonded strengthening was not strongly affected by debonding and it was able to prevent a flexural failure; the collapse of the wall occurred at almost double load with respect to the unreinforced configuration, despite previous significant damage, and that the failure was governed by shear sliding. Future developments include experimental tests of strengthened walls not previously damaged, to investigate on the effect of pre-damage on out of plane strengthening capacity of FRCM.

Lap-splice regions are amongst the most critical regions of Reinforced Concrete (RC) members, especially in seismic design. The goal of wrapping with Fibre Reinforced Polymer (FRP) is provide confinement to concrete, however, a further important role is either to increase the bond between the reinforcement bars (in pre-cracked conditions) or to provide for bond (in fully cracked cover conditions). The proposed study aims to quantify the beneficial effect of this retrofit technique on the performance of the longitudinal reinforcement with a first attempt to account explicitly for the pointwise variability of confining stresses. For this purpose, both the reinforcement bar working stress and the anchorage length needed to prevent the bar slippage have been analytically assessed. The model has been validated against experimental tests and a good agreement with the model predictions has been found in both the cases of square and rectangular cross sections.

The paper discusses the experimental seismic performance assessment of a structural prototype simulating typical existing highway bridges which were designed with poor seismic details. The structural system is a reinforced concrete (RC) 1:3 scale single span bridge which has been tested dynamically with shaking tables by considering strong motions of the 1980 Irpinia (Italy) earthquake. Low-strength concrete and smooth bars were used for the RC circular bridge piers of the tested prototype. Comprehensive modal response analysis has been carried out for the single piers and for the bridge sub-assemblage to estimate period elongations and variations of equivalent viscous damping coefficients at increasing levels of strong motions. The effects of cumulative damage induced by earthquake sequences have also been investigated experimentally. The sample bridge pier possesses low aspect ratio; nevertheless the piers exhibited a flexural response. Fixed-end rotations, with significant longitudinal reinforcement slip, were observed at the base of the bridge pier at about 0.40% lateral drift ratio. As a consequence, a rocking mechanism of the bridge pier initiated; such mechanism affected significantly the pier response at large shaking intensities. An in-depth analysis of local and global response quantities has been provided in order to accurately identify the structural behaviour. Finally, available analytical formulations and refined numerical models were considered to simulate the earthquake response of the tested bridge. The pier lateral response has been investigated by means of push-over analysis and nonlinear time histories. The accuracy of the proposed models, the differences and recommendations for numerical modelling of bridge piers with smooth internal reinforcements are also discussed.

Existing RC buildings may suffer of brittle failure due to the limited shear capacity of non-conforming columns. To reduce the vulnerability of such members, several retrofit techniques based on composite materials can be successfully adopted for enhancing the shear capacity of RC columns. The use of FiberReinforced CementComposite (FRCC) jacketing has been re-cently recognized as an effective solution for improving the durability of RC members and some experimentaltests have been carried out for investigatingthe role of FRCC jacketing on the shear capacity of RC members.However, poor indicationsare availableregarding the modelling of strengthened members capacity and the design of the strengthening solution. In this work, an in deep analysis about the available analytical modelsfor assessing the shear capacity of membersis reported and thendifferent methods are proposed for assessing the shear capacity of RC members with FRCC jacketing.

Unreinforced masonry buildings are particularly vulnerable to brittle failures during seismic events due to the poor in-plane shear capacity of masonry walls. The use of strengthening solutions with polymeric matrices is not often recommended for masonry buildings, due to breathability issues, and the adoption of inorganic matrices is sometimes considered preferable. In this paper, the use of inorganic composite materials for improving the in-plane shear capacity of tuff masonry walls is investigated. The experimental data from 83 diagonal compression tests carried out at the University of Naples Federico II in recent years have been collected and the main results are herein discussed to outline the main features of different strengthening techniques with inorganic composite materials such as Reinforced Plaster (RP), Composite Reinforced Mortar (CRM) and Fabric Reinforced Cementitious Matrix (FRCM).

This study focuses on the seismic vulnerability of masonry buildings damaged by the 2009 L’Aquila earthquake. A geo-referenced database of 32,520 masonry residential buildings was compiled in the aftermath of the earthquake under the coordination of the Italian Department of Civil Protection through the AeDES survey form. The availability of this enormous amount of data provides an exceptional opportunity to examine in depth damage data and their correlation with the main parameters available from the post-earthquake survey. The original database was grouped into 20 building classes, defined as a function of vertical and horizontal structural types. Damage levels defined according to the European Macroseismic Scale classification are used to derive damage probability matrices and relevant vulnerability curves for these classes. The influences of connection systems, the quality/regularity of the masonry wall layout and the horizontal structural type on the building response are analysed in detail. A vulnerability classification, also supported by the use of statistical post hoc tests, is used to detect a reduced number of independent classes. The parameters of the non-crossing fragility curves are determined via the maximum likelihood estimation method by adopting a lognormal cumulative function to determine the exceedance probabilities of the considered damage levels. The impact of “mixed” classes, characterized by multiple vertical and/or horizontal structural types, on the derivation of the fragility curves is also investigated. Finally, the adaptation of the general version of the fragility curves to large-scale applications based on poor (census) data is also demonstrated, leading to curves that are easily usable in regional/national seismic loss assessments.

In-plane seismic behaviour of Cross-Laminated Timber (CLT) walls is influenced by panel-to-panel and panel-to-foundation mechanical connections, which consist of hold-downs and angle brackets. Due to the platform constructional technology, the orthogonal to grain timber-to-timber contact is also involved in the seismic response of the panels. To date, literature theoretical approaches to evaluating the flexural load-bearing capacity of CLT panels focus their attention on the schematization of hold-downs and angle brackets only, under evaluating the role of timber compressed in the perpendicular direction. In this paper the influence of orthogonal to grain timber properties on the overall seismic behaviour of CLT walls has been investigated, proposing a general theoretical model to schematize the panel-to-panel and panel-to-foundation connections. A parabola-rectangle constitutive behaviour has been defined to describe the orthogonal to grain timber behaviour in the connection zones, while hold-downs and angle brackets are modelled adopting literature models. Five different failure conditions, described by mathematical formulations, able to describe the entire axial force-bending moment interaction domain have been defined. The proposed model has also been employed to schematize the connection zones in multi-storey CLT walls with openings, allowing to investigate the effect of the orthogonal to grain properties on its seismic behaviour. Results of nonlinear analyses demonstrate a significant influence of orthogonal to grain timber properties on seismic behaviour of the walls, affecting their strength, stiffness, ductility and collapse mechanisms.

The study analyses the data related to a database of 7597 private Reinforced Concrete buildings located in the city and the province of L’Aquila surveyed after the 2009 earthquake. Survey data were collected by the Italian Department of Civil Protection during post-earthquake usability inspections including information on building characteristics, level and extent of damage to structural and non-structural components. For each building, the Peak Ground Acceleration demand has been determined according to data available from the ShakeMap of the event and the georeferenced building location. The analysis of data highlights the key role played by the damage to non-structural components—namely, infills and partitions. Damage Grades according to the European Macroseismic Scale EMS-98 have been derived from damage data to single building components. Two building classes have been defined in the study in order to investigate the influence of number of storeys of buildings on the observed damage. Damage Probability Matrices have been derived for the assumed building classes and bins of Peak Ground Acceleration, and observed trends are analyzed. Different methodologies for estimating fragility functions from data on Damage Grades and Peak Ground Acceleration demand are illustrated, discussed and applied to the database, leading to the derivation of EMS-98-based fragility curves for the defined building classes. Finally, the proposed fragility curves are compared with main empirical fragility curves for RC buildings from literature studies.

In a performance based approach, the knowledge of ultimate capacity of reinforced concrete (r.c.) columns subjected to simultaneous compressive axial load and biaxial bending becomes essential to correctly assess the seismic capacity of existing structures. In the present work, the reduction of ultimate deformation (i.e. rotational) capacity of r.c. members due to the two components of bending moment is analysed by using a specific simplified numerical model. The influence of axial load, geometry, amount of longitudinal reinforcement and mechanical properties on the ultimate chord rotation of r.c. columns is investigated on a dataset of 780 numerical tests on non-conforming columns with plain bars governed by flexural mode. Then, a practice-oriented formulation for the ultimate rotation domain, based on the Load Contour method extended to the chord rotations, is proposed and discussed. © 2016 Elsevier Ltd

Significant part of the world cultural heritage is represented by masonry buildings. Many of them are characterised by a complex architecture like as the religious buildings and need to be preserved, from a structural point of view, especially in high seismic risk areas. The recent earthquakes showed that the Historical and Monumental buildings are often characterised by high seismic vulnerability. The lowest seismic performances are associated with the presence of thrusting elements like as arches and vaults. In this background, the numerical analyses and experimental simulations provide important information about the structural behaviour of such elements. The structural behaviour of curved elements can be complex to simulate and to predict exclusively by numerical analyses. Indeed, the experimental tests can provide an efficient contribution to the calibration and interpretation of the numerical models. The present work focuses on a particular typology of vaults generally used as roofs in religious buildings. These vaults typically do not include any backfill and are slender. These typologies of masonry vaults cannot be analysed with classical approaches where no-tension is assumed. In fact, the tensile strength must be included in order to assess the seismic capacity of these masonry elements. A simplified analytical model, which includes the tensile strength, was proposed. Validation of the analytical model is provided by comparing predictions of the load capacity and the failure mode with those obtained from previous shaking table test series on two full scale masonry vaults. The proposed method represents a useful modelling tool in order to design dynamic tests on masonry vaults and to assess their vulnerability.

Sustainability goals are essential driving principles for the development of innovative materials in the construction industry. Natural fibres represent an attractive alternative as reinforcing material due to both good mechanical properties and sustainability prerequisites. The present work investigates the shear behaviour of masonry panels strengthened with a mortar-based system reinforced with an innovative hemp fibre composite grid. The objective of the study is to assess the feasibility of using the proposed strengthening system for external retrofit of existing masonry walls and to compare its performances with typical retrofitting solutions. © 2015 Elsevier Ltd. All rights reserved.

Reinforced concrete bridges represent a majority of the Italian stock and they play a primary role to ensure the efficiency of the transportation network and prompt rescue in the case of an emergency. However, most of them have been designed and built according to outdated codes, or even without any seismic detailing. The significant impact of strong motions on the road network as well as the human life and economy emphasizes the need for effective strategies for post-earthquake emergency management and to support rescue operations. The present paper aims at evaluating, against real data, the effectiveness of automated modal parameter monitoring for vibration-based Structural Health Monitoring (SHM) of existing bridges in earthquake prone areas. This objective has been pursued in the context of shaking table tests on a 1:3 scale single span bridge representative of existing highway bridges built in the 60's in Italy. The dynamic response of the structure before and after the application of asynchronous seismic input has been analyzed for damage detection and performance assessment. Results show that partially hidden damage can be remotely detected, thus validating the interesting applicative perspectives of automated output-only modal identification and modal-based damage detection for fast assessment of existing bridges in the early earthquake aftershock. The robustness of the SHM system to sensor overload due to earthquake shaking has been also assessed, demonstrating the applicability of modal-based SHM in seismic regions even in the absence of a measurement chain specifically designed to resolve the large amplitude vibrations induced by earthquakes. Finally, the possibility of complementing modal-based SHM with drift-based estimates is explored.

This study deals with the seismic behavior of old- type reinforced concrete (RC) beam-column joint and the effectiveness of an innovative application of Fiber Reinforced Concrete (FRC) as seismic strengthening solution. Two real joint subassemblies were extracted from an existing building damaged and demolished after the L’Aquila 2009 earthquake and tested in laboratory. The joints exhibited poor quality concrete and reinforcement details typical of old design practice, which are very difficult to reproduce in laboratory simulations. The joint tested in the as-built configuration showed a brittle failure with joint diagonal cracking, as commonly observed in the aftermath of recent devastating earthquakes. The FRC thin jacketing avoided the joint panel shear failure promoting a more favorable beam yielding. This resulted in a significant increase of the shear strength (until 50%) and energy dissipation (85%). The strengthening phases and the details of the proposed strengthening layout are described. A direct comparison between as-built and strengthened specimen in terms of global and local behavior is reported. Strain measurements on the FRC jacketing are also discussed as an effective design parameter.

The corrosion of steel in reinforced concrete structures surely represents the main form of degradation. Carbonation and chloride attacks lead to a loss of performance during the service life of the structure. The reduction of the cross section of the steel bars and the formation of corrosion products lead to reduction of bond between steel and concrete, to concrete cover cracking and spalling, to reduction of concrete cross section resulting in a reduction of structural capacity. The structural engineer needs to face corrosion starting from the design phase, however in presence of real existing structures the first step is the evaluation of corrosion level and the evaluation of actual global structural capacity. The most critical corrosion involves the stirrups, being the most exposed steel elements, yielding to brittle failures in the most stressed elements, generating unexpected structural collapses. In particular in seismic conditions, the structure is not able to exploit its ductility, since limited ductile failures (i.e. combined shear/flexure) could occur. The last phase of the study is on the structural retrofit by using High Performance Concretes. Such materials allow recovering some of the bending capacity of the structural elements and can increase their ductility, reducing dramatically the vulnerability of the structures. This is particular true for seismic vulnerability, since the strength recover is partial if the structural retrofit intervention is designed to have a negligible impact on the structure. In fact the considered intervention is aimed to recover the original geometry of the elements with a reduced cost and impact on the fruition.

Summary Recent studies have addressed the computation of fragility curves for mainshock (MS)-damaged buildings. However, aftershock (AS) fragilities are generally conditioned on a range of potential post-MS damage states that are simulated via static or dynamic analyses performed on an intact building. Moreover, there are very few cases where the behavior of non-ductile reinforced concrete buildings is analyzed. This paper presents an evaluation of AS collapse fragility conditioned on various return periods of MSs, allowing for the rapid assessment of post-earthquake safety variations based solely on the intensity of the damaging earthquake event. A refined multi-degree-of-freedom model of a seven-storey non-ductile building, which includes brittle failure simulations and the evaluation of a system level collapse, is adopted. Aftershock fragilities are obtained by performing an incremental dynamic analysis for a number of MS–AS ground motion sequences and a variety of MS intensities. The AS fragilities show that the probability of collapse significantly increases for higher return periods for the MS. However, this result is mainly ascribable to collapses occurred during MSs. When collapse cases that occur during a MS are not considered in the assessment of AS collapse probability, a smaller shift in the fragility curves is observed as the MS intensity increases. This result is justified considering the type of model and collapse modes introduced, which strongly depend on the brittle behavior of columns failing in shear or due to axial loads. The analysis of damage that is due to MSs when varying the return period confirms this observation. Copyright © 2017 John Wiley & Sons, Ltd.

The beam-column joints are very restricted areas in which the internal forces, generated by boundary elements, act on the concrete core and reinforcing bars with a very high gradient. They are the link between horizontal and vertical structural elements, and therefore, they are directly involved in the transfer of seismic forces. Thus, they are crucial to study the seismic behavior of reinforced concrete (RC) structures. To fully understand the seismic performances and failure modes of beam-column joints in RC buildings, a simplified analytical model of joint behavior is proposed and theoretical simulations are performed. The aim of the model, focusing on internal perimetric joints, is to identify the strength hierarchy in terms of capacity for different failure modes (namely failure of cracked joint, bond failure of passing through bars, flexural/shear failures of columns or beams). It could represent a tool for the designers of new joints to quantify the performance of new structures, but also as a tool for the designers of external strengthening of existing joints in order to calculate the benefits of the retrofit and pushing the initial failure to a more desirable failure mode. Further, some experimental results of tests available in the scientific literature are reported, analyzed and compared.

In this work, the seismic capacity of single and multi-span masonry arch bridges was assessed by limit analysis. A preliminary statistical survey was carried out on a stock of about 750 railway bridges in Italy, classified according to characteristics and expected collapse mechanisms under seismic excitation. A comprehensive parametric study was carried out on identified homogeneous classes, to calculate limit horizontal accelerations triggering the collapse mechanism in longitudinal and transverse directions. Iso-acceleration envelope curves, representing limit horizontal acceleration of the bridge as a function of geometric parameters, were then derived. These graphs can be used for preliminary seismic safety checking of existing masonry bridges, once the main geometric parameters are available by simple visual inspections and geometric surveys, and can easily be implemented in a Bridge Management System to prioritise seismic retrofitting interventions.