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The paper presents the experience of a working group within the Rilem Technical Committee 223-MSC ‘Masonry Strengthening with Composite materials’, aimed at developing a standardized, reliable procedure for characterizing the bonding mechanism of masonry elements strengthened with composite materials under shear actions. Twelve laboratories from European universities and research centers were involved. Two different set-ups were compared, for single-lap and double-lap shear tests (the latter in two versions). Four kinds of fiber fabrics, i.e., glass, carbon, basalt and steel, were applied with epoxy resins (wet lay-up system) to clay brick units, for a total of 280 monotonic tests. The results provided information regarding the response of externally bonded-to-brick composites in terms of observed failure mechanisms, load capacity, effective transfer length, and bond shear stress-slip behavior. The test results of the twelve laboratories constitute a set of statistically representative data which may conveniently be used for setting appropriate design provisions and guidelines.

Existing masonry buildings and infrastructures are often characterized by curved elements like arches, where the settlements could induce damages up to compromising their stability. Curved elements are very sensitive to settlements due to the modification of the lateral thrust. The effects of settlements could be very critical on heritage buildings, where the intrados of curved elements are often characterized by decorated plasters. These issues caused by settlements are very important also in the infrastructures, where the displacement of the foundations could affect the main structural elements. When dealing with existing heritage buildings the analysis cannot be focused on the ultimate state only. In order to preserve the heritage value, it is important to refer to elastic behaviour to minimize the damages at serviceability limit state (e.g., newly defined artistic limit state). In this work, an existing theory has been used to obtain the closed-form solution for a specific curved system (i.e., Standard arch). The behaviour of semi-circular and parabolic curved elements is investigated under several load conditions of vertical loads and settlements. The solutions were numerically estimated according to the Principle of Virtual Works and are dimensionless in order to obtain generalizable results. A parametrical analysis was performed, providing several useful design charts to assess the impact of settlements and vertical loads on the behaviour of curved elements. The closed-form solution derived for standard arch if applied to different cases yields to approximated solutions and the scatter was estimated by comparing them with refined numerical evaluations. The outcomes of this work are useful tools to assess the sensitivity to structural damage of curved elements under settlements.

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.

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.

This paper presents the results of an experimental program conducted on H-shaped reduced-scale reinforced masonry spandrels subjected to monotonic loadings. It summarized tests units, test set-up and experimental results relative to seventeen samples reinforced by thin-steel stripes arranged with different configurations, and compared with those unreinforced. The first configuration comprised masonry spandrels strengthened by unbonded horizontal and diagonal steel stripes (i.e., stripes connected by means of threaded rods to the nodal area of the panel), while the second masonry spandrels reinforced by bonded horizontal stripes (i.e., stripes connected with 5 or 13 threaded rods over the spandrel length). For each reinforcement configuration, slender, intermediate and squat slenderness ratios have been considered for the samples. The conducted research investigated the effectiveness of the reinforcement to enhance the seismic response of the spandrels. Test results demonstrated that the application of steel stripes is beneficial in changing the failure modes from shear-dominated into flexural-dominated, especially for intermediate and squat panels prone to brittle shear mechanisms. Despite that increases of strength are reduced with respect to unreinforced samples, when reinforced the post-peak response changes significantly being it characterized by a remarkable ductile response for whatever spandrels’ slenderness ratios.

The strengthening of masonry structures is nowadays performed by means of high-strength fibers embedded in inorganic matrix (FRCM) where lime or cement-based matrix is used instead of epoxy adhesive to reduce debonding issues between substrate and matrix. However, some sliding phenomena and cohesive failures between fibers and the matrix mortar can occur. The paper examines the effect on the FRCM efficiency of the mechanical properties of fiber and matrix and potential geometrical defects, which are possible in real field applications or in qualification tests. The model application to simulate bond tests on typical PBO-FRCM and Glass-FRCM allowed to analyse slips as well as normal and shear stresses both in the bundle and in the matrix constituting the FRCM, for different defects due to application issues. The result of numerical simulations seems to interpret well the results of the qualification tests with a multi-bundle effect that justifies their scatter. The approach can be applied by varying main mechanical properties of the materials (e.g. elastic modulus, fiber cross section, bond properties) to consider their intrinsic variability in the assessment of the performance of the FRCM system or by changing the type of materials (i.e. mortar and fibre) to optimize the FRCM system.

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.

Scientific community showed particular interest in tsunami risk assessment in the last years due to several worldwide tsunami events where high damages and human casualties were recorded during post-event surveys. This paper investigates the behaviour of Italian coastal residential masonry buildings under tsunami loads. Main fragility curves available in literature are based on empirical databases and consequentially, the structural behaviour is strictly related to local building typologies of other countries. For masonry buildings, it is complex to predict global response due to high material inhomogeneity, especially in the case of regional scale analysis; a critical review on local mechanisms activation of masonry walls under tsunami loads is briefly performed. Therefore, local mechanisms activation for masonry walls are investigated depending on out-of-plane and in-plane mechanisms assuming flexural and shear failure. Structures designed for gravity or seismic loads are generated based on several building classes depending on number of storeys and age of construction. Monte Carlo analyses generated building models for each identified building class to simulate the behaviour of Italian masonry buildings. Preliminary analytical tsunami fragility curves are developed in order to assess the vulnerability of Italian coastal residential masonry buildings under tsunami loads. A critical review is proposed on developed fragility curves.

In the last decades, several tsunamis hit international coasts and engaged scientific awareness to the retrofit of coastal buildings against tsunami loads. Structural design under tsunami loads is difficult due to the high uncertainties of the phenomenon. Local collapse mechanisms of masonry walls, like as out of plane mechanisms, have an high probability due to flexural actions; a higher flexural capacity can be reached using specific retrofit systems; in particular, this paper aims to deepen the behavior of masonry walls retrofitted with innovative retrofit systems like as natural fibers applied with inorganic mortar matrices. The retrofit of structures under tsunami actions could be an innovative research topic for international research community dealing with coastal buildings located in areas characterized by a high tsunami risk. Recent engineering applications demonstrated the innovative strengthening systems to be effective for the retrofit of existing masonry buildings. These strengthening systems are of great interest in the practical applications due to the low costs and their sustainability. In fact, the lower costs compared to the synthetic fibers allow their diffusion in emerging countries. In a first part the impact of constituents on the structural capacity of masonry elements strengthened with natural systems has been discussed. Important results have been provided in order to improve the knowledge and encourage the development of these systems in many engineering applications. Finally, the effects of retrofit systems on masonry walls under tsunami loads will be discussed in terms of critical inundation depth variations before and after the interventions.

Assessment of the mechanical properties of masonry materials is a key issue for evaluating the strength capacity of masonry walls. Two types of tests are usually adopted for experimentally evaluating the shear capacity of masonry walls: diagonal-compression and shear-compression tests. Different approaches are available in the literature for their interpretation. This paper reports an investigation into the behaviour of both unstrengthened and in-plane strengthened masonry walls with fibre-reinforced cementitious matrix materials under the two tests by means of a bi-dimensional non-linear-finite-element model. The model was first calibrated on the basis of comparisons with experimental results of diagonal-compression tests available in the literature. It was then used for comparing the numerical results obtained for the two tests in terms of local stress distributions for both unstrengthened and strengthened walls. The differences in the stress distributions in the tests, and the role of the reinforcement both on the distribution of stresses and on the global behaviour of the masonry walls, was highlighted.

The seismic performance of masonry churches is mainly governed by the out-of-plane mechanisms. Among them, the greater seismic vulnerability can be associated to the out-of-plane mechanism of the façade. If the masonry quality ensures a monolithic out-of-plane behaviour, the dynamic analysis of a rigid rocking block allows a reliable estimation of the seismic capacity of the façade, provided that the element boundary conditions are well assessed. In the present paper, the literature rocking models are adopted for a vulnerability assessment of churches' masonry façades characterized by different geometries. At this aim, fragility curves are defined by means of the Cloud Analysis approach considering earthquakes recorded in the Central Italy area to account for the record-to-record variability.

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 strengthening intervention strategies that exist for masonry buildings are based on the use of thin composites and are a recent activity used in structural engineering. Nowadays, mortar matrices are frequently found instead of epoxy resins, since the fiber reinforced cementitious matrix (FRCM) composites are more compatible with masonry than fiber reinforced plastic (FRP) ones. The mortar matrix in FRCM composites is not comparable to the epoxy resin, and therefore its contribution is different not only in traction but above all on the compression side. Due to its larger thickness, if compared to the epoxy resin, the impact of the mortar matrix on the flexural response of strengthened cross sections is not negligible. This paper aimed to investigate the influence of the contribution of the mortar matrix on the compression side on the flexural capacity of strengthened cross section. As such, p&ndash, m interaction domains and bending moment&ndash, curvature diagrams were evaluated to understand the influence of several mechanical properties of fiber and mortar matrices on FRCM efficiency, typical of real applications. Hence, the impact of several constitutive relationships of composites (linear and bilinear behavior) was considered for the structural analysis of the strengthened cross section. The presented results are all completely in a dimensionless form, therefore, independent of geometry and mechanical parameters can be the basis for developing standardized design and/or verification methodologies useful for the strengthening systems for masonry elements.

Structural analysis represents a valid tool to evaluate the seismic capacity of existing structures and to plan retrofit strategies. Howsoever, structural modelling performed on existing masonry buildings could become very complex. This issue increases when the interest focuses on heritage buildings due to the strong heterogeneities that characterise them. This study focuses on the analysis of a religious masonry building: the case study of S. Giuseppe delle Scalze in Naples (Italy). The structure is characterised by a clear deterioration and several damages. Various modelling approaches have been carried out to estimate the main structural behaviour of the church. Starting from surveys, a finite element (FE) model was developed. According to a limited knowledge level, various structural models have been developed, to take into account many variables. Starting from these numerical models, several analyses have been performed: static gravitational, linear dynamic and linear time history analyses. The goal of the analyses is to assess the main sources of damage by comparing the peak stresses with the current damage. Given the linear-elastic assumption due to the limited knowledge level, the results are useful to assess triggering of damage only.

[Excerpt] 17.1 Introduction Fiber-reinforced polymers (FRPs) have been extensively used for seismic strengthening of existing concrete and masonry structures. The ease of application and high strength-to-weight ratio of these composites have made them an interesting solution for strengthening purposes.[...], (undefined)

Several experimental tests recently performed on tuff or clay brick masonry elements (i.e. walls and arches) demonstrated the benefits of Fiber Reinforced Cementitious Matrix (FRCM) systems used as externally bonded reinforcement for strengthening and seismic retrofitting of masonry structures. Tensile tests on coupons made of different FRCM materials allowed defining constitutive laws in tension, which are characterized by a post-cracking behaviour with more or less effective tension stiffening effect. This paper is focussed on the assessment of the influence of the mechanical properties of both the masonry substrate and the FRCM systems on the overall behaviour of strengthened masonry walls subjected to diagonal compression. To this aim, several numerical analyses were carried out for simulating diagonal compression tests by means of a bi-dimensional Finite Element Model. A non-linear behaviour was assumed for both masonry substrates and FRCM reinforcements. For the latter ones, a perfect bond condition was assumed and the tension stiffening effect of the mortar was taken into account in the tensile behaviour of the FRCM reinforcement based on experimental results previously carried out by the Authors.

Textile Reinforced Mortar (TRM), also known as Fabric Reinforced Mortar or Fabric Reinforced Cementitious Matrix, composites are an emerging technology for the external repair and strengthening of existing structures. For most applications, the effectiveness of the TRM reinforcement relies on its bond performance. This recommendation identifies the best practice to characterize the bond behaviour of TRM. A shear bond test method is proposed to determine the peak axial stress (associated with the maximum load that can be transferred from the structural member to the externally bonded TRM reinforcement), the stress-slip relationship and the failure mode that controls the TRM-to-substrate load transfer capacity. Guidelines on specimen manufacturing, experimental setup, test execution, and determination of test results are provided., info:eu-repo/semantics/publishedVersion

Retrofit of existing structures is one of the most demanding and challenging tasks for practitioners. The research community is providing newer solutions and systems improving the compatibility and sustainability both in environmental and conservation fields. Textile reinforced mortars (TRMs) represent a good balance between strength provided by fibres and compatibility of mortars by the matrix. The main aim of the paper is to provide fast assessment tools for the effects of tsunami actions on masonry structures, assuming as main parameter the inundation depth, and to provide a comparably fast tool to design retrofit interventions with innovative strengthening systems. The peculiar multilinear behaviour of systems, like as TRM, is accounted for and some design equations and charts are provided, discussing the peculiarities of the material property variability to orient the designer to coherent and effective decisions; potential uncertainty and variability of substrate masonry are taken into account, too.

Beam-column joints represent very important elements of reinforced concrete (RC) structures. In fact, beams and columns, at the boundary, generate internal forces acting on concrete core and on reinforcement bars with a very high gradient. To fully understand the seismic performances and the failure modes of T-shaped beam-column joints (external corner-positioned) in RC structures, a simplified analytical model of joint behaviour is proposed and theoretical simulations have been performed. The model is based on the solution of a system of equilibrium equations of cracked joint portions designed to evaluate internal stresses at different values of column shear forces. The main aim of the proposed model is to identify the strength hierarchy. Limit values of different internal stresses allow us to detect the occurrence of different failure modes (namely the failure of the cracked joint, the bond failure of passing through bars, and the flexural/shear failures of columns or beams) associated with column shear forces; the smaller one represents the capacity of the joint. The present work, focusing on T-shaped joints, could represent a useful tool for designers to quantify the performance of new structures or of existing ones. In fact, such a tool allows us to push an initial undesired failure mode to a more appropriate one to be evaluated. Finally, some experimental results of tests available in literature are reported, analysed, and compared to the predictions of the proposed model (by means of a worked example) and of some international codes. The outcomes confirm that failure modes and corresponding joint capacities require an analytical model, like the proposed one, to be accurately predicted.

The external confinement of reinforced concrete (RC) columns by means of externally bonded fiber reinforced polymer (FRP) laminates is a well established technique for strengthening and retrofitting purposes. This paper presents a pilot research that includes laboratory testing of full-scale square and rectangular (with side-aspect ratio smaller than 1.5) RC columns externally confined with glass and basalt-glass FRP laminates and subjected to pure axial load. Specimens that are representative of full-scale building columns were designed according to a dated ACI 318 code (i.e., prior to 1970) for gravity loads only. The study was conducted to investigate how the external confinement affects peak axial strength and deformation of a prismatic RC column. The results showed that the FRP confinement increases concrete axial strength, but it is more effective in enhancing concrete strain capacity.

The present work deals with the analysis of unreinforced and FRCM reinforced masonry walls subjected to out-of-plane loading. In particular, numerical simulations of full scale experimental clay brick walls, previously tested, are developed. The out of plane behaviour is relevant not only for flat walls, but also for curved structures, like as domes and vaults, for which FRCM demonstrated to be highly effective in improving their structural behaviour. In this paper, two tested walls are numerically analysed. The first wall has been tested in an unreinforced configuration inducing a significant damage distribution; then, it has been retrofitted by FRCM and tested again. The second wall has been reinforced without pre-damage and tested applying the same loading history adopted for the first wall. This allowed to remark the effect of retrofitting to damaged and undamaged walls. Both the walls were constrained on two consecutive sides and loaded by a pointwise force orthogonal to the wall mid-plane, applied at the top free corner inducing a biaxial behaviour. The numerical simulations are developed performing nonlinear three-dimensional (3D) FE analyses to clearly remark the potential benefits of the strengthening technique involving FRCM systems on the out of plane behaviour. On the basis of a micro-modelling approach, bricks and equivalent interfaces were modelled separately assigning the nonlinearity only to equivalent interface. In fact, experimental testes demonstrated that the cracking and failure localize in the mortar joints. The FRCM system was modelled by means of an equivalent layer bonded on one side of the wall through interfaces. A parametric analysis is performed on the mechanical properties of the interface to investigate on the influence of these parameters on the wall response. This allowed to discuss the main parameters governing the out-of-plane behaviour of such masonry walls.

The aim of the proposed work is to clarify the dynamic behaviour of asymmetric bodies in the case of rocking behaviour. The proposed algorithm is based on Housner theory and the integration of the equations of motion is evaluated with the Runge-Kutta-Fehlberg (RKF45) method. The significant accumulation of numerical errors is evaluated during the integration between two consecutive acceleration points where the rotation sign changes owing to the adoption of an equation that is wrong. An iterative calculation is developed to reduce numerical error depending on a specific tolerance and, therefore, the algorithm accuracy is investigated. In addition, the reduction of energy due to the impact at the point of change of the sign of rotation is analysed by means of a restitution coefficient. It is important to note that this is highly dependent on the rigid block properties, and experimental programmes are required to calibrate the restitution coefficient properly. Sensitivity analyses are performed in order to clarify the effects of convergence parameters and tolerances on the results, due to high numerical instabilities. Furthermore, fragility curves are retrieved based on far-field and near-field sets of accelerograms proposed by the Applied Technology Council in 2008, ATC-63, and a critical discussion is provided concerning the most efficient intensity measure parameters.