Masonry Elements Research Articles

The Selected Issues of Adaptation of 19th and 20th Century Post-Industrial Buildings in Łódź

The paper deals with selected technical problems related to the adaptation for new uses of the structure of existing post-industrial buildings from the turn of the 19th and 20th centuries. A major difficulty is the fact that the strength and geometric properties of cast-iron, steel, and masonry elements often differ significantly from the values characterizing contemporary materials. Due to uncertainty regarding the load-carrying capacity of historical structures, in many cases there is a need to carry out destructive tests of elements taken from the buildings. As the example of cast-iron girders in the former spinning mill of “I. Poznański” demonstrated, such tests can prove a significant margin of load-carrying capacity and confirm the possibility of adapting the structure to new purposes. The paper also presents examples of strengthening the existing wooden ceilings by joining with the reinforced concrete structure, which allowed the keeping of the original elements and an increase of the allowable load. Selected problems related to the assessment of historical masonry structures were also described. The discussed examples of structural failures showed that they often resulted from incorrect assessment of the strength of historical masonry elements as well as improperly conducted construction works.

Numerical modeling of confined brick masonry structures with parametric analysis and energy absorption calculation

The objective of this paper is to propose a new modeling methodology for numerical analysis of full-scale confined brick masonry structures. Two modeling strategies are used within a single structure, where the in-plane walls are modeled using “simplified micro-modeling” approach and out-of-plane walls are modeled using “macro-modeling” approach. The lateral load capacity is associated with the in-plane shear resistance of masonry elements, therefore more detailed analysis is required for in-plane walls to achieve a comprehensive understanding of the damage mechanism and load transfer. The investigation of the in-plane shear behavior of confined brick masonry structures is of significant importance. Additionally, the proposed hybrid model is validated by comparing the results of experimental studies of confined brick masonry structure. A parametric study is then conducted to investigate the effect of brick and mortar properties on the structural response metrics (e.g. base shear coefficient, effective stiffness, response modification factor, the three performance levels (i.e. Immediate Occupancy, Life Safety and Collapse Prevention limits) and the energy absorption properties). It is observed that these structural response metrics, changed considerably by varying the material properties. Apart from that, the damage behavior and damage pattern are also assessed for the better understanding of effect of these parameters on the response of the structure. The proposed hybrid-modeling approach gives sufficient accuracy in predicting the lateral load behavior as well as the damage mechanism of confined brick masonry structure, subjected to lateral loading.

Compressed and stabilized soil blocks with fly ash-based alkali-activated cements

In this study, blocks were manufactured from clay soil and alkali-activated binders. The soils used were classified as A-4 and A7-5 according to ASTM D3282. The binder was produced from fly ash with a high content of unburned material (carbon). Blast furnace slag and lime were used as calcium sources. The physical–mechanical results of the blocks showed that the texture of the soil is a very important parameter for manufacturing this type of compacted soil masonry element, because the soil with the highest sand content (soil A-4) showed a higher dry density, indicating that this property corresponded to a lower percentage of permeable pores, a lower water absorption and an average compressive strength of 17 MPa at an age of 28 days. A life cycle analysis of the blocks was carried out and the results compared to that of the concrete paving blocks and fired clay blocks, which showed that the Global Warming Potential (GWP) can be reduced from 38 to 75%. Of the materials used to prepare the activated blocks, lime and silicate generate the greatest impact. In general, the results show the technical feasibility of manufacturing alternative blocks to traditional pavers with alkaline activation processes by using natural soils as the basic raw material and a low-quality fly ash as precursor.

Masonry subjected to semi-cyclic compression: Inelastic response modelling

A series of load tests on unreinforced masonry elements (triplets and wallettes with inclined bed joints) subjected to semi-cyclic compression have been performed in order to investigate the response of masonry under such loading conditions. The specimens exhibited inelastic and extremely nonlinear response and substantially different behaviour during the loading, unloading and reloading phases. Further investigations revealed that the observed behaviour was governed by the response of the block-mortar interfaces. A new mechanical model has been developed, which combines the conventional stress–strain model for the masonry with a non-linear model describing the response of the block-mortar interfaces. The model was calibrated using the Monte-Carlo simulation method and validated against the semi-cyclic compression tests on masonry specimens. The model developed is expected to improve significantly the simulation of the force–displacement response of unreinforced masonry walls subjected to seismic loading.

Comparison between Design Formulations and Numerical Results for In-Plane FRCM-Strengthened Masonry Walls

Strengthening strategies and structural rehabilitation of existing buildings with innovative materials and techniques are today one of the main activities in the field of structural engineering. Externally bonded Fiber Reinforced Cementitious Matrix (FRCM), materials are spreading as an alternative strengthening technique to the more traditional Fiber Reinforced Polymer (FRP) ones, especially for masonry elements. This research focuses on the assessment of the shear strength of in-plane FRCM-strengthened masonry walls by means of code predictions and numerical results, with particular attention on the interpretation of diagonal compression tests simulated by means of Finite Element (FE) models. Firstly, the various approaches commonly adopted for the interpretation of diagonal compression tests in terms of shear strength were examined, since codes give generally provisions in terms of maximum shear force, while several experimental and numerical results of diagonal compression tests are available in literature. Then, the numerical simulations of diagonal compression tests obtained by several FE analyses in a previous work were examined in light of these different approaches; the corresponding predictions of the shear force are compared with code indications in order to individuate the most reliable approach both for the un-strengthened and the FRCM-strengthened walls. For the latter ones, a detailed analysis of the actual strain levels in the reinforcement was carried out, too, by means of FE analysis.

Spandrel panels in masonry buildings: Effectiveness of the diagonal strut model within the equivalent frame model

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.

In vitro matured horse oocytes from aged mares show weakened centromeric cohesion and a higher incidence of aneuploidy

This paper presents a 3D brick-based model that aims at the derivation of in- and out-of-plane homogenized failure surfaces for masonry. The considered masonry panel is discretized into regular parallelepiped 3D finite elements that are supposed to be rigid; the model here introduced uses a Kirchhoff-Love plate kinematics for the out-of-plane description of the displacement rate field of the elements. A linear programming problem formulated in standard form is scripted into Matlab to derive the in- and out-of-plane homogenized failure surfaces, also enabling the extraction of failure modes for the considered masonry element. The constraints of the linear programming problem come from the combination of an upper bound limit analysis problem and a homogenization-based approach. The proposed model is validated for two separate case studies: a running bond masonry test-window and an English bond masonry test-window. The homogenized failure surfaces resulting from the current model show good correspondence to those presented in three distinct works available in literature. Also, a few relevant failure modes are derived for the two case studies, and they are consistent with the expected deformed shapes at collapse for their related load conditions.

Finite element model application to flexural behavior of cement stabilized soil block masonry

A finite element model for cement-stabilized soil block (CSSB) masonry members—including nonlinear stress-strain relationship—has been developed and compared with experimental results. Primarily, this model serves as a simulation tool to study various problems for a large number of stress–strain state and loading conditions of CSSB masonry elements. The model presented is characterized by several parameters experimentally ascertained through triaxial and other testing. Furthermore, these parameters allow the model to capture the elastic, plastic, and softening behavior of CSSB masonry. From a constitutive behavioral standpoint, at small strain levels, the material is approximated as linear elastic. Plastic deformation of the material is captured with a modified version of the Sandia Geomodel, which is specifically designed to replicate geological material behavior. Lastly, at localized softening failure, a damage-like constitutive model which takes into account the normal and shear traction balance on the slip-weakening surface is employed. This model includes cohesion degradation as well as friction under compression. Within the finite element framework, the Strong Discontinuity Approach is used to track localized material failure from element to element. In addition to this, a novel method for modeling interfaces in finite elements is used to replicate the behavior of brick-mortar interfaces. The two featured experiments which are simulated in this study are normal to bedjoint and parallel to bedjoint masonry setups, simplified via a plane strain approximation.

Compressive behaviour of fired-clay brick and lime mortar masonry components in dry and wet conditions

This paper examines the fundamental mechanical properties of masonry elements incorporating fired-clay bricks and hydraulic lime mortars under ambient-dry and wet conditions, corresponding to 48 h submersion in water. In addition to complementary material characterisation assessments, two types of specimens are tested: cylindrical cores in compression, and wall elements in compression. Overall, a detailed account of more than 50 tests is given. Apart from conventional measurements, the use of digital image correlation techniques enables a detailed assessment of the influence of moisture on the constitutive response, confinement effects and mechanical properties of masonry components. The uniaxial compressive strengths of wet brick elements and brick–mortar components, resulting from tests on cylindrical cores with height-to-depth ratios of around two, are shown to be 13–18% lower than those in ambient-dry conditions. The tests also show that enhanced confinement levels in brick units mobilise 67–92% higher strengths than in the corresponding unconfined cylinders. Moreover, experimental observations indicate that the presence of significant confinement reduces the influence of moisture on the mechanical properties as a function of the brick and mortar joint thickness and their relative stiffness. As a result, the failure of wet masonry walls in compression is found to be only marginally lower than those in ambient-dry conditions. Based on the test results, the influence of moisture on the constitutive response and mechanical properties of masonry components is discussed, and considerations for practical application are highlighted.

Traditional and innovative systems for injected anchors in masonry elements: Experimental behavior and theoretical formulations

Over the last recent years, the interest in the use of injected anchors as a strengthening method for avoiding out-of-plane mechanisms in existing masonry buildings has been strongly increased. Common traditional techniques made by steel bars are currently integrated by alternative ones based on the use of innovative materials as Fibre Reinforced Plastic (FRP) bars. The paper firstly focuses on a critical analysis of several strength models available in literature for anchors embedded in both concrete and masonry substrates. Moreover, the analysis of literature about injected anchors in masonry elements has been completed by the collection of experimental results of pull-out tests carried out by several researchers. The collected database is also enriched by the results of pull-out tests directly carried out by the Authors and described in detail in the paper. Then, the reliability of the existing strength models into predict the pull-out forces has been investigated by means of comparisons with the available experimental results. Finally, according to the ‘design by testing’ approach, regression analyses have been carried out on the whole database in order to assess new formulations taking into account the most important parameters influencing the performance of injected anchors made of both traditional and innovative materials.

Bond behaviour of steel-TRM composites for strengthening masonry elements: Experimental testing and numerical modelling

Textile reinforced mortar (TRM) composites are an innovative solution for strengthening masonry structural elements due to their effectiveness and sustainability, as well as their compatibility with masonry substrates. As TRM composites are externally bonded to the surface of structural elements, the bond behaviour at the textile-mortar matrix and mortar matrix-substrate interfaces is a critical issue that needs to be investigated. In this study, an extensive study is carried out which includes a series of experimental tests combined with advanced numerical modelling with the aim to provide a better understanding of the bond behaviour of steel-TRM composites for strengthening a specific type of masonry which made by grey clay bricks. The experiments mainly consist of 28 single-lap shear bond tests on steel-TRM strengthened masonry elements. The effect of the masonry substrate condition, configuration of the textile, mechanical properties of the mortar matrix, and length of the bond are presented. The test results are discussed in terms of the full range of load-slip responses and failure modes. Then, an advanced numerical model based on simple interfacial local bond-slip constitutive laws is validated by agreement with the experimental findings. Finally, the numerical results are also used to evaluate the effective bond length and further understand the bond behaviour.

Study on Retrofitted Masonry Elements under Shear Using Digital Image Correlation.

Architectural heritage is usually built with masonry structures, which present problems under lateral in-plane loading conditions, such as wind pressure or earthquakes. In order to improve the shear behavior of masonry, the use of a fabric-reinforced cementitious matrix (FRCM) has become an interesting solution because of its synergy of mechanical properties and compatibility with masonry substrates. For a proper structural evaluation, the mechanical behavior of reinforced masonry and the FRCM itself needs to be characterized. Hence, a numerical model to evaluate the FRCM reinforcement requires some mechanical parameters that may be difficult to obtain. In this sense, the shear behavior of masonry can be evaluated by means of diagonal tension tests on small specimens (71 × 71 cm). In this work, a digital image correlation (DIC) monitoring system was used to control displacements and cracking patterns of masonry specimens under shear stress (induced by diagonal tension with FRCM layers) applied to one or two sides. In addition, the mechanical behavior of FRCM coupons under uniaxial tensile tests was also registered with DIC. The displacement measurements obtained by DIC were validated with the measurements registered with LVDT. Unlike LVDT-based techniques, DIC monitoring allowed us to measure deformations in masonry during the full test, detecting crack initiation even before it was visible to the eye.

The ratio of shear to elastic modulus of in-plane loaded masonry

When designing unreinforced masonry buildings, the wall stiffness and, consequently, the masonry elastic and shear modulus E and G are essential parameters. Current codes provide empirical estimates of the masonry elastic modulus and a ratio between the shear and elastic modulus, G/E. This ratio, commonly taken as 0.4, is not based on scientific evidence and there appears to be no consensus concerning its value and influencing parameters, meaning that current code standards might not accurately portray the shear deformations of masonry elements. To give the choice of the G/E ratio a theoretical foundation, this paper presents closed-form expressions for the G/E ratio of running-bond masonry that capture the effects of finite joint thickness, finite wall thickness and orthotropic block properties. Based on the geometry of blocks and joints as well as their elastic parameters, a validation of the developed expression using 3D finite element analyses shows good performance. For modern masonry typologies with hollow clay bricks, a G/E ratio of 0.20–0.25 is obtained. For historical masonry typologies, such as dry stacked or mortared stone masonry, as well as solid clay brick masonry, ratios between 0.30 and 0.40 are computed.

Effectiveness of design formulations for injected anchors in masonry elements

The paper is aimed to carry out a critical analysis of the available experimental results of pull-out tests related to several types of injected anchors in masonry elements. The database is also comprehensive of the results of some experimental pull-out tests directly carried out by the Authors. Both data on traditional steel bars and on anchors made by innovative materials embedded in several types of masonry made of natural stones and clay bricks are included in the database. Firstly, the main parameters influencing the experimental pull-out forces in the collected database were analyzed. Successively, the experimental values of the pull-out forces were compared with theoretical predictions provided by existing formulations and their reliability was discussed. Finally, regression analyses were carried out on the available database in order to assess new design formulations taking into account the main parameters influencing the performance of injected anchors.

Micromechanical and multiscale computational modeling for stability analysis of masonry elements

This paper presents two micromechanical and a multiscale finite element models for the analysis of masonry walls under out-of-plane instability effects. A two-dimensional modeling of the wall is considered in all approaches, assuming a cylindrical bending. The micromechanical analyses are performed considering elastic beams to model the bricks and either nonlinear beams or interfaces to model the mortar layers. The beam finite elements rely on the force-based formulation and account for large displacements by making use of the corotational approach. This latter is properly formulated and extended to interface elements to include nonlinear geometry effects. The multiscale model is defined by applying a two-scale beam-to-beam homogenization procedure, developed for masonry elements with periodic brick arrangements. Hence, a Unit Cell made of a single linear elastic brick and a single nonlinear mortar layer is introduced at the microscopic level, which is linked to the macroscale level through a semi-analytic homogenization technique. In all models, a damage formulation with friction plasticity governs the mortar constitutive relationship. Computational details on model implementation and solution procedures are given for all approaches. Correlation studies are performed to assess the proposed numerical micromechanical and multiscale procedures. In particular, the behavior of an unreinforced wall tested under a compressive eccentric load is reproduced and advantages and disadvantages of the proposed approaches are discussed.

Modelling and testing of large-scale masonry elements under three-point bending – Tough and strong nacre-like structure enlarged by a factor of 20,000

Large-scale brick-mortar structures and tough/strong nacre have common layered structure features. If enlarged by 20,000 times, fracture patterns in natural nacre consisting of micro-layered structures around 2 μm in thickness are virtually identical to those in large-scale brick walls. In this study, large brick-wall blocks about 3 m long and over 1 m tall were tested under three-point-bending and explained by a simple closed-form model. Two notch lengths (two and four brick heights) and two wall heights (about 1.1 and 0.6 m) were tested with 35 brick-mortar blocks. A linear relation between the maximum fracture load Pmax and the equivalent area Ae was established with the “structureal” tensile strength ft of brick walls as its slope, affirming one of the most common physical relations in Solid Mechanics, Pmax = ft × Ae. The equivalent area Ae contains all brick wall dimensions including the brick height Cch. As the characteristic structural measurement of brick wall elements, Cch plays a key role in modelling of the overall damage zone in front of the initial notch.

Analysis of bond behavior of injected anchors in masonry elements by means of Finite Element Modeling

Injected anchors made of steel bars embedded in masonry elements by means of cement-based grout represented in the past a wide solution for avoiding out-of-plane mechanisms. Corrosion phenomena in steel bars reduced the effectiveness of such type of intervention over time. Innovative materials, as the Fiber Reinforced Plastic ones, can represent a suitable alternative to increase durability and performance of injected anchors. Since the effectiveness of injected anchors is strictly related to bond behaviour along both the bar-grout and the grout-masonry interfaces, a detailed analysis by means of a Finite Element model was developed for different types of bars embedded in masonry elements. The numerical model was firstly calibrated on some experimental results of pull-out tests available in literature and, then, is used for investigating the effects of several parameters on both local and global behaviour. Load-displacement curves and local distributions of shear stresses are examined in detail. The numerical analyses evidenced that the maximum tensile force in the anchor mainly depends on the shear strength of the bar-grout and the grout-masonry interfaces and on the embedded length, but for very long embedded length, it can be limited by the tensile failure in the anchor or in the masonry.

A gradient elastic homogenisation model for brick masonry

The elastic macro-mechanical properties of masonry are investigated herein by taking into account the presence of a weakly non-local heterogeneity within a simple gradient elasticity model. Masonry has a heterogeneous structure composed of masonry units bound by mortar. The homogenisation of masonry walls is a challenging task but also a very appealing method for modelling heterogeneity effects exhibited by masonry elements. In particular, it allows the use of smeared mechanical properties, thus avoiding the need of knowing the exact unit-to-unit and joint-to-joint geometry. Current codes provide very simplified empirical expressions to estimate an isotropic elastic modulus of masonry on the basis of its strength properties. The respective equations which do not take into account the anisotropy of masonry, present high scatter resulting in ambiguous safety. The homogenization argument employed in this work is based on a simple procedure utilising Aifantis’ gradient elasticity (GradEla) model. The GradEla model is a straight-forward extension of Hooke’s law by enhancing it with the addition of the Laplacian of the classical expression of the Hookean stress multiplied by an internal length accounting for the local heterogeneity. It has been successfully used to eliminate singularities from dislocation lines and crack tips, as well as in interpreting size effects. However its use in masonry structures has not yet been explored. A first step in this direction is attempted in this paper with emphasis on obtaining practical easy-to-use results rather than exhausting all other possibilities and complexities encountered in GradEla and its generalisation, as well as in more involved homogenisation procedures. In our analysis uniform vertical, horizontal and shear loads are assumed to act on the boundaries of the representative volume/surface element. The components of masonry are assumed to follow a gradient elastic stress distribution resulting in a gradient elastic homogenised model (GREHM). GREHM comprises a set of closed-form concise equations which estimate the elastic moduli in the longitudinal and transverse directions, the shear modulus and the Poisson’s ratio. The aforementioned orthotropic material properties are verified using experimental results and also, compared to other homogenisation models. The validation shows that the proposed equations can effectively estimate with considerable precision the elastic properties of masonry walls. To illustrate the resulting estimation of the orthotropic elastic properties, normalised graphs are provided.

Selected Aspects Regarding the Restoration/Conservation of Traditional Wood and Masonry Building Materials: A Short Overview of the Last Decade Findings

Vernacular buildings are usually constructed using materials at hand, including wood, natural stone and bricks (either clay or mud bricks). All those materials are exposed to a series of environmental factors, affecting their structure and integrity. The literature review was conducted using different databases (Scopus, Web of Science, ScienceDirect, SpringerLink) using as keywords the historical material, “heritage” and the terms regarding the desired effect, within the envisaged time period (2010–2019). The assessment of the results was performed by manual inspection (reading the entire article) and the selection of the works to be inserted in the current review was made by evaluating the contribution to the field. This review summarizes different aspects related to the restoration and conservation of wooden and masonry elements of traditional buildings, including materials used for biocidal interventions, protection against abiotic factors, cleaning and consolidation agents. Finally, a critical discussion regarding the current limitations and future perspectives concludes the review work, envisaging the role of researchers specialized in materials science in the context of cultural heritage conservation.

Fast brick-based homogenized limit analysis for in- and out-of-plane loaded periodic masonry panels

This paper presents a 3D brick-based model that aims at the derivation of in- and out-of-plane homogenized failure surfaces for masonry. The considered masonry panel is discretized into regular parallelepiped 3D finite elements that are supposed to be rigid; the model here introduced uses a Kirchhoff-Love plate kinematics for the out-of-plane description of the displacement rate field of the elements. A linear programming problem formulated in standard form is scripted into Matlab to derive the in- and out-of-plane homogenized failure surfaces, also enabling the extraction of failure modes for the considered masonry element. The constraints of the linear programming problem come from the combination of an upper bound limit analysis problem and a homogenization-based approach. The proposed model is validated for two separate case studies: a running bond masonry test-window and an English bond masonry test-window. The homogenized failure surfaces resulting from the current model show good correspondence to those presented in three distinct works available in literature. Also, a few relevant failure modes are derived for the two case studies, and they are consistent with the expected deformed shapes at collapse for their related load conditions.