Mortar Joints Research Articles

Anchors to solid clay brick masonry in tension: Behavior under monotonic and repeated loading for varied embedment depths

The paper presents the results of tension tests on anchors installed in solid brick masonry walls. Anchors were installed in various locations (either in bricks or in mortar joints), in walls either uncracked or with cracks passing through mortar joints. All tests, either monotonic or repeated, were executed under displacement-controlled conditions. The purpose of the experimental campaign was to investigate the behavior of anchors embedded to masonry under seismic conditions. To this aim, several parameters were investigated, namely, the depth at which anchors are embedded in masonry, their location within the wall, the presence of cracks, either crossing the anchor or being located at its vicinity. The measured tension resistances, depending on the examined parameters, are compared against values calculated based on current design guidelines. This comparison shows that the calculated values for the expected failure mode are sufficiently conservative.

A unified modeling approach for concrete masonry shear walls: Conception, validation and insights

Distinct modeling strategies have been developed to simulate concrete masonry shear walls; however, each is validated with a limited number of specimens tested under identical laboratory conditions and only covers specific detailing scenarios. This research seeks a unified finite element-based modeling approach integrating macro-modeling concepts for grouted masonry (GM) regions and simplified micro-modeling for ungrouted masonry (UGM) regions. The objective is to facilitate accurate simulation of the in-plane behavior of diverse typologies of concrete masonry shear walls: unreinforced masonry (URM), fully grouted reinforced masonry (FGRM), and partially grouted reinforced masonry (PGRM). A smeared crack approach is used to capture the crushing and cracking of grouted masonry (GM) and ungrouted masonry (UGM), and interface elements are incorporated into UGM regions to model the mortar joints, resulting in a combined smeared-discrete model. The validation process comprises two levels. The first-level evaluation focuses on URM and FGRM walls, emphasizing the analysis and comparison of lateral force–displacement curves. Second-level validation is done through simulation of PGRM walls by evaluating lateral force–displacement curves, damage patterns, and reinforcement strains. The implemented modeling approach generally simulates the response of the different experimental masonry shear walls evaluated with good accuracy. A sensitivity analysis was also performed to reveal the influence of some parameters on the numerical results, providing additional perceptions into the reliability of the modeling approach. Relevant insights into the modeling approach were obtained, allowing complex phenomena in the tested walls to be simulated, thus contributing to advances in the simulation of in-plane loaded concrete masonry walls.

Retrofit of damaged reinforced concrete frame by autoclaved aerated concrete blocks infill wall: Experimental validation and strength estimation

This study introduces a novel approach for the global retrofitting of seismic performance in destructively damaged reinforced concrete (RC) frames through the application of autoclaved aerated concrete (AAC) blocks infill walls to enhance both structural strength and stiffness. Three full-scale RC frames are designed and fabricated, comprising an intact bare frame, a damaged frame strengthened by carbon fiber-reinforced polymer (CFRP), and a damaged frame retrofitted with the same CFRP and AAC blocks infill walls. To verify the cyclic behaviors and working principle of the retrofitted system, the two frames undergo a pre-damage scenario with a maximum inter-story drift ratio (MIDR) of 2.52%, and then both specimens are retrofitted. Afterward, a pseudo-static cyclic test is conducted on three specimens, with a MIDR of 3.36%. The test data is analyzed and discussed in terms of hysteretic responses, secant stiffness, displacement ductility, and energy dissipation capacity. The findings indicate a significant improvement in the lateral strength and stiffness of the seismic-damaged frame through the implementation of AAC blocks infill walls, demonstrating performance comparable to the intact RC frame. Also, the slight local crushing of AAC blocks and their interaction with mortar joints effectively dissipates a considerable amount of input energy, thereby reducing the energy dissipation demands on retrofitted structural components. Moreover, the theoretical deduction of the lateral strength of the retrofitted RC frames is presented. The errors between the predicted and test results fall within 5%, suggesting that the analytical outcomes can reasonably predict the lateral strength of the specimens.

A study of the seismic resistance performance of strengthened masonry walls using polypropylene mesh-composite on the surface

To investigate the seismic performance of masonry walls in village buildings strengthened with polypropylene mesh materials on the surface, five reduced-scale masonry walls were designed for low-cyclic reversed loading tests. The research observed the failure processes and characteristic forms of masonry walls, conducting a comparative analysis of the hysteresis curves and energy dissipation of the walls. Then, ABAQUS finite element software was used to simulate the performance of the strengthened walls to analyze the damage mode of these walls. The results indicated that under compression-shear loading, unreinforced masonry walls experienced shear failure along horizontal mortar joints, exhibiting lower shear load, lateral stiffness, and ductility. The reinforced walls with polypropylene mesh-composite effectively delayed and mitigated the failure. Weak zones in the wall gradually extended from the structural sides towards the central core area. Ultimately, after the reinforcement material had fully engaged, delamination failure occurred, leading to the formation of "X" or "Y" shaped through cracks. After reinforcement with single-side polypropylene materials, the load-bearing capacity of the wall increased by 165 % compared to the unreinforced wall. The ductility is improved compared to the unreinforced wall, whereas the initial stiffness increased by 133 %. Upon reinforcement with double-sided materials, the wall's load-bearing capacity surged by 180 %. The initial stiffness climbed to 171.3 %. The finite element analysis results closely aligned with the experimental data, suggesting that reinforcing the surface with polypropylene mesh-composite cement mortar significantly bolstered the wall's shear strength and deformation capabilities. This method effectively strengthens the seismic resistance of masonry structures.

An interface-based microscopic model for the failure analysis of masonry structures reinforced with timber retrofit solutions

This paper presents a refined Finite Element (FE) modeling strategy for analyzing the failure behavior of regular masonry structures reinforced with timber-based retrofit solutions. The proposed model schematizes the masonry as brick units, modeled using two-dimensional linear elastic plane stress elements, mutually joined through zero-thickness cohesive interface elements. These interface elements serve to reproduce the nonlinear behavior of masonry because of the occurrence of failure mechanisms of the mortar joints. Reinforced timber frame elements are modeled using truss elements that exhibit elastic brittle fracture behavior. The interaction between the masonry sub-structure and the reinforced timber frame system is accounted for using special constraint conditions that simulate the mechanical behavior of anchorage connections. The reliability of the proposed model in reproducing the failure behavior of masonry is assessed through comparisons with experimental and numerical data available in the literature. Additionally, the efficacy of the retrofit technique based on timber frame structures is investigated in detail through pushover analyses on a two-story masonry wall representative of real-life masonry buildings. The results indicate that the proposed retrofitting strategy is an effective and eco-friendly retrofit solution to enhance the in-plane bearing capacity of masonry structures subjected to horizontal forces.

Applying a 2D Variational Rigid Block Modeling Method to Rubble Stone Masonry Walls Considering Uncertainty in Material Properties

ABSTRACT The computational cost of detailed micro-modeling of masonry structures can be minimized with rigid block analysis methods, where a variational formulation is particularly interesting as it allows for nonlinear pushover analysis. This work investigates the accuracy of this modeling method in predicting the response of rubble stone masonry walls in shear compression tests. To this end, we extend the mathematical programming problem by including cohesion, compressive strength, and tensile strength in the formulation and implement an improved pushover procedure, which guards compatibility of the displaced shape and crack patterns at the intersection of elastic and rigid contact models. Additionally, we reduce model uncertainty, introduced through sampling material properties with distributions estimated based on results from tests on mortar masonry joints and on mortar specimens, by correlating the predicted crack patterns with the observed ones. The findings show that (i) model falsification based on crack pattern is an effective method for reducing the parameter uncertainty of stone masonry walls; and that (ii) the improved pushover procedure predicts the pre- and post-peak response of stone masonry walls very well with analysis times of less than 20 minutes for 2D models where stones and mortar are modeled explicitly.

Experimental Evaluation of Compressive Properties of Early-Age Mortar and Concrete Hollow-Block Masonry Prisms within Construction Stages.

Early-age masonry structures require temporary support until they achieve full strength. Nevertheless, there is a limited understanding of the properties of freshly laid masonry and the design of newly constructed, unsupported masonry walls. This situation has led to numerous instances of structural damage and injuries to workers, prompting conservative construction bracing techniques. This paper presents comprehensive experimental studies on early-age mortar cubes and masonry prisms to assess the effects of curing time on the compressive properties of masonry assemblies, which is necessary for the design of temporary bracing. The change in modulus of elasticity and compressive strength of masonry prisms and mortar with curing time has been experimentally assessed. The results indicate that the compressive strength of freshly cast mortar cubes is relatively insignificant until approximately 24 h after construction, when it was observed to increase logarithmically. Regarding the performance perspective, the compressive strength of early-age masonry prisms is inconsiderable, less than 15% of full strength during the first day after construction. By contrast, regarding the life safety perspective, the compressive properties of a mortar joint within a masonry assembly (which is of more practical interest) appear to have no effect on the failure strength of concrete masonry prisms over the range of ages tested. The failure modes of the early-age mortar cubes and early-age masonry prism samples depend on the curing time, and different failure modes occurred before and after the start of the primary hydration phase, which is 20.8 h after construction. It is anticipated that the proposed research will provide valuable material properties leading to efficient design of control devices (e.g., temporary bracing) and improved guidelines for concrete-block masonry construction.

A contact-based constitutive model for the numerical analysis of masonry structures using the distinct element method

This study presents a robust contact constitutive model in the distinct element method (DEM) framework for simulating the mechanical behavior of masonry structures. The model is developed within the block-based modeling strategy, where the masonry unit is modeled as deformable blocks with potential crack surfaces in the middle of the bricks, while the mortar joints are defined as zero-thickness interfaces. The modeling strategy implements multi-surface plasticity with damage mechanics, including a tension cut-off, Coulomb failure criterion, and an elliptical compressive cap for the damage in tension, shear, and compression, respectively. Two new features are introduced in this contact model: a piecewise linear softening function for strength degradation in tension and shear and a hardening/softening function to phenomenologically define the compressive damage of masonry composite into the unit-mortar interface. The constitutive model is implemented in commercial DEM software using the small displacement configuration and validated against material and experimental tests on masonry walls subjected to constant pre-compression and monotonically increasing in-plane load. The experimental and numerical results regarding the force-displacement relationship and damage pattern produced by the proposed constitutive model are compared and critically discussed, demonstrating the capability of DEM coupled with the suitable constitutive law in simulating the behavior of masonry structures.

Nonlinear static analysis of masonry structures with mortar joints and cracking units by optimization‐based rigid block models

AbstractA rigid block model with elasto‐plastic softening interfaces is developed for nonlinear static analysis of masonry structures subject to monotonic loading. Cracking, crushing, and shear failures are taken into account at interfaces, following a simple micro‐modeling approach. An optimization‐based formulation is used for the solution of the equation systems governing the behavior of the rigid block assemblage. A simple incremental solution procedure is implemented to take into account the material softening behavior and the effects of large displacements on equilibrium conditions. The interface models are validated against tension and shear tests on bi‐block prisms from the literature. Applications to numerical and experimental out‐of‐plane loaded masonry walls as well as to circular arches with mortar joints are presented to evaluate the effects of tensile strength and the accuracy of the developed model against responses involving P‐Δ effects. Comparisons with experimental tests on shear walls also involving cracking of the units in the failure mechanisms are finally reported to discuss the potentialities and limitations of the proposed modeling approach.

Research on new technology of resource-saving ultra-thin stone curtain wall

Ultra thin stone curtain wall technology is a resource-saving innovation. This article explores the application of ultra-thin stone in building exterior wall decoration, including pasted curtain walls, self insulated walls, AAC walls, and decorative insulation composite board exterior wall insulation systems. This technology has advantages such as thin thickness, light weight, low cost, convenient construction, and excellent self insulation performance. The key construction points include waterproofing, rust prevention treatment, use of high standard adhesives, embedding of steel wire mesh in the plaster layer, and small mortar joint technology. The future development direction should focus on innovation in the production technology of ultra-thin stone panels and new directions for stone products.

Derivation of elastic and inelastic characteristics of non-periodic masonry using homogenization techniques and micro-modelling approaches

The present study is aimed to develop an ad hoc four-steps procedure, based on the use of Digital Image Processing (DIP) techniques, homogenization methods and micro-modelling approaches, able to provide an effective tool for characterizing the mechanical properties of non-periodic masonry. More in detail, after creating, through a DIP technique and automated procedures, a finite element mesh from the Red-Green-Blue (RGB) image of a real masonry wall with non-periodic texture (Step 1 and Step 2), a homogenization method, which considers the properties of each masonry constituent (stone units and mortar joints), is used to derive the main elastic characteristics of a homogeneous continuum equivalent to the random masonry (Step 3). Specifically, this estimate can be achieved following the test-windows method based on the use of least-sized partitions subjected to boundary conditions in terms of displacements or stresses until a chosen convergence criterion is fulfilled. The non-linear response is then accomplished by means of a micro-modelling approach (Step 4). To this end, a three-dimensional finite element (FE) analysis can be therefore developed to characterize the main inelastic material parameters of the random masonry. Lastly, as a benchmark of the method, the proposed procedure has been validated against the laboratory outcomes obtained from a previous experimental campaign on non-periodic masonry walls.

Anchors to solid clay brick masonry in shear: Behavior under monotonic and cyclic loading

To investigate the behavior of injected anchors installed in solid clay brick masonry, an extensive experimental campaign was performed at the National Technical University of Athens (NTUA). The focus of the research is on the behavior in seismic conditions, to contribute to the design of relevant retrofitting applications. In this paper, the results of shear tests on metal injection anchors under monotonic or cyclic loading are presented. The anchors are installed in uncracked or cracked solid clay brick wallettes subjected to compressive stress of 0.2 MPa. The tests are performed under displacement-controlled conditions. In this part of the experimental campaign the main parameters investigated are the anchor location (in mortar joints or center of bricks), the presence of a crack crossing the anchor, the substrate properties (wallettes made with two different solid bricks, laid either in strong or in weak mortar) and the loading history (monotonic or cyclic). The experimental results illustrating the effect of the investigated parameters are presented, while the effect of cracking due to seismic loading and the reduction of shear resistance due to cycling are evaluated.

A 3D pilot simulation of masonry walls retrofitted with steel strips using a novel meso-scale damage-plasticity interface model

A novel interface model is introduced to faithfully and effectively simulate masonry walls retrofitted with steel strips (MWSS) under monotonic/cyclic lateral loads at the meso-scale level, where bricks and mortar joints are explicitly represented by 3D continuum elements and interface elements, respectively. The interface model’s formulation, rooted in a damage-plasticity framework, is presented herein, which allows for an accurate depiction of the complex nonlinear behaviors of masonry joints under tension, shear and compression. Subsequently, the model is calibrated and verified against existing experimental data from large-scale masonry specimens subjected to monotonic/cyclic lateral loading. The resulting push-over/hysteretic curves, along with the failure modes of the specimens, show relatively good agreement with their experimental counterparts. Leveraging this validated modelling approach, an extensive parametric study is undertaken to assess the impact of various factors on the in-plane behavior of MWSS. It turns out that the boundary conditions dictate the overall response of MWSS, whereas the material properties of the masonry have relatively minor effects. Given these insights, an improved truss-based analytical model is suggested to predict the lateral strength of MWSS, addressing the limitations of existing design procedures, particularly in scenarios where MWSS’s top edge is confined by high pre-compression.

Investigating the confinement effects on masonry behavior based on friction interface

As a material masonry is anisotropic in nature as it is constituted of various components that differ each other in many ways. Though, the ideas of modeling of concrete are also valid for masonry, still there are difficulties in determining the exact behavior of masonry. The micro modeling (simplified) approach has been adopted in this study for modeling masonry samples subjected to various nature of loadings. The brick masonry units were modeled as discrete elements and linked together by interface element. The coulomb friction model was used to describe the interface element as mortar joint. Damage was assumed to be governed by the compressive strength of both the constituents i.e., mortar and brick. The mechanical properties of the masonry samples were determined by means of variety of tests and those properties then served as input parameters in the constitutive model. The results clearly indicate that numerical model predicted the behavior of the experimentally tested samples, in compression as well as tension prims for both unconfined and confined cases. The proposed model is suitable for modeling any type of brick masonry walls.

Formulation, Implementation, and Validation of a 3D Damage-Plasticity Cohesive-Interface Model with Multiple Yield Surfaces for Cyclic Modeling of Mortar Joints

Formulation, Implementation, and Validation of a 3D Damage-Plasticity Cohesive-Interface Model with Multiple Yield Surfaces for Cyclic Modeling of Mortar Joints

Two-heads brick masonry walls strengthened by basalt and glass chopped fiber mortar: Effect of bed joints and coating reinforcements

It is urgent finding strengthening systems for masonry structures located in seismic areas. This paper studies the effect of chopped fibers embedded in a cementitious mortar to be used as a strengthening system for two-heads brick masonry panels subjected to diagonal compressive forces. The strengthening system provides the use of two types of chopped fibers dispersed in the mortar matrix, i.e. a glass fiber reinforced mortar (GFRM) and a basalt fiber reinforced mortar (BFRM). The retrofitting composite material is disposed in three different ways: (i) the reinforced mortar is placed within the mortar joints of masonry panel; (ii) the reinforced mortar is disposed on both external surfaces of the masonry panel, but the mortar joints are in plain mortar; (iii) the reinforced mortar is placed both within the mortar joints and as a double reinforcing system on the external surfaces of each masonry panel. Experimental results show that in all the three cases the use of fiber reinforced mortar enhances both the shear strength and the post-peak capacity of the two-heads brick masonry panel. The most suitable behavior is related to panels reinforced with mortar both within the joints and as external reinforcing system. From the comparison between GFRM and BFRM it is shown that the best performance is related to basalt fibers mortar, that is also the most sustainable one. Authors always recommend the use of dispersed fibers within the mortar matrix, as it stands as effective strengthening system for new and existing masonry structures, above all when they are located in areas characterized by seismic hazard.

One-head masonry panels reinforced with industrial-waste fiber reinforced mortar: Investigating the effect of bed joints and coating reinforcement in the diagonal compressive behavior

Construction industry is a human activities that most contributes to the world pollution. Recent studies conducted by the EU Commission in 2019 highlighted that buildings and construction materials are responsible for 39% of the global emissions of carbon dioxide and 50% of the raw materials extraction, as well as one-third of the world’s drinking water consumption. Analyzing the world of recycling mineral fibers, authors found that glass and basalt fibers from recycled waste, among other things, request less energy to obtain new filaments when compared to virgin fibers production. In this way, one can obtain a consistent reduction of energy consumption for building or retrofitting structures. In particular, authors explore in this study the benefits of using mineral fibers from recycled sources for strengthening brick masonry walls, carrying out diagonal compressive tests of one-head brick panels retrofiited with chopped fibers reinforced mortar. The aim of this study is twofold: understanding which type of chopped fibers is the most effective when dispersed in the mortar mix, i.e. basalt or glass fibers, and recognize the optimal location of the fiber reinforcement mortar with respect to the masonry panels. Under this perspective, three different set of panels are tested: (i) the reinforcing mortar is placed within the mortar joints of masonry panel; (ii) the reinforcing mortar is disposed as a double reinforcing layer on both the surfaces of the masonry panel, but the mortar joints are made out of plain mortar; (iii) the reinforcing mortar is placed both within the mortar joints of masonry bricks and as a double reinforcing layer on the surfaces of the masonry panel. Results are compared with reference panel made out of plain mortar and show that the most effective strengthening system is the one enriched by chopped basalt fibers. Generally, fiber reinforced mortar effectively strengthens both the loading and the post-peak capacity of the masonry panels, above all when used as coating layer on the external surfaces.

Axial compressive and cyclic lateral behavior of a structural masonry prism constructed from crushed COVID‐19 face masks concrete bricks

AbstractDiscarded medical face masks endanger the environment worldwide. In this study, experiments were conducted to investigate the effect of a shredded face mask (SFM) at 0% (control mix), 0.5%, 1.0%, and 2.0% by volume of concrete in the form of pieces that were 1 cm wide and 2 cm long on the properties of fresh and hardened concrete. After performing experimental testing on the materials, finite element masonry prisms with dimensions of 400 × 200 × 560 mm3 were modeled on the ANSYS platform. Four prisms with different fabric contents were numerically examined to study the compressive behavior, and 12 prisms with three different mortar joints were analyzed under an incremental horizontal load in the presence of four vertical displacements of 0.5, 1.0, 3.0, and 4.5 mm. The results revealed that increasing the SFM content in concrete led to a decrease in fresh and hardened concrete properties, including density, slump, split‐tensile strength, and compressive strength, by 9.5%, 20%, 24%, and 34%, respectively, compared with the control concrete at 0.5%. Moreover, the addition of 0.5% SFMs to the prism bricks reduced the maximum compressive load, deflection, and strain energy by 24%, 10%, and 39%, respectively. Altering the mortar type and vertical load affected the lateral cyclic behavior of the prisms. Compared with the M3 prism subjected to the same axial displacement, the M2 prism had 21.36%, 11%, 27.2%, and 10.48% higher lateral peak load, lateral peak displacement, equivalent stress, and strain energy, respectively. Furthermore, the lateral stiffness of the prism increases as the axial pressure increases. The lateral peak load of the M3 prism measured at 1.0, 3.0, and 4.5 mm axial displacement was raised by 60%, 142%, and 182%, respectively, as compared with the same prism at 0.5 mm axial displacement. The outcome provides a feasible concept for reusing masks in concrete construction with controllable strength deterioration on the masonry prism at 0.5% recycled SFM, resulting in attractive responses of these composites at the nonstructural scale

An Empirical Formula for Assessing the Characteristic Strength of Unreinforced Laterite Stone Masonry

This study aims to determine the needed coefficients for evaluating the uniaxial compressive strength characteristic value for masonry structures made of Laterite Stone (LS) and cement mortar, resulting from experiments conducted in the laboratory evaluating the compressive strengths of the laterite stone and mortar separately in masonry. It proposes calculation coefficients for the completion of Eurocode 6 data that fit the behavior of laterite stone-based masonry. The laterite stone blocks are extracted from three quarries in southern Burkina Faso. The dimensions of the masonry samples tested are 800 mm × 800 mm × 135 mm (±5 mm) with a cement mortar joint of 20 mm (±5 mm) thick. The different failure modes of masonry were also explored. The tests carried out on the masonry showed that the failure is initiated by vertical cracks through the block-mortar interface at a quarter of the width of the walls, generally at 40 to 60% of their maximum strength. The statistical analysis made through a linear regression from the standard model of approximation of the characteristic strength of masonry in Eurocode 6 was used to set out parameters for the empirical relation. The proposed formula considers the intrinsic properties of the block and the mortar, the thickness of the mortar, the dimensions of the masonry block, and the geometry of the masonry itself to evaluate its compression strength. The adequacy between the model and the experimental values is evaluated through the coefficient of determination and the standard error of 0.94 and 0.041 MPa, respectively. Doi: 10.28991/CEJ-2024-010-04-07 Full Text: PDF

Mechanistic model for the compression strength prediction of masonry columns strengthened with fibre–polymer composites

A mechanistic model is presented for the strength prediction of squared columns made of masonry with a periodic arrangement and strengthened with a fibre–polymer composite jacketing. The formulation is based on an incremental plasticity theory that relies on equilibrium, compatibility, and kinematic equations. The strength domain of brick units and mortar joints is bounded by a multi-surface yield criterion: a Mohr–Coulomb strength domain with a linear cap in compression and a Rankine cut-off in tension. An elasto-plastic response with limited ductility is assumed for both masonry components. Differently, the FRP response is assumed elastic with a brittle failure governed by a limited tensile strain. Phenomenological-based assumptions are undertaken and justified. Details are also provided for the computational implementation of the procedure. The model accuracy is validated against experimental data on masonry squared columns and compared with existing standard-based formulas. Results demonstrate it provides real-time and accurate compressive strength solutions for squared masonry columns with or without a polymer-based wrapping and yet requiring few input parameters for the masonry constituents and reinforcement.