Masonry Specimens Research Articles

Experimental investigation on the shear behaviour of the brickwork-backfill interface in masonry arch bridges

This paper presents the results from an experimental campaign to characterise the shear behaviour of the brickwork-backfill interaction in masonry arch bridges. Two representative backfill materials found in real masonry arch bridges (compacted crushed limestone and clay) were sheared against brickwork masonry specimens with two different bond patterns (a soldier course bond and an English bond). The results demonstrated that the interface shear behaviour between masonry and backfill was different from the internal shear behaviour of backfill materials. When compacted crushed limestone was adopted as the backfill material, the ratio between the masonry-limestone interface friction angle (φi) and the internal friction angle (φ) of limestone was determined to lie within the range from 0.70 to 0.75. However, when clay was used as backfill material, the φi/φ ratio was much lower, and of the order of 0.51 to 0.52 under the assumption of zero-cohesion at the interface, or 0.35 to 0.39 if interface cohesion was considered. Moreover, the properties of the backfill material had a significant influence on the interface shear behaviour, whereas the effects of brickwork bonding pattern were marginal. This study provides valuable insight into the identification of brickwork-backfill interface parameters for the numerical analysis of masonry arch bridges.

Modelling the in-plane/out-of-plane interaction of brick and stone masonry structures using Applied Element Method

This research focuses on the numerical modelling of the seismic behaviour of unreinforced masonry (URM) structures with interconnected in-plane (IP) loaded and out-of-plane (OOP) loaded walls. The mechanical behaviour of such wall assemblies is complex and comparatively more challenging than that of isolated components, involving the interaction between interlocked orthogonal elements subjected to different load types. IP/OOP interaction phenomena are also challenging to model numerically, and their simulation is still relatively unexplored using the Applied Element Method (AEM) – the discrete simplified micro-modelling strategy employed in this paper. To fill this knowledge gap, the AEM is herein adopted to simulate the experimentally observed seismic behaviour of two URM building prototypes, one made of clay bricks and the other of stone blocks. The AEM models developed are calibrated and validated against previous experimental data, showing a satisfactory agreement between measured and numerical responses. In addition, a parametric study was performed using pushover analysis to investigate the influence of key material properties on the overall behaviour of the clay brick masonry specimen. The study suggests that the AEM models used in this study are suitable for conducting subsequent seismic assessment of URM structures with interlocked IP/OOP loaded walls, providing validated modelling strategies that can be useful to both researchers and engineering practitioners.

Experimental and DEM numerical analyses of the flexural and diagonal compression behavior of masonry reinforced with polyurea coating

The brick masonry specimens in this paper were strengthened with polyurea reinforcement before flexural and diagonal compression tests. The influence of one-sided and double-sided polyurea coatings on the load capacity and displacement were studied. According to the findings, the polyurea coating used for strengthening provided a considerable increase in load capacity as well as deformation. Two modeling approaches, macro-modeling and micro-modeling based on the Discrete Element Method (DEM), were applied. The Three-Dimensional Distinct Element Code (3DEC) program was used to simulate the behavior of the brick masonry. Several parameters, including joint-normal stiffness, joint-shear stiffness, and friction angle, were investigated, and their influence on the brick masonry structure was evaluated. The research determined that the prediction of ultimate load and behavior failure in the models could be predicted with accurate results. Furthermore, computational models were developed to compare against experimental tests. The results obtained from the simulation showed that the proposed modeling may be effectively used to verify the experimental results.

Analysis of Chinese ancient brick masonry characteristics under uniaxial compression fatigue loading

Urban expansion and diversified traffic aggravate the damage and deterioration of ancient buildings. It is crucial to evaluate the long-term fatigue performance of ancient brick masonry structures for the safety and maintenance of ancient buildings. A series of indoor tests were conducted on the ancient brick masonry. The images for the whole process of the test were collected using VIC-3D technology. The relationship between the stress level and the number of failure cycles under compressive fatigue load and the stress–strain evolution under different stress levels were determined. A mathematical model of p-S-N fatigue life prediction based on probability was proposed, which comprehensively considered the maximum stress level, stress range, number of load cycles, and survival probability. The equivalent fatigue life of ancient brick masonry specimens under each failure probability obeys Weibull distribution, and then the fatigue life of masonry can be predicted at any expected confidence level. The test results provide reliable theoretical and data support for fatigue deterioration and life prediction of ancient masonry structures in service.

Developing Hydrostatic Beehive Brickwork

Abstract In this paper, a new masonry construction is proposed based on honey beehive cell internal geometry as a unique structure and hydrostatic pressure principle. The considered experimental program involved suggestion, manufacturing, testing and analysis of masonry specimens of honey beehive units’ arrangement as well as corresponding specimens of custom arrangement, two classes of cementations bonding mortars are used. Plan strain concept and Saint Venant’s principle are adopted to model and assign proper boundary conditions of testing specimens. The significant improvement of masonry construction bearing capacity is confirmed by the obtained results and could be related to the presence of internal or self-confining pressure, which is produced due to the specific internal geometry of proposed honey beehive units’ arrangement of hexagonal construction units. The obtained results show that, the masonry specimens of proposed honey beehive arrangement Mode II exhibited higher bearing capacity in term of ultimate and service loads besides stiffness improvement in comparison with the customary arrangement Mode I.

Waste polyethylene terephthalate (PET) fiber reinforced mortar in enhancing the bond behavior of masonry

Fast-paced urbanization and population growth have increased the daily use of plastic. Although plastic is used for different purposes, a sharp rise in the utilization of bottled water and other beverages in both developing and developed countries has been observed. In spite of the fact that plastic as containers has several benefits, improper plastic waste management has resulted in the disposal of a large amount of plastic waste in landfills and marines. This has negatively affected the ecosystem as plastics are non-biodegradable. Therefore, there is an urgent need to recycle and reuse plastic waste. The field of civil engineering has a vast scope of utilizing waste polyethylene terephthalate (PET) bottles as a raw material; nonetheless, not much has been studied regarding the utilization of plastic waste in masonry structures. Hence, the current research focused on the experimental investigation of PET fiber-reinforced mortar in enhancing the mechanical properties of masonry, as the bond between brick and mortar significantly affects the strength of masonry. Different proportions and two different sizes of PET fibers were reinforced in mortar to obtain the optimum quantity and size of fiber. In the first phase, the compressive and flexural strengths of reinforced mortar were determined and compared with unreinforced mortar. Further, compressive strength and bond strength (shear and tensile) of masonry specimens cast with reinforced mortar were evaluated. Additionally, field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) analysis were conducted to study the change at the microstructure level. The outcomes of the experimental tests are encouraging. A significant improvement in the mechanical properties (up to 1.87 times for compressive strength, up to 3.2 times for tension bond strength and up to 6 times for shear bond strength) of PET fiber-reinforced masonry was observed.

High temperature creep behavior of fireclay refractory and its masonry

The creep behavior of refractory lining is crucial, which is determined by both material and masonry structure. In this paper, the effect of temperature and stress on the creep behavior of fireclay refractory and brick–mortar couplets were studied by using advanced uniaxial compression creep test. The creep behavior of fireclay refractory is sensitive to temperature due to formation of liquid phase. Meanwhile, the closure of discontinuous interfaces contributes to the increase of compressive creep in couplets. The masonry specimen with two mortar layers deforms less than that with one mortar layer, as thermal stresses are moderated by the additional mortar layer.

Experimental quasi-static out-of-plane test of a U-shaped brick masonry wall

Past earthquakes demonstrated the vulnerability of brick masonry façade walls even against moderate earthquakes. The present work aims at providing an insight into the out-of-plane response of clay brick masonry walls, especially focusing on a traditional Portuguese building typology, namely the ‘placa’, towards a correct interpretation and assessment of their seismic behaviour. A thorough experimental campaign in laboratory environment was conducted, including material characterisation through destructive and non-destructive techniques and the quasi-static test with airbag on a U-shaped clay brick masonry specimen. Main experimental results are discussed with specific attention to the analysis of the masonry wall cyclic response, the damage pattern, the seismic performance, and the evolution of the modal parameters at distinct stages of the test. The material characterisation demonstrates the low mechanical properties of the masonry associated with such buildings. The specimen presents a stiff and almost linear behaviour until the peak, followed by an initial softening until about 60% of the peak. The damage pattern evidences a failure governed by an out-of-plane rotation combined with shear sliding.

Mechanical and Structural Investigation of Traditional Masonry Systems with Diverse Types of Bricks and Hydrated Lime Mortars

ABSTRACT This paper presents an experimental study on the mechanical behavior of masonry specimens made from two brick types, factory-made and hand-made bricks, and three types of lime mortars, quicklime lumps, powdered hydrated lime, and commercial hydrated lime. The characteristics of the bricks and mortars and the interaction between each brick and mortar type were expected to have a significant effect on masonry strength. The results indicated that the compressive strength and specific surface area of the factory-made bricks were 15% greater and 22% lower, respectively, than those of hand-made bricks. Specifically, the factory-made bricks have a beneficial effect on specimens under compression, while hand-made bricks improve the specimen’s shear strength. In addition, the commercial hydrated lime-based mortar exhibited the best bonding quality for both types of bricks

Modeling of shear-lap tests of flat and curved masonry specimens strengthened by FRCM

Nowadays Fiber Reinforced Cementitious Matrix (FRCM) systems play a relevant role in the context of innovative interventions for the seismic rehabilitation of masonry structures. Their capacity in improving the strength of masonry components is comparable with the one observed in case of Fiber Reinforce Polymer (FRP) systems, but with additional advantages (lower costs, environmental compatibility, removability, etc.). Nevertheless, although a relevant number of applications concerns curved structures (arches, vaults, domes, etc.), the majority of studies available in literature provide a contribution mainly concerning the specific case of applications on flat masonry substrates. The present paper is part of a research activity carried out by the Authors with the main goal to provide a contribution toward the study of the bond behavior of FRCM systems externally applied to curved masonry elements. In particular, the results of numerical analyses carried out by means of a simple modeling approach proposed by the Authors are here carried out by considering as case studies specimens object of a recent experimental investigation. Specific aspects influencing the local bond behavior of FRCM systems applied on curved masonry substrates are then analyzed by opportunely introducing them into the numerical model. The obtained results allow for understanding the effect of important features, experimentally observed in terms of global response, and here assessed in terms of local bond behavior, by particularly emphasizing the role of the curvature and the strengthening position.

Damage of Infill Masonry Walls due to Vertical Loads in Buildings with Reinforced Concrete Structure

Buildings are subjected to deformations of their reinforced concrete structure due to vertical loads that can lead, in certain cases, to the significant cracking of the unreinforced masonry (URM) infill walls, therefore requiring the development of specific knowledge of these types of deformations in order to minimise them. Aiming the evaluation of buildings with reinforced concrete structures subjected to vertical deformations, the mechanical characteristics of their infill masonry walls, as well as of their interface with the supporting concrete elements, are here analysed. The basic compression behaviour of brick masonry is assessed particularly through the previous analysis of a vertical compression test of a masonry specimen. The mechanical behaviour characteristics of the constituents (bricks, and mortar joints) are analysed to account for their influence on the compression behaviour of masonry infill, aiming particularly for the prevision of their cracking in case of vertical deformations of the supporting reinforced concrete (RC) elements. Based on that evaluation, the analysis of masonry walls subjected to vertical deformations of their supports is made through the assessment of the relevant characteristic behaviour of masonry wall-beam/slab assembly in case of vertical load. A general modelling approach of the behaviour of URM infills and the interaction with their supports is generally accessed. Finally, the preventive control of deformations of masonry wall-beam/slab assembly is discussed.

A reassessment of the CSA S304 chi-factor for design of reinforced concrete masonry members: large-scale experimental investigation

An experimental investigation was conducted that consisted of 12 pairs of reinforced masonry specimens in which the two specimens were constructed with their longitudinal axes oriented parallel and perpendicular to the laboratory floor, respectively. This work was conducted to reassess the need for the χ-factor accounting for the direction of compressive stresses in masonry members in relation to the direction used to establish their masonry assemblage strength included in CSA S304-14— Design of Masonry Structures. Parameters investigated included block size and reinforcement ratio. Test results suggest that the χ-factor can be eliminated from future editions of CSA S304 but should be considered with caution: a review of the literature and the current tests show that, in some cases, voids may develop between the exterior webs of adjacent blocks and so may be the source of the reduction in the magnitude of the equivalent rectangular compressive stress block.

FRCM-to-masonry bonding behaviour in the case of curved surfaces: Experimental investigation

Fabric-reinforced cementitious matrix (FRCM) are composite materials more and more used for the reinforcement of masonry structures. The combination of high tensile strength fabrics (or meshes) with cementitious matrices, having good thixotropic capabilities and vapour permeability, makes such composites suitable for reinforcing a large number of masonry structures, including the one belonging to the historic heritage. FRCMs are bonded to the outer surfaces of structural masonry elements and, thanks to their adhesive capacity, bear much of the tensile stresses that unreinforced masonry cannot withstand. The effectiveness of such reinforcements, which is highly dependent on their ability to adhere to the masonry substrate, is generally investigated throughout specific experimental investigations (shear tests). Almost all the papers in the literature devoted to bond-slip analysis refer to the case of flat bonding surfaces, although these reinforcements are also widely used on curved structural elements such as arches and vaults. Therefore, this paper reports and examines the results of an extensive experimental program concerning the behavior of FRCM systems applied on curved masonry specimens. The results point out the influence of both curvature and reinforcement position (intrados or extrados) on the response of specimens in terms of bearing capacity, failure mode and post-peak response.

Influence of Mixing Water Content and Curing Time on Bond Strength of Clinker Masonry: The Wrench Test Method

In the present study, experimental investigations on the influence of mixing water content used for the preparation of mortar mix using factory-made dry-mix mortar dedicated to bricklaying with clinker masonry units are presented, as well as the curing time on flexural bond strength of masonry made of these two materials. The flexural bond strength was tested using the "wrench test" method. The masonry tests specimens were prepared using three volumes of mixing water as follows: 4.0 L (the value recommended by the mortar manufacturer); 4.5 L; and 5 L of tap water per one 25 kg bag of dry pre-mixed mortar. The influence of the mixing water content was analyzed in relation to curing time. All masonry specimens were tested in four series after 9, 14, 21, and 28 days of sample curing. The results showed that the use of 6 and 18% more mixing water than recommended by the manufacturer (4.5 and 5 L per bag) adversely affected flexural bond strength. Moreover, for all three mixing water amounts, it was found that the maximum values of bonding strength were reached after 9 days of curing, which decreased over time. The largest decreases (30-40%) were recorded after 14 days. After 21 days, these values continued to decrease, but more slowly. The final value of the ratio of bond strength to flexural strength of the mortar was similar for all amounts of mixing water and for the 28-day curing time, it oscillated around 0.2.

A robust computational strategy for failure prediction of masonry structures using an improved multi‐surface damage‐plastic based interface model

AbstractIn this study, a new traction‐separation based constitutive model for use in finite element simulation of masonry joints under complex loading conditions is developed for cohesive elements. The proposed model is formulated using damage parameters and plastic deformation with mutual couplings, and can accurately simulate the complex nonlinear behaviors of masonry joints considering hardening or softening of strength and stiffness degradation. To enhance the numerical stability of the model, plasticity and damage are separated algorithmically and implemented in two phases. In the first phase, the plastic deformations are treated using a multi‐surface plasticity model composed of a smooth hyperbolic yield surface for tension‐shear mixed‐mode failure and an elliptical cap primarily for the compressive failure. This is implemented in effective stress space and helps restrict the evolution of yield surfaces with no softening, significantly enhancing the efficiency of stress return mapping by the closed point projection method. In addition, an adaptive sub‐stepping scheme is adopted to further improve the robustness of the numerical implementation. In the second phase, nominal stresses are computed from the effective stresses using damage parameters. The evolution of these damage parameters is defined in terms of plastic work which is defined by a polynomial form, and is recommended in this study for a better calibration capability. Improvements are made in the formulation of compressive cap including incorporation of hardening of strength and stiffness degradations as these are ignored in existing interface models. This approach helped improve simulation of masonry under cyclic loads with tension‐compression transitions. For the structural level applications, the interface model is implemented within a finite element program, which is utilized to simulate failure of a number of masonry specimens under in‐plane/out‐of‐plane monotonic/cyclic loading. The simulated results are rigorously validated with existing experimental data that shows a good potential in modeling masonry structures.

Assessment of optimal specimen to measure the compressive strength of earthen-based masonry

The compressive strength of masonry is regarded as an essential primary mechanical parameter of this kind of structure. However, standard specimens used to test compressive strength of earthen-based masonry vary considerably in issued codes, which hinders the intercomparison of experimental results. In this study, two kinds of adobe and two kinds of new earthen bricks were selected for preparing masonry specimens. A series of uniaxial compression tests were performed to reveal the compression behaviors of several types of earthen-based masonry, while considering the influence of the specimen bonding arrangement and h/t ratio. Analytic hierarchical processes were used to evaluate the bonding arrangement and h/t ratio of earthen-based masonry specimens from operability, reproducibility, instrument, and equipment requirements for determining an optimal specimen with excellent comprehensive performance. The results showed that optimal specimens for compressive strength tests of different earthen-based masonry can use the same bonding arrangement and h/t ratio. The stretcher bonded specimen with a h/t ratio of 3/1–4/1 should be used as the optimal specimen for compressive strength testing of earthen-based masonry. The results can be used as a reference for establishing a simple and general compressive test method for earthen-based masonry.

ОЦЕНКА МЕХАНИЧЕСКИХ ХАРАКТЕРИСТИК КАМЕННОЙ КЛАДКИ СУЩЕСТВУЮЩИХ ЗДАНИЙ

An analysis of known methods for evaluation the compressive strength and modulus of elasticity of existing masonry structures have been carried out. A method for determining the mechanical characteristics of masonry, based on tests of the specimens cutted from the body of the masonry in the form of triangular prisms have been given. Comparison of compressive strength, initial shear strength and angle of internal friction, obtained from the results of tests of prism specimens, with the results of tests of masonry specimens in accordance with the standards STB EN 1052-1 and STB EN 1052-3 has been carried out. Satisfactory agreement between the values of the compressive strength of the masonry and the secant modulus of elasticity obtained by testing the prisms with a compressive load acting perpendicular to the plane of the horizontal mortar joints with the test results according to the STB EN 1052-1 method has been shown. The initial shear strength of masonry, obtained from the results of tests according to STB EN 1052-3, differed downward from the strength established from the results of tests of prism specimens for compression, while the values of the angle of internal friction determined by the two methods were close.

Study on the effectiveness of a CRM system: in-plane and out-of-plane cyclic tests on masonry piers

The results of a broad experimental campaign on full scale masonry samples are presented in the paper, to evidence the effectiveness of a CRM (Composite Reinforced Mortar) strengthening System. In particular, shear-compression tests were carried out on masonry samples strengthened with the application of the CRM System on one or both faces of the wall, consisting of a mortar coating reinforced with a preformed GFRP (Glass Fiber Reinforced Polymer) mesh. In the former case, to connect wall leaves, artificial diatones were used; in the latter case, these diatones and couples of GFRP L-shape connectors were used to confine the masonry wall. The three-point bending test was also carried out on one-side reinforced masonry specimen, in which also artificial diatones were used. The sample was arranged vertically and loaded cyclically according to a three-point bending scheme. The results of all reinforced specimen tests were compared with those of the equivalent unreinforced ones.

Lime-based nanocomposites for masonry restoration: Towards the implementation of small-scale restoration

The structural integrity of historic and traditional buildings can be affected by natural weathering and incompatible restoration interventions. Traditionally, lime binders have been used extensively for restoration applications, while the incorporation of multi walled carbon nanotubes (MWCNTs) in such a binder, enhances the restoration material with increased mechanical as well as with self-sensing properties due to its piezoresistive characteristics. The focal point of the present investigation was the examination of the electrical, mechanical, and piezoresistive properties of a composite nano-reinforced lime-based mortar paste under different geometrical sizes (scale-up tests). Firstly, prismatic specimens of two different sizes, composed of the proposed nano-reinforced lime-based mortar were subjected to testing and compared against reference prismatic prisms of traditional non-reinforced lime-based mortar with a similar composition. The results showed a 24 % increase in the compressive strength and a 37.5 % decrease in the electrical resistance. Secondly, electrical resistance measurements were carried out on a small-scaled masonry specimen built with the MWCNTs reinforced lime-based mortar, to determine potential structure inhomogeneity effects. The tests revealed approximately 50 % electrical resistance decrease in comparison to the non-reinforced reference prismatic specimens. Lastly, the composite restoration material was applied at an actual masonry restoration project at the public library “Korais” of Chios Island, Greece, with the aim to monitor the composite material’s electrical resistance under real conditions.

Experimental Research and Numerical Analysis of CFRP Retrofitted Masonry Triplets under Shear Loading.

This paper presents an experimental and numerical study into the shear response of brick masonry triplet prisms under different levels of precompression, as well as samples reinforced with carbon fiber-reinforced polymer (CFRP) strips. Masonry triplets were constructed with two different mortar mix ratios (1:1:3 and 1:1:5). In this study, finite element models for the analysis of shear triplets are developed using detailed micro-modelling (DMM) approach and validated with the experimental data. The failure mechanisms observed in the masonry triplets were simulated using a coupled XFEM-cohesive behaviour approach in ABAQUS finite element software. The nonlinear behaviour of mortar and brick was simulated using the concrete damaged plasticity (CDP) constitutive laws. The cohesive element with zero thicknesses was employed to simulate the behaviour of the unit–mortar interfaces. The extended finite element method (XFEM) was employed to simulate the crack propagation in the mortar layer without an initial definition of crack location. CFRP strips were simulated by 3D shell elements and connected to masonry elements by an interface model. The changes in failure mechanism and shear strength are calculated for varying types of mortar and fiber orientation of CFRP composite. Based on this study, it was concluded that the ultimate shear strength of masonry triplets is increased due to the external bonding of CFRP strips. The performance of masonry specimens strengthened with CFRP strips is assessed in terms of gain in shear strength and post-peak behaviour for all configurations and types of mortar considered. The comparison of FE and experimental results proved that the models have the potential to be used in practice to accurately predict the shear strength and reflect damage progression in unreinforced and CFRP-reinforced masonry triplets under in-plane loading, including the debonding of the CFRP reinforcement. Additionally, XFEM was found to be a powerful technique to be used for the location of crack initiation and crack propagation in the mortar layer.