Masonry Mortar Joints Research Articles

Modeling of masonry structures using a new 3D cohesive interface material model considering dilatancy softening

This study presents a new 3D multi-yield surfaces material model for masonry mortar joints, which can be used with interface elements for finite element (FE) modeling of masonry structures to capture various failure mechanisms. This model is featured with (1) two hyperbolic yield surfaces, capable of capturing various failure modes of mortar joints, including tensile cracking, shear sliding, and compressive crushing, (2) an unassociated flow rule to capture the ‘dilatancy’ phenomenon in the mortar joints, and (3) the dilatancy softening and variation of mode II fracture energy under different normal stress levels. An implicit Euler backward integration algorithm, combined with local-global Newton-Raphson (NR) solver, is adopted to achieve the predictor-corrector return mapping in the numerical formulation. The error-based auto-adaptive sub-stepping algorithm is employed to achieve the robustness and efficiency in the integration procedure. The developed model is implemented in the general-purpose FE software ABAQUS with the specialized capability of modeling masonry structures. The developed model is validated through three brick-mortar-brick assemblages and three un-reinforced masonry (URM) walls under in-plane (IP) loading or out-of-plane (OOP) loading. The importance of appropriate modeling of dilatancy on simulating the IP and OOP behavior of URM walls is highlighted. The validation results show that the developed constitutive model is capable of modeling masonry structures at various scales with improved accuracy by considering dilatancy softening.

Shear test method analysis of earth block masonry mortar joints

A series of triplet shear strength tests and numerical simulations were conducted in this study to secure a suitable shear test method for earth block masonry mortar joints. The effects of the block type, horizontal mortar joint, loading location, mortar material, specimen form, block dimensions, and elasticity modulus on the shear performance on the masonry joints were analyzed. The optimal test method was determined based on comprehensive evaluation via Analytic Hierarchy Process (AHP). The shear test method significantly affects the shear performance along the mortar joint of earth block masonry; the shear strength of specimens with horizontal mortar joints is generally higher than that without a horizontal mortar joint. The loading location affects the shear strength of the 6-block specimen, and the shear strength of the specimen loaded at the half-block is higher than that of specimen loaded at the whole block in most cases. The distribution of the shear stress along the height of the mortar joint varies unevenly by specimen form. The stress distribution at the mortar joint tends toward uniformity as the block’s elasticity modulus increases. The 4-block specimen showed favorable test operability and stress state in addition to the highest comprehensive AHP value, 0.322. The 4-block triplet shear strength test is recommended as the standard assessment for earth block masonry.

On the Seismic Performance of Autoclaved Aerated Concrete Self-Insulation Block Walls.

Autoclaved aerated concrete (AAC) self-insulation block masonry is often used for the infill walls in steel and concrete frame structures. To work together with the frame under earthquake action, it is essential to understand the seismic behavior of AAC self-insulation block masonry walls. In this paper, six AAC self-insulation block masonry walls were experimentally studied under the pseudo static test. The load-displacement hysteretic curves were drawn with the test data. The failure characteristics, loading capacity, stiffness degeneration, energy dissipation capacity and hysteretic behavior are analyzed. The results indicate that the blocks underwent internal failure due to the lower strength with a larger size, but the walls had good energy dissipation capacity with a rational bearing capacity. Accompanied by the influence of vertical compressive stress on the top surface of the walls, the cracking resistance, ultimate bearing capacity, deformability and energy dissipation capacity of the walls were affected by the masonry mortar joints. Comparatively, the walls with thin-layer mortar joints had better seismic performance than those with insulation mortar joints or with vertical joints filled by mineral wool plates. Finally, the shear capacity of the walls under seismic load is evaluated referring to the formulas of current design codes for masonry walls.

Experimental characterization of the constitutive materials composing an old masonry vaulted tunnel of the Paris subway system

ABSTRACTA significant proportion of the Paris metro tunnels comprise a masonry vault built out of stone blocks and mortar joints, and sidewalls and slabs made of unreinforced concrete. In order to provide the necessary data for future structural evaluation, an extensive laboratory testing programme has been conducted to characterize the materials of the tunnel separately, i.e., mortar, stone, and concrete. The tests, carried out on specimens taken from cores extracted from a 1930s tunnel, enabled to determine the mechanical properties, including direct tensile, shear strength, and mode I fracture energy, as well as the properties of the stone-mortar interface. Results show that the masonry mortar joints could reach 10 cm in width, and that blocks of stone varied in composition and porosity, thus producing a wide range of mechanical properties. The concrete was composed of large-sized aggregates and showed low stiffness and strength. Based on these experimental results, ratios between mechanical characteristics are hereby proposed. Perspectives on the use of this experimental data in a finite element model are then discussed.

Numerical Simulation of Masonry-Infilled RC Frames Using XFEM

Evaluation of the seismic performance of masonry-infilled reinforced concrete (RC) frames is challenging because a number of damage patterns can be induced by the interaction between the infill and the frame. In this paper, the extended finite-element method (XFEM) is adopted to model the cracking behavior and the compressive failure of concrete in frame members as well as masonry units in infill panels, and the discrete interface element is employed to simulate the behavior of the masonry mortar joints and the joints at the frame-to-infill interface. With the XFEM, the crack can propagate in an arbitrary manner during the analysis. In addition, multiple continuous cracks are allowed in this model. The nonlinear finite-element model is validated by the available experimental data. It can be concluded that the proposed model is capable of predicting the load-displacement response of a masonry-infilled RC frame structure. The damage patterns regarding cracking and crushing of frame members and masonry panels, tensile fracture and compressive compaction in mortar joints, and shear sliding of masonry units along mortar joints are also reproduced very well.

Bond of Steel Bars to Masonry Mortar Joints: Test Results and Analytical Modelling

In this paper, the preliminary results of a series of pull-out tests conducted on mortar cylinders with embedded bars are presented. The bars are made of high strength stainless steel and are of helical shape to increase mechanical interlocking with the surrounding mortar. Usually, such bars are employed in situ to realize structural repointing in the case of fair-faced masonry walls. To this aim, they are inserted in the mortar bed joints of masonry for providing tensile strength to the walls and with the function of crack stitching. The aim of the present experimental tests is to determine the bond-slip relationship for bars embedded in masonry. Firstly, pull-out tests are conducted on mortar cylinders considering different embedded lengths of the bars. Further tests are on-going on masonry specimens with bars embedded in the mortar joints. An analytical investigation is also carried out for the interpretation of the pull-out test results.

Three-dimensional micromodel of clay block masonry wall

In designing and implementing earthquake resistance for clay block masonry infill integrated into a structural frame, with or without openings, the infill wall should be taken into account. Presumably, simplified models, acceptable for practical use, could be applied for that purpose. However, the anisotropy of clay block masonry units, masonry mortar joints, and unit contact properties as well as the high variance of material properties limit their ability to describe the actual earthquake resistance of clay block masonry. In this work, we consider a three-dimensional micromodel of a clay block masonry wall, with the inclusion of masonry unit anisotropy and masonry mortar joint and unit contact properties. To avoid the excessive calibration procedure of the wall micromodel, the wall constituents were calibrated separately beforehand, which resulted in a high correlation of computational and experimental results without further need for calibration. Using a calibrated micromodel, the influence of variance in material properties on the wall's resistance was investigated. The influence was showed not to be negligible, which may significantly affect the presumed behaviour of the whole structure.

New Local Compression Test to Estimate In Situ Compressive Strength of Masonry Mortar

Abstract A new partially destructive test (PDT) method called local compression test method (LCTM) is proposed to estimate the in situ compressive strength of masonry mortar. In this method, the mortar pieces are taken out from horizontal masonry mortar joints and compressed mutually by means of two flat head round bars, the compressive force crushing the mortar piece is measured. The compressive test for the mortar pieces can be interpreted as the compressive strength test for the radially constrained mortar cylinder. The correction coefficient formula is first established through the tests for the local compressive strength of mortar pieces in the standard thickness (10 mm) and other thickness. The empirical correlation relationships between the local compressive strength of mortar pieces and the compressive strength of mortar cubes are presented for the masonry mortar with compressive strength ranging from M2.5 to M15.0. A good correlation between the cube compressive and local compressive strength has been found. The in situ verification tests are undertaken on a number of mortar structures to determine the accuracy of the LCTM. The experimental and analytical results show that this method is accurate and applicable to in situ tests of the masonry mortar compressive strength.

Seismic Design Parameters for Special Masonry Structural Walls Detailed with Confined Boundary Elements

AbstractIn this paper, the results from a test program focusing on the behavior of eleven fully grouted reinforced masonry (RM) structural walls containing confined boundary elements are analyzed and presented according to force, displacement, and performance-based seismic design considerations. To be consistent with current force-based seismic design codes, analysis is presented to predict the strength, stiffness, displacements, and ductility-related force modification factors using the eleven test specimens. A new estimate of the plastic hinge region for displacement calculations is also proposed which considers the inherent planes of weakness in masonry mortar joints as well as the angle of inclination of shear cracks. Finally, within the context of performance-based design methodologies, the occurrence of specific damage states is identified. A methodology is proposed to estimate crack width in the walls based on curvature measurements which is also verified using digital image correlation analysis. T...

Numerical modeling of masonry-infilled RC frames subjected to seismic loads

The behavior of masonry-infilled reinforced concrete frames under cyclic lateral loading is complicated because a number of different failure mechanisms can be induced by the frame-infill interaction, including brittle shear failures of the concrete columns and damage of the infill walls. In this study, nonlinear finite element models have been used to simulate the behavior of these structures. Diffused cracking and crushing in concrete and masonry are described by a smeared-crack continuum model, while dominant cracks as well as masonry mortar joints are modeled with a cohesive crack interface model. The interface model adopts an elasto-plastic formulation to describe the mixed-mode fracture of concrete and masonry. The model accounts for cyclic crack opening and closing, reversible shear dilatation, and joint compaction due to damage. The constitutive models have been validated with experimental data and successfully applied to the dynamic analysis of a three-story, two-bay, masonry-infilled, non-ductile, reinforced concrete frame tested on a shake table. The results have demonstrated the capabilities of the finite element method in capturing the nonlinear cyclic load–displacement response and failure mechanisms of the structure, and indicated the important contribution of infill walls to the seismic resistance of a non-ductile reinforced concrete frame.

Cracking due to shear in masonry mortar joints and around the interface between masonry walls and reinforced concrete beams

Cracking occurs frequently in building masonry walls, and are usually located in the joints between the units because they represent generally planes of weakness, in some cases due to their low shear resistance. Sometimes cracks can appear in the interface between masonry blocks and reinforced concrete beams. That cracking has negative implications in building performance, namely, due to the possibility of rain penetration through the cracks and to negative aesthetic aspect. So, the objective of this paper is essentially to achieve a better knowledge of the shear behaviour of joints in masonry, for the particular cases of solid lightweight concrete blocks (blocks of aerated autoclaved concrete and blocks of lightweight concrete with expanded clay aggregates) and solid clay bricks, and to find preventive solutions to minimize those defects. This paper presents the principal results and conclusions of an experimental study that concerned the determination of mortar joints shear behaviour. From the results of the experimental tests, it can be concluded that the properties of the referred joints are significant for the wall overall behaviour, and the inclusion of reinforcing elements in these joints may in some cases serve as a preventive measure and can determine positive implications on that behaviour.

Estimation of service life of coated brickwork mortar joint

This work reports an investigation into the permeation of chloride in brick masonry mortar joints in three different media (water from rain, runoff, and sea). The coated and uncoated (control) masonry prisms were subjected to 3% chloride solutions for periods of 1–5 weeks each, and the chloride concentration at depth of 20 mm was determined (ranging from 0.012 to 0.327 for immersion days of 7 to 35, respectively, for coated and uncoated prisms of 0.03 to 0.887, respectively). The results show that the service life of the coated brick mortar joint has been increased by 36 years for the sea water sample.

Finite Element Modeling of Masonry-Infilled RC Frames

Experimental and analytical studies have been carried out to investigate the performance of masonry-infilled RC frames under in-plane lateral loadings. In this paper, the experimental results are concisely summarized, and a constitutive model is presented for the modeling of masonry mortar joints and cementitious interfaces in general. A smeared-crack finite element model is used to model the behavior of concrete in the RC frames and masonry units. It is shown that the finite element models are able to simulate the failure mechanisms exhibited by infilled frames including the crushing and cracking of the concrete frames and masonry panels, and the sliding and separation of the mortar joints. The lateral strengths obtained with these models are in good agreement with those obtained from the tests.

Technology and behavior of rubble masonry mortars

Rubble masonry mortars are distinct to the masonry mortar joints due to the different construction techniques used and the prerequisites concerning their behavior in the structure. In the present work, physico-chemical and mineralogical examination of rubble masonry mortars is performed on the development of cohesion and adhesion bonds. A working hypothesis on production technology is deduced consequently. Recent collapses of the rubble masonry at several bastions of the knights' period in the Medieval fortifications of Rhodes allow for sampling. Investigations by optical microscopy, scanning electron microscopy, fiber optics microscopy, X-ray diffraction analysis, differential thermogravimetric analysis, porosimetry as well as total soluble salts measurements were performed. Various types of rubble masonry mortars are evidenced and all of them present a very coherent matrix, either ‘cementitious’ or very finely crystallised and compact. From the top to the bottom of the masonry, different microstructural characteristics are observed in the mortar nucleus, indicating different lime-to-aggregates ratios. The microstructural stratification of the cementing material points out different carbonation and drying levels and implies successive supply of water to slake the lime in situ. The evidence of hydraulic components all around the bulk, but not on the outer top of the walls, is of particular interest and proves the in situ slaking of lime as the energy source to activate either hydraulic reactions among lime and clay minerals or the crystallization of portlandite. The high levels of soluble salts measured indicate the mortars' susceptibility to salt decay, specifically when pore size distribution is in favor, as in the case of the modern cement or the pure calcitic mortar, in comparison with the more resistant hydraulic mortars.

Interface Model Applied to Fracture of Masonry Structures

The failure of unreinforced masonry structures subjected to lateral loads is dominated, to a large extent, by the fracture of mortar joints as well as the cracking and crushing of masonry units. This can be simulated by means of a finite element approach in which the mortar joints are modeled with interface elements and the masonry units are modeled with smeared crack elements. To this end, a dilatant interface constitutive model capable of simulating the initiation and propagation of interface fracture under combined normal and shear stresses in both tension‐shear and compression‐shear regions, and capable of simulating the experimentally observed dilatancy was developed in this study. The performance of the interface model in representing the behavior of masonry mortar joints is evaluated with the available experimental results. Furthermore, the failure of unreinforced concrete masonry panels is analyzed with the aforementioned approach. It is concluded that the numerical model is capable of predicting the response of a masonry assemblage based on the response of its basic constituents.

Finite Element Method for Interface Problems

A method for incorporating interface discontinuities in a finite element analysis of discontinuous media is presented. For computational purposes the procedure is implemented into the nonlinear structural analysis program NONSAP. Several example problems concerning the modeling of concrete masonry mortar joints are presented, and demonstrate the accuracy and efficiency of the algorithm.