Bed Joints Research Articles

Cracking and Failure Mechanism of Masonry Walls Loaded Vertically and Supported by Deflecting Structural Member

The paper describes some results of tests on solid walls and walls with openings in full scale, which were built on the steel structure subjected to vertical deflection. The walls had the length of 4550 mm, the height of 2450 mm and the thickness of 180 mm and were made of silicate blocks of group 1 per PN-EN 1996-1-1 standard with mean compressive strength of 17.7 N/mm2. The specimens had thin bed joints and unfilled head joints. Solid walls (A type), walls with one door opening located unsymmetrically in relation to the vertical axis (B type), specimens with two door openings located symmetrically (C type) and walls with one door and one window opening (D type). The tests were carried out in the specially designed steel stand that allowed to test masonry full scale walls subjected to simultaneous increasing of vertical compression load and deflection of the structure which they are supported on. The vertical load of the top walls edge was realized with the use of two hydraulic jacks with range up to 500 kN. The vertical deflections of steel structure supporting the masonry wall were realized in two ways, by means of loading the top edge of wall and with use of the elements of deflection enforcement system. Apart from vertical loading and support displacements, the displacements of the masonry along the eleven sections on each surface in two fields were also measured. The measurement of changes of the measuring sections length was used for calculating the mean deformation angles of the specimen in both fields. The walls without openings were rigid enough to separate from the support even at the deflection not exceeding 1.5 mm. The walls with one door opening located unsymmetrically also crack at early stage of tests. In this case, the separation from the support of a part of the wall without opening occur and cracks appear at the end of lintels caused by rotation of parts of wall separated by door opening (at early stage of tests treated as rotations of rigid bodies). In the case of walls with two symmetrically located door openings, the first crack appeared at the ends of the lintels as a result of rotations of pillars caused by small, smaller than 3 mm support deflection. The first cracking of walls with the window and door openings took place under the window opening and in the area, where lintel was supported by external pillar adjacent to the window opening.

Design of interlocking masonry units and mechanical properties of masonry assemblages

This paper describes the design of a new interlocking masonry system, the production of designed interlocking units and mechanical properties of interlocked masonry assemblages with mortar. In this proposed system, units have horizontal and vertical locks to integrate the units to the wall and have a channel to enable the use of horizontal reinforcements in the wall. Using these units, unfilled, filled or reinforced walls can be constructed with or without mortar. In the production of the interlocking units, it was decided to use foamed concrete. 12 trial productions have been carried out at different mix proportions to obtain the optimum concrete mix. At the end of the mentioned productions, the units were produced with foam concrete which is selected as the most suitable in terms of compressive strength and specific gravity. Then, axial compression, diagonal tension and bed joint shear tests were carried out to determine the mechanical properties of the interlocked masonry assemblages with mortar. Results from the tests showed that interlocks designed to strengthen the system against shear stresses by creating discontinuity throughout the joints have been successful to achieve their aim. Obtained data will enable structural analysis of walls to be constructed with these new units.

The Influence of Compressive Stress on the Load-Bearing Capacity of Masonry Subjected to Vertical Displacements

The paper describes the results of tests of masonry wallets made of solid clay bricks with joints of normal thickness (10 specimens) and filled vertical joints and autoclaved aerated concrete (AAC) blocks with thin joints and unfilled vertical joints (5 specimens). The specimens made of clay bricks were 1290 mm wide, 1415 mm high and 250 mm thick, while the specimens made of AAC blocks had the width of 1250 mm, the height of 1510 mm and the thickness of 240 mm. The tests were carried out in a specially designed steel test stand witch which the masonry specimens were monolithised. The force applied along the vertical edge of the specimens and causing the vertical displacements was carried out by means of hydraulic cylinder. The masonry specimens were tested without participation of vertical compressive stresses perpendicular to the bed joints σc or the tests were carried out after initial compression, which induced stress in the wall with mean values from 0.3 to 1.5 N/mm2 for solid clay brick specimens and 0.9 N/mm2 in walls made of AAC blocks. The compressive loads were implemented using four pairs of tensioned steel tendons equipped with springs to compensate the influence of masonry displacements. The deformation angles of masonry were also investigated. Deformation angles were calculated based on changes in the length of the system of measuring bases placed on both surfaces of the specimens. The compressive stresses σc influenced the values of the mean shear stress τcr,σ (force inducing vertical displacements divided by the area of the vertical cross-section of the specimen) at which the first oblique crack appeared. The τcr,σ stress was always greater than the stress τcr,0 at which the first crack occurred in the specimens tested without compression. The ratio τcr,σ/τcr,0 for solid clay brick specimens ranged from 1.38 to 2.24, depending on the stress value σc and 2.18 for masonry made of AAC blocks. Compressive stresses also influenced the increase of the masonry deformation angles at the moment of the first cracking θcr,σ in relation to the deformation angle θcr,0 of the specimens tested without compression. This effect was proportional to the increase of τcr so that the mean modulus of deformation was about 1630 N/mm2 for clay brick walls. In the case of specimens made of AAC blocks a ratio of stress to angles of deformation Gcr equal to 631 N/mm2 when the tests were not accompanied by compressive stresses (σc = 0) and 461 N/mm2 when σc = 0,90 N/mm2. Similar results were obtained in the case of the effect of the compressive stress σc on the increase of shear stress τu and the accompanying deformation angles λu at the maximum force inducing vertical displacements of masonry specimens obtained in tests.

An Investigation on Mechanical Properties and Damping Behaviour of Hardened Mortar with Rubber Tire Crumbs (RTC)

Masonry wall has been used for ages as a part of non-engineered building structures, due to its ease of manufacture, strength, and stiffness to support gravity loads, but brittle enough to resist earthquake shake. One solution to increase its ductility when the earthquake shake stroked, ductile materials at bed joints that binding the masonries may apply. Mortar is a composite material consisting of sands, cement, and water that is generally used for masonry construction as a binder at bed joints. On the other hand, rubber has been used to isolate vibration of machinery because of its good damping behaviours. Those materials will be mixed and be elaborated to provide a ductile mortar binder at bed joints. This research aims to investigate the mechanical properties and the damping behaviour of hardened mortar with rubber tire crumbs at proportions of 0%, 40%, and 60%. Three types of specimens in forms of mortar cubes of 50x50x50 mm3, tensile specimens and mortar beams of 100x100x500 mm3 were tested to provide strength and damping behaviour. The addition of rubber tire crumbs in the mortar decreased the compressive strength, tensile strength, flexural strength and unit weight. Despite its weakness in the mechanical strengths, the addition of rubber tire crumbs could increase the damping behaviour significantly. This research recommended that mortar containing RTC is still appropriate use for non-structural component although it has low mechanical properties.

The Structural Design of Wooden Solid Log Wall

Alternative solutions to joints of outer wooden solid log walls are based on the current situation on the construction market, which reflects general change in attitude towards the environment. Apart from the evaluation of materials and products in accordance with technological and economic aspects, attention is paid to the effect of individual elements on the environment. This trend is reflected in construction practice by a comeback to original materials and expanding designs of residential buildings on the basis of easily renewable material resources, e.g. wood, which is relatively easily available and renewable construction material. When designing and constructing wooden buildings, it is necessary to take into account specific properties of wood (particularly volume changes), which need to be considered for solutions of individual details. Bed joints of wooden solid log walls are still a problematic detail in terms of thermal technology. It is a contact of two horizontal construction elements – beams, where maximum weakening of the wall thickness occurs. This spot is a relatively frequent place of a recurring thermal bridge during the wall construction. Analysis and improvement of this critical place of wooden houses, which has been more and more frequently built in the Czech Republic, would lead to their better evaluation in terms of heat-technical properties. The aim of the project was to design and examine adjusted variants of shape solutions of joints in between individual solid wooden elements. The project particularly focused on monitoring of surface temperatures in the areas of critical details – bed joints.

Monotonic tests on masonry elements with different angles of inclination of the bed joints under uniaxial compression

This paper describes the results from monotonic tests performed on masonry elements with different angles of inclination of the bed joints relative to the horizontal under uniaxial compression. Two different types of bricks (calcium-silicate and clay bricks) were tested under uniaxial compression stress state. The main test parameter was the angle of inclination of the bed joints, which was varied between 0 and 90 degrees in the interval of 15 degrees. The tests were performed in displacement control in order to capture the post-peak response of the masonry elements as well. The applied displacements were increased monotonically. During the tests, main measurements were performed to measure the edge deformation, detection of strain on the masonry surface using a photogrammetric method, and documentation of the crack propagation and fracture behaviour. The strength and the stiffness properties, as well as stress-strain relationships as a function of the angle of inclination of the bed joints and the comparison between the principle directions of stresses and strains is reported here.

Experimental assessment of large displacement cyclic in-plane shear behaviour of semi-interlocking masonry panels

A semi-interlocking masonry (SIM) building system has been developed in the Centre for Infrastructure Performance and Reliability at The University of Newcastle, Australia for seismically vulnerable regions as an alternative to traditional masonry panels. This innovative masonry building system consists of mortar-less masonry panels with multiple sliding bed joints made of semi-interlocking units. The study presented herein focused on the experimental investigation of large cyclic in-plane shear behaviour of three different types of panels: 1) panel with an open gap between the steel frame and the top of the panel; 2) panel with foam in the gap; 3) panel with grout in the gap. This paper reports the results of this testing program with mechanically interlocking units with main focus on the force-displacement relationship and the energy dissipation capacity of panels. The structural performance of the SIM panels is also analysed, and potential displacement patterns are identified under large displacement.

Monotonic tests on masonry elements with different angles of inclination of the bed joints under uniaxial compression

This paper describes the results from monotonic tests performed on masonry elements with different angles of inclination of the bed joints relative to the horizontal under uniaxial compression. Two different types of bricks (calcium-silicate and clay bricks) were tested under uniaxial compression stress state. The main test parameter was the angle of inclination of the bed joints, which was varied between 0 and 90 degrees in the interval of 15 degrees. The tests were performed in displacement control in order to capture the post-peak response of the masonry elements as well. The applied displacements were increased monotonically. During the tests, main measurements were performed to measure the edge deformation, detection of strain on the masonry surface using a photogrammetric method, and documentation of the crack propagation and fracture behaviour. The strength and the stiffness properties, as well as stress-strain relationships as a function of the angle of inclination of the bed joints and the comparison between the principle directions of stresses and strains is reported here.

Experimental study of in-plane shear strength of confined concrete masonry walls with joint reinforcement

Six full-scale confined masonry walls made with multi-perforated concrete units were subjected to reversal cyclic lateral loads. The only variable investigated was the amount of joint reinforcement. All other variables were fixed, the height to length aspect ratio was set to one. The reinforcement, placed in the bed joints every two courses, consisted in small diameter bars with 588 MPa nominal yielding stress. Numerous strain gages were installed on the rebars to monitor deformation and subsequently estimate the lateral strength contributed by the reinforcement. The strength due to the masonry was estimated as the difference between the total lateral strength and the strength attributed to the reinforcement. The results show that the contribution of the reinforcement to the lateral strength increases with the amount of reinforcement to a certain limit and that the contribution of the masonry decreases. The limit is related to the masonry compressive strength. The experiments and results are presented in detail, followed by a discussion and conclusions.

Strength characteristic of novel mesh embedment technique for new brick construction with least expensive material

An extensive experimental study aims to enhance the structural performance of masonry by using meshes on the surfaces of brick units and bed joints. The novel mesh embedment technique of masonry units is supported with the least expensive meshes. They are 0.71 mm thick GI expanded wire mesh (EWM), 0.41 mm thick SS stainless steel mesh (SSM) and 0.33 mm thick SS poultry netting mesh (PNM) or chicken wire mesh are the three types of embedded mesh used in this novel approach. The mesh embedded masonry technique (MEM) administers by alternative sides of bricklayer that passes through bed joints. To envisage brickwork quality, reasonable trial programs are necessary like the compressive strength of twenty masonry prism with height to thickness ratio of 1.6 as per the ASTM C1314, the flexural bond strength of thirty three masonry prism as indicated by the ASTM E518 Test method A and small-scale diagonal shear (Tension) test on six masonry panel as per the ASTM E519. The present study concedes that the embedment of meshes increases the strength and ductile performance of masonry units.

Assessment of the combined in‐plane and out‐of‐plane behavior of brick infill walls within reinforced concrete frames under seismic loading

SummaryUnderstanding the out‐of‐plane response of masonry infill walls and preventing their progressive collapse mechanisms is very important for earthquake‐prone countries to prevent loss of life and economic loss. In fact, having a realistic collapse mechanism assessment allows suitable prevention measures to be adopted. With this purpose in mind, two full‐scale one‐bay one‐story substructures of reinforced concrete frames (RCF) with infill walls were tested on a shake table. These 2 specimens were designed to represent the response of a typical RC Frame at the fifth floor of an 8‐story building, namely the out‐of‐plane failure of its infill wall under combined bidirectional seismic load. Both specimens were composed of a single‐leaf clay brick infill wall surrounded by the RC Frame. However, while the first specimen corresponds to an unreinforced masonry configuration, the second specimen includes horizontal bed joint reinforcement as a strengthening/retrofitting technique. The main novelty of this study is the application of a bidirectional and simultaneous dynamic loading to the specimen, such that in‐plane and out‐of‐plane effects are evaluated together. This work presents several interesting experimental results, with particular emphasis on the bearing capacity of the specimens against out‐of‐plane failure. As expected, the in‐plane capacity of the reinforced infill specimen is larger than that of the unreinforced infill specimen. Nevertheless, the out‐of‐plane bearing capacities of the two specimens are very similar, in contrast to their ductility capacity, which is significantly increased in the reinforced masonry specimen. The capacities of the two specimens for both in‐plane and out‐of‐plane directions, as predicted by formulations in the literature, are given. The differences found between these calculations and the results of the tests are discussed, and may possibly be explained by the parameters considered in the different formulations.

Flexural strength of AAC masonry with bed joint reinforcement

AbstractThe paper presents the results of comparative investigations of flexural strength of unreinforced and reinforced autoclaved aerated concrete (AAC) masonry. The plane of masonry failure was perpendicular to the bed joints plane. Reinforcement in the form of steel wire, glass, and basalt fibers placed in masonry bed joints influenced the higher flexural strength and crack resistance of masonry specimens. Reinforced masonry showed plastic nature after cracking allowing for large horizontal displacements and transferring the substantial loads perpendicular to the surface of masonry in relation to the unreinforced masonry. For most reinforced masonry specimens, the strengthening after cracking was observed which means that the maximum value of load occurred in the cracked masonry.

Comparisons of confined and different types of reinforcement on the behavior of masonry shear walls

AbstractThis paper presents a comparison of results for shear walls: unreinforced (three walls), confined (six walls), and reinforced with two different types of reinforcements (four walls). Masonry walls made of autoclaved aerated concrete (AAC) had a thickness t = 0.18. Four series of different walls of the same length equal to l = 4.43 m and the height of h = 2.43 m were made and tested. Compressive strength of material masonry units and mortar for thin joints was equal to fb = 4.0 N/mm2 and fm = 6.1 N/mm2. Compressive strength of walls (according to EN 1052‐1:2000) was fc,mv = 2.97 N/mm2 and (fk = 2.48 N/mm2) and elastic modulus was Ecm = 2.040 N/mm2. Walls were tested at the same initial compressive stresses perpendicular to the plane of bed joints σc = 0.1, 0.75, and 1.0 N/mm2. In confined models, two external vertical cores and two horizontal beams were made and reinforced in accordance with the requirements of the European Standard EN‐1996‐1‐1. Steel truss‐type reinforcement and plastic grid placed in each bed joint were used in walls. The obtained values of stresses were compared at the time of cracking and destruction. The morphology of cracking and the mechanism of destruction were analyzed.

Reinforced and unreinforced AAC masonry walls supported on deflecting structure

AbstractThe paper presents selected results of wider comparative experimental tests on masonry walls in full‐scale made of autoclaved aerated concrete masonry units. The walls were unreinforced and reinforced. The reinforcement in form of steel wire, glass, and basalt fiber meshes was applied in each masonry bed joint. The walls were subjected to simultaneous incrementing vertical loads and deflection of the structure which they are supported on. The carrying capacity of reinforced walls was up to 1.5 times higher than unreinforced walls. Test results of reinforced walls also showed lower values of deformation angles in relation to the walls without reinforcement for given load and deflection of support. In case of reinforced walls, much smaller widths of the cracks were obtained. The reinforcement allows to keep integrity of walls even after reaching the maximum load and deflection of supporting structure. The paper describes cracking and damaging mechanism of the walls as well.

Experimental investigation of mortar mechanical properties for glass brick masonry

The main advantage of solid bricks over hollow blocks is substantially higher compressive strength. On the other hand, solid bricks have much higher thermal conductivity, which would lead to major heat loss when used for exterior walls. Masonry pillars and walls are usually loaded in compression and/or bending resulting from the eccentricity of vertical load or wind load. In case of solid glass bricks, compressive strength is about ten times higher than tension strength therefore the limiting factor of the glass masonry is tensile stress resulting from the bending. Whether compared to ceramic or concrete bricks masonry, the glass bricks have a smooth and non-absorbent surface and the adhesion of the mortar to the glass surface is the critical parameter. Presented paper is focused on the experimental investigation of mortar applicable for glass brick masonry with regard to use for load bearing brick walls or columns. Shear, compression and tension tests have been recently performed. Shear and tension resistance and failure modes of brick bed joint were determined during series of tests using various mortar composition, two types of surface treatment and different thickness of the mortar joint. Significant influence of the joint thickness on the resistance was found. The compression tests were performed on two small pillars to determine the compression resistance and failure mode of glass bricks walls and pillars. In parallel to these tests, several small-scale tests have been performed to determine flexural and compressive strength of hardened mortar.

Fragility functions and floor spectra of RC masonry infilled frames: influence of mechanical properties of masonry infills

A wide number of experimental studies conducted in latest years pointed out the high influence of the mechanical properties of masonry units and mortar bed joints on lateral strength and stiffness of masonry panels. This feature significantly modifies the global response of infilled frames under seismic actions as well as the local interaction phenomena. Despite a wide investigation on the influence of the infills on global behaviour of reinforced concrete (RC) frames has already been provided, different features characterizing the seismic performances of buildings suggest the need of accurately evaluating local interaction phenomena as well as the influence of the panel on specific and relevant aspects, as the accelerations transferred to non-structural components. This study provides a parametrical analysis of the influence of shear strength and elastic modulus of masonry infills on the seismic behaviour of RC frames originally designed for gravity loads. Regular buildings with different height were analysed using the Incremental Dynamic Analysis in order to provide fragility curves, investigate on the collapse mechanisms and define the floor spectra depending on the properties of the infills. Results obtained pointed out the high influence of the considered parameters on the fragility of existing RC frames, often characterized by inadequate transversal reinforcement of columns, which may lead to brittle failure due to the interaction with the infills. Floor response spectra are also significantly affected by the influence of masonry infills both in terms of shape and maximum spectral accelerations. Lastly, on the basis of the observed failure mechanisms, a parameter defining the ductility of the frames depending on the properties of the infills was also provided (Capacity Design Factor). The correlation between the mechanical properties of the infills and this parameter suggests its reliability in the simplified vulnerability analysis of existing buildings as well as for the design of new buildings.

Improving the Masonry Brick Ductility using Mortar Bed Joint from Rubber Tire Crumbs: A Review

Improving the Masonry Brick Ductility using Mortar Bed Joint from Rubber Tire Crumbs: A Review

Out-of-plane flexure behaviour of fly ash-lime-gypsum brick masonry walls

Industrial by-products such as fly ash is being used for the manufacture of building products such as fly ash bricks. This paper is focused on understanding the out of plane flexural behaviour of fly ash-lime-gypsum (FaL-G) brick masonry, through experimental investigations. Results of the flexure strength of FaL-G brick masonry walls (under different pre-compression) in the two orthogonal directions, are discussed. Load displacement and moment-curvature relationships for the two cases presented. The cracking flexural stress using linear elastic analysis was predicted and compared with the experimental value. The results reveal that (a) the flexure strength of FaL-G brick masonry walls increases linearly with the increase in pre-compression, (b) the flexure strength parallel to bed joints is two times more than that of the flexure strength perpendicular to bed joints under zero pre-compression, (c) lateral displacements for the FaL-G brick masonry walls are larger for the case of bending perpendicular to bed joints when compared with those for bending parallel to bed joints and (d) The cracking flexural stress for the FaL-G brick masonry can be predicted closely with those of experimental values using linear elastic analysis.

Experimental investigation of the bed joint influence on mechanical properties of hollow calcium silicate block masonry

The article discusses the influence of the bed joint thickness and mortar strength on properties of calcium silicate (CS) block behavior under short-term static load. The investigation of masonry samples made of hollow CS blocks is presented in this paper. The specimens were made of two types of hollow CS blocks, combined with general purpose mortar of three different strengths and thin layer mortar of two different strengths. During the analysis of masonry with thin layer mortar the moisture influence on mechanical properties of masonry was also investigated. The experimental investigation has shown that the height of mortar bed joints has a larger influence on the mechanical properties of masonry when mortar of lower strength is used. Moistening CS blocks with thin layer mortar did not have a significant influence on the mechanical properties of masonry.

Detailed micro-modelling of the direct shear tests of brick masonry specimens: The role of dilatancy

The mechanical parameters (shear strength of bed joints) derived from triplet tests can apparently be significantly different from those obtained through the so called “shove test” procedure executed on the same type of masonry. It was observed that this discrepancy may be caused by a wrong estimation of the compressive stress in the bed joints of the shove test. This article describes a numerical technique implemented in Abaqus to provide a sound interpretation of the phenomena involved in the failure of a mortar bed joint. The level of accuracy required to accomplish the objectives of the present study has driven the attention toward the detailed micro-modelling approach. Units and mortar joints have been modelled with continuum elements whereas the cohesive interfaces with zero thickness have been used for the unit-mortar interfaces. The material nonlinearities of masonry have been attributed to mortar and unit-mortar interfaces. The dilatancy of the bed joint during the shear failure process can generate, under certain boundary conditions, a local increase of the normal compression stress. Hence, particular attention has been dedicated to the modelling of this phenomenon. Several triplet tests and shove tests have been used as experimental benchmark for the numerical simulations. With the aim to accurately calibrate the parameter that controls the dilatancy, this work has paid attention also to the numerical-experimental comparison in terms of normal expansion of the joints, whereas commonly the comparison is generally carried out only in terms of shear stress-displacement curve. With the proposed technique, the triplet test and the shove test can be simulated with great accuracy. Thanks to these features, it has been also possible to relate the two types of test by highlighting the factors that affect the local normal stress during the shear failure process, providing a more detailed explanation of why and how the shove test results must be carefully interpreted in order to derive a realistic estimate of the shear strength of bed joints.