Compressive Strength Of Masonry Research Articles

Quantification of uncertainty in compressive strength of fly ash brick masonry

The compressive strength of brick masonry, an important property for the structural assessment and design, can show a significant variation because of several influencing factors like source and proportion of constituent materials, workmanship, curing condition, etc. Quantification of uncertainty in masonry compressive strength is essential for reliability based limit state design of masonry structures. The present study investigates this aspect of fly ash brick masonry and recommends the most suitable statistical distribution to describe the variability in compressive strength. Experimentally obtained compressive strength data are analysed using various probability distribution functions capable of modelling strength properties of brittle materials and three goodness of fit tests, i.e. Kolmogorov-Smirnov, Kolmogorov-Smirnov-Lilliefors and Anderson-Darling tests. The analysis concludes that lognormal distribution is best suited among other distributions to describe the variability associated with the compressive strength of fly ash brick masonry.

Out-of-plane seismic safety assessment of URM infills accounting for the in-plane/out-of-plane interaction in a nonlinear static framework

Past and recent earthquakes showed the occurrence of Out-Of-Plane (OOP) failures of Unreinforced Masonry (URM) infills in Reinforced Concrete (RC) frames. Such a type of failure, which is promoted by In-Plane (IP) damage (IP/OOP interaction), is dangerous for human life safety and its effects can be associated with the attainment of the Life Safety limit state.In this work, the seismic capacity of Reinforced Concrete buildings at the first OOP collapse is evaluated with a linear analysis based on code provisions and with a procedure based on nonlinear static analysis.More specifically, 16 buildings designed to Eurocodes, different for number of storeys and design Peak Ground Acceleration (PGA), are infilled by two infill layouts different for thickness and masonry properties. For these buildings, the PGA at which the first OOP infill collapse occurs is evaluated by applying two different approaches. The first is based on linear analysis and consists in the simple application of the demand and capacity models currently provided by the Eurocodes. So, it accounts neither for the effect of the IP/OOP interaction on the OOP capacity nor for the effect of structural non-linearity on the OOP force demand. The second approach is based on nonlinear static analysis and on the application of refined literature formulations accounting for the IP/OOP interaction and for structural non-linearity for the definition of the OOP capacity and force demand.The PGAs at the OOP collapse of infills obtained by applying both approaches are compared to show their significant overestimation if the IP/OOP interaction and structural non-linearity are not considered, i.e., if current code provisions are applied. Considerations concerning the influence of the number of storeys and of the design PGA of buildings on the PGA at the OOP collapse of infills are reported. Frequency distributions of OOP collapses at different storeys and fragility curves relating the probability of OOP collapse to both the PGA acting in the OOP direction and the maximum IDR attained in the IP direction are shown.For all case-study buildings, a range of 42 infill layouts, different for thickness and masonry compressive strength, is considered and, with the application of the more refined, not code-based approach, a “limit state” curve defining the infill height-to-thickness ratio/masonry compressive strength couples for which the OOP safety check of infills can be neglected is reported.

Application of the Minor Destructive Test (MDT) method for determination of AAC masonry compressive strength

Non-destructive methods (NDT) in masonry made of autoclaved aerated concrete (AAC) are not used as commonly as in concrete or reinforced concrete constructions. The porous structure and sensitivity to atmospheric factors, especially humidity, makes it necessary to determine the compressive strength of the wall in existing and used objects. The article presents a proposal of a semi-non-destructive method for determining the compressive strength of AAC, and then a wall made with thin-layer joints. An empirical curve developed for cellularconcrete with nominal density classes 400, 500, 600 and 700 in an air-dry condition was used for calibration.In addition, an empirical relationship was developed to take into account the impact of ABK moisture.

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.

An investigation of laterite as fine aggregate to develop eco-friendly mortar

Major objective of the study was to examine the suitability of laterite as fine aggregate in mortar. Conventional Cement mortar was prepared using river sand for different cement mortar ratios from 1:3, 1:2 and 1:6. Replacing the natural sand by laterite and manufactured sand by laterite for the replacement level of 20, 40 and 60 % were cured at room temperature and tested in accordance with IS:2250-1981. Water absorption and durability tests (sulphate attack, chloride attack and acid attack) are conducted after the initial curing of mortar cubes. Compressive strength of masonry was examined by testing masonry prisms. The test result shows that up to 40 % of replacement of laterite in river sand and manufactured sand is suitable for masonry work. The rebound losses, has a moderate impact on the workmanship of the masonry work.

Behavior of unreinforced masonry piers strengthened using centercore method; experimental investigation

This research deals with the behavior of masonry piers made by fired bricks and gypsum-clay mortar, strengthened using centercore method. Compressive strength of masonry is evaluated along one year using 66 samples. Shear behavior of joints is defined using Mohr-Coulomb failure criterion; the friction angle and cohesion was measured using 54 triplet samples at 40-day age. Moreover, the cohesion is evaluated along one year using 66 triplet samples. Seven identical pier specimens were constructed and strengthened using centercore with two different retrofitting schemes (anchorage of the centercore to the base) and two different rebar sizes. All of the specimens were tested under cyclic in-plane loading. The retrofitted specimens without anchoring the centercore to the foundation, showed an increase of ultimate strength, ductility capacity and normalized energy dissipation up to 10%, 25% and 100%, respectively. The retrofitted specimens with anchored centercore to the foundation, showed a similar ductility capacity and normalized energy dissipation, but with a significant increase of ultimate strength, up to 230%.

The effective stiffness of modern unreinforced masonry walls

SummaryCode design of unreinforced masonry (URM) buildings is based on elastic analysis, which requires as input parameter the effective stiffness of URM walls. Eurocode estimates the effective stiffness as 50% of the gross sectional elastic stiffness, but comparisons with experimental results have shown that this may not yield accurate predictions. In this paper, 79 shear‐compression tests of modern URM walls of different masonry typologies from the literature are investigated. It shows that both the initial and the effective stiffness increase with increasing axial load ratio and that the effective‐to‐initial stiffness ratios are approximately 75% rather than the stipulated 50%. An empirical relationship that estimates the E‐modulus as a function of the axial load and the masonry compressive strength is proposed, yielding better estimates of the elastic modulus than the provision in Eurocode 6, which calculates the E‐modulus as a multiple of the compressive strength. For computing the ratio of the effective to initial stiffness, a mechanics‐based formulation is built on a recently developed analytical model for the force‐displacement response of URM walls. The model attributes the loss in stiffness to diagonal cracking and brick crushing, both of which are taken into account using mechanical considerations. The obtained results of the effective‐to‐initial stiffness ratio agree well with the test data. A sensitivity analysis using the validated model shows that the ratio of effective‐to‐initial stiffness is for most axial load ratios and wall geometries around 75%. Therefore, a modification of the fixed ratio of effective‐to‐initial stiffness from 50% to 75% is suggested.

Dynamic characterisation of a historic bell-tower using a sensitivity-based technique for model tuning

The most relevant results of the vibration-based investigations performed on a historic masonry tower in Italy namely the Santa Maria a Vico bell-tower is here presented. The first part of the study involves preliminary full-scale ambient vibration measurements in operational conditions and dynamics-based finite element (FE) modelling. At first, a manual tuning of the uncertain parameters of the model was carried out to adjust material properties, soil-structure interaction and constraining effect of the neighbouring structures. Then, based on the sensitivity analysis, only the most sensitive parameters were chosen as updating parameters. Finally, a model updating technique based on a sensitivity-based method was used to minimise the error between experimental vibration data and numerical response values. To this aim, a residual vector defined as the weighted difference between the measured quantities and calculated quantities was used. The uncertain structural parameters of the FE model were identified by minimising a robust penalty function. The calibrated model was used as an important tool for the seismic assessment of the structure using pushover analysis. Since the assumed value of the masonry compressive strength is the most sensitive parameter of non-linear behaviour, a sensitivity analysis was performed considering reference values in the range of interest. The seismic safety corresponding to increasing levels of the seismic hazard was finally investigated.

Effect of moisture condition on mechanical behavior of low strength brick masonry

The purpose of the research presented in this paper was to determine the influence of moisture on mechanical properties of brick, mortar and masonry. The strength of masonry structure was primarily influenced by a number of factors such as brick/block, bedding mortar, construction quality, pre/post environmental condition, etc. Among the factors affecting such behavior, the presence of moisture plays a key role in the deteriorating state of masonry structures. For this reason, in the present paper the compressive strength of bricks, cement mortars as well as compressive, shear and bond strength of masonry prisms are investigated, in oven-dry, air-dry and wet conditions. The experimental results demonstrate that moisture significantly reduces the compression strength of a brick and cement mortar; the greater the moisture content the lower compression strength. However, the compressive strength of masonry not improve in oven-dry condition, but reduce in wet condition. Moreover, shear and bond strength of masonry reduce with increase in moisture condition.

Experimental study on scale effects in clay brick masonry prisms and wall panels investigating compression and shear related properties

Scaled masonry model testing has been performed for many decades, with earlier researchers establishing that it is possible to model masonry behaviour at reduced scale, but that strength and stiffness are affected and with many studies suggesting that masonry is anisotropic. The effects of scale on clay brick masonry compressive strength, Young’s Modulus, shear modulus and diagonal tensile strength was investigated through material and component testing at two scales. Firstly, the effect of scaling the brick and mortar joints to half scale was assessed, and secondly, the effect of scaling the size of the specimen without scaling the brick and mortar size was assessed. Scale was found to have minimal to no effect in both test cases on the compressive strength characteristics of masonry and brick, and to have no effect on the stiffness of masonry in compression. The effects of scale were found to be significant for diagonal shear strength and shear modulus.

The influence of the moisture content in historical masonry walls on the load bearing capacity

The moisture content in historical masonry walls, particularly on the ground floor, caused by i.e. lack of damp insulation, is a phenomenon of common occurrence. It is usually analysed in terms of mycological changes, thermal insulation and frost damage. The paper discusses the influence of the increased moisture content on the weight and load bearing capacity of the structure. The determination of moisture content in masonry elements, performed during the inspection of the building, provides information from which an increase in the structure's weight can be defined. Reliable tests for the moisture content and compressive strength of masonry and mortar components are invasive, and the number of testing in historical buildings should be limited to the minimum necessary to preserve their vintage nature. As a result, the received overall picture of the work of masonry may not be consistent with its actual state since historical buildings could have been rebuilt or repaired, and consequently, contain masonry conversions made of various materials with different properties. Absorbability can serve here as an example as it is a factor that disrupts a reliable determination of load bearing capacity values of masonry structures. The article attempts to determine the change in load bearing capacity of a moist masonry structure compared to the original - in the air-dry state - for various types of historical masonry and mortar components. The main influence analysed was due to capillary action, whereas the effect of other sources of moisture, i.e. salinity, was excluded.

On the in-plane shear response of the high bond strength concrete masonry walls

Conventional unreinforced masonry walls subject to in-plane shear loading fail due to exceedance of shear and tensile bond strengths. This paper examines whether or not the in-plane shear capacity of masonry walls would increase with the increase in the bond strengths through experimental and numerical investigations. For these investigations, shear walls were built with high bond strength polymer cement mortar; they were applied in thin layers of 2 mm thickness each. Material tests were carried out to characterise the bond and the compressive strengths of the high bond strength thin layer mortared masonry; the bond strengths were found approximately double that of the conventional 10 mm thick cement mortars. The shear walls, however, exhibited significantly lower capacity (contrasting the expectation) and displayed base course sliding mode of failure. To ascertain the validity of the experimental results, a combined surface contact—interface element micro finite element (FE) modelling technique was formulated; the results adequately reproduced the experimental datasets. The validated FE model was then applied to examine the effect of the aspect ratios and pre-compression levels to the failure modes, deformation and strength of the high bond strength shear walls and is shown that once the pre-compression exceeds 15% of the masonry compressive strength, the base sliding failure mode changes to the diagonal cracking mode with corresponding increase in in-plane shear capacity. Therefore, it is concluded that the increase the bond strength without regard to pre-compression could adversely affect the safety of the high bond strength unreinforced masonry shear walls.

English

The paper reports results of study on standard masonry mortar containing sand and sawdust as aggregates in a mix proportion of 1:3 and water-cement ratio of 0.55. A modified mortar of same design mix proportion (1:3) but varying water/cement ratio and constant slump of 74.3 mm to achieve higher workability was also evaluated. Six different percentages (5, 10, 15, 20, 30 and 50%) of sand replacement were investigated. The flexural tensile strength, compressive strength, dry density, masonry wallet compressive strength, water absorption and slump were evaluated. The British code recommended masonry wallet compressive strength of 5.3 N/mm2 was achieved with 8 and 13% sawdust contents in the standard and modified mortars, respectively. Such mortars can be used as jointing and rendering materials on interior walls of buildings where water absorption by the mortar would be reduced. Key words: Sawdust, mortar, wallet, masonry compressive strength, water absorption.

Rubble Stone Masonry Walls in Portugal: Material Properties, Carbonation Depth and Mechanical Characterization

ABSTRACTA significant proportion of Portuguese ancient buildings have structural masonry walls. Therefore, it is important to study this building typology in order to define appropriate structural rehabilitation interventions, whenever necessary. This article presents the results of research carried out at Universidade NOVA de Lisboa on the material properties, of rubble stone masonry walls, including the evolution of carbonation depth over time and mechanical characterisation under compression and shear load tests. It was found that the mechanical behavior of the unreinforced masonry specimens is mostly influenced by the reduced compression and tensile strength of the air-lime mortar. A formulation to estimate the carbonation depth and the masonry compressive strength as a function of time is proposed and the Strut-and-Tie Method is used to estimate the resistance of specimens under compression and shear forces.The results of this study are part of a major research project studying the mechanical behavior of unreinforced rubble stone masonry walls (unreinforced masonry—URM), evaluating different strengthening solutions for ancient rubble stone masonry walls (Pinho 2007; Pinho et al. 2012a, 2014a, 2014b) and characterizing the building materials used in both URM and strengthened walls.

Spatial variability and sensitivity analysis on the compressive strength of hollow concrete block masonry wallettes

This probabilistic study investigates the effect of material uncertainties on the numerical analysis of masonry wallette axial compressive strength. Detailed micro-modeling techniques are adopted to model hollow concrete block masonry by separately describing the specific equations for material constituents (blocks and mortar) and block-mortar interfaces. A Latin hypercube sampling technique is used to generate random input variables from the empirical distribution functions of the material parameters. A quasi-static nonlinear analysis is then carried out using a Monte Carlo simulation to evaluate the effect of the spatial variability of material parameters on the compressive behavior of masonry wallettes. The results show that ignoring the spatial variability of material properties may cause a model to overestimate the probability of compression failure. Additionally, the independent and cooperative effects of the material parameters on masonry compressive strength are investigated using first order, second order, and total sensitivity indices. The numerical results indicate that block tensile strength influences masonry compressive strength the most. Several parameters for masonry compressive strength are also ranked in order of importance.

Strength, behavior, and failure mode of hollow concrete masonry constructed with mortars of different strengths

This study reports the failure modes of hollow concrete masonry prisms, taking into account the block and mortar stress-strain behavior. An extensive and detailed experimental program has been conducted on three-block high stack-bonded prisms, built using a combination of one hollow block type and three mortars with different strengths. Based on the results of the experiments, masonry failure was assessed. The main conclusion of this is that the mortar in all cases governs the masonry failure mechanism.The ratio between the masonry and block moduli of elasticity, which can be used as a measure of loss of stiffness, indicates that masonry built with a strong mortar behaves almost as a homogenous material. The typical failure mode observed during testing for this type of masonry was due to tensile stresses developed in the block. A crack developed at and propagated instantly through the block face until reaching the mortar bed joint; the crack then propagated through the head joint causing a localized split at the interface between block and mortar. For masonry built with two different weak mortars, as the stress/strength ratio increased, the ratio between the masonry and mortar moduli of elasticity decreased to 0.32 and 0.55, for the weak and the weaker mortar respectively. The observed failure mode, however, was independent of how weak the mortar was since, for both cases, the masonry failed due to localized mortar crushing.Another conclusion from the study presented herein is that a robust and reliable prediction of the masonry compressive strength requires the use of the nonlinear stress-strain relationship of the component materials.

Stress–strain model for hollow concrete block masonry under uniaxial compression

Accurate evaluation of the stress–strain relationship of hollow concrete block masonry is essential for the detailed analysis and reliable design of hollow concrete block masonry structures. This paper presents the results of an investigation of the compressive stress–strain behavior of hollow concrete block masonry. Testing was carried out on 23 masonry wallettes constructed in the laboratory using four different block/mortar combinations. The failure mechanism and characteristics of stress–strain curves were studied. Simple relationships between the elastic modulus and corresponding compressive strength were identified. The mortar compressive strength, masonry compressive strength, and masonry elastic modulus were used to predict the peak strain. Finally, a new model for the stress–strain behavior of hollow concrete block masonry was developed and was found to yield predictions in good agreement with the experimental results and better than the predictions of other models.

Longitudinal compressive strength of masonry – Simplified calculation approach / Längsdruckfestigkeit von Mauerwerk – Vereinfachter Berechnungsansatz

AbstractFor the structural analysis of the bending compression zone of masonry building elements, which are loaded under bending compression parallel to the bed joints, the longitudinal compressive strength of the masonry is required. According to the code, this value has until now been determined in laborious tests on masonry building elements or calculated analogously to the approach for the determination of the compressive strength perpendicular to the bed joints. In such a way, the actual failure mechanisms of masonry under compression loading parallel to the bed joints and relevant influential parameters for the longitudinal compressive strength however remain unconsidered. The article presents a proposal for the determination of minimum values of the longitudinal compressive strength of masonry in a simplified form for structural design purposes, which include consideration of both the relevant failure cases and also the significant influential parameters.

Mechanisms governing the compressive strength of unconfined and confined rubble stone masonry

In the safety assessment of masonry constructions the estimate of the compressive strength of masonry is often required, especially for those structures subjected to high stresses or stress concentration. Focusing on rubble stone and conglomerate-like masonries, a typology which is quite common in historical constructions, a theoretical formulation identifying the phenomena governing the collapse mechanism was recently proposed for the evaluation of the compressive strength of unconfined and confined masonries. The theoretical formulation also provides useful insights on the design of the necessary confinement stress level, anytime improvement of the compressive strength and ductility of the masonry walls is needed. In this paper the reliability of the theoretical predictions is substantiated by an experimental study. Specific and challenging tests on masonry samples replicating historical rubble stone masonry elements and the inner core of three leaf walls are conceived to offer experimental evidences of the phenomena governing collapse, such as the cohesion, the aggregate interlocking and the residual tensile strength after cracking, as well as the possible confinement stress level. The experimental investigation also provides preliminary values of the parameters affecting the masonry compressive strength.

Experimental and numerical study of Interlocking Stabilized Earth Blocks mechanical behavior

One of the modern techniques of earth construction is the Interlocking Stabilized Earth Block (ISEB), which realizes the requirement of a certain type of construction in an economic and technical way compared to conventional materials. The use of this technique fits suitably within the framework of high environmental quality since the process uses an abundant material not requiring a lot of transformation energy.The aim of this study is to perform compressive tests on superposed ISEB that are laid dry without grout mortar. Testing results show that the ​​contact area and the clearance between the blocks have an effect on the masonry's compressive strength, causing it to decrease. For that, particular attention is given to analyzing the contact area effect on the mechanical behavior of superposed ISEB. A finite element method (FEM) analysis is also performed in order to highlight the effect of the local stress around the clearance on the macroscopic compressive behavior of the masonry. Finally, a simplified spring model is considered in order to estimate the vertical apparent Young's modulus of ISEB walls.