Deformation Of Masonry Research Articles

Plastic deformation and fracture of masonry under biaxial stresses

Masonry is a complex multicomponent composite composed of dissimilar materials (brick / stone and mortar). The process of masonry deformation under load depends on the mechanical characteristics of the basic composite materials, as well as of the parameters belonging to the elements, which define the link between brick and mortar being the structural elements. The paper provides an analysis of the experimental study results of masonry behaviour in two-dimensional stress state at primary stresses of opposite signs; identifies the mechanisms of masonry failure that are in compliance with the conditions of stress state. The work shows the key role that structural elements play in the formation of masonry failure processes. On the basis of failure mechanisms educed from the experiments, there was developed a discrete model of masonry. The processes and the corresponding strength criteria, which play a key role in the implementation of plastic deformation phase, have been detected. It has been shown that the plastic deformation of masonry under biaxial stresses occurs in case of the physical linear behavior of the basic materials (brick and mortar). It has been also substantiated that the plastic properties of masonry under biaxial stresses are determined by the processes occurring at the contact interaction nodes between brick and mortar in bed and cross joints. The values of the plasticity coefficients for masonry depending on the mechanical properties of a brick, a mortar and adhesive strength in their interaction have been obtained basing on the results of the performed numerical investigations.

An experimental evaluation of prediction models for the mechanical behavior of unreinforced, lime-mortar masonry under compression

This paper contributes to the understanding of lime-mortar masonry strength and deformation (which determine durability and allowable stresses/stiffness in design codes) by measuring the mechanical properties of brick bound with lime and lime-cement mortars. Based on the regression analysis of experimental results, models to estimate lime-mortar masonry compressive strength are proposed (less accurate for hydrated lime (CL90s) masonry due to the disparity between mortar and brick strengths). Also, three relationships between masonry elastic modulus and its compressive strength are proposed for cement-lime, hydraulic lime (NHL3.5 and 5), and hydrated/feebly hydraulic lime masonries respectively.Disagreement between the experimental results and former mathematical prediction models (proposed primarily for cement masonry) is caused by a lack of provision for the significant deformation of lime masonry and the relative changes in strength and stiffness between mortar and brick over time (at 6 months and 1 year, the NHL 3.5 and 5 mortars are often stronger than the brick). Eurocode 6 provided the best predictions for the compressive strength of lime and cement-lime masonry based on the strength of their components. All models vastly overestimated the strength of CL90s masonry at 28 days however, Eurocode 6 became an accurate predictor after 6 months, when the mortar had acquired most of its final strength and stiffness.The experimental results agreed with former stress–strain curves. It was evidenced that mortar strongly impacts masonry deformation, and that the masonry stress/strain relationship becomes increasingly non-linear as mortar strength lowers. It was also noted that, the influence of masonry stiffness on its compressive strength becomes smaller as the mortar hydraulicity increases.

Characterisation of thin layer polymer cement mortared concrete masonry bond

Masonry bond is affected by many parameters such as the type of mortar used, the techniques of dispersion of mortar and the surface texture of the concrete blocks. Additionally it is understood from the studies on conventional masonry that the bond characteristics are also influenced by the curing methods as well as the age of the bond at the time of testing. These effects on thin layer mortared masonry employing polymer cement mortars are not well understood. Therefore, the effect of curing methods and age to the bond strength and deformation of masonry containing thin layered polymer cement mortar was investigated as part of an ongoing research program at the Queensland University of Technology. This paper presents an experimental investigation of the flexural and shear bond characteristics of the thin layer mortared concrete masonry. The parameters examined include the effects curing and ageing to the bond development over a period from 14days to 56days after fabrication. The results exhibit that dry cured thin layer mortared masonry exhibits higher bond strength and Young’s and shear moduli compared to the wet cured specimens.

Modeling Nonlinear Deformation and Destruction Masonry under Biaxial Stresses Part 2 - Strength Criteria and Numerical Experiment

Masonry is a complex multicomponent composite consisting of dissimilar materials (brick / stone and mortar). Masonry deformation process under loading depends on the mechanical characteristics of the basic composite materials, as well as of the parameters of the elements defining binding between brick and mortar being the interface elements. Traditional methods of masonry modeling are based on the use of generalized ("effective") mechanical properties of the composite as a continuant homogeneous continuant medium. This paper presents an overview and analysis of continuant masonry models adequately reflecting the process of elastic, and in some cases elastic-plastic masonry deformation within the composition of stone structural elements. The paper provides analysis of the experimental research results of masonry behaviour in a biaxial stress state at primary stresses of opposite signs; identifies masonry destruction mechanisms complying with the conditions of stress state. The work demonstrates the key role played by interface elements in the formation of masonry destruction processes. Based on destruction mechanisms deduced from experiments, there was developed a discrete model of masonry. A system of masonry strength criteria was proposed corresponding to the biaxial stress state conditions at primary stresses of opposite signs. For purposes of studying the elastic-plastic deformation and destruction of masonry, there was developed a technology of numerical experiment performance using calculation technologies with a stepwise tracking of stress-and-strain state, at step-by-step loading. The scope of this paper includes verification of modeling method and technology of numerical experiment at various parameters of interface elements defining binding between bricks and mortar

Modeling Nonlinear Deformation and Destruction Masonry under Biaxial Stresses Part 1 – Masonry as Simulation Object

Masonry is a complex multicomponent composite consisting of dissimilar materials (brick / stone and mortar). Masonry deformation process under loading depends on the mechanical characteristics of the basic composite materials, as well as of the parameters of the elements defining binding between brick and mortar being the interface elements. Traditional methods of masonry modeling are based on the use of generalized ("effective") mechanical properties of the composite as a continuant homogeneous continuant medium. This paper presents an overview and analysis of continuant masonry models adequately reflecting the process of elastic, and in some cases elastic-plastic masonry deformation within the composition of stone structural elements. The paper provides analysis of the experimental research results of masonry behaviour in a biaxial stress state at primary stresses of opposite signs; identifies masonry destruction mechanisms complying with the conditions of stress state. The work demonstrates the key role played by interface elements in the formation of masonry destruction processes. Based on destruction mechanisms deduced from experiments, there was developed a discrete model of masonry. A system of masonry strength criteria was proposed corresponding to the biaxial stress state conditions at primary stresses of opposite signs. For purposes of studying the elastic-plastic deformation and destruction of masonry, there was developed a technology of numerical experiment performance using calculation technologies with a stepwise tracking of stress-and-strain state, at step-by-step loading. The scope of this paper includes verification of modeling method and technology of numerical experiment at various parameters of interface elements defining binding between bricks and mortar.

Flax and polyparaphenylene benzobisoxazole cementitious composites for the strengthening of masonry elements subjected to eccentric loading

To address the structural problems caused by eccentric loads in unreinforced masonry, three different types of masonry were prepared based on clay bricks bonded with a natural hydraulic lime mortar combined with a flax or polyparaphenylene benzobisoxazole (PBO) fabric-reinforced cementitious matrix (FRCM) composite. The mechanical behaviour when subjected to concentric and eccentric loads was studied by performing axial compression tests, with eccentric load tests only carried out in instances of large eccentricities. Analysis of the load–displacement and moment–curvature response revealed that both the flax- and PBO-based strengthening systems improve the strength and deformability of masonry. However, compared to the PBO fabric composite, the use of flax fabric provides a greater deformability that helps prevent the composite and substrate debonding.

Study on Rational Ratios of Lateral Stiffness for Masonry Building with Frame Structure at First Two Stories

There are two typical seismic damage characteristics to the masonry building with frame shear wall structure at first two stories, and the lateral stiffness ratio of the third storey to the second storey is one of the key factors mostly affecting the seismic performance of this kind of building. However, some factors are not considered sufficiently in current Chinese seismic codes. According to the theory of performance-based seismic design, the seismic performance of this kind of structure is analyzed in this paper by taking time-history analysis on models which with different storey stiffness ratios. The results show that when the lateral stiffness ratio controlled in a reasonable range, the upper masonry deformation can be ensured in a range of elastic roughly, and the bottom frame can be guaranteed to have sufficient deformation and energy dissipation capacity. Finally, according to the seismic performance characteristics of masonry building with frame shear wall structure at first two stories, especially the characteristics under strong earthquakes, a method of simplified calculation model for the upper masonry is discussed in this paper.

Mūro Gaminių Ir Gulsčiųjų Siūlių Įtempių Deformacijų Būvio Ypatumų Analizė

In this paper, the analysis of various effects that have influence to the mechanical properties of masonry is made. Masonry is nonhomogeneous and anisotropic material composed of two materials with different stiffness properties. In order to analyze masonry deformations it is necessary to evaluate all effects that have influence to masonry mechanical properties (Table 1). The analysis of stress-strain state of masonry is presented in this paper. During the analysis of stressstrain state, the mechanical properties of masonry units and mortar were defined from experimental investigation of samples of unit and mortar materials. The following conclusions were reached based on the analysis of experimental data: 1) The deformations and stresses along the height of masonry unit distributes unevenly. The stresses and deformations near the bed joint are higher than in the middle of the unit (4 pav). 2) From experimental data it was determined that the deformation of bed joints mostly depend on contact zone between units and mortar. The contact zone deformation contains about 80…90% of all bed joint deformation. 3) The elastic modulus of mortar inside the composite is different from modulus of mortar specimens cast separately due to different laying and curing conditions. The elastic modulus values performed from composite were 15…25 times less than the values from standard mortar prisms (EN 1015-11). It is advisable to use real (defined from experiments) masonry units and mortar properties when detailed, numerical stress-strain analysis is performed. 4) Experimental analysis showed that bed joints have big influence to vertical deformation of masonry in axial compression. Masonry units have influence to mechanical properties of mortar joints. The experiment was carried out, during which dry and wet masonry units were used. Units were wet out to eliminate there absorption characteristics. Extra wet out units had an effect to the stiffness of bed joints (12 pav).

Masonry Columns Confined by Steel Fiber Composite Wraps.

The application of steel fiber reinforced polymer (SRP) as a means of increasing the capacity of masonry columns is investigated in this study. The behavior of 23 solid-brick specimens that are externally wrapped by SRP sheets in low volumetric ratios is presented. The specimens are subjected to axial monotonic load until failure occurs. Two widely used types of masonry columns of differing square cross-sections were tested in compression (square and octagonal cross-sections). It is concluded that SRP-confined masonry behaves very much like fiber reinforced polymers (FRP)-confined masonry. Confinement increases both the load-carrying capacity and the deformability of masonry almost linearly with average confining stress. A comparative analysis between experimental and theoretical values computed in compliance with the Italian Council of Research (CNR) was also developed.

Masonry Confinement with Fiber-Reinforced Polymers

The application of fiber-reinforced polymer (FRP) as a means of increasing the axial capacity of masonry through confinement, a subject not addressed before, is investigated in this study. Four series of uniaxial compression tests, with a total of 42 specimens, were conducted on model masonry columns with these variables: number of layers, radius at the corners, cross-section aspect ratio, and type of fibers. It is concluded that, in general, FRP-confined masonry behaves very much like FRP-confined concrete. Confinement increases both the load-carrying capacity and the deformability of masonry almost linearly with the average confining stress. The uniaxial compression test results enabled the development of a simple confinement model for strength and ultimate strain of FRP-confined masonry. This model is consistent with the test results obtained here but should attract further experimental verification in the future to account for types of masonry materials other than those used in this study.

Shrinkage and creep of masonry mortar

Shrinkage and creep results are presented for different types of masonry mortars having a wide range of strength. The range of values implies that the type of mortar has an appreciable influence on deformation of masonry. The results are analysed, together with other data obtained from other investigations carried out over several years in the same laboratory, and predictive models developed. Factors quantified are strength, volume/surface/ ratio, time of exposure to drying (shrinkage) and time under load (creep). While creep is unaffected, for a given strength, shrinkage of water-cured mortar is greater than shrinkage of mortar that is cured under polythene. When based on 28-day strength, the average error of prediction for shrinkage is 19% but if based on the strength at the start of shrinkage, the error coefficient is reduced slightly to 16%. Creep is estimated with an average error of 24%.

ESTIMATION OF SHRINKAGE DEFORMATIONS OF MASONRY BY DETERMINING CRACKING OF INTERNAL BUILDING WALLS/MŪRO SUSITRAUKIMO DEFORMACIJŲ ĮVERTINIMAS, ANALIZUOJANT PASTATŲ VIDINIŲ SIENŲ SUPLEIŠĖJIMĄ

In practice a lot of cases are found, that loadbearing masonry walls of buildings are cracked. The main reason of these cracks is reinforced or metal lintel, reinforced concrete floors, waist-band and other elements. They impede free shrinkage deformation of masonry. In masonry, tension stresses appear and compression stresses, in impedemental elements. The formulas for calculation of these stresses and strains are suggested in the article. Analysis of this formulas show that stresses-strains depend on the ratio of areas of sections and the modulus of elasticity of masonry walls and impedimental structures or elements. It is important to evaluate the shrinkage of masonry and its further development. Such shrinkage begins before mounting other structures on walls. There are suggested methods and formulas for estimating changes of shrinkage deformations in time. Limiting shrinkage deformations are suggested according to the recommendations of Eurocodes 6. Theoretical and experimental results of changing of masonry shrinkage are compared. The comparison shows good agreement of these results. The suggested methods allow to choose such materials for masonry and time of mounting of other structures, which decrease the tension stresses in masonry because of its shrinkage and give opportunities to decrease danger of appearing cracks in walls or to avoid them, in general.

ESTIMATION OF SHRINKAGE DEFORMATIONS OF MASONRY BY DETERMINING CRACKING OF INTERNAL BUILDING WALLS

Summary In practice a lot of cases are found, that loadbearing masonry walls of buildings are cracked. The main reason of these cracks is reinforced or metal lintel, reinforced concrete floors, waist-band and other elements. They impede free shrinkage deformation of masonry. In masonry, tension stresses appear and compression stresses, in impedemental elements. The formulas for calculation of these stresses and strains are suggested in the article. Analysis of this formulas show that stresses-strains depend on the ratio of areas of sections and the modulus of elasticity of masonry walls and impedimental structures or elements. It is important to evaluate the shrinkage of masonry and its further development. Such shrinkage begins before mounting other structures on walls. There are suggested methods and formulas for estimating changes of shrinkage deformations in time. Limiting shrinkage deformations are suggested according to the recommendations of Eurocodes 6. Theoretical and experimental results of chan...

Composite modelling of masonry deformation

Based on the measured properties of individual bricks, blocks and mortar specimens, composite model expressions are presented for elasticity, creep and moisture movement of masonry in two directions. The model demonstrates the influence of creep in horizontal moisture movement, and allows for anisotropy of brick or block. Simulation of the role of moisture diffusion in masonry is a requirement for statisfactory predictions by the model, this being achieved by testing specimens having the same volume/exposed surface area ratio as the masonry component phases. Experimental verification is shown for clay brickwork walls and piers, and for calcium silicate walls.

Evaluation of the mechanical properties of the mass of a concrete dam with interblock joints

1. The strength of a mass with undisturbed interblock and grouted joints in compression across the joints is at least no less than the strength of a monolith. 2. Within a dam section with undisturbed interblock joints and in the absence of significant cracks the average modulus of deformation of the masonry in tension and compression in all directions can be assumed equal to the modulus of deformation of the concrete. 3. The average modulus of deformation of masonry with grouted joints in compression by stress of more than 1 MPa across the joints can be assumed equal to the modulus of deformation of the concrete. 4. Zones of the mass in the immediate vicinity of the joints have increased deformability, which depends on the magnitude of stresses and number of loading cycles. To estimate the deformability of the interblock joint of concrete masonry, we can take for the investigated concrete t=1 mm; in tension Ej=2.3 GPa; in compression: for placement in 1-m layer under stress up to 8 MPa Ej=5.4 GPa, under stress from 8 to 12 MPa Ej=3 GPa; for placement in 0.37-m layers under stress up to 6.53 MPa Ej=4 GPa. 5. The modulus of deformation of grouted joints can be assumed equal to 2.5 MPa under stresses less than 2.5 MPa and equal to 7–10 GPa under greater stresses. In the presence of residual opening of joints after their grouting the values of the modulus of deformation of the joint will be greater than those indicated.

Creep Behaviour Of Mortars Used In Restoration

Experimental results on mortar deformations used in Restoration of historical buildings and monuments are given in this paper. The time depending deformations of specimens from mortars with different composition (lime, natural sand, pozzolana, crushed bricks and a varying percentage of cement) were measured in laboratory up to 6 month. The difference in creep behaviour between mortars having varying compositions studied in this research can be used in the evaluation of the mortar influence concerning the deformation of masonry with thick mortar joints (stone or brick masonry of historical structures).