The results of five experimental test series on masonry walls supported by reinforced concrete beams or slabs are reported and compared to theoretical predictions of the load bearing capacity. The ...experiments were performed on deep masonry beams built with respectively calcium silicate and clay brick. Investigated parameters were: position of the supports, concrete beam-masonry interface, concrete beam stiffness, type of loading, and height of masonry wall and concrete beam. Based on literature, the method proposed by Davies and Ahmed as well as the method according to Eurocode 6 were used to estimate the load bearing capacity of the tested masonry walls supported by concrete beams. The method of Davies and Ahmed allows for the determination of the stresses and stress resultants in the masonry. The analysis shows that near the support an inclined compressive force acts at the bed joint, which means that a shear-compression stress state exists in the bed joint. Strength evaluation has been carried out using the Mann-Müller criterion that is adopted in Eurocode 6.
Based on the test results, it may be concluded that both methods yield conservative values of the load bearing capacity, as could be expected. Before cracking a linear elastic behavior was observed, while after cracking a strut-and-tie model may be applied. To develop more accurate design models, it is recommended to investigate the post-cracking behavior in more detail.
The in-plane shear behaviour of a new seismic retrofit concept which combines two standalone retrofit measures for in-plane and out-of-plane strengthening of masonry walls was investigated. The ...in-plane reinforcement consists of a single-sided carbon fabric-reinforced cementitious matrix (FRCM) overlay, while the out-of-plane reinforcement consists of deep mounted carbon fibre reinforced polymer strips embedded in a viscous-elastic epoxy. An experimental program was undertaken in which clay brick masonry wallettes were subjected to the diagonal compression test to assess the effectiveness of the strengthening system on the in-plane behaviour. The obtained results showed that the single-sided carbon FRCM overlay increased the shear capacity with 80%, compared to the unstrengthened control specimens. Moreover, by testing two different FRCM overlay thicknesses it was found that a thicker matrix layer does not increase the shear capacity of wallettes. However, wallettes provided with a thicker FRCM overlay did show a higher level of ductility. Furthermore, the obtained experimental results showed that the presence of only the aforementioned out-of-plane reinforcement does not affect the in-plane strength of masonry wallettes loaded under shear, and even prevented the disintegration after reaching the failure load compared to the unstrengthened control specimens. Finally, an existing analytical model as well as the Eurocode 8 design provisions were compared to the found failure mechanisms and failure loads. The analytical model developed showed good correspondence with the experimental values for both the failure mechanism and failure load, with an experimental/model ratio
φ
of 0.98, while Eurocode 8 proved to lead to conservative values.
► Eight unbonded post-tensioned CASIEL-TLM masonry shear walls were tested. ► Rectangular walls failed by overturning, i.e. base separation and toe crushing. ► T-shaped walls failed prematurely by ...shear of the interlocked web-flange interface. ► A model was developed, based on global compatibility between masonry and UPT bars. ► Due to the kicker course, deformations of the shear walls are larger than expected.
The mechanical behaviour of unbonded post-tensioned (UPT) shear walls of high-strength CAlcium SIlicate ELement masonry with Thin-Layer Mortar (CASIEL-TLM masonry) was investigated experimentally and numerically. Eight walls were tested with the following key variables: unit type, prestress level and cross-sectional shape (rectangular or T-shaped with interlocking of web and flange). An extensive measurement scheme was adopted that allowed derivation of average curvatures and strains in the bottom region of the wall in addition to wall displacements. Since UPT masonry is characterised by the absence of local compatibility between masonry and the UPT tendons, a numerical model for quasi-static, monotonic push-over analysis was developed that provides an iterative solution for the global interaction between masonry and UPT tendons. A common masonry stress–strain diagram was adopted in the numerical model. A peculiarity of CASIEL-TLM masonry is the kicker course, which reduces the stiffness of the bottom region of the shear wall. This layer was modelled with no-tension, linear-elastic behaviour and a reduced stiffness. Nevertheless, the model underestimates the experimental deformations of the rectangular shear walls, while the strength is in reasonable agreement. The walls with T-shaped cross-section failed prematurely by shear of the web-flange interface, resulting in diagonal splitting cracks in the interlocking units. This paper deals with the experimental results of UPT CASIEL-TLM masonry shear walls with rectangular and T-shaped cross-section and with the numerical modelling of the overturning behaviour of UPT shear walls with rectangular cross-section.
Data on creep and shrinkage of high-strength calcium silicate element masonry with thin-layer mortar (CASIEL-TLM masonry) is not currently available in international literature. A novel application ...of this material in unbonded post-tensioned shear walls requires creep and shrinkage data to predict prestress loss. Therefore, creep and shrinkage were measured on 38 large-scale high-strength CASIEL-TLM specimens, including a TLM bed joint or a wall-floor connection, for a period of 300 days. Initial moisture content of the specimens and temperature and relative humidity of the environment were carefully controlled. Creep and shrinkage data were used to predict prestress loss by means of visco-elastic finite element simulations as well as a simple analytical expression. These predictions were validated by prestress loss experiments, conducted simultaneously with the creep and shrinkage experiments. Predictions for final prestress loss due to creep and shrinkage are below 16 or 24 % for CASIEL-TLM masonry with prestressing strands or prestressing bars respectively.
Abstract The main goal of this research is to determine the mechanical properties of bedding mortar by assessing the mortar damage onset, the stiffness plasticity degradation and the apparent ...Poisson´s ratio under compression. Two mortar types, 1:0.5:4 and 1:1:6 (cement:lime:sand ratio), were used and tested at 28 days; specimens had diameter-to-height (d/h) ratios of 0.3 and 1.0. These diameter-to-height (d/h) ratios were chosen to evaluate the effect of confinement caused by the friction between the steel plates of the testing machine and the sample. Numerical models were developed, and their response compared with the experimental results. From the experimental results, it was concluded that there are meaningful differences in their responses with weak and strong mortar types and different d/h ratios. The d/h ratio influences the relationship between the stress and strength and the apparent Poisson´s ratio of the specimen, which is defined herein as the ratio of the horizontal to vertical strain, regardless of cracking of the specimen. The mortar damage onset and stiffness plasticity degradation for both mortar types and d/h ratio are different and depend on the stress/strength ratio level. All samples with a d/h ratio of 0.3 show a constant decrease in the volumetric strain until failure but with negligible expansion on the horizontal deformation. In contrast, samples with a d/h ratio of 1.0 present an increase of stiffness after development of the first crack, which causes the increase of the sample volume. Numerical simulation and experimental results for mortar 1:0.5:4 with a d/h ratio of 0.3 are similar until approximately 10 MPa, after which the numerical results diverge from the experimental results. For the d/h ratio of 1.0, the vertical strain results are also similar, but the horizontal strains results near failure are very different. The model can not represent the nonlinear increase of the horizontal strain near failure probably because the crack propagation and the stiffness plasticity degradation could not be controlled. For mortar 1:1:6, vertical strains from numerical and experimental results are similar, but again the model can not reproduce the nonlinear increase of horizontal strain near failure.
Resumo O objetivo principal desta pesquisa é determinar as propriedades mecânicas da argamassa de assentamento à compressão, avaliando o início do dano, perda de rigidez e variação do coeficiente de Poisson aparente. Foram testados dois tipos de argamassa, com traços em volume de 1:0,5:4 e 1:1:6 (cimento, cal e areia), testadas aos 28 dias, com corpos de prova de prova cilíndricos com duas relações diâmetro/altura (d/h), de 0,3 e 1,0. Estas relações diâmetro/altura foram escolhidas de forma a avaliar o efeito do confinamento causado pelo atrito entre os pratos de aplicação de carga da prensa e o corpo de prova. Foram desenvolvidos, também, modelos numéricos de maneira a confrontar os resultados com os experimentais. Dos resultados experimentais conclui-se que há diferenças significativas de comportamento mecânico entre os dois tipos de argamassa e as duas relações diâmetro/altura. A relação d/h influenciou a relação tensão-deformação e o coeficiente de Poisson aparente do material, definido aqui como a relação entre as deformações específicas lateral e axial, independentemente da formação das fissuras. O início da fissuração e a perda de rigidez para os dois tipos de argamassa e relações d/h são diferentes e dependem do nível de tensão aplicado. Todas as amostras com relação d/h igual a 0,3 apresentaram decréscimo de volume específico constante até a ruptura, mas com uma pequena expansão das deformações laterais. Por outro lado, as amostras com relação d/h igual a 1,0 apresentaram um crescimento da rigidez após o aparecimento da primeira fissura, resultando em aumento do volume específico. O comportamento tensão-deformação obtido nas análises numéricas e experimentais das amostras de argamassa 1:0,5:4 com relação d/h igual a 0,3 foram similares até, aproximadamente, 10 MPa, depois disso, houve divergência entre os resultados dos dois conjuntos. Para a relação d/h igual a 1,0, as deformações específicas verticais foram similares, mas as deformações específicas laterais foram muito diferentes próximo à ruptura. O modelo numérico não foi capaz de representar o crescimento não linear das deformações específicas laterais próximo à ruptura porque a propagação de fissuras e a perda de rigidez não puderam ser controladas. Para a argamassa 1:1:6, as deformações específicas verticais dos modelos numéricos e experimentais foram semelhantes, mas mais uma vez não foi possível repetir o crescimento não linear das deformações específicas laterais próximo à ruptura.
Masonry component products are increasingly made industrially with reduced variation in mechanical properties. The joint is the only part of the masonry that is affected by manual action and so the ...load bearing capacity is not only determined by the quality of the bricks and mortar used but moreover by the way the masonry has been built and cured. As a result, it may be expected that the largest material variations are at the brick-mortar interfaces. This has been observed as irregular interface bonding with a bonded central area surrounded by fissures. As a consequence of the final shape of the joint, forces concentrate in the central part of the joint and strain variations occur near fissure tips which result in spalling of bricks in experiments. This paper demonstrates the need for detailed deformational measurements in the brick-mortar interface region. To overcome the limitations with traditional measuring instruments, a refined methodology based on the laser speckle technique is introduced in a companion paper Canadian Journal of Civil Engineering, 34(11), 1467 (2007) by the authors of this paper. PUBLICATION ABSTRACT
An experimental program was undertaken to assess the effectiveness of a new retrofit concept to improve the in-plane behavior of unreinforced clay brick walls by means of full-scale static-cyclic ...in-plane tests. The proposed seismic retrofit system combines two standalone retrofit measures for in-plane and out-of-plane strengthening of masonry walls. The in-plane reinforcement consists of a single-sided carbon Fabric-Reinforced Cementitious Matrix (FRCM) overlay, and anchors embedded with a flexible adhesive in the masonry. The out-of-plane reinforcement, which consisted of deep mounted Carbon Fibre Reinforced Polymer (CFRP) strips embedded with a flexible adhesive in the masonry, was included in the study to investigate the possible degrading effects of the deep groove on the in-plane behavior. A total of nine full-scale reinforced masonry walls with three different geometries were tested under three different axial loads. None of the specimens showed shear failure at both the reinforced and the as-built side. Cracking predominantly occurred at the interface between the bottommost bed-joint and the foundation beam. The out-of-plane reinforcement did not affect the in-plane strength, as no vertical shear cracks occurred. Moreover, it was found that the anchors increased both the rocking and sliding resistance of the walls. An analytical model was proposed covering the rocking and sliding resistance of the reinforced walls, providing a good approximation of the experimentally obtained in-plane strengths. Additional pull-out experiments showed that the testing scenario where the tensile forces in the anchor were transferred to CFRP strip, provided a good approximation of the analytically determined anchorage strength.
The brick-mortar interaction is important in the mechanical behaviour of masonry. It affects the load transfer considerably, as shown by detailed deformation measurements taken using electronic ...speckle pattern interferometry (ESPI), a laser speckle interference technique. A companion paper Canadian Journal of Civil Engineering, 34(11), 1475 (2007) by the authors of this paper argues that the joint is the only part of contemporary masonry significantly affected by manual action, which is why large material variations appear at the brick-mortar interface. To evaluate this phenomenon, ESPI measurements were performed and compared with accompanying linear variable differential transformer (LVDT) results. The behaviour of specimens loaded with various eccentricities was relatively soft in the brick-mortar interface area when compared with the behaviour shown in the surrounding stiff brick and mortar. The brick-mortar interface was characterized by a central part surrounded by fissures. Most of the load was transmitted in the central part. Because of this, the axial strain curve over the width of the specimens was U-shaped for concentrically loaded specimens (i.e., those with zero eccentricity). Over the height of the two-brick one-joint specimen, a smooth, B-shaped lateral strain curve was observed, in which the largest strains were found in the bricks. PUBLICATION ABSTRACT
This study focuses on the comparison of the results of a laser speckle technique, ESPI, and numerical simulations with DIANA when used for research into the role of brick–mortar interaction on the ...deformation of masonry loaded in compression. When a masonry structure is loaded, the interaction of brick and mortar is considered of paramount importance with respect to the mechanical behaviour of masonry. As a consequence of the brick laying process and positioning of the unit, masonry has weak spots at the mortar-unit interface. The clay–brick–mortar interaction was measured in detail with ESPI, a specially designed laser speckle test equipment. It was shown that most of the deformation occurred in the brick–mortar interface. DIANA was used for some numerical simulations of the brick–mortar interaction. Simulated specimen dimensions were as in the experiments. An interface layer of 1 mm thickness was modelled between mortar and top unit to simulate the contact layer. Fissures were modelled as 15 mm deep openings. Similarities between ESPI and DIANA are seen in the way the results i.e. node displacements are presented. Both DIANA and ESPI produce a similar tabular output with node coordinates and their displacements. This output can be used in spread sheet programs for further analyses. As DIANA and ESPI give comparable results, the advantage of DIANA – i.e. the calculation of stresses – can be utilized. Results of the study can be used for more detailed modelling of masonry.
Masonry Wall Damage by Restraint to Shrinkage van Zijl, G. P. A. G; de Vries, P. A; Vermeltfoort, A. T
Journal of structural engineering (New York, N.Y.),
07/2004, Volume:
130, Issue:
7
Journal Article
Peer reviewed
Restrained shrinkage has been identified as a major source of damage to buildings in The Netherlands. Several numerical studies have been performed and reported. Yet, successful experimental ...simulation and quantification have not yet been performed. In this paper, the successful design, setup, and execution of such an experiment are described. The specimen was a solid masonry wall of 2 m length, 1.3 m height, and 220 mm thickness, with a central opening of 420 mm×420 mm. An inverse approach to restrained shrinkage was followed by heating the constraining boundaries, in this case stiff, solid aluminum beams simulating rigidly connected upper and lower floors. To simulate upper wall and floor bearing weight, precompression was applied through six pairs of steel rods spanning between the aluminum beams. At a temperature difference of about 12°C a crack was initiated in the wall at the opening, which instantly and audibly propagated up and down over the full height of the wall. This was in good agreement with the predicted behavior, based on computational modeling with the recently developed finite element models for masonry, with parameters extracted from separate compression, shear, and tensile tests on small specimens of the same masonry.
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