Numerical analysis of concrete block masonry beams under three point bending

A parametrical study of masonry beams through numerical modelling has been performed in order to better understand the mechanical behaviour of these elements. Boundary conditions, geometry and reinforcement ratios are the main parameters analysed in this study. The numerical simulation is performed with DIANA® software, based on the Finite Elements Method. A comparison between numerical and experimental results is presented in order to validate the simulation. In conclusion, it was verified that the behaviour of masonry beams is greatly affected by the boundary conditions and geometry, as expected. With regard to reinforcement, it was noted that horizontal reinforcement increases the flexural strength of beams. On the other hand, variation in horizontal reinforcement had no influence on the shear resistance of masonry beams. Finally, the combination of horizontal and vertical reinforcement is shown to enhance the flexural and shear behaviour of masonry beams.This work was in part supported by a contract from DISWall - "Development of innovative systems for reinforced masonry walls' - (COOP-CT-2005-018120) awarded by the European Commission. The first author was supported by the Programme Alssan, the European Union Programme of High Level Scholarships for Latin America, Scholarship no E06D100148BR

Development of a design method for reinforced masonry subjected to in-plane loading based on experimental and numerical analysis

Tese de doutoramento em Engenharia Civil (ramo do conhecimento Estruturas)Masonry walls consist of the main elements responsible for the global stability of masonry buildings when subjected to lateral loads such as wind and seismic forces. These elements are subjected to gravity forces, bending moments and shear forces due to the horizontal loading. The masonry beams above the openings are important structural elements promoting the coupling behaviour of the masonry piers enabling the transfer of forces between them. Besides, the consideration of these elements leads to higher stiffness of the building. The anisotropic behaviour added to bi-axial stress state generated by the combination of those efforts becomes the behaviour of masonry walls and beams very complex. Therefore, this research aims at better understanding the behaviour of masonry walls and beams subjected to in-plane loading and propose analytical methodology for their design. Based on the literature review, an extensive experimental program is planned, being composed by experimental tests for the characterization of mechanical behaviour of masonry and masonry materials, in-plane cyclic tests on masonry walls and tests on masonry beams under flexure and shear. Based on experimental results, calibration of numerical micro-model using software DIANA® is presented. Moreover, a parametric analysis of masonry walls and beams is performed in order to assess the influence of different boundary conditions, aspect ratios, loading and reinforcement arrangements that could not by studied in experimental program. Results indicates that masonry walls and beams are described by similar flexural and shear resisting mechanisms. Unreinforced walls and beams present a very brittle behaviour. On the other hand, the application of reinforcement increases the deformation capacity, controls the crack opening and allows a better distribution of stresses. Longitudinal reinforcements (vertical in case of walls and horizontal in case of beams) increase the flexural strength, even if they seem not to influence the shear behaviour. Transversal reinforcements (horizontal in case of walls and vertical in case of beams) increase the shear strength, even if they do not influence the flexural behaviour. Effectiveness of reinforcements on the increase of the resistance of masonry walls and beams is highly related to the failure mode of the element. Based on numerical and experimental results, a new analytical method is proposed for the design of masonry walls and beams subjected to in-plane loading. Comparison between the results provided by the proposed method with other design methods presented in literature and experimental results of several authors is presented.As paredes consistem no elemento estrutural responsável pela estabilidade global dos edifícios em alvenaria estrutural quando sujeitos a acções laterais como vento e sismos. Estes elementos estão sujeitos a forças verticais e adicionalmente a momentos flectores e esforços de corte devido as forças laterais. Um elemento estrutural secundário mas muito importante na interacção de paredes são as vigas sobre as aberturas. Este elemento permite a transferência de esforços entre os troços de parede e confere uma maior rigidez à estrutura. O comportamento anisotrópico da alvenaria aliado ao estado bi-axial de tensão provocado pela combinação dos esforços referidos torna o comportamento das paredes e vigas bastante complexo. Desta forma, este trabalho tem como principal objectivo a melhor compreensão do comportamento de paredes e vigas de alvenaria quando sujeitos a acções no plano e a proposição de um método de dimensionamento para estes elementos. Assim, com base na revisão bibliográfica relativa ao comportamento de paredes e vigas de alvenaria, tanto em termos numéricos quanto experimentais, é proposto um plano extenso de ensaios para a caracterização mecânica dos materiais, para o estudo do comportamento de paredes sob a acção combinada de forças verticais e horizontais cíclicas aplicadas no plano das paredes e, finalmente, para o estudo do comportamento de vigas de alvenaria sujeitos à flexão e ao corte. Com base nos resultados experimentais é feita a calibração de um micro-modelo numérico com o aplicativo DIANA®, utilizando como ferramenta básica o método dos elementos finitos (MEF). Além disso, uma análise paramétrica é realizada nas paredes e nas vigas para avaliar o efeito das condições de fronteira, da geometria, da relação altura/largura dos elementos e das percentagens de armadura transversal e longitudinal. Os resultados indicam que o comportamento das paredes e vigas é descrito pelos mesmos mecanismos de resistência. Ambos os elementos apresentam um comportamento bastante frágil quando não são armados. Por outro lado, a utilização de armaduras aumenta a capacidade de deformação, controla a abertura de fissuras e permite uma melhor distribuição de tensões. As armaduras longitudinais (verticais no caso das paredes e horizontais no caso das vigas) aumentam a resistência à flexão dos elementos mas parecem não ter grande influência no comportamento ao corte. As armaduras transversais (horizontais no caso das paredes e verticais no caso das vigas) aumentam a resistência ao corte dos elementos não tendo grande influência no comportamento à flexão. A eficiência das armaduras no aumento de resistência das paredes e vigas está bastante relacionada com o modo de ruptura. Com base nos resultados numéricos e experimentais é proposto um método de dimensionamento de paredes e vigas sujeitos a acções no plano. A comparação dos resultados fornecidos pelo método proposto e por outros métodos de dimensionamento com resultados experimentais de diversos autores é apresentada.European Union Programme of High Level Scholarships for Latin America - Programme Alβan nº E06D100148B

Influence of aggregates grading and water/cement ratio in workability and hardened properties of mortars

Mortar is the material responsible for distribution of stresses in masonry structures. Knowledge about the fresh and hardened properties of mortar is fundamental to ensure a good performance of masonry walls. Water/cement ratio and aggregates grading are among several variables that influence physical and mechanical behaviour of mortars. An experimental program is presented in order to evaluate the influence of aggregates grading and water/cement ratio in workability and hardened properties of mortars. Eighteen compositions of mortar are prepared using three relations cement:lime:sand, two types of sand and three water/cement ratios. Specimens are analyzed through flow table test, compressive and flexural strength tests. Results indicate that the increase of water/cement ratio reduces the values of hardened properties and increases the workability. Besides, sands grading has no influence in compressive strength. On the other hand, significant differences in deformation capacity of mortars were verified with the variation of the type of sand. Finally, some correlations are presented among hardened properties and the compressive strength.This work was partly supported by contract DISWALL - "Development of innovative systems for reinforced masonry walls" - COOP-CT-2005-018120 from the European Commission. The first author was supported by the Programme Al beta an, the European Union Programme of High Level Scholarships for Latin America, Scholarship No. E06D100148BR

Experimental analysis of reinforced concrete block masonry beams using pre-fabricated planar trussed bars

Masonry spandrels together with shear walls are structural components of a masonry building subjected to lateral loads. Shear walls are the main components of this structural system, even if masonry spandrels are the elements that ensure the connection of shear wall panels and the distribution of stresses through the masonry piers. The use of prefabricated truss type bars in the transversal and longitudinal directions is usually considered a challenge, even if the simplicity of the applications suggested here alleviate some of the possible difficulties. This paper focus on the experimental behavior of masonry spandrels reinforced with prefabricated trusses, considering different possibilities for the arrangement of reinforcement and blocks. Reinforced spandrels with three and two hollow cell concrete blocks and with different reinforcement ratios have been built and tested using a four and three point loading test configuration. Horizontal bed joint reinforcement increased the capacity of deformation as well as the ultimate load, leading to ductile responses. Vertical reinforcement increased the shear strength of the masonry spandrels and its distribution play a central role on the shear behavior.This work was partly supported by contract DISWALL - "Development of innovative systems for reinforced masonry walls" - COOP-CT-2005-018120 from the European Commission. The first author was supported by the Programme Al(ss)an, the European Union Programme of High Level Scholarships for Latin America, Scholarship No. E06D100148BR

Assessment of compressive behavior of concrete masonry prisms partially filled by general mortar

The usage of general mortar for embedding and partially filling of units in 12 masonry prisms is evaluated through compressive tests. Filled and unfilled prisms were 13 tested in order to verify the differences on their compressive behavior. Four mortar 14 mixes with three water/cement ratios for each mix were used in tests. Results indicated 15 small differences between filled and unfilled masonry prisms. Mortar had a small 16 influence in the compressive strength of the masonry. However, a more significant 17 influence could be observed on secant elastic modulus, compressive fracture energy and 18 deformations of masonry prisms. Besides, an analytical model to represent the stress vs. 19 strain diagram of masonry prisms is proposed. The analytical model depends on the 20 compressive strength of mortar and masonry prism. Furthermore, results indicated that 21 the usage of general mortar for embedding and filling masonry prisms can be a solution 22 in terms of building technology.This work was partly supported by the European Commission's DISWALL contract (Development of innovative systems for reinforced masonry walls - COOP-CT-2005-018120). The first author was supported by the Alssan Programme, the European Union Programme of High Level Scholarships for Latin America, Number E06D100148BR

Parametrical study of masonry walls subjected to in-plane loading through numerical modeling

This paper deals with the numerical assessment of the influence of parameters such as pre-compression level, aspect ratio, vertical and horizontal reinforcement ratios and boundary conditions on the lateral strength of masonry walls under in-plane loading. The numerical study is performed through the software DIANA® based on the Finite Element Method. The validation of the numerical model is carried out from a database of available experimental results on masonry walls tested under cyclic lateral loading. Numerical results revealed that boundary conditions play a central role on the lateral behavior of masonry walls under in-plane loading and determine the influence of level of pre-compression as well as the reinforcement ratio on the wall strength. The lateral capacity of walls decreases with the increase of aspect ratio and with the decrease of pre-compression. Vertical steel bars appear to have almost no influence in the shear strength of masonry walls and horizontal reinforcement only increases the lateral strength of masonry walls if the shear response of the walls is determinant for failure, which is directly related to the boundary conditions.This work was partly supported by contract DISWALL - "Development of innovative systems for reinforced masonry walls" - COOP-CT-2005-018120 from the European Commission. The first author was supported by the Programme Alssan, the European Union Programme of High Level Scholarships for Latin America, Scholarship No. E06D100148BR

Masonry components

Masonry is a non-homogeneous material, composed of units and mortar, which can be of different types, with distinct mechanical properties. The design of both masonry units and mortar is based on the role of the walls in the building. Load-bearing walls relate to structural elements that bear mainly vertical loads, but can serve also to resist to horizontal loads. When a structural masonry building is submitted to in-plane and out-of-plane loadings induced by an earthquake for example, the masonry walls are the structural elements that ensure the global stability of the building. This means that the walls should have adequate mechanical properties that enable them to resist to different combinations of compressive, shear and tensile stresses.The boundary conditions influence the resisting mechanisms of the structural walls under in-plane loading and in a buildings the connection at the intersection walls are of paramount importance for the out-of-plane resisting mechanism. However, it is well established that the masonry mechanical properties are also relevant for the global mechanical performance of the structural masonry walls. Masonry units for load-bearing walls are usually laid so that their perforations are vertically oriented, whereas for partition walls, brick units with horizontal perforation are mostly adopted

Study of the behaviour of reinforced masonry wallets subjected to diagonal compression through numerical modelling

Shear walls are subjected to flexure and shear efforts in conjunction with compressive stresses associated to the gravity loads. In shear mode, diagonal cracks develop at the unit-mortar interface or both at the unit-mortar interface and through units as result of a biaxial tension-compression stress state, which in unreinforced masonry generally mean the collapse. The brittle failures of unreinforced masonry shear walls, which are more remarkable with high axial loads, may be prevented by the use of steel reinforcement. Diagonal compression tests allow obtaining a good prediction of the tensile strength of masonry walls in this biaxial tension-compression stress state. This paper aims to study the behaviour of reinforced masonry in diagonal compression tests through numerical modelling. A series of diagonal compression tests carried out on concrete block masonry with distinct types of reinforcement’s arrangements are modelled using the software DIANA®. Results indicate that horizontal and vertical reinforcements applied in conjunct provide an increase on the shear strength and ductility. On the other hand, the application of horizontal reinforcements alone leads only to an increase of ductility

Assessment of the flexural behavior of concrete block masonry beams

This paper focus on the experimental flexural behavior of masonry beams. In the sequence of the development of a novel structural solution for reinforced masonry walls at University of Minho, different possibilities for the construction of lintels with concrete block masonry have been tested. Reinforced concrete beams with three and two hollow cell concrete blocks and with different reinforcement ratios have been built and tested in a four point loading test configuration. It was clear that horizontal bed joint reinforcement increased the ultimate flexure capacity as well as the ultimate deflection, leading to much more ductile responses. Moreover, it was also clear that a more deep analysis should be made regarding the role of the compressive strength of masonry in the parallel direction to the bed joints on the global behavior of the masonry beams.This work was partly supported by contract DISWALL – “Development of innovative systems for reinforced masonry walls” – COOP-CT-2005-018120 from the European Commission. The first author was supported by the Programme AlBan, the European Union Programme of High Level Scholarships for Latin America, Scholarship nº E06D100148BR

Influence of the geometry of units and of the filling of vertical joints in the compressive and tensile strength of masonry

Attention is given to the mechanical properties of concrete block masonry, with respect to its compressive and tensile strength. These properties are important parameters in the in-plane lateral behaviour of masonry walls, determining their resistance and ductility. Such properties play also a central role when analytical and numerical analysis is used for simulating or predicting the behaviour of masonry structures. The influence of two selected parameters on the mechanical properties of masonry is discussed, namely the geometry of the units and the filling of the vertical joints. Results show that masonry under compression behaves as a homogeneous material and the stress-strain diagrams can be represented by a parabola similarly to what is suggested for structural concrete. in case of tensile strength, filling of vertical joints appears to influence considerably the tensile strength. The filling of the vertical joints increased the strength but lead to a more brittle behaviour.The first author was supported by the Programme Alβan, the European Union Programme of High Level Scholarships for Latin America, Scholarship nº E06D100148BR