Performance of autoclaved aerated-concrete masonry walls in Kuwait

The masonry walls used in building construction in Kuwait are non-load bearing. Traditionally, normalweight concrete blocks have been used throughout the region. However, with the enforcement of the Kuwaiti energy conservation code, autoclaved aerated-concrete blocks were introduced in 1985 as an efficient masonry material that can provide the necessary thermal insulation properties without the use of specific thermal insulation materials. This paper discusses the influence of material properties and specific construction practices on the performance of aerated-concrete-block walls. The provision of a partial movement joint through the use of sand-cement mortar, in place of higher strength epoxy glue mortar in the construction of wall and column intersections, reduced cracking in the immediate vicinity of the intersections. Studies are ongoing to recommend more effective measures for allowing greater movement at the wall and column intersections, thereby eliminating wall cracking due to restraint of movement.     

Strength and elasticity of brick masonry prisms and wallettes under compression

The characteristics of brick masonry are influenced by the properties of bricks and mortar. This paper attempts at studying the properties of brick masonry using table moulded bricks and wire-cut bricks of India with various types of mortars. The strength and elastic modulus of brick masonry under compression have been evaluated for strong-brick soft-mortar and soft-brick strong-mortar combinations. Various sizes of prisms and wallettes have been tested during these experiments to study the size effect and different bonding arrangements. The failure mechanisms of such specimens have been studied. Attempts are also made to derive empirical relationships for masonry strength as a function of brick and mortar strength in the Indian context.     

Micro VS. Macro Reinforcement of Brickwork Masonry

In this paper the effect of different modifications of mortar on the behaviour of brick masonry has been experimentally studied. Two modifications of ordinary cement lime rich mortar were made by introducing polypropylene fibres (micro reinforcement) and by reinforcing mortar bed joints by means of non-metallic meshes (macro reinforcement). Experimental tests were carried on the constituents of the masonry, as well as on masonry specimens consisting of wallettes and panels. Following different methodologies of testing masonry by means of compressive, diagonal and shear tests, the results of the investigation revealed that by reinforcing masonry material both compressive and tensile (shear) strength could be improved. Also from the results of the different test methods, it has been concluded that diagonal tests are not suitable for investigations of reinforced masonry.     

The bending strength of masonry / Biegezugfestigkeit von Mauerwerk

Bending strength of masonry becomes an important design aspect especially when the walls subjected to lateral loads like, cellar walls which are subject to earth pressure, and façades/ infill walls which are exposed to the wind actions. Bending strength is required wherever the applied load is perpendicular to the wall. It is also required in non‐load‐bearing partition walls, where the load applied in both the normal and perpendicular directions. Besides, the tensile properties of the brick/block and lengthwise parameters related to geometry and materials technology also influence the bending strength of masonry. These include the thickness of the wall, the extent of overlap, and both the shear and the tensile strength of the bond. Consideration must also be given to the possible presence of mortar in the head joints, which can significantly increase bending strength, especially where joints fail. In addition to these materials technology factors, it is very important to observe the realistic influence of the boundary conditions. The degree of fixity is among the factors to be considered in calculation models. In this contribution, two aspects are going to be observed and analysed, namely: the principles of bearing capacity under lateral loading alongside the models derived from these for cellar walls and areas of infill; and the influence of materials technology/geometric parameters on the bending strength of masonry.     

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.     

我国农村典型砖砌体墙片拟静力试验研究

农村房屋抗震是我国防震减灾工作的重要内容。砖砌体结构作为农村房屋的主要结构形式,如何提高其抗震能力具有重要研究意义。为研究砂浆强度、构造措施和窗洞口对砖砌体抗震性能的影响,该文首先对农村砖砌体房屋常用的几种砂浆和砖砌体进行了抗压强度试验,得到了相应材料及构件的强度参数;然后对不同砂浆强度、不同构造措施和开洞的12个墙片进行了拟静力试验,对比分析了不同因素对墙体力学性能影响。试验结果表明,砂浆强度影响最大,构造措施和开洞影响次之。最后依据试验分析结果为我国农居防震减灾工作提出建议。该文相关研究可为农居的抗震设防、标准制定以及施工提供参考。     

The effects of pre and post construction moisture condition on the in-plane and out-of-plane strengths of brick walls

An important factor affecting the strength of a masonry wall is the capacity of the bond between the mortar and the bricks to transfer the loads within the wall. The main parameter influencing the bond strength is the moisture content of the brick units and the consistency of mortar paste at the time of construction. Another important, but little known, factor is the post-construction moisture curing of the wall. In this paper, the results of a series of standard tests, aimed at determining the effects of moisture condition on the flexural strength, direct tensile bond strength, shear bond strength, compressive strength and diagonal shear strength of brick masonry are presented. The results indicate a substantial increase in the bond strength when saturated, surface dry, brick units are used and show the favorable effects of post-construction water curing of brickwork. Also, in-plane shear and out-of-plane bending tests are carried out on a number of brick wallets and infills, constructed with different pre and post construction moisture conditions and results are compared to drive at quantitative conclusions on the effects of pre-wetting the brick units at the time of construction and post-construction moisture curing on the behavior and strength properties of brick wall construction.     

高延性混凝土加固无筋砖墙抗震性能试验研究与承载力分析

为研究高延性混凝土(HDC)加固无筋砖墙的抗震性能,设计制作了3片HDC面层加固砖墙、1片钢筋网水泥砂浆面层加固砖墙和1片作为对比试件的未加固砖墙,通过拟静力试验,研究了HDC面层加固砖墙的破坏形态、滞回性能及耗能能力。试验结果表明:HDC面层可对墙体形成约束作用,延缓墙体开裂并改变墙体的破坏模式,提高墙体的承载力和延性;与钢筋网水泥砂浆面层加固相比,单面HDC加固的墙体开裂荷载与耗能能力明显提高,承载力下降缓慢。针对试件的破坏形态,考虑未开裂区加固面层对墙体水平承载力的贡献,提出了加固墙体的承载力计算方法,并根据试验结果进行了验证。     

Flexural bond strength of masonry using various blocks and mortars

This paper deals with an experimental study on flexural bond strength of masonry using various blocks in combination with different mortars. Flexural bond strength of masonry has been determined by testing stack-bonded prisms using a modified bond wrench test set-up. The effect of mortar composition and strength on the masonry's flexural bond strength using three types of masonry units (stabilized mud blocks, stabilized soil-sand blocks and burnt brick) has been examined. The effect of the masonry unit's moisture content on flexural bond strength has also been studied. Increases in mortar strength lead to increased flexural bond strength for cement mortar, irrespective of the type of masonry unit. It has been found that combination mortars, such as soil-cement mortar and cement-lime mortar, lead to better bond strength compared to cement mortars. The moisture content of the masonry unit at the time of casting has displayed significant influence on the flexural bond strength of the masonry. It has been found that for each type of masonry unit, an optimum moisture content exists, beyond which the flexural bond strength falls off quickly.     

Bond behaviour of a textile‐reinforced mortar for AAC masonry

The bond behaviour of a textile reinforced mortar (TRM) applied to autoclaved aerated concrete (AAC) masonry has been evaluated experimentally. The TRM is composed of a glass‐fibre mesh combined with a cementitious mortar and is intended to strengthen AAC masonry walls subjected to out‐of‐plane bending during an earthquake. The main components have been characterized with preliminary tests. Then, pull‐off and shear bond tests have been performed to determine the bonding properties of the TRM applied to the AAC substrate. Three types of AAC blocks have been used, which differ in the bulk density and compressive strength, to evaluate possible variation in the bond strength. The results of the experimental campaign have shown a good performance of the strengthening system. In most cases, the bonding between TRM and masonry was maintained up to tensile failure of the dry textile. As expected, the masonry samples realized using AAC blocks with a higher bulk density showed better performances. The paper presents and discusses main test results, providing background data for future recommendations for the use of the analysed strengthening system in AAC masonry structures.     

藏式石砌体在剪-压复合作用下抗剪性能研究

为研究藏式石砌体抗剪性能,对4组共13个不同压力作用下的泥浆砌筑石墙试件进行双剪试验,分析藏式石砌体沿通缝抗剪强度和破坏机理,研究利用灰缝抗剪强度评估墙体整体抗剪性能的方法。试验结果表明,藏式石砌体灰缝受剪破坏为泥浆层自身变形与界面分离同步发展的延性破坏过程,最终达到完全的界面剪切滑移状态。通过对试验数据的统计回归提出藏式石砌体灰缝的抗剪强度计算公式,计算结果和试验值吻合程度较好。泥浆与水硬性砂浆的主要性能差别在于粘结强度和摩擦系数均较低。通过2种理论模型,分析了砌体灰缝抗剪强度与剪-压复合作用下抗剪强度表达式之间的关系,利用其他研究者的试验数据进行了验证。提出了基于双剪试验结果的藏式石砌体抗剪强度预测表达式,可供藏式石砌体抗剪性能研究参考。     

A comparative study on the approximate analysis of masonry structures

In this paper, numerical analysis of structural masonry subject to a uniform in-plane tensile stress/strain field is investigated employing various homogenisation techniques. Here, structural masonry is regarded as a composite material with brick, bed joints and head joints as its constituents. Assuming a perfect bonding between constituents. Assuming a perfect bonding between constituent materials, two homogenisation techniques based on the strain energy approach are applied to derive equivalent elastic moduli of masonry. Structural relationships for the constituent materials are next derived to relate strains and stresses in constituents to the average strains and stresses in the masonry. In addition, a slightly different concept of the homogenisation technique based on Eshelby's solution of the ellipsoidal inclusion problem is also applied to compare the results with the energy based methods. The tensile strength of the masonry is found on the basis of the failure of any of the constituent materials. It is shown that tensile strength is a function of the elastic parameters of brick/mortar as well as the tensile strength of mortar. These studies also show that, although initial cracking occurs under horizontal tensile forces, the ultimate strength of the panel is higher in this direction than in the vertical direction.     

Reinforced bending load‐stressed masonry – Suggestions for future designs / Bewehrtes biegedruckbeanspruchtes Mauerwerk – Vorschläge für zukünftige Bemessungen

European standardization bodies are currently working on the amendment to EN 1996‐1‐1, which will also affect the evaluation of reinforced masonry in Germany. For that reason, discussion suggestions are being made here for revisions to lay the groundwork for building materials evaluations and especially, evaluations of bending load‐stressed masonry walls or beams at their serviceability limit state (SLS) for load‐bearing capacities. Information already presented in E DIN 1053‐3:2008‐03 [N3] is being incorporated as well. Characteristic values for the compressive strength of the masonry parallel to the bed joints f_k,∥ are essential for the design of reinforced masonry, although they are currently not included in national application documents for Germany. For the time being, they can be mathematically calculated using conversion factors for the characteristic compressive strength values vertical to the bed joints f_k or by using the declared axial compressive strengths of the masonry units. The ultimate strains for masonry in general should be set consistently at ?_mu = ∣–0.002∣ as several masonry types do not exhibit higher compressive strain values. The use of steel strains higher than ?_su = 0.005 does not change any measurement results. Varying stress‐strain curves of the constitutive equations on masonry under compressive strain (parabolic, parabolic‐rectangular, tension block) lead to differing values of recordable bending moments despite having the same mechanical reinforcement percentage at higher normal forces. Therefore, clear guidelines should be made for the type of applicable constitutive equation for masonry walls under compressive strain. With the introduction of a tension block, the number values of the reduction factors λ for the compression zone height x, which is dependent on limit strains, and where applicable, reduced compressive strength, need to be determined, as with reinforced concrete construction. A modification of the bending moment based on the second order theory according to [N4] is presented for the calculation of reinforced masonry walls in danger of buckling. The use of reduction factors for the load capacity of the masonry cross section, such as for unreinforced masonry, does not appear to be appropriate as buckling safety evidence because here, the design task is the determination of a required reinforcement cross section.     

碱矿渣陶粒混凝土砌块砌体受压本构关系

为考察碱矿渣陶粒混凝土砌块砌体的受压本构关系及基本力学性能,完成了126个用碱矿渣陶砂砂浆和碱矿渣陶粒混凝土砌块砌筑的砌体试件的轴心抗压试验。研究结果表明:当砌块抗压强度和砌筑砂浆抗压强度相同时,由于碱矿渣陶砂砂浆收缩大,该类砌体的峰值压应变、极限压应变均低于普通混凝土砌块砌体。建立了以砌体抗压强度、砌块抗压强度和砌筑砂浆抗压强度为自变量的这类新型砌体峰值压应变、极限压应变以及弹性模量计算公式。     

Textile reinforcement in the bed joint of basement masonry – First findings from a current research project

The successful structural verification of basement walls under earth pressure loading with light imposed loading is often difficult. This situation is often encountered for external basement walls under terrace doors, stairs, masonry light wells etc., where the theoretically necessary imposed loading is missing. This makes it impossible to resist the acting bending forces from earth pressure using a vertical arch model. In such cases, the earth pressure has to be resisted in a horizontal direction. Since however the bending moment capacity of unreinforced masonry parallel to the bed joint is low, another possibility is to use a textile‐reinforced bed joint with longitudinal fibres of alkali‐resistant glass or carbon fibre. With an appropriately adapted textile reinforcement in the bed joints, the masonry can fulfil the requirements for load‐bearing capacity against earth pressure with horizontal load transfer, even under a small imposed load. Textile reinforcement has the advantage above all of corrosion resistance compared to conventional steel reinforcement, and textiles can also be inserted into thin bed joints. The Chair of Structural Design in the Faculty of Architecture of the TU Dresden is currently carrying out extensive numerical and experimental studies for this purpose. The objective is to develop an optimal configuration of material and textile form for use as bed joint reinforcement. The investigations are concentrating on the tension strength, bonding and durability of the composite material ”textile mortar“. This report should give a brief overview of the state of the work in the currently running research project.     

Behavior of unreinforced masonry prisms and beams retrofitted with engineered cementitious composites

The impact of a thin layer of a ductile fiber-reinforced concrete referred to as engineered cementitious composites (ECC) on unreinforced masonry (URM) prisms and beams has been evaluated. The objective of the research was to characterize the performance and potential benefits of using ECC to retrofit URM with eventual application to masonry infill walls in non-ductile reinforced concrete frames. Compression tests of masonry prisms and flexural tests of masonry beams with different ECC retrofit schemes were conducted. The variables studied were the use of wall anchors to improve the ECC-masonry bond and alternate steel reinforcement ratios within the ECC layer in the form of welded wire fabric. The ECC retrofit was found to increase the strength and stiffness of URM prisms by 45 and 53 %, respectively compared to those of a plain specimen. When wall anchors were installed on the masonry specimens, the bond between the ECC layer and the masonry surface was improved. Four-point bending tests indicated that the strength and more importantly the ductility of an ECC retrofitted brick beam are increased significantly, especially when light reinforcement is added to the ECC layer, relative to an URM beam. Analytical models for estimating the strength and stiffness of ECC retrofitted masonry specimens are proposed and evaluated.     

Low-velocity flexural impact response of fiber-reinforced aerated concrete

Impact response of fiber-reinforced aerated concrete was investigated under a three-point bending configuration based on free-fall of an instrumented impact device. Two types of aerated concrete: plain autoclaved aerated concrete (AAC) and polymeric fiber-reinforced aerated concrete (FRAC) were tested. Comparisons were made in terms of stiffness, flexural strength, deformation capacity and energy absorption capacity. The effect of impact energy on the mechanical properties was investigated for various drop heights and different specimen sizes. It was observed that dynamic flexural strength under impact was more than 1.5 times higher than the static flexural strength. Both materials showed similar flexural load carrying capacity under impact, however, use of 0.5% volume fraction of polypropylene fibers resulted in more than three times higher flexural toughness. The performed instrumented impact test was found to be a good method for quantifying the impact resistance of cement-based materials such as aerated concrete masonry products.     

Model validation and parametric study on the blast response of unreinforced brick masonry walls

Numerical simulations are carried out to estimate the response and damage of unreinforced brick masonry walls subjected to explosive blast loading based on the transient dynamic finite element program LS-DYNA. A previously developed dynamic plastic damage model was used for brick and mortar. A new model for strain rate effects of bricks and mortar is included in the numerical analysis. The results obtained from the numerical models are compared with field test data and good agreement can be found. Parametric studies are conducted to evaluate the effect of material strength, boundary conditions, and thickness of the wall on the blast response of unreinforced brick masonry walls. It was found that boundary conditions and wall thickness significantly affect the blast response, while the effect of material strength is relatively small.     

Compressive strength and elasticity of pure lime mortar masonry

The procedure and findings of an experimental campaign for the mechanical characterization of brick masonry with lime mortar joints are presented. The campaign includes the determination of the properties of the constituent materials and of the resulting masonry composite. The masonry consisted of masonry stack bond prisms made of solid clay bricks and two types of pure lime/sand mortars, material combinations which correspond to the vast majority of historical and existing masonry structures. The paper includes a discussion on the ratio between the elastic modulus and the compressive strength of the masonry constituents and the comparison of these ratios with the ones suggested in design codes. The implications of this comparison are discussed in the context of interventions on historical masonry structures using modern and traditional materials.     

Numerical derivation of homogenized dynamic masonry material properties with strain rate effects

Masonry is a composite material composed of bricks and mortar disposed in a regular arrangement. It is commonly used as load bearing or partition walls in building structures. Owing to limitations of computer power, detailed distinctive modelling of brick and mortar of a realistic masonry structure or a structure with masonry infilled walls is usually not possible. Moreover, no dynamic masonry material model can be found in the open literature. Dynamic masonry material properties are important for an accurate prediction of masonry failure and fragmentation under dynamic loads. In this paper, a continuum damage model with strain rate effect is developed for masonry materials based on the homogenization method. The equivalent elastic properties, strength envelope and dynamic increase factors (DIFs) of strength and moduli for the homogenized masonry material are numerically derived from the simulated responses of a representative volume element (RVE). A numerical model of an RVE is analyzed with detailed distinctive modelling of brick and mortar with their respective dynamic material properties obtained from laboratory tests. The homogenized material model can be used to analyse large-scale masonry structures subjected to dynamic loading.