Behavior and modeling of strengthened three-leaf stone masonry walls

The application of three different intervention techniques on three-leaf rubble stone masonry walls are discussed here. Injections, repointing, and the placing of ties connecting the two external whytes were considered, both singularly and in combination. Lime-based products were chosen for injection grouts and repair mortars, to ensure better compatibility with the original materials. The experimental tests, performed on seventeen large scale samples under compressive loads, showed that: (i) injections are very effective to improve the mechanical characteristics of the walls; (ii) the other techniques have less influence on the strength but can operate in avoiding ‘brittle’ failure modes (ties placing) and in improving the durability of the masonry (repointing); (iii) the combination of the techniques ensures the enhancement of the global behavior of the walls. The integration of the experimental results with data available in literature allowed the calibration of an analytical model able to predict the compressive strength of injected walls, based on parameters given by simple experimental tests.     

Strengthening of three-leaf stone masonry walls: an experimental research

The paper summarizes the results of an experimental research carried out on three-leaf masonry walls of typical granite stone constructions from the North of Portugal. The research aimed at studying the behaviour under compression of this wall typology, as well as the improvements introduced by common strengthening techniques applied for the structural rehabilitation of masonry heritage buildings. Ten masonry specimens were tested, plain or strengthened by transversal tying of the external leaves, with GFRP bars, or/and by injection of the inner leaf, with a lime-based grout. The results obtained showed that these strengthening techniques were successful in increasing the compressive strength of the walls and in improving their behaviour under compressive loads.     

Experimental study of dry stone masonry walls using digital reflection photoelasticity

Response of dry stack stone masonry walls under mechanical loading is complex and difficult to determine, mainly due to heterogeneous and discrete nature of the components of the stone wall. In this paper, reflection photoelasticity is used on scaled down models of stone masonry wall under uniaxial compression. Two walls are tested, and the methods to obtain near perfect dry stack masonry for reflection photoelastic studies are presented. Five-step phase-shifting methods are employed with TFP/RGB photoelasticity to quantitatively analyse the mechanical behaviour of the dry stack masonry walls. Isochromatics and isoclinic data are processed to obtain other whole field experimental stress data. Highly stressed zones are observed resulting in distinctive localised vertical failure in some of the stone units. In dry stack masonry construction, the failure mechanism is found to be dictated by the contact mechanics, which are governed by the non-uniformity of block geometry even in very regular dry stack masonry.     

老旧砌石拱坝的结构安全度研究

依据现行《砌石坝设计规范》(SL25—2006)的坝体拉压应力的控制准则去评估砌体胶凝材料已老化劣化的小型砌石拱坝的结构安全度,往往无法得出符合定性判断的结论,因此须研究新的分析和评估方法.基于非线性多拱梁法,采用ADAO(arch dam analysis and optimization,拱坝分析与优化)软件模拟分...     

Evaluation of the repair on multiple leaf stone masonry by acoustic emission

Aim of this research was to evaluate the possible application of the AE technique to study the response of multiple leaf masonry repaired with different techniques. The results of shear tests carried out on three specimens repaired after failure are presented on an explorative basis; on two of them the acoustic emission (AE) technique was also used. Through a number of sensors and by triangulation, this technique makes it possible to identify the location of the damage, unknown initially, and subsequently to assess the stability of its evolution. Using the AE technique the area of the material where the cracks propagated during shear tests was identified. These analyses made it possible to evaluate the effectiveness of repair interventions through parameters other than stress and strain, and contributed to the identification of the most suitable methodology for their optimisation.     

Local phenomena around a steel dowel embedded in a stone masonry wall

The study of the local behaviour of steel dowels used to transfer horizontal shear loads between concrete slabs and stone masonry walls has been carried out. Monotonic loading tests have been performed on six specimens of stone masonry made in the laboratory concerning three different embedding techniques for dowels. The geometric interferometry technique was adopted to survey the surface displacements, in the load direction, of the loaded stone block and surrounding mortar joints. For applying the shear load to the connection, a special experimental apparatus has been designed so as to allow the arrangement of moiré gratings as well as to capture the sequence of the fringe pattern.     

Laboratory studies of properties of the stone masonry in the Old Aswan Dam

The paper describes the results of mechanical and physical tests carried out on the masonry of the Old Aswan Dam for later assessment of its seismic stability and structural integrity. Mechanical tests were performed on 150 mm diameter cores obtained from various stages of construction of the dam. Tests indicate that the masonry in the first heightening exhibits higher strength characteristics than the masonry in the rest of the dam. Noticeably lower strength properties of the masonry in the second heightening were due to a higher water/cement ratio. The weakest link in the masonry of all three stages of construction from the point of view of its mechanical performance was the granite-mortar interfacial region. Analyses of test results show that the modulus of elasticity and the splitting tensile strength of the masonry may be expressed as a function of the compressive strength using the power regression equation and the logarithmic regression equation, respectively. The split cylinder test provides a more reliable measure of the tensile strength of the stone masonry than the direct tension test. In general, a wide scatter of test results in relation to the mean value appeared to be an inherent characteristic of this type of masonry. Variations were more pronounced in the case of the Poisson’s ratio test and in all instances when fracture at the horizontal mortar-stone interface was a primary mode of failure.     

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.     

The hygrometric behaviour of some artificial stone materials used as elements of masonry walls

The hygrometric behaviour of four artificial stone materials utilised in the building industry for thermal insulation has been investigated utilising analytical methods typical of the applied petrography. The experimental data on the water absorption both in the liquid and in the vapour phase are in agreement with the data obtained from the natural stone materials and point out the existence in each material of a strong correlation between the absorption mechanisms and the porosimetric characteristics.

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Résumé On a étudié, à l’aide de méthodes analytiques utilisées en pétrographie appliquée, le comportement hygrométrique de quatre matériaux pierreux artificiels utilisés dans l’industrie du batiment pour leurs propriétés d’isolants thermiques. Les données expérimentales sur l’absorption d’eau aussi bien à l’état liquide qu’à l’état de vapeur, sont en accord avec les données obtenues sur les matériaux pierreux naturels, c’est-à-dire que dans chaque matériel il y a de fortes corrélations entre les mécanismes d’absorption d’eau et les caractéristiques porosimétriques.

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Editorial Note The CNR (Consiglio Nazionale delle Ricerche) is a RILEM Titular Member. The University of Florence is a RILEM Associate Member.     

Stress rate sensitivity of stone masonry units bound with fibre reinforced hydraulic lime mortar

It is well established that most construction materials behave differently under static and dynamic loading. However, the literature on the time-dependent response of masonry joints is scarce, particularly with regard to the bond behaviour in historical stone masonry. This paper describes the dynamic response of sandstone masonry units bound with hydraulic lime mortars (HLMs). A drop weight impact machine was used to generate stress rates up to 10⁷ kPa/s. The dynamic impact factor and stress rate sensitivity were evaluated for the flexural strength of the sandstone, mortar and for the bond strength of the unit and further, the pattern of failure was noted in the units for each mortar mix and loading rate. Based on a related study on the fracture toughness of HLM, polypropylene micro-fibres were incorporated at 0, 0.25 and 0.5% volume fraction into the mortar. Results show that the flexural bond strength was more sensitive to stress rate than the flexural strength of the mortar, at similar rates of loading. Further, the stress rate sensitivity of the bond strength decreased with an increase in the fibre content. Also, whereas the mode of failure in the masonry units under quasi-static loading was through fracture at the mortar-block interface, the failure plane transferred to within the mortar under dynamic loading, particularly in the presence of fibre reinforcement.     

藏式石砌体受压应力-应变全曲线特征研究

石砌体结构的力学性能研究已经取得一定的成果,但很少有研究考虑构造的随机性对石砌体结构性能产生的影响。该文基于代表性体积单元(RVE单元),针对几何构造具有一定随机性的石砌体,提出了一种有效模量计算方法,并与文献的试验和数值模拟结果对比,证明了所得有效模量的准确性。分别根据该方法和有限尺度测试窗法,对比分析了藏式古建石砌体的有效模量,并探讨了RVE单元尺寸大小对有效模量的影响。最后提出了一个基于所得有效模量建立砌体整体式模型的建模方法,并与传统分离式建模和基于有限尺度窗口法的整体式建模进行对比分析。研究结果表明：该方法与有限尺度测试窗法所得有效模量的数值大小和变化趋势相近,但该方法弥补了有限尺度测试窗法不能获得泊松比的缺陷;RVE单元尺寸的增大,使得其组元分布逐渐向完整结构的组元分布接近,导致大部分的Voigt、Reuss有效模量分量呈现先快后慢的收敛趋势;单元尺寸变化对厚度方向的轴向模量几乎没有影响,对其他面外的模量分量影响较小,对面内的模量分量影响较大;基于该方法所建整体式模型,可以在节约计算成本的同时,较为精确复制分离式模型的宏观变形。     

Design and evaluation of hydraulic lime grouts for the strengthening of stone masonry historic structures

The present paper discusses an experimental procedure realized in order to design hydraulic lime based grouts adequate for the strengthening of stone masonry historic structures. With the aim to minimize incompatibility problems between the original materials and the grouts, several natural hydraulic lime based grouts, as well as a ternary (lime–pozzolan–cement) grout with reduced cement content, have been studied. The selection of the most suitable grouts was performed based on a set of criteria, namely injectability, mechanical and durability characteristics. The selected grouts were subsequently injected into cylindrical specimens that simulate the infill of three-leaf stone masonry. The experimental results obtained from mechanical tests carried out on the injected cylinders demonstrated that all grout mixes studied within this work were efficient in strengthening the infill material; they exhibited, however, differences in terms of durability properties. Finally, an empirical formula was developed to predict the compressive strength of the injected infill, as a function of the mechanical properties of grouts.     

Experimental tests on the shear behaviour of dowels connecting concrete slabs to stone masonry walls

An experimental investigation has been conducted on the behaviour of dowels used to connect concrete slabs to stone masonry walls in order to transfer horizontal shear forces. A technique for embedding the dowels in the stone block without injection of grouting material or resin has been developed. Special experimental equipment has been designed in order to allow the execution ofin situ load tests on representative ancient buildings. Monotonic loading tests have been carried out on eight specimens with the purpose of measuring both stone block displacement and dowel deformation     

Experimental study of traditional stone masonry under compressive load and comparison of results with design codes

This study addressed the mechanical behaviour of a natural stone masonry typical from the Spanish Romanesque, both in Heritage and conventional buildings. The objective of this research was to provide new data about the mechanical properties, especially the compressive strength values. The characterisation of the basic materials and different stone masonry prisms is presented. Sandstone and low strength lime-cement mortar were used for this experimental work, because of their availability and similarity with the masonry found in many historic buildings from the north of Spain. The morphological characteristics of the original ancient walls were also taken into account, in order to manufacture prism specimens that were as representative as possible of the Spanish Romanesque typology (i.e. in terms of its geometry, composition of the internal core, relative size, etc.). Additionally the experimental values were compared with the analytical ones provided by the main recommendations and standards. The analysis of the results permits a better understanding of these materials and a reliable source of data for the validation of the existing structures.     

Flexural strength characteristics of non-load bearing masonry walls in Kuwait

The controlling factor in designing non-load bearing masonry walls, such as those used in Kuwait, is the lateral resistance to wind loads. To ensure safety of the walls, data is needed on the flexural strength characteristics of walls constructed with locally-available materials. The flexural strength of masonry walls constructed with autoclaved aerated-concrete blocks, sand-cement concrete blocks or calcium silicate bricks was evaluated in a test program that involved testing small-scale walls or wallettes. The tests were performed in accordance with the British Standard for unreinforced masonry. The autoclaved aerated-concrete block wallettes were constructed with epoxy glue mortar, whereas the concrete block and calcium silicate brick walletters were constructed with sand-cement mortar. Two stages of testing were undertaken to evaluate bending parallel to bed joints and bending perpendicular to bed joints. The flexural strengths required by British and American codes exceed the strengths of the concrete block and calcium silicate brick walls used in Kuwait, implying that the allowable tensile stress requirements of these codes are not safe for assessing the lateral resistance of the walls. The format used for the autoclaved aerated-concrete block wallters, which is identical to the standardized format for concrete block wallettes in the British standard, is suitable for determining the flexural strength of full-size autoclaved aerated-concrete block walls.     

Strength characteristics of coatings in electric-arc metallization

The adhesive and cohesive strengths of powder-wire metal coatings as functions of the technological parameters in electric-arc metallization are investigated experimentally.     

石粉粉磨时间与其颗粒分布特性的相关性

选取大理石和白云石粉为材料,测试其不同粉磨时间的粒径分布,计算勃氏比表面积;粒径分布模型采用RosinRammler-Bennet(RRB)方程进行拟合,运用粉磨动力学和线性回归方法分析粉磨过程石粉的特征粒径、均匀性系数和比表面积。结果表明:随粉磨时间增加,粒径为0~10μm的颗粒逐渐增加,大于10μm的颗粒逐渐减少,两者粉磨效率随时间增加逐渐减小;相同时间时,大理石粉的高于白云石粉的;随时间增加,大理石粉均匀性系数增大,颗粒集中现象增多,白云石粉则相反;两者的比表面积和特征粒径与其粉磨时间呈对数和双对数相关。