Rubble Stone Masonry Walls Strengthened by Three-Dimensional Steel Ties and Textile-Reinforced Mortar Render,Under Compression and Shear Loads

This article addresses the results of a structural strengthening solution for rubble stone masonry walls. The strengthening includes inserting three-dimensional steel ties across the thickness of the walls and a 30-mm layer of air-lime and cement mortar render reinforced with glass fiber mesh (textile-reinforced mortar), on both sides of the wall. The strengthening solution was found to be efficient for rehabilitating ancient rubble stone masonry walls due to the “three-dimensional” confinement, provided by the steel wires, by offsetting the low cohesive capacity of the mortar used in the walls and thus improving the mechanical resistance and delaying the collapse mechanisms. This study is part of an experimental research program carried out in Universidade Nova de Lisboa, to evaluate structural strengthening solutions for ancient rubble stone masonry buildings. To this end, three specimens of rubble stone masonry walls without strengthening (unreinforced masonry) and other three, with the mentioned strengthening solution, were subjected to compression and shear load tests. Building materials were also tested in order to characterize physical, chemical and mechanical properties.     

A MICROMECHANICAL INELASTIC MODEL FOR HISTORICAL MASONRY

A micromechanical damage model for the Snite element modelling of historical masonry structures is presented in this article. Masonry is considered as a composite medium made up of a periodic assembly of blocks connected by orthogonal bed and head mortar joints. The constitutive equations, in plane stress, are based on the homogenisation theory and they consider the non linear stress-strain relationship in terms of mean stress and mean strain. Different in-plane damage mechanisms, involving both mortar and blocks, are considered and the damage process is governed by evolution laws based on an energetic approach derived from Fracture Mechanics and on a non-associated Coulomb friction law. The failure domain of the model is analysed both in the equivalent stress and in the principal stress space considering different orientations of the bed joints relative to the loading direction. A comparison with experimental results is provided. A numerical simulation of masonry walls subjected to horizontal forces proportional to their own weight is shown in order to discuss the model's capability of describing the influence of the masonry microstructure on its mechanical behaviour.     

Experimental analysis of rubble stone masonry walls strengthened by transverse confinement under compression and compression-shear loadings

Stone masonry walls of ancient buildings have reasonable resistance to vertical loads but lower resistance to shear forces and reduced tensile strength. However, to achieve such compressive strength the masonry must not disaggregate when subjected to loading. This can be achieved if during the construction of the walls larger stones, usually referred as “through stones”, are used, spanning the thickness of the wall, making it possible to improve the transverse confinement of the masonry. For rehabilitation projects and structural reinforcement of such buildings, the transverse confinement can be achieved by fixing steel elements perpendicular to the wall. This confinement technique is often part of a more comprehensive rehabilitation solution, which includes the application of mortar or concrete reinforced layers applied to the wall surface.

This article presents results of an experimental research on material properties and mechanical characterisation of stone masonry specimens strengthened by two transverse confinement solutions (independent steel reinforcing rods and continuous steel ribbons wrapping the specimen). Specimens were tested under compression and compression and shear loadings.

This experimental work is part of a major research project to study the mechanical behavior of URM and strengthened walls, and the characteristics of the building materials of such specimens.     

In Situ Flat-Jack Testing of Traditional Masonry Walls: Case Study of the Old City Center of Coimbra,Portugal

Single and double flat-jack tests are presently used widely for assessing the mechanical characteristics of stone masonry. This technique remains as one of the most versatile in situ test procedure for the estimation of the main mechanical properties of masonry walls. Nevertheless their application is still controversial due to the difficulty of accepting in some cases the results as reliable. This article presents and discusses the results of an experimental campaign resorting to flat-jack technique carried out with the scope of the rehabilitation process of the historical city center of Coimbra.     

中国古代砖砌体力学性能研究综述

古代砖砌体建筑由于材料劣化、环境影响,材料特性及力学性能均受到不同程度的影响和损伤,为了保护历史文化的载体,结合古建筑材料获取原始且必要的数据,系统总结了古砖、传统灰浆的制备工艺和材料性能,简要归纳了古砖、传统灰浆和古砖砌体基本力学性能及其测试方法,对比分析了单砖和砌体抗压强度的差异以及古建筑砌体材料力学性能研究现状。并对今后古砌体如弹性模量等力学性能、古砌体材料及结构的损伤机理等的研究提出了展望或建议,可为砖石古建筑的修缮保护提供参考依据。     

Mineralogical and Mechanical Properties of Masonry and Mortars of the Lucknow Monuments Circa the 18th Century

The Lucknow monuments of the 18th century are large masonry structures built using thin burnt-clay bricks (Lakhauri) and lime-crushed brick aggregate (surkhi) mortars. Investigations were carried out to characterize the engineering properties of old masonry materials and new mortars being used for renovation work. Mechanical properties of reclaimed Lakhauri bricks were found comparable to good quality contemporary bricks of the region. Moreover, X-ray diffraction (XRD) and scanning electron microscopy–energy dispersive X-ray spectrometry (SEM-EDS) analyses indicated that mineralogical composition is not too different, except for few minerals. The lime-surkhi mortar used in old masonry work was found to be lime-rich with binder to aggregate ratio of approximately 1:2 to 3 by volume. The renovation mortar had poor hydraulic property as compared to old mortars indicated by thermal gravimetric analysis–differential thermal analysis (TGA-DTA) analyses. The compressive behavior of multi-wythe recreated Lakhauri masonry prisms was characterized with low compressive strength, low modulus, and significant deformability which result in lower stress demands imposed on the structural assemblages by various environmental forces.     

Material Characterization and Micro-Modeling of a Historic Brick Masonry Pillar

A masonry pillar composed of solid clay bricks, cement mortar and infill is extracted from a historical structure and tested in concentric compression. It is subjected to cyclic and monotonic loads up to compressive failure.

In parallel, samples are extracted from the pillar and are subjected to destructive tests. Non-destructive tests are performed on the pillar, as well. The properties of the constituent materials are critically examined and their role in the maximum load reached and the failure mode obtained are discussed.

Finally, a finite element micro-model of the pillar is used for the simulation of the pillar test. The influence of the existing damage on the pillar is investigated using the model, resulting in a fair approximation of the global Young’s modulus, maximum load and the failure mode.

Highlights

●?A brick masonry pillar extracted from a historical building is tested in compression.

●?Material samples extracted from the pillar are characterized by mechanical tests.

●?A finite element micro-model of the pillar is used for the simulation of the compressive test.

●?The effect of damage on the compressive strength of the pillar is numerically investigated.     

Assessment of Construction Techniques and Material Usage in İzmir Rural Houses

The domestic architecture in the rural villages of ?zmir comprises a unique built environment with their masonry wall textures, semi-open sofas, round tiled-hipped roofs, and chimneys, and represents an important part of the cultural and architectural heritage. This assessment is mainly based on field observations that focus on the architectural and structural layout of intact, damaged, and destroyed houses. During field observation and the analysis of data certain plan typologies and relationships between the geological formations of the region and choice of materials and construction techniques were observed. While load-bearing masonry and timber skeleton systems are common, extensive use of timber laces, stone, and fired or adobe brick masonry with mud mortar and timber frames infilled with masonry materials were frequently seen. Generally, round timber elements such as wall plates, laces, lintels, posts, and frames of flooring systems are used. Architectural degenerations in authentic houses, defective details and partially due to the earthquake-prone nature of the region seismicity have been evaluated. An overall approach for the preservation and sustainability of this heritage is suggested.     

Characterization of pozzolanic lime mortars used as filling material in shaped grooves for restoring member connections in ancient monuments

This article presents a set of mechanical characteristics for a pozzolanic mortar consisting of hydrated lime and metakaolin, which is used as filler between metallic connectors and marble blocks during restoration activities of ancient monuments in Greece. Mechanical properties include the uniaxial and triaxial compressive strength, the indirect tensile strength, the bending strength, the elastic modulus and Poisson’s ratio, and a shear failure criterion. Cored cylindrical specimens are used for determining the uniaxial and triaxial compressive behavior and the indirect tensile strength of the mortar, thus ensuring the repeatability of the experimental results. The triaxial tests indicated a plastic behavior of the mortars under study, enabling them to perform well in conditions of high shear forces. Calcite and hydraulic components formed in the setting procedure contributed to the plasticity of the final mortar. The mechanical properties that were developed can be utilized to model material behavior and failure under conditions of confined or triaxial loading. The development of a shear failure criterion for a pozzolanic mortar is a substantial accomplishment that has not been previously reported in the international literature.     

Damage Assessment of Unreinforced Stone Masonry Buildings After the 2010–2011 Canterbury Earthquakes

The sequence of earthquakes that has affected Christchurch and Canterbury since September 2010 has caused damage to a great number of buildings of all construction types. Following post-event damage surveys performed between April 2011 and June 2011, an inventory of the stone masonry buildings in Christchurch and surrounding areas was carried out in order to assemble a database containing the characteristic features of the building stock, as a basis for studying the vulnerability factors that might have influenced the seismic performance of the stone masonry building stock during the Canterbury earthquake sequence. The damage suffered by unreinforced stone masonry buildings is reported and different types of observed failures are described using a specific survey procedure currently in use in Italy. The observed performance of seismic retrofit interventions applied to stone masonry buildings is also described, as an understanding of the seismic response of these interventions is of fundamental importance for assessing the utility of such strengthening techniques when applied to unreinforced stone masonry structures.     

Experimental Characterization of Ancient Metal Tie-Rods in Historic Masonry Buildings

Metal tie-rods play a decisive role in the control of horizontal thrusts in historic masonry buildings. The main goal of the present study is to investigate the relationship between metallurgical and mechanical properties of original tie-rods in order to contribute to a wider study on ancient building stability and their restoration protocols. This article presents the results of an experimental test campaign carried out on 14 historic tie-rods (dating back from 16^th–19^th century) recovered from restoration works or building demolitions. Stress-strain mechanical tests showed that the elastic modulus of the material is comparable to that of modern structural steel, while the strength and the elongation capability are significantly lower, with a large scatter. Further analyses based on metallography allowed us to assess that this mechanical behavior depends on the heterogeneous nature of the material, which can eventually be compared to a composite with vitreous elongated particles in a ferritic or ferrito-pearlitic matrix. The origin of such metallurgical condition is related to the iron making based on direct smelting from ores.     

OUT-OF-PLANE SEISMIC RESISTANCE OF MASONRY WALLS

Seismic vulnerability of unreinforced masonry buildings is studied by means of simplified out-of-plane collapse mechanisms that take into account connections with transversal walls. According to experimental evidence, the analysis assumes that failure is reached with a rigid body motion of a part of the facade that falls down. Two classes of mechanism are examined: the overturning of the facade due either to a vertical crack at the connection or a diagonal crack on the transversal wall, both defined resorting to a simple model of masonry fabric, viewed as a regular assembly of rigid blocks and elastic plastic joints with friction but no cohesion. The use of simplified mechanisms give rise to an explicit evaluation of the seismic resistance to changes in the geometry and in the masonry fabrics, that could be used by practising engineers. This formulation is developed for both static horizontal actions and ground velocity peak, in the belief that the latter probably gives a better approximation of seismic action, while also providing, by comparison with the results of static forces, an estimate of the behaviour factor for unreinforced masonry. Eventually, the analytical forecasts are compared with numerical results obtained by means of the distinct element method.     

Determination of Shear Strength of Masonry Panels Through Different Tests

This study addresses the problem of evaluation of strength of masonry walls. In-plane behavior of masonry panels has been studied under monotonic diagonal-compression and shear-compression loading in quasi-static test facility. The results of 35 laboratory and in situ tests are analyzed to show that in the case of the diagonal compression test results are lower than the strength of masonry walls evaluated trough the shear-compression test, highlighting the problem of choosing the test which best simulates to the real behavior of the masonry when stressed by lateral loads. A presentation is also given of the results of a F.E. investigation for shear strength evaluation of masonry walls. F.E. modeling non-linear procedure was used for the representation of masonry panels. The numerical simulations are compared with experimental results and the reliability of the different finite element models is discussed, thus confirming the different shear strength values measured in the experimental campaign.     

Contact Dynamics of Masonry Block Structures Using Mathematical Programming

A simple variational formulation for contact dynamics is adopted to investigate the dynamic behavior of planar masonry block structures subjected to seismic events. The numerical model is a two-dimensional assemblage of rigid blocks interacting at potential contact points located at the vertices of the interfaces. A no-tension and associative frictional behavior with infinite compressive strength is considered for joints. The dynamic contact problem is formulated as a quadratic programming problem (QP) and an iterative procedure is implemented for time integration. Applications to analytical and numerical case studies are presented for validation. Comparisons with the experimental results of a masonry wall under free rocking motion and of a small scale panel with opening subjected to in-plane loads are also carried out to evaluate the accuracy and the computational efficiency of the formulation adopted.     

水硬石灰在花山岩画加固保护中的应用研究

水硬石灰兼具石灰和水泥的优点,低收缩、耐盐、适中的抗压和抗折强度、水溶盐含量低,同时与传统的砖石建筑兼容性好,是一种天然、无污染、耐老化的无机材料。本工作针对花山岩画的开裂特点制订出相应的力学参数要求,配制出两种不同的水硬石灰砂浆,并对这两种砂浆的力学性能进行了分析。同时探讨了不同养护条件对水硬石灰砂浆拉拔强度的影响。现场试验结果说明,填补粘结材料可以提供一定的粘结强度,并且具有使用方便,污染小的特点,可用于花山岩画开裂岩体应急保护加固处理。     

Petrochemical Identification and Insights on Chronological Employment of the Volcanic Aggregates Used in Ancient Roman Mortars

Through the assistance of trace element and petrographic analyses on 14 samples of mortar aggregates from Roman monuments, including the Porticus Aemilia, the Temple of Concordia, the Temple of the Dioscuri, Temple B and other structures of the Area Sacra di Largo Argentina, and the Villa di Livia, we establish the source area and we investigate the chronological employment of the volcanic materials used in ancient Rome's masonry. In contrast to previous inferences, the petrochemical data presented here show that systematic exploitation of the local ‘Pozzolane Rosse’ pyroclastic deposit has occurred since the early development of concrete masonry, at the beginning of the second century bc , through the early Imperial age. Subsequently, exploitation was extended to the overlying Pozzolane Nere and Pozzolanelle deposits. Only during the early phase of development of the concrete masonry in Rome, volcaniclastic sediments outcropping near the construction sites were mixed with the sieved remains of the tuff employed as the coarse aggregate, to produce the fine aggregate. The results of the study on the investigated monuments suggest the possibility of establishing the chronological identification of three different types of mortars, as a function of the composition of the volcanic material employed in the fine aggregate, which, when implemented by future studies, may contribute to the dating of monuments and archaeological structures.     

Updating Numerical Models of Masonry Arch Bridges by Operational Modal Analysis

This article aims at presenting and discussing the strategies for updating the finite element numerical modeling of stone masonry arch bridges using operational modal analysis. The study comprehended three bridges: two old ones, the St. Lázaro and the Lagoncinha bridges, and a recently constructed bridge in Vila Fria, Portugal. Updating of the bridge models is performed by comparing the numerical and experimental modal parameters. Three-dimensional detailed numerical models are used to perform modal analysis of the bridges. Experimental modal identification of the bridges is based on the measurement of their acceleration responses during normal operation. The assigned material properties are also based on available results obtained from in situ and laboratory tests and on the results of visual inspection and historical research carried out for both old bridges.     

Window opening effects on structural behavior of historical masonry Fatih Mosque

Structural walls of old historical structures are either blind or have openings for functional requirements. It is well known that in and out of plane responses of structural walls are affected by the size, locations, and arrangements of such openings. The purpose of this investigation is to study the window opening effects on static and seismic behaviors of historical masonry old mosques. Fatih Mosque, which was converted from a church, constructed in 914 in Trabzon, Turkey, is selected for this purpose. The mosque is being restored. Structural exterior walls of the mosque were made using stone and mortar materials. When the plaster on the walls was removed during the restoration, 12 window openings were found as blind on the exterior structural walls of the mosque. Within the scope of restoration works, it is aimed to open such blind windows. In order to investigate the effects of the window openings on the structural behavior of the mosque, 3D solid and finite elements models of the mosque with and without window openings are initially developed. The experimental dynamic characteristics such as frequency, damping ratio, and mode shapes of the current situation of the mosque, where some windows openings are blind, are determined using Ambient Vibration Testing. Then, the finite element model of the current situation of the mosque is updated using the experimental dynamic characteristics. The static and seismic time history analyses of the updated finite element model with and without window openings are carried out. Structural behaviors of the mosque with and without window openings are compared considering displacement and stress propagations.     

A DAMAGE MODEL FOR THE ANALYSIS OF THE SEISMIC RESPONSE OF MONUMENTAL BUILDINGS

In this paper the Author proposes a damage model for the analysis of masonry plates and shells, which is based on an improvement of a previous constitutive model. The modifications introduced, connected to the head joint damage, allow us to study the influence of masonry texture on the damage modes once the mechanical characteristics of the elements constituting the masonry and the results of tests on simple assemblages are known. Having a nonlinear constitutive model is certainly one of the basic elements for understanding the damage mechanisms in masonry buildings. If, in fact, an elastic-linear constitutive model may be used under normal loading conditions, in critical situations it is necessary to model the damage and the dissipation mechanisms that occur between the elements, stone (brick) and mortar, in correlation with their characteristics and kind of masonry. To validate the model a comparison is made between the numerical and experimental results, in the case of tests available in the literature in masonry panels subjected to out-of plane loading and in a real structure through the observation of the damage in Umbria (Italy) surveyed after the 1997 earthquake.