Rubble Stone Masonry Walls Research Articles

Applying a 2D Variational Rigid Block Modeling Method to Rubble Stone Masonry Walls Considering Uncertainty in Material Properties

ABSTRACT The computational cost of detailed micro-modeling of masonry structures can be minimized with rigid block analysis methods, where a variational formulation is particularly interesting as it allows for nonlinear pushover analysis. This work investigates the accuracy of this modeling method in predicting the response of rubble stone masonry walls in shear compression tests. To this end, we extend the mathematical programming problem by including cohesion, compressive strength, and tensile strength in the formulation and implement an improved pushover procedure, which guards compatibility of the displaced shape and crack patterns at the intersection of elastic and rigid contact models. Additionally, we reduce model uncertainty, introduced through sampling material properties with distributions estimated based on results from tests on mortar masonry joints and on mortar specimens, by correlating the predicted crack patterns with the observed ones. The findings show that (i) model falsification based on crack pattern is an effective method for reducing the parameter uncertainty of stone masonry walls; and that (ii) the improved pushover procedure predicts the pre- and post-peak response of stone masonry walls very well with analysis times of less than 20 minutes for 2D models where stones and mortar are modeled explicitly.

Simulating the damage of rubble stone masonry walls using FDEM with a detailed micro-modelling approach

Simulating the damage of rubble stone masonry walls using FDEM with a detailed micro-modelling approach

Experimental investigation of the behaviour of injection anchors in rubble stone masonry

The seismic response of historical masonry buildings is largely controlled by the effectiveness of wall-to-diaphragm connections, which can be improved using injection anchors. Despite their use, there is a need for a better understanding of the performance of such anchoring system in stone masonry walls. This paper presents quasi-static pull-out tests performed on twelve specimens to investigate the behaviour of injection anchors in rubble stone masonry walls when breakout failure occurs. For each specimen, the experimental results are presented in terms of force–displacement curves, propagation of damage and crack pattern. It is shown that the anchoring details adopted in this study had a negligible influence on the pull-out force capacity of the anchoring system, while an increase in peak pull-out force was observed with increasing overburden stress applied. Because stone masonry specific capacity formulations have not yet been presented in the literature, the capacity is predicted using state-of-the art formulations for the pull-out load capacity of anchors installed in brick masonry. The limits of their applicability are discussed using the obtained experimental results.

Numerical Evaluation of Transverse Steel Connector Strengthening Effect on the Behavior of Rubble Stone Masonry Walls under Compression Using a Particle Model

The structural rehabilitation of historic/traditional rubble masonry wall constructions requires consolidation and retrofitting solutions to be employed in order to withstand dynamic loads, high vertical loads, and differential settlements. One of these strengthening techniques is based on the use of steel bar connectors perpendicular to the wall, considered individually or integrated into more complex strengthening techniques. The aim of this study is to evaluate numerically the strengthening effect of transverse steel connectors on rubble masonry walls. With this purpose, a 2D particle-reinforced model (2D-PMR) was devised and applied to model uniaxial compression tests. The results presented show that predictions calculated using the proposed 2D-PMR model are very close to known experimental results, particularly in the corresponding failure modes, the increase of the maximum uniaxial compression value, and ductility. Parametric studies are also conducted by varying the diameter of the steel bars and the level of strengthening to assess the influence of the bar-bond effect and lateral plates. The presented parametric numerical studies show that (i) a two-level strengthening solution guarantees a similar response to the three-level strengthening solution adopted in the experiments; (ii) it is not relevant to apply a grout injection during the application process of the steel connectors if lateral plates are adopted; and (iii) the 2D-PMR model can be used in the definition of the steel bar diameter and properties; as shown, a smaller (8 mm) bar diameter predicts a similar strengthening effect to the (12 mm) bar size adopted in the experiments. Given the performance of the proposed 2D-PMR model, further work is underway that will allow the 2D-PMR model to numerically assess other reinforcement techniques, namely, reinforced micro-concrete layers and textile reinforced mortar.

Detecting Damage Evolution of Masonry Structures through Computer-Vision-Based Monitoring Methods

Detecting the onset of structural damage and its progressive evolution is crucial for the assessment and maintenance of the built environment. This paper describes the application of a computer-vision-based methodology for structural health monitoring to a shake table investigation. Three rubble stone masonry walls, one unreinforced and two reinforced, were tested under natural earthquake base inputs, progressively scaled up to collapse. White noise signals were also applied for dynamic identification purposes. Throughout the experiments, videos were recorded, under both white noise excitation and environmental vibrations, with the table at rest. The videos were preprocessed with motion magnification algorithms and analyzed through a principal component analysis. The natural frequencies of the walls were detected and their progressive decay was associated with damage accumulation. Results agreed with those obtained from another measurement system available in the laboratory and were consistent with the crack pattern development surveyed during the tests. The proposed approach proved useful to derive information on the progressive deterioration of the structural properties, showing the feasibility of this methodology for real field applications.

Experimental Response of Rubble Stone Masonry Walls Retrofitted with Basalt Textile Reinforced Mortar under Compressive-and-Shear Load

Seismic events recently occurred in Europe highlighted the vulnerability of unreinforced masonry structures, representing the majority of the built heritage, to earthquake-induced loads. In particular, the in-plane capacity of shear walls under seismic loadings appeared sensibly modest, both in terms of strength and ultimate displacement, and their failure mode sudden and brittle. Textile Reinforced Mortar (TRM) composites proved to be a proper strengthening solution for the seismic upgrade of such walls. With the aim of gaining a deeper knowledge on the behavior of historical walls retrofitted with TRM and subjected to compression-and-shear, this paper summarizes the results of an experimental campaign characterized by quasi-static cyclic shear-compression tests. The specimens under study reproduced the rubble stone masonry typical of vernacular structures of the UNESCO historical district of Lyon (France). Specifically, the work concerns a full scale masonry wall tested under loading until the development of diagonal cracks and than repaired by a composite constituted by a basalt textile embedded in a lime mortar matrix applied onto the external surfaces as a plaster. The use of a lime mortar plaster to reinforce the structural element permits the development of a solution compatible with the historical substrate. Experimental outcomes revealed how Basalt TRMs succeeded in improving the response of damaged vernacular wall, both in terms of strength and displacement capacity.

Mechanical characterization of historical rubble stone masonry and its correlation with the masonry quality assessment

The paper presents a study on the mechanical characterization of eight rubble stone masonry walls from different structures of a Portuguese monument and on the assessment of their quality using the Masonry Quality Index (MQI) and the Italian Building Code Commentary (IBCC 2019). Rebound hammer tests were used to evaluate the quality of stone units and mortar joints, and flat-jack tests to assess the mechanical properties of masonry walls. The results allowed to propose new quantitative criteria to rate the quality of mortars and stones in MQI and to support the decision of applying the multiplication factor concerning the quality of mortars in IBCC 2019 methodology.Image processing was used to quantify several features of masonry walls and introduce new quantitative criteria on MQI. The results identified the amount of mortar, the mortar quality, the shape features of stone units and the horizontal alignment of joints as key parameters in the mechanical resistance of rubble masonry made of irregular hard stone and lime-based mortars. The mechanical properties obtained by IBCC 2019, MQI and double flat-jacks tests showed good correlations, highlighting the advantages that come from the quality assessment of masonry to estimate masonry mechanical properties.

Seismic retrofit of stone walls with timber panels and steel wire ropes

Historic constructions are common in Europe, but natural hazards can produce significant damage. Shear reinforcement of historic walls, especially in seismic areas, is often necessary and new retrofitting methods have recently been proposed to restore or increase the lateral capacity of shear walls. In this paper the combined use of cross-laminated timber panels and steel wire ropes is proposed to reinforce rubble stone masonry walls with the aim of increasing their lateral load capacity while improving the energy performance of the building envelope. An experimental programme was carried out in the laboratory to assess the mechanical effectiveness of this retrofitting method. The results from a series of quasi-static cyclic shear tests are presented. The test programmes are described and the analysis of test results is included. The potential benefits and limitations regarding the use of the proposed combined method for reinforcing masonry structures are discussed, with an emphasis on the in-plane behaviour.

In-plane behaviour of rubble stone masonry walls: Experimental, numerical and analytical approach

Unreinforced masonry construction is predominant in many urban areas world-wide.Many of these constructions are vulnerable to earthquakes, which are the main cause of damage and loss of cultural heritage. Understanding the in-plane behaviour of masonry walls when subjected to horizontal loadings will improve the society capacity to preserve and protect this cultural heritage. An experimental campaign on rubble stone masonry walls under different loading conditions is presented. This experimental campaign allows calibrating non-linear numerical models used to study these elements in a more comprehensive way, performing parametric studies regarding the geometry, pre-compression level, boundary conditions and mechanical properties. The capacity to estimate the shear strength using available analytical models is also reviewed, applied and compared.

The role of aggregate and binder content in the physical and mechanical properties of mortars from historical rubble stone masonry walls of the National Palace of Sintra

The relevant role of mortars for the structural behavior of historical rubble stone masonry and the scarce information available justifies the research on these materials. Mortars collected from several masonry structures of the National Palace of Sintra (Portugal), built across different centuries, were examined in situ and in laboratory. The influence of b:a ratio, pore structure, aggregate and binder attributes on the mortars properties is discussed. The results led to purpose drilling resistance and modified Schmidt hammer to assess and distinguish the mortars quality from a mechanical point of view based on their hardness and drilling strength. Moreover, a contribution is provided to estimate a possible order of magnitude of rebound values and drilling resistance with respect to the binder content for similar mortars.

Experimental investigation of strength, stiffness and drift capacity of rubble stone masonry walls

There is limited available research on rubble stone masonry walls, which are vulnerable under seismic loading. This paper presents an experimental campaign of cyclic shear compression tests on six large-scale walls of this topology. The effect of the axial load and shear span ratio on the wall behaviour, notably on the wall stiffness, strength, and drift capacity, was investigated. It was found that the drift at crack onset is only half of that in previous campaigns on stone masonry walls, likely because one face of each wall was plastered, making the damage more visible. Additionally, splitting cracks opening between the wall leaves appear to play a key role in the collapse mechanism. Finally, testing the walls up to the loss of their axial-load-bearing capacity provides new input for the collapse risk analysis of stone masonry buildings.

Triplet Test on Rubble Stone Masonry: Numerical Assessment of the Shear Mechanical Parameters

Rubble stone masonry walls are widely diffused in most of the cultural and architectural heritage of historical cities. The mechanical response of such material is rather complicated to predict due to its composite nature. Vertical compression tests, diagonal compression tests, and shear-compression tests are usually adopted to investigate experimentally the mechanical properties of stone masonries. However, further tests are needed for the safety assessment of these ancient structures. Since the relation between normal and shear stresses plays a major role in the shear behavior of masonry joints, governing the failure mode, a triplet test configuration is herein investigated. First, the experimental tests carried out at the laboratory of the University of L’Aquila on stone masonry specimens are presented. Then, the triplet test is simulated by using the total strain crack model, which reflects all the ultimate states of quasi-brittle material such as cracking, crushing, and shear failure. The goal of the numerical investigation is to evaluate the shear mechanical parameters of the masonry sample, including strength, dilatancy, normal, and shear deformations. Furthermore, the effect of (i) confinement pressure and (ii) bond behavior at the sample-plate interfaces are investigated, showing that they can strongly influence the mechanical response of the walls.

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

ABSTRACTStone 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.

Rubble Stone Masonry Walls in Portugal: Material Properties, Carbonation Depth and Mechanical Characterization

ABSTRACTA significant proportion of Portuguese ancient buildings have structural masonry walls. Therefore, it is important to study this building typology in order to define appropriate structural rehabilitation interventions, whenever necessary. This article presents the results of research carried out at Universidade NOVA de Lisboa on the material properties, of rubble stone masonry walls, including the evolution of carbonation depth over time and mechanical characterisation under compression and shear load tests. It was found that the mechanical behavior of the unreinforced masonry specimens is mostly influenced by the reduced compression and tensile strength of the air-lime mortar. A formulation to estimate the carbonation depth and the masonry compressive strength as a function of time is proposed and the Strut-and-Tie Method is used to estimate the resistance of specimens under compression and shear forces.The results of this study are part of a major research project studying the mechanical behavior of unreinforced rubble stone masonry walls (unreinforced masonry—URM), evaluating different strengthening solutions for ancient rubble stone masonry walls (Pinho 2007; Pinho et al. 2012a, 2014a, 2014b) and characterizing the building materials used in both URM and strengthened walls.

On the seismic response of buildings in aggregate: Analysis of a typical masonry building from Azores

In 1980, an earthquake of magnitude 7.2 ML caused severe damage to the existing buildings in some islands of the Azores Archipelago, Terceira being the most affected one. The traditional Azorean buildings are mostly made of rubble stone masonry walls and are often inserted in aggregates (or blocks), including adjacent buildings with different heights or/and different floor levels. This paper presents the results from the seismic performance-based assessment of a case study of such masonry building stock. The assessment was addressed to the global seismic response of the building, assumed to be governed by the in-plane capacity of the masonry walls, and taking into account the interaction with the adjacent buildings, shorter and with different floors heights. The global behavior was determined by nonlinear static analyses and the effects of some relevant modeling options were considered, including the analysis of the building either as an isolated structure and inserted in its aggregate. This study has shown the relevance of modeling the structure with the adjacent buildings' floors at their actual height to assess the real expected damage.

Mechanical Characterization of Masonry Walls With Flat-Jack Tests

The results from an experimental campaign on old masonry buildings from Lisbon are presented and discussed. The tests aim at the evaluation of the masonry deformability properties in compression and the shear strength parameters based on flat-jack testing technique. Tests were carried out in both internal brick masonry walls and external rubble limestone masonry walls. The evaluation of the shear parameters was done according to a new testing technique—shear tests onmasonry walls with flat-jacks—involvingmore than one masonry unit. One of the goals is the calibration and development of this testing technique and to show its first application to the test of rubble stone masonry walls. For that, the experimental technique is fully explained in this paper, and the results of some in situ tests are used to discuss the calibration procedure. Because of the characteristics of the walls, in particular, the great heterogeneity and thickness of the external masonry walls, the application of the flat-jack testing technique involved some uncertainties that are described and debated in this work.

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.

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

This article concerns the results of a structural strengthening solution for rubble stone masonry walls. The strengthening involved inserting three-dimensional steel ties through the thickness of the walls and applying a 30 mm layer of air-lime/cement mortar render, reinforced with glass fiber mesh (textile reinforced mortar), on both sides of the wall. This study was part of an experimental research program carried out in Universidade Nova de Lisboa, to evaluate a number of structural strengthening solutions for ancient rubble stone masonry buildings and it was sponsored by several industrial companies. In this research program, specimens of rubble stone masonry walls without strengthening (reference specimens) and others with the specified strengthening solution were subjected to compression tests. The strengthening solution was found to be efficient for rehabilitating ancient rubble stone masonry walls due to confinement, which offsets the low cohesive capacity of the mortar used in the walls, thus improving the mechanical resistance and delaying collapse mechanisms.

Experimental assessment of shear strength parameters on rubble stone masonry specimens

Rubble stone masonry walls were widely used in traditional buildings in Mediterranean countries. However, the mechanical behaviour of those walls is not completely characterized due to a lack of experimental data. This paper presents an experimental campaign carried out to characterize the shear strength parameters of traditional Mediterranean rubble stone masonry walls. Fifteen masonry specimens were built using old techniques and traditional materials. Two types of mortar were used in the specimens’ execution, air and hydraulic lime mortars, with intend to simulate different masonry construction periods. The goal of the experimental campaign was to evaluate the most important mechanical parameters needed for numerical modelling of traditional rubble stone masonry walls, namely, the compressive strength and Young’s modulus through compression tests; the cohesion and friction coefficient by triplet tests; and the diagonal tensile strength via diagonal compression tests. The tests’ setup and load–displacement diagrams are presented for all tests and the obtained shear strength parameters are compared with values from the literature.

Mechanical characterization of rubble stone masonry walls using non and minor destructive tests

As is well known, the diagnostic analysis of ancient buildings supposes important challenges from the point of view of its evaluation under field conditions. In this context, Non and Minor Destructive Techniques (N&MDTs) can be used for the mechanical characterization of ancient buildings. However, there are not many examples of application of the techniques in rubble stone masonry. Therefore, this paper presents a preliminary experimental study by using N&MDTs applied in a particular construction: the Riva–Herrera palace located in Santander, Northern Spain. In this way, different non and minor destructive techniques as flat jack, hole-drilling and sonic tests have been used in order to evaluate the mechanical and morphological characteristics of different rubble stone masonry walls, under field conditions. The results of this study show that the N&MDTs used in this study can be potentially used for providing valuable information about the mechanical and morphological characteristics of rubble stone masonry walls. In addition, this knowledge of great important in the intervention process has been obtained with a minimal effect on the structural component analyzed.