Full-scale Unreinforced Masonry Research Articles

Experimental study on the pullout behavior of steel rebars in masonry shotcreted layer

Unreinforced masonry (URM) buildings are quite popular worldwide due to their low construction costs, despite being susceptible to significant damage even from moderate earthquakes. In many cases, reconstruction may not be the most viable option due to financial and time constraints. Among the available retrofit solutions, steel-reinforced shotcrete (SRS) proves to be a cost-effective, straightforward, yet effective method for repair/retrofitting. This paper presents the results of an experimental study aimed at evaluating the effects of various construction conditions on the rebar pullout resistance of steel-reinforced shotcrete used as a retrofit method for URM walls. To achieve this, a total of 46 full-scale URM specimens were manufactured and tested, each consisting of a one-sided 50 mm-thick shotcrete layer with a single 8 mm steel rebar. The variables examined included the condition of the URM surface before the shotcrete application (wet/dry, with/without finishing including plaster/scratched plaster/oil paint), the condition of the rebar surface (rusty/clean), the type of rebar (plain/ribbed), rebar cover in the shotcrete layer (20/25/30 mm), and the URM substrate temperature before application of shotcrete (20 °C/-16 °C). The results indicate that there is an increase in pullout resistance of the specimens under the following conditions: when the wall's finishing is removed, the wall's surface is wetted before shotcrete application, ribbed steel rebar is utilized, and the temperature of URM before shotcrete application is 20 °C, there is an increase in pullout resistance of the specimens by 58 %, 56 %, 32 %, and 13 %, respectively. Additionally, when the steel rebar cover is sufficient, ribbed steel rebar is utilized, and this rebar is rusted, there is an increase in pullout resistance of the specimens by 55 %, 10 %, and 6 %, respectively.

Failure analysis and structural reliability of unreinforced masonry veneer walls: Influence of wall tie corrosion

Corrosion appears to be a very common problem in historical and aged structures with steel ties and anchorages. A potential rapid deterioration of the wall tie due to the corrosion leading to a premature structural failure poses a serious threat to the built heritage infrastructures’ safety. This paper describes an overview of the probabilistic failure analysis of the unreinforced masonry (URM) veneer wall system with flexible backup under uniformly distributed out-of-plane loadings. Moreover, a framework is proposed to consider the wall tie corrosion in the stochastic finite element analysis (FEA) while estimating the structural reliability. A probabilistic experimental study where 18 full-scale URM veneer wall systems with theoretically identical geometries and properties were tested under inward and outward lateral loading. Wall failure statistics along with the probabilistic characterisation of veneer wall constituent materials including mortar, wall tie and timber were accomplished. A stochastic computational model was then developed which combines the FEA and Monte Carlo simulation to evaluate the failure progression and system peak load (veneer capacity) while considering the spatial variability of veneer wall material properties. Two scenarios, with and without wall tie corrosion, are considered, and the probabilistic characterisation of the veneer capacities for these scenarios under inward and outward out-of-plane loading is also reported. The model error statistics were combined with the probabilistic load models to determine the reliability index corresponding to the Australian Standard for Masonry Structures AS 3700. Annual reliabilities are compared to target reliabilities recommended by ISO 2394. Capacity reduction factor and design minimum tie strength consideration for corroded wall tie is also discussed.

Out-of-Plane lateral load capacity of unreinforced masonry walls

ABSTRACT This study tests two full-scale unreinforced masonry (URM) walls under constant axial stress and cyclic out-of-plane lateral loads and proposes mathematical models to predict their rocking and toe crushingstrengths based on the elasticity and plasticity theorems of concrete. The two specimens were designed to simulate a non-perforated URM wall without opening and a URM wall with a door opening. Parallel walls with a length of 590 mm and thickness of 190 mm were constructed at the both ends of the walls in the out-of-plane direction, producing a barbell-shaped section. Test results showed that the URM wall specimens were initially governed by the rocking rotation and then ultimately failed with compressive toe crushing. The value of the equivalent damping coefficient mostly remained constant up to the occurrence of rocking rotation, beyond which it gradually increased. The effect of a door opening on the out-of-plane seismic response of the URM wall was insignificant because the applied lateral loads were resisted mainly by the in-plane action of the auxiliary parallel walls. The proposed models accurately estimated the rocking and toe crushing strengths of URM walls under out-of-plane lateral loads.

Material aging effects on the in-plane lateral capacity of tuff stone masonry walls: a numerical investigation

Recent studies have shown how the variability of material properties affects the nonlinear behaviour of unreinforced masonry (URM) walls. To preserve the historical built heritage, variations in structural capacity of URM buildings associated to aging and deterioration of masonry should be quickly predicted, by integrating with structural health monitoring and risk management. In this study, relationships between structural capacity features and material properties are numerically investigated for single walls, based on a structural modelling strategy that was experimentally validated on full-scale URM walls. The paper proposes an evaluation of the effects of degradation of material properties on the macroscopic descriptors of single masonry walls, such as peak strength and stiffness, also considering the uncertainties in the estimate of those properties. The authors do not attempt to model the physical processes of material aging with time, but assume certain levels of material degradation and investigate their effects on the structural response and capacity. Force–displacement curves and failure modes are associated with the overall nonlinear response of masonry walls due to progressive deterioration of material properties. Regression models are then proposed to predict variations in the peak load-bearing capacity and in -plane lateral stiffness when the mechanical properties of the constituents changed.

Quasi-static in-plane behavior of full-scale unreinforced masonry walls retrofitted using ferro-cement overlay

Quasi-static in-plane behavior of full-scale unreinforced masonry walls retrofitted using ferro-cement overlay

Monte-Carlo laboratory testing of unreinforced masonry veneer wall system under out-of-plane loading

This paper presents the results of a probabilistic experimental study into the behaviour of full-scale unreinforced masonry (URM) veneer walls with flexible backup subjected to out-of-plane loading. The actual safety and reliability of the contemporary Australian URM structures are unknown due to the absence of information regarding the probabilistic behaviour of the whole veneer wall system and material characterisation of the wall constituent materials. The study focused on masonry typologies representative of modern URM buildings in the Australian context. In this study, 18 full-scale URM veneer wall systems with theoretically identical geometries and properties were tested under inward and outward out-of-plane loading. For each loading type, one specimen was tested under semi-cyclic loading to check whether the monotonic loading can capture the overall behaviour of the cyclic response. For each mortar batch mixed, bond wrench testing was conducted at the same age as the test for the associated wall constructed using that mix. Batch to batch variabilities were statistically analysed, and probability distributions for flexural tensile strength were established. Lognormal distributions with aggregated means of 0.40 MPa and 0.42 MPa for inward and outward loading, respectively, were estimated for flexural tensile strengths. After the wall tests, all timber studs used to build the veneer walls were tested to evaluate the probabilistic characterisation of timber stiffness. This probabilistic information is essential for a stochastic finite element analysis (FEA) to conduct the reliability analysis. From the wall tests, veneer wall system behaviour was observed and measured until the collapse or 20% post-peak drop of the peak load. Outward loaded specimens exhibited higher variabilities for masonry cracking and system peak load compared to inward loading due to variabilities from materials, testing arrangements and failure mechanism. The true coefficient of variations of system peak loads were calculated as 0.10 and 0.19 for inward and outward loadings, respectively, considering the effect of testing variability.

Shake-table response simulation of a URM building specimen using discrete micro-models with varying degrees of detail

Recent technological advances have enabled earthquake engineering researchers to develop numerical models of increasing complexity, capable of duly reproducing even the smallest structural detail. In the case of unreinforced masonry (URM) structures, however, because of their discrete and heterogeneous nature, computational performance tends to decrease exponentially as a function of the adopted refinement level, thus confining the applicability of advanced micro-models, according to which each masonry unit is typically modelled separately, to reduced-scale problems. To enable their use at a building scale, and benefit from considering simultaneously out-of-plane failures, local wall-diaphragm interaction and collapses, researchers often need to decrease the level of detail of specific members or sub-structures. In the current literature, however, the influence of the abovementioned simplifications on the quality of micro-modelling predictions has been only marginally investigated so far, while code-based guidelines are missing. To start addressing such knowledge gap, the dynamic response of a shake-table-tested full-scale URM building specimen has been simulated in this work using a very detailed micro-model, and the results obtained were then compared with those of nominally identical models in which, however, the idealisation of some specific structural elements has been purposely simplified. Aimed at further extending the impact of this study, pushover analyses were also performed using the same models. Preliminary outcomes, which may serve as a reference to develop more informed, effective and targeted multi-scale micro-modelling strategies in the future, indicate that: (i) maximum base shear predictions tend to be less impacted by the introduction of modelling simplifications, (ii) despite requiring more labour, the explicit representation of the brickwork pattern generally led to better results in terms of predicted damage propagation, failure mechanisms and displacement capacity, (iii) using equivalent membranes, as opposed to modelling each component of timber diaphragms, provided acceptable results, making it a plausible alternative for practical applications of micro-modelling approaches.

Modelling the experimental seismic out-of-plane two-way bending response of unreinforced periodic masonry panels using a non-linear discrete homogenized strategy

A non-linear discrete homogenized strategy is used to reproduce out-of-plane two-way bending shake table tests on full-scale unreinforced masonry walls. The numerical strategy represents unreinforced masonry walls as an assemblage of rigid quadrilateral plates connected through non-linear interfaces represented. The material response laws for these non-linear interfaces are derived from a homogenization procedure performed at the meso-scale by a finite-element plate model. This discrete model can simulate masonry orthotropy, full softening behaviour and failure. Bending and torsional deformation modes are represented. The performance of the numerical models in describing the response of the experimentally tested full-scale specimens is presented. The numerical strategy is then used to study the behaviour of unreinforced masonry walls in configurations hitherto untested. Such numerical results are then compared to state-of-the-art analytical approaches. Potential avenues of improvement for the implemented analytical methods are also highlighted.

Cyclic Test on a Full-Scale Unreinforced Masonry Building Repaired with Steel Fiber-Reinforced Mortar Coating

The present work reports the results of two quasi-static reverse cyclic tests performed on an unreinforced hollow clay block masonry building before and after repairing with a single 30-mm thick layer of mortar applied on the façades. Unlike traditional coating-based retrofitting techniques, the one proposed herein adopts a cement-based mortar reinforced with short high-strength steel fibers randomly diffused in the mortar matrix. In order to assess the effectiveness of the strengthening intervention, a preliminary cyclic test was carried out on the unstrengthened building in order to predamage masonry. The experimental results showed that the repaired structure exhibited a significant improvement of seismic behavior both at the serviceability and ultimate limit state conditions. Moreover, based on the observed ultimate ductility of the retrofitted building, some considerations on the behavior factor are reported.

Out-of-plane behaviour of masonry wall structures strengthened with steel-bar truss system

An experimental study was performed to investigate the effect of external prestressed truss steel-bar units installed on an unreinforced masonry (URM) wall under out-of-plane loadings. The key components of this new retrofitting method are prestressed vertical and diagonal bars. The prestressed vertical bars induce a prestressing force onto the horizontal section of the URM wall and the diagonal bars resist lateral loadings. Reverse cyclic tests were conducted on a full-scale URM wall as a control specimen and URM walls retrofitted in-plane and/or out-of-plane (parallel to short intersecting walls). The test results showed that the specimen strengthened using the new technique was superior to the control specimen in terms of seismic performance, including lateral load resistance, stiffness, energy dissipation and restrained slip of the entire specimen. Two units installed on short intersecting walls exhibited the same shear strength as four units installed on the in-plane and in-plane retrofitted masonry walls. The out-of-plane masonry specimen demonstrated the best performance. It was confirmed that aligning the retrofitting method based on the loading direction was effective, despite the lower axial load level.

Experimental Evaluation of Full-Scale URM Buildings Strengthened Using Surface-Mounted Steel Bands

AbstractConstruction of unreinforced masonry (URM) buildings has been a common practice in many countries. Strengthening of such buildings located in seismically active regions has become extremely...

A Macro-Distinct Element Model (M-DEM) for simulating the in-plane cyclic behavior of URM structures

In this work, a new Macro-Distinct Element Model (M-DEM) for the analysis of the in-plane behavior of unreinforced masonry (URM) structures, aimed at combining the efficiency of simplified approaches with the accuracy of discontinuum-based micro-modeling methods, is presented and validated through comparison against a number of both experimental and numerical tests on URM components. In the M-DEM framework, Finite Element (FE) homogenized macro-blocks are connected by discrete spring interfaces, whose layout is determined a priori as a function of the masonry texture. In-plane diagonal and sliding shear failure mechanisms, as well as flexural damage, are accounted for by the discrete spring interfaces. Meanwhile, a new methodology to simulate crushing, which makes use of a strain-softening model originally conceived for modeling concrete failure, is proposed and calibrated against small-scale tests on masonry samples. The strategy is to simulate shear/tension failure in the block interfaces and compression failure within the FE macro-blocks, while discretizing to allow the possibility of simulating out-of-plane failure modes. Using the M-DEM, the observed experimental damage and the hysteretic behavior of various reduced-scale URM specimens, subjected to shear-compression cyclic loading, were satisfactorily reproduced numerically. The capabilities of the M-DEM to predict the influence of the bond pattern on the monotonic behavior laterally-loaded URM piers were also scrutinized through comparison with standard micro-modeling outcomes, focusing on potential differences concerning both accuracy and computational expense. Finally, given the encouraging results obtained, the proposed approach was extended to the simulation of the in-plane cyclic response of a full-scale URM façade. Although the model marginally underestimated the energy dissipation in the first test phases, a good agreement was obtained in terms of peak and residual base shear capacity, initial in-plane stiffness and its progressive deterioration, governing failure mechanisms and final crack pattern, whilst simultaneously keeping computational costs within acceptable limits.

Mesoscale Modeling of a Masonry Building Subjected to Earthquake Loading

Masonry structures constitute an important part of the built environment and architectural heritage in seismic areas. A large number of these old structures showed inadequate performance and suffered substantial damage under past earthquakes. Realistic numerical models are required for accurate response predictions and for addressing the implementation of effective strengthening solutions. A comprehensive mesoscale modeling strategy explicitly allowing for masonry bond is presented in this paper. It is based on advanced nonlinear material models for interface elements simulating cracks in mortar joints and brick/block units under cyclic loading. Moreover, domain decomposition and mesh tying techniques are used to enhance computational efficiency in detailed nonlinear simulations. The potential of this approach is shown with reference to a case study of a full-scale unreinforced masonry building previously tested in laboratory under pseudodynamic loading. The results obtained confirm that the proposed modeling strategy for brick/block-masonry structures leads to accurate representations of the seismic response of three-dimensional (3D) building structures, both at the local and global levels. The numerical-experimental comparisons show that this detailed modeling approach enables remarkably accurate predictions of the actual dynamic characteristics, along with the main resisting mechanisms and crack patterns.

Two-way bending experimental response of URM walls subjected to combined horizontal and vertical seismic excitation

This paper presents the results of incremental dynamic tests on full-scale unreinforced masonry (URM) walls constructed with an intentionally weakened mortar under two-way bending excitation in the out-of-plane (OOP) direction. A specimen was also subjected to simultaneous vertical and horizontal excitation. Walls were also tested in boundary conditions that have not been previously reported in the literature. Emphasis was placed on the development and interpretation of a characterisation test to estimate the torsional shear strength of bed-joints, a parameter of prime importance in the OOP two-way bending behaviour of URM walls. Analytical formulation to estimate the initial stiffness of walls based on the theory of plates is then proposed and validated. Being the first experimental campaign to address the dynamic OOP two-way bending response of full-scale URM wall panels provided the opportunity to propose simple yet mechanically rational methodologies with which both the peak force resistance as well as the displacement at which such resistance is attained can be easily estimated.

Dataset from shake-table testing of four full-scale URM walls in a two-way bending configuration subjected to combined out-of-plane horizontal and vertical excitation.

This data article provides experimental data obtained from the incremental dynamic shake-table testing of four single leaf unreinforced masonry (URM) walls constructed in Calcium Silicate (CS) bricks reported in “Two-way bending experimental response of URM walls subjected to combined horizontal and vertical seismic excitation” [1]. These walls were tested in the second phase of a larger experimental campaign addressing the out-of-plane (OOP) response of full-scale URM panels in two-way bending configurations at EUCENTRE, Pavia, Italy. Data corresponding to the first phase of testing for four single leaf and one cavity wall has already been made available through Tomassetti et al.[2] and the information necessary to interpret these results can be found in Graziotti et al.[3]. The walls of the tests reported in this data article were constructed in an intentionally weakened mortar but using the same Calcium Silicate (CS) bricks as Graziotti et al.[3]. The walls were also tested in boundary conditions that were not addressed in [3] and a specimen was also subjected to simultaneous horizontal OOP and vertical seismic excitation in one of the tests. Videos documenting the failure of specimens tested in both phases of the experimental campaign can be viewed online on YouTube [4].

Influence of Individual Wall Strengths on Lateral Strength of URM Buildings Constructed Using Low-Strength Masonry

ABSTRACT Estimation of the lateral load-carrying capacity of unreinforced masonry (URM) buildings is essential for their design, vulnerability assessment, and rehabilitation. Lateral strength of URM buildings can be assessed using experimental studies or numerical simulation, but conducting such studies on full-scale building specimens is expensive and requires huge computational effort and input data, which is not easily available. Therefore, the availability of test results and data is scarce in many developing countries having a huge concentration of URM buildings. Moreover, the quality and strength of masonry found in these countries are inferior to those found in some developed countries where data are available. This results in under-developed design codes and thus improper design and construction of URM buildings in seismically active regions of many developing countries. Therefore, simple analytical methods are required to be developed for the estimation of lateral load-carrying capacity of URM buildings with the help of systematic experimental and numerical studies on full-scale specimens. The paper presents a comparative assessment of the lateral strength of a URM building using experimental, analytical and numerical approaches. Pseudo-static in-plane cyclic tests were carried out over three full-scale URM walls with different opening configurations followed by testing of a single story URM building having a single room, constituting the walls, which were already tested. The walls and a building were then numerically analyzed in Abaqus and Strand7 to estimate the lateral load-carrying capacity. The lateral strength of individual walls was also estimated analytically using several existing methods. Finally, the effectiveness of combining the lateral strength of individual walls to estimate the lateral strength of full URM building was assessed that can be handy to the practicing engineers.

Seismic analysis of a masonry cross vault through shaking table tests: The case study of the Dey Mosque in Algiers

This paper presents the results of a monodirectional shaking table test on a full-scale unreinforced masonry cross vault characterized by asymmetric boundary conditions. The specimen represents a vault of the mosque of Dey in Algiers (Algeria), reproducing in detail the mechanical characteristics of masonry, and the constructive details including the presence of some peculiar wooden logs placed within the vault\'s configurations were studied by using an incremental dynamic analysis up to the collapse of the vault without the steel bars. The use of an innovative high-resolution 3D optical system allowed measure displacement data of the cross vault during the shake table tests. The experimental results were analysed in terms of evolution of damage mechanisms, and in-plane and out-of-plane deformations. Moreover, the dynamic properties of the structure were investigated by means of an experimental modal analysis.

Two-way bending out-of-plane collapse of a full-scale URM building tested on a shake table

This paper describes a shake table test on a one-storey full-scale unreinforced masonry structure, which complements an earlier testing of a two-storey structure with similar characteristics. The building specimen was meant to represent the upper floors of the end-unit of a terraced house, built with cavity walls and without any particular seismic design or detailing. In these specimens, the masonry walls were composed of two leaves: a load-bearing inner one made of calcium silicate bricks sustaining a reinforced concrete floor and an external leaf made of clay-bricks connected to the inner leaf by means of metallic ties. A pitched timber roof was supported by two triangular gable walls. Floor acceleration response histories of the previously tested two-storey specimen were used as input motions. An incremental dynamic test, with vertical and horizontal inputs, was carried out up to the explicit collapse of some bearing elements of the structure. In particular, a two-way bending out-of-plane collapse of a load-bearing wall was observed and described.

Masonry walls with a multi-layer bed joint subjected to in-plane cyclic loading: An experimental investigation

A series of static-cyclic shear tests on full-scale unreinforced masonry (URM) walls with multi-layer bed joints have been performed within a research project on the seismic behaviour of unreinforced masonry walls with soft layer membrane placed in the bed joint to induce sliding. Walls were made using typical perforated Swiss clay blocks and standard cement mortar and the so-called multi-layer bottom bed joints, which comprise a core soft layer protected by two layers of extruded elastomer and placed in the middle of mortar joint. The preliminary testing phase was aimed at choosing the most suitable core soft layer type among the four types considered (rubber granulate, cork, cork-rubber granulate and bitumen). The main testing phase comprised five tests on storey-high URM specimens with rubber granulate core soft layers performed to investigate the influence of the size, the pre‐compression level and the aspect ratio on the seismic behaviour of URM walls with a multi‐layer bed joint. Sliding occurred in all tested specimens. However, the final failure mode as well as the displacement capacity of test specimens were governed by the extent of shear and tensile (vertical) cracks that developed from the bottom brick course. The response of specimens can be interpreted using a multilinear horizontal force-displacement response idealization, whose parameters can be estimated using the proposed equations.

Experimental results on the retrofitting of hollow brick masonry walls with reinforced high performance mortar coatings

Many masonry buildings in Europe were built after the Second World War during a booming economy when seismic risk was not properly considered and, as a consequence, seismic codes were not available yet. Several of these buildings are quite small since they are used by one or two families. Because of the huge developments in the knowledge on seismic actions, there is now a major concern for the vulnerability of these buildings under possible earthquakes.The present work focuses on seismic strengthening of a masonry typology widely used for social housing. It is based on hollow masonry bricks with horizontal holes and poor cementitious mortar. Results of quasi-static cyclic tests carried out on full-scale unreinforced masonry walls with different geometries, representing either a shear wall or a pier-spandrel assembly, are presented. The specimens were repaired or strengthened with a thin layer of high-performance mortar reinforced with light steel-mesh. The test results show the effectiveness of the proposed technique since it provides a remarkable enhancement of both lateral strength and displacement capacity.