Behavior Of Masonry Walls Research Articles

Effects of aspect ratios and strengthening methods on seismic behavior of masonry piers strengthened by using hybrid-fibers modified reactive powder concrete

Piers are the main load-bearing elements of masonry structures. Damage to piers in earthquakes will lead to the collapse of the whole structure, so piers need to be strengthened. In order to study the effectiveness of hybrid-fibers modified reactive powder concrete (HFMRPC) coating strengthening on masonry piers and the influence of different strengthening methods and aspect ratios on the seismic behavior of masonry structures, six masonry walls with different aspect ratios (0.8, 1.0, and 1.4) and strengthened by different methods (unreinforced, single-sided coverage in piers, double-sided coverage in piers, and double-sided cross-bracing) were tested under in-plane quasi-static loading. The test and analysis results showed that the seismic behavior of masonry walls in terms of bearing capacity, displacement ductility, stiffness, and energy dissipation was effectively enhanced by HFMRPC coating. The improvement range of ductility coefficient, initial stiffness, and cumulative energy dissipation were 86.3% ∼ 229.3%, 18.2% ∼ 104.0%, and 57.0% ∼ 139.7%, respectively. The most suitable strengthening method for strengthening piers was double-sided cross-bracing compared with other methods. The strengthening effect of the double-sided coverage in piers was improved with the increased aspect ratio. Additionally, masonry wall shear strength and flexural capacity calculation methods were proposed based on GB 50003-2011, N-M interaction diagrams, and equivalent rectangular stress block.

Behaviour of masonry walls reinforced by fiber reinforced polymers

Masonry structures revealed their vulnerability to seismic loads through the damage sustained during the earthquake. Consequently, a problem with load transmission has arisen due to the failure of structural elements. To address this issue, various studies have been conducted to explore reinforcement or repair solutions aimed at enhancing the stability of damaged elements by increasing their resistance. Reinforcing a structure consists in improving the mechanical characteristics of the different elements that compose it. Choosing the accurate fiber reinforced polymers (FRPs) configuration to reinforce masonry walls increase the adhesion between the fiber reinforced polymer (FRP) and the wall subjected to the diagonal compression. The reinforcement system performance is mainly related to the quality of the adhesion between the masonry base and the material used for reinforcement. The assessment of the bonding quality is important and allows measurement of the tensile adhesion of FRP composites.

Hygro-Thermo-Mechanical Analysis of Brick Masonry Walls Subjected to Environmental Actions

Masonry walls comprise an important part of the building envelope and, thus, are exposed to environmental effects such as temperature and moisture variations. However, structural assessment usually neglects the influence of these hygro-thermal loads and assumes ideal conditions. This paper presents a hygro-thermo-mechanical model and its application to simulate the impact of temperature- and moisture-related phenomena on the structural behavior of masonry walls. A fully coupled heat and mass transfer model is presented and a 2D finite element model is prepared to simulate the behavior of a brick masonry wall under various hygro-thermal scenarios. Two different mortars are considered: namely, cement mortar and natural hydraulic lime mortar. The results are evaluated in terms of temperature and moisture content distribution across the wall thickness. The hygro-thermal model is further extended to incorporate mechanical effects through the total strain additive decomposition principle. It is shown that the hygro-thermo-mechanical response of the brick masonry wall is a complex 2D phenomenon. Moreover, the environmental loads change the natural stress distribution caused by gravitational loads alone. Finally, the wall with cement mortar develops higher levels of stress when compared to the one with lime mortar, due to the dissimilar hygro-thermal behavior between the constituent materials.

Geopolymer versus cement-based textile-reinforced mortar: Diagonal compression tests on masonry walls representative of infills in RC frames

Cement production industry is responsible for about 5% of the total anthropogenic CO2 emissions. Alternative materials with reduced carbon footprint progressively introduced in the construction industry could be an effective and sustainable solution to mitigate this impact. This paper examines the replacement of standard cement-based binder with geopolymer-based binder in the application where inorganic-based composites are used for strengthening of existing substandard masonry structures. The focus is given to the in-plane behaviour of masonry walls which serve as infills in reinforced concrete buildings. Past earthquakes have revealed the vulnerability of such structures, which is associated to the brittle nature of infill walls and the poor detailing of the RC frame members. The experimental programme consisted of eighteen diagonal compression tests on square 700 × 700 × 65 mm single-leaf masonry wallettes. The investigated parameters included the matrix of the TRM overlays (geopolymer versus cementitious mortar), the type of the textile reinforcement (14 × 18 mm mesh opening glass textile versus 6 × 6 mm mesh opening basalt textile), and the strengthening layout (two TRM layers on one side only versus one TRM layer per side). The experimental results are discussed in terms of the failure mechanisms, in-plane mechanical properties, ductility and are accompanied by analytical estimates of the experimental TRM contribution. The results of this study prove that geopolymer-based systems are suitable for such retrofitting applications leading to similar – if not better – mechanical response compared to the walls retrofitted with ordinary cementitious binder.

Lateral behaviour of masonry walls with different types of brick bonds, aspect ratio and strengthening measures by polypropylene bands and wire mesh

The paper presents a comparative study of the performances of unreinforced masonry (URM) wall units with each of the four types of brick bonds: Header bond, Stretcher bond, English bond and Flemish bond under lateral or representative seismic loading. The load-carrying capacity, stress distribution, and failure mechanisms for each case have been obtained and interpreted. A plasticity-based simplified micro-model approach and the extended finite element method (XFEM) were used, including surface-based cohesive behaviour. The model is validated against the experimental and computational results available in the literature by a well-known software named ABAQUS. The hysteretic curves obtained in each case under cyclic loading are presented to compare the energy dissipation capacity for each case. The aspect ratio of the wall significantly influences the failure mechanism and peak load-carrying capacity. After that, the effect of strengthening using polypropylene band and wire mesh is also studied, showing a considerable increase in strength for a marginal cost increase.

Experimental and numerical evaluation of the out-of-plane bending behavior of masonry walls retrofitted by Steel Fiber Reinforced Mortar coating

The Out-of-Plane (OP) bending behavior of Un-Reinforced Masonry (URM) walls retrofitted by Steel Fiber Reinforced Mortar (SFRM) coating was investigated by performing in-situ experimental tests on two one-way vertically spanning walls. The latter were part of a full-scale two-story hollow block masonry building provided with seismic floor diaphragms and a 30 mm thick SFRM coating applied only on the external surface of the structure. One of the two test walls was tested under monotonic loading whereas the remaining one was subjected to reverse cyclic loading.Non-linear finite element analyses were performed to simulate the behavior of the specimens. To this end, a plane-stress model based on the smeared crack approach was implemented in the commercial code Diana 10.5. The simulations allowed to predict the response of both the strengthened walls and the un-strengthened (reference) member not included in the experimental campaign.The paper reports the results of the experimental tests including some important considerations on the observed failure mechanisms, the resistance and the displacement capacity of the walls. Moreover, the main results of the numerical simulations are reported and compared with those obtained from the tests in order to get a full comprehension of the different mechanisms affecting the response of the specimens.

Mesh reinforcement in masonry mortar coatings: a systematic literature review

Mortar coatings have a major influence on a building’s aesthetics, valorization, and habitability, with significant effects on the mechanical behavior of masonry walls. Multiple types of meshes can be embedded in plaster to enhance both masonry and coating’s mechanical behavior, restrain crack formation, enhance the bonding between layers, and increase the wall’s seismic resistance. The reinforcement technique has simple execution and is suitable for many applications, including the strengthening of non-load bearing walls, façade performance improvement, and restoration of historical buildings. However, there is an absence of guidelines and specifications for design and execution, resulting in high variability in field applications due to the many variables involved and few in-depth studies. This paper presents a systematic review of the effects of mesh reinforcement in cementitious mortar coatings and its major applications. Mortar and mesh parameters and influences, the status of analytical and simulation models, and suggestions for future research are described.

Non-Linear Analysis of URM Structures through a Multi-Unit Discretization Approach

This paper presents a benchmark study for the numerical simulation of unreinforced masonry walls under lateral loads using a new modelling strategy. The proposed MUDis (Multi-unit discretization) procedure foresees the discretization of masonry walls into a layout composed of modules, with pre-established geometry and sizes, identified to appropriately reproduce the typical in-plane collapse behaviour of masonry walls subjected to lateral loading. These modules are made of four elastic units separated by nonlinear interface elements that allow to reproduce the failure mechanisms along their surfaces. The mechanical parameters of the interface elements are described through appropriate parametric formulas that modify the “combined cracking-shearing-crushing” model proposed by Lourenco and widely used in the simplified micro-modelling of masonry structures for FE analysis purposes. The reliability of the proposed procedure, already calibrated and validated for two-dimensional panels, is assessed by reproducing the experimental behaviour of a more complex structure subjected to pushover analyses. The benchmark test considered herein is a masonry façade belonging to a three-dimensional building experimentally tested under lateral loads for which results are available in literature.

Experimental Analysis of Surface Application of Fiber-Reinforced Polymer Composite on Shear Behavior of Masonry Walls Made of Autoclaved Concrete Blocks

This paper presents the results of an experimental study of the shear behavior of masonry walls made of aero autoclaved concrete (AAC) blocks strengthened by externally bonded fiber-reinforced polymer (FRP) composites. Fifteen small wall specimens were constructed and tested in a diagonal compression scheme. Two types of composite materials—carbon- and glass-reinforced polymers—were arranged in two configurations of vertical strips, adopted to the location of the unfilled head joints. The effect of the strengthening location and strengthening materials on changes in the strength and deformability parameters are discussed and the failure process of unstrengthened walls is also presented. The placement of the composite on unfilled head joints proved to be a better solution. Carbon-fiber-reinforced polymer (CFRP) strips provided a threefold increase in stiffness, a 48% increase in load-bearing capacity and a high level of ductility in the post-cracking phase. Glass-fiber-reinforced polymer (GFRP) strips offered a 56% increase in load-bearing capacity but did not change the stiffness of the masonry and provided relatively little ductility. Placing the composite between unfilled joints was only reasonable for CFRP composites, providing a 35% increase in load-bearing capacity but with negligible ductility of the masonry.

Shear strengthening of masonry walls with Textile Reinforced Mortars (TRM) under high temperature exposure

The behavior of masonry walls strengthened with Textile Reinforced Mortars (TRM) is a topic that has received considerable attention from researchers in recent years. However, the response of such elements after exposure to high temperature is an issue that remains to be explored extensively. This study analyzes the behavior of TRM-strengthened brick masonry panels with glass and carbon fiber meshes subjected to temperatures up to 600 °C, and subsequently tested under diagonal compression. The reinforcements were applied before or after temperature exposure, to analyze the effectiveness of damaged or undamaged TRMs, thus simulating different scenarios that might occur in a real building under a fire event. In general terms, the results showed that TRMs with carbon fibers exhibited a better response in these conditions, restoring the walls to their original capacity and providing additional ductility, whilst reinforcements with glass fibers seemed to be more affected by temperature. Finally, the experimental results are here compared to predictions from available design guides, in order to assess the accuracy that these codes would provide in these circumstances.

Seismic vulnerability assessment of buildings: case study of Al Khalifa district, Fatimid Cairo

This work intends to provide seismic vulnerability analysis for a building stock in Al Khalifa District, Fatimid Cairo while focusing on the historic buildings in the area. The work represents part of an interdisciplinary study targeting the management and conservation of a UNESCO World Heritage Site. The project inspects several aspects including behavior of masonry walls, structural health monitoring of selected structures, conservation studies, in addition to influence of rising ground water. In the current study, seismicity of Egypt generally and Cairo specifically is reviewed. Afterwards, large-scale seismic vulnerability is adopted to calculate the vulnerability index for buildings within the study area. Data are collected through extensive on-site surveys for more than one hundred buildings. Observed typologies are listed alongside possible mechanisms of failure. Egypt has moderate seismic hazard; however, many buildings are prone to damage due to inadequate seismic design. This leads to retrofitting requirements to reduce seismic vulnerability and adhere to imposed seismic requirements in design codes. The study is intended to understand seismic risk of buildings within study area as part of a comprehensive study. Developed vulnerability map show that many buildings are prone to damage during seismic events.Article HighlightsSeismic vulnerability of building samples in a study area within Old Cairo is assessed and presented in the form of a vulnerability map.Structural characteristics of buildings are detailed and investigated.Signs of deterioration are analyzed, and mechanisms of failure are featured.

Investigation of Behavior of Masonry Walls Constructed with Autoclaved Aerated Concrete Blocks under Blast Loading

Autoclaved aerated concrete (AAC) blocks have widespread popularity in the construction industry. In addition to lightness, these materials have other advantages, including fire resistance, low acoustic and thermal conductivity, ease of cutting and grooving, and simple transportation. Since the behavior of AAC under severe dynamic loading conditions such as blast loads has not been adequately studied in the literature, in the current paper, the behavior of masonry walls constructed with AAC blocks was evaluated under blast loading. In this study, after performing experimental testing on materials and obtaining their compressive, tensile, and shear strength values, the finite element (FE) models of AAC-based masonry walls were created in the ABAQUS/Explicit nonlinear platform. Three different wall thicknesses of 15, 20, and 25 cm were simulated, and the models were analyzed under a lateral explosion caused by 5 and 7 kg of TNT at the stand-off distances of 2, 5, and 10 m from the wall face. The stress distributions, displacement responses, adsorbed energy, and crack propagation pattern were investigated in each case. The results showed the inappropriate behavior of these materials against explosion loads, especially at shorter distances and on walls with less thickness. The outcome gives valuable information to prioritize these walls for possible blast strengthening.

MUDis: A low computational effort multi-unit discretization procedure for modelling masonry walls with periodic arrangement

This paper presents an innovative modelling approach for assessing the in-plane behaviour of masonry walls characterized by periodic arrangements of units and mortar joints. The proposed model is a typical d-FEM (Discontinuum Finite Element Model) consisting of deformable macro-blocks covering more than a single unit of masonry and separated by a reduced number of interface elements, which are properly arranged along pre-established potential crack/slip surfaces. To account for the modelling simplifications deriving from the proposed multi-unit discretization (MUDis), three of the mechanical parameters describing the adopted interface model, i.e. the Composite Interface (CI) model formulated by Lourenço & Rots, are optimised through an Evolutionary Polynomial Regression (EPR) technique relying on a Multi-Objective Genetic Algorithm (MOGA).In the first part of the paper, benchmark experimental tests taken from literature are reproduced to calibrate conventional CI-based FEM models and to generate therefrom a wide stock of masonry panels. Afterwards, the novel MUDis approach is applied to the generated wall population in order to evaluate its capability of replicating the in-plane response of a considerable number of masonry walls regardless of their geometrical and mechanical features. Extensive details on how deriving the optimal parameters of the CI model to allow for the reduction of interface elements inherent to the MUDis approach are provided, followed by a sensitivity analysis to evaluate the mesh dependency of the results.Finally, the proposed MUDis procedure is cross validated against the experimental results of the initial benchmark tests, allowing to demonstrate its computationally efficiency with respect to conventional micro-modelling procedures.

A numerical homogenization method for the determination of the thermal bowing of a masonry wall exposed to fire: Application to natural stone masonry

Thermal bowing is one of the major concerns when analysing the structural behaviour of masonry walls in fire conditions, along with the loss of resistance due to material degradation. This contribution proposes a new homogenization method aimed at determining the thermal deformed shape of a masonry wall exposed to fire. First, the homogenized thermo-elastic characteristics of a natural stone masonry wall are determined taking into account the material properties of stone and mortar as functions of temperature increase, as well as the geometrical characteristics of their assembly. As a result, membrane and bending stiffness coefficients, as well as thermal-induced efforts, of the wall modelled as a homogenized plate are obtained. Such homogenized thermo-mechanical characteristics make it possible to determine the deformed shape of the wall after a certain time of fire exposure, through the formulation and the resolution of a finite element plate problem, making use of the previous homogenized stiffness characteristics. Numerical simulations show that the presence of joints has little influence on the deformed shape of the masonry wall compared to a homogeneous stone-only wall. They appear to be in rather good agreement with previous full-scale experimental tests carried out on limestone masonry walls, therefore providing a first validation of the proposed method, even though further improvements could be envisaged as regards a more reliable determination of the temperature gradient across the wall thickness.

In-plane behaviour of masonry walls embedding with steel welded wire mesh overlay with mortar

ABSTRACT This paper presents an experimental study of the structural behaviour of masonry walls strengthened with steel-welded wire mesh (WWM) overlay with mortar to improve their in-plane shear strength and deformation capacity. The experimental programme consists a compression testing of masonry prism and a diagonal compression testing of 15 wall specimens made of clay brick strengthened with four different WWM systems: (i) embedding WWM along the bed joint, (ii) embedding WWM along the bed joint and a strip diagonally crossing on wall surface, (iii) WWM alternately embedding along the bed joint and continue to the surface of wall and (iv) WWM fully cover on wall surface. The experimental results show that the adopted WWM-strengthening solutions produce a beneficial increase of compressive strength, shear resistance, ductility and energy dissipation capacity making them suitable for seismic strengthening.

Numerical Analysis to Evaluate the Structural Performance of NFRCM (Natural Fabric-Reinforced Cementitious) Strengthened Masonry

The innovative sustainable technology based on natural fabric-reinforced cementitious matrix (NFRCM) is analyzed for strengthening masonry. A new frontier for composite materials is proposed as an alternative to well-known traditional technologies used to improve the seismic behavior of buildings, such as the portuguese technique ‘gaiola pombalina’, the Italian ‘baraccata house’ and the turkish ‘himis house’. Preliminary sensitivity analysis is performed on NFRCM and ‘baraccata’ numerical models. Both technologies are numerically compared. From the experimental results of in-plane incremental load test carried out by CNR-Ivalsa a numerical model is calibrated by non-linear pushover analysis to evaluate the behavior of masonry wall strengthened with natural fibers. This paper demonstrates the effectiveness of NFRCM systems for strengthening masonry as: i) a non-invasive solution without significant thickness; ii) a sustainable technology; iii) an intervention involving the whole wall surface avoiding failure local mechanisms.

Retrofitting with FRCM Composites: Shear and Flexural Behaviour of Strengthened Masonry Walls

Structural strengthening using composite materials is nowadays one of the most interesting techniques to overcome weaknesses of masonry structures constituting large part of the building heritage. The use of FRCM composites is becoming more and more widespread due to some limitations of FRP retrofitting systems. In this framework, the presented experimental study is aimed at evaluating the in-plane and the out-of-plane behaviour of masonry walls strengthened with different types of FRCMs, analyzing in detail failure modes, capacity increments and efficiency of the strengthening systems when tested using two different configurations. To this purpose, bidirectional basalt grids and unidirectional steel fiber sheets, coupled with a lime based mortar, were used for retrofitting clay brick masonry walls subjected to diagonal compression tests and out-of-plane flexural tests. Experimental outcomes, when considering the in-plane or the out-of-plane direction, show that the adopted different layout strictly influences the flexural and shear strengthening efficiency of the reinforcement.

A theory-based simplified trilinear model for characterisation of the out-of-plane behaviour of URM walls

Observations recorded after recent earthquakes have shown that out-of-plane failure of unreinforced masonry elements on unreinforced masonry buildings and to reinforced concrete buildings constitutes a serious hazard to life. This has led to the development of a wide variety of models and approaches, from simple analytical to complex numerical simulations. Within this framework, the present paper proposes an analytical approach derived from theoretical considerations to characterise the complete out-of-plane seismic response curve of unreinforced masonry cantilever walls. Masonry parapets and historical façades fall within this scope, since it was not customary to firmly connect walls to the horizontal structural elements in the past.This research also provides a straightforward way of elaborating a simplified trilinear version of these curves by means of a series of non-dimensional mathematical expressions. Additionally, the characterisation of the oscillating periods and the kinetic energies of the walls are thoroughly discussed. Finally, the capability of the approach in terms of capturing linear and non-linear behaviour of masonry walls under horizontal loads is demonstrated via comparison with several tests reported in the literature.

Experimental study on one-way arching masonry specimens under monotonic and cyclic loads

Characterizing the behavior and the mechanical properties of masonry assemblies subjected to out-of-plane static loading is a fundamental step towards the understanding of their response to more complex loading scenarios. The more challenging case is that of arching walls where the load resistance mechanism couples bending and axial components. This study presents a combined experimental and theoretical effort aiming at gaining insight into the behavior of such arching walls. The experimental phase is conducted on small-size one-way specimens that are comprised of two or four masonry units loaded in a four-point-bending scheme. The experimental methodology aims at collecting new quantitative data on the response under monotonic and cyclic loadings. The 2-block configuration mimics the basic form of arching walls and focuses on the interaction between the masonry units and the mortar layer, features that are essential for any quantitative, analytical or numerical assessment of such walls. The 4-block configuration mimics the more complex response when additional mortar joints are part of the structural system. Along with the global load–displacement curve, the experiments also monitor the arching force, as well as local aspects such as the axial deformations at the tensed and compressed extreme fibers of the mortar joints. The latter aims at studying the constitutive behavior of the mortar joints. The complete set of test results is then used as a benchmark for comparison with an analytical model. The comparison examines the model capabilities, reveals further aspects of the physical behavior, and explores the cracking process, the deformation profile, and the effect of inelastic behavior of the mortar material. The combined experimental and theoretical findings reveal the spectrum of phenomena governing the behavior of masonry walls and highlight the role of the arching mechanism through macro and micro perspectives.

Micro-mechanical FE modelling and constitutive parameters calibration of masonry panels strengthened with CFRP sheets

This paper describes the development of a micro-mechanical Finite Element model apt to reproduce the behavior of masonry walls reinforced with Carbon Fiber Reinforced Polymer (CFRP) sheets, monotonically loaded by out of plane actions. According to the results of previous experimental programs carried out by the Authors, in the case of CFRP sheets bonded parallel to the bed joints, such walls behave like un-connected masonry portions (similar to strengthened masonry beams). For this reason, only such effective part was considered in both the experimental program (already published by the Authors) and the numerical simulations. Both simply bonded and anchored CFRP reinforcements have been considered in the paper.Particular attention was paid to the definition of the constitutive parameters, calibrated on the basis of several experimental campaigns previously performed by the Authors. Since fracture energy of bulk materials and adhesive tangential strength of the reinforcement are generally thought of as difficult to experimentally determine and can be affected by uncertainties, a sensitivity analysis concerning such parameters is described in the paper.The numerical predictions have been compared to the experimental outcomes in terms of load displacement diagrams, stress distribution and damage evolution; the proposed numerical model seems to well reproduce the general experimental behavior.