Unreinforced Brick Masonry Walls Research Articles

A block-based numerical strategy for modeling the dynamic out-of-plane behavior of unreinforced brick masonry walls

AbstractIn this paper, a numerical procedure is proposed to simulate the dynamic out-of-plane response of unreinforced masonry (URM) walls. A state-of-the-art damaging block-based model, originally developed for quasi-static simulations, is extended for the first time in a dynamic regime. The blocks are represented using solid 3D finite elements governed by a plastic-damage constitutive law for both tension and compression. A cohesive-frictional contact-based formulation is used to account for interactions between the blocks. A simplified mechanical characterization is formulated to improve efficiency in wall-level analyses. Dynamic simulation is performed using a generalized HHT-$$\alpha$$ α direct integration implicit solver and by implementing Rayleigh damping in the bulk. Such consideration allows the use of both mass and stiffness proportional terms of the Rayleigh damping without compromising efficiency. The strategy is applied to simulate incremental dynamic experiments performed on full-scale walls, showing good agreement between numerical and experimental results. The calibrated numerical model is then optimized to reduce computational effort while maintaining accuracy. The optimized model is used to investigate the effect of relative support motion on the one-way bending out-of-plane seismic response of URM walls, demonstrating the potential of the modeling strategy to explore the effect of boundary conditions that occur in real buildings but are often overlooked in laboratory experiments. This investigation also explores the adequacy of simplifications in capturing the effect of relative support motion, which can be adopted for simple modeling strategies commonly used in standard engineering practice.

Masonry Shear Triplets Coated with Fiber Reinforced Mortars

Unreinforced brick masonry walls (URM) have been widely used in construction for centuries and represent a large part of building heritage. However, these walls are prone to cracking and failure under certain loading conditions. Addressing this issue requires a comprehensive understanding of URM structures and the implementation of effective retrofitting techniques to enhance their structural integrity. wherefore, researchers have proposed the use of thin Fiber reinforced mortar coating as a reinforcement technique. This experimental study aims to investigate the effectiveness of this approach in improving the behavior of perforated brick masonry walls. To carry out this investigation, a shear triplets test under uniaxial loading has been conducted to evaluate the performance of the reinforcement technique. A series of shear triplets were built with perforated masonry of dimensions (220 x110 × 55) using bastard mortar (1: 1: 5). These specimens were coated with a thin layer of polypropylene fiber reinforced mortar. The test results of the reinforced and unreinforced specimens were compared to analyze the effectiveness of this technique of reinforcement. The test results showed that the application of fiber reinforced coating significantly increased the deformation ability and improved the stiffness and the bond strength of the masonry walls.

Low-velocity out-of-plane impact tests on double-wythe unreinforced brick masonry walls instrumented with optical measurements

Unreinforced brick masonry makes up today a significant piece of the European built environment, including not only residential buildings but also strategically important structures that are not designed to withstand blasts and impacts. Yet, it is difficult to accurately estimate the response of these structures and the extent of damage they sustain during such extreme loading conditions. This paper presents the implementation and discusses the results of laboratory impact tests conducted on natural-scale double-wythe unreinforced brick masonry walls, a typology that is frequently found in Northern Europe. The walls were spanning vertically between two reinforced concrete slabs and were subjected to low-velocity drop-weight pendulum tests in which they were repeatedly hit until the opening of a breach in the centre of the wall. The tests were instrumented with both hard-wired and optical measurements, the latter consisting of high-speed cameras and digital image correlation techniques, to face the difficulty of observing cracks and determining the deflections of the walls with adequate accuracy at the time of the impact. Investigated in these tests were the out-of-plane response of the walls and their capacity to resist the impacts. The axial load applied on the top of the walls was varied for two wall configurations and monitored throughout the tests to study the effect of arching on the failure mechanism produced and number of repeated hits needed to open the breach. Of interest was also the evidence of cracking, more specifically the way it initiated on the undamaged walls and next propagated upon consecutive hits. The data generated from these tests are made available to support further investigations on masonry structures subjected to extreme actions.

Modeling of crashworthy foam mounted braced unreinforced brick masonry wall and prediction of anti-blast performance

Explosions are continually occurring in many parts of the world endangering human lives and seriously affecting the health of infrastructures and facilities. Low-rise buildings having a height of fewer than 13 m are load-bearing structures generally made of unreinforced masonry (URM), particularly in semi-urban areas, villages, and war-prone border areas. Many structures of importance including buildings constructed in the pre- and post-independence era of courts, monuments, etc., are masonry load-bearing structures. URM is also used as non–load-bearing partition walls and compound/boundary walls. Such walls are susceptible to out-of-plane blast loading. Under such loadings, these walls fail to survive and thus either get severely damaged or collapsed, jeopardizing the stability of the entire structure. Resistance of masonry walls against blast loading is vital for the safety of the building and its users as injuries sustained and casualties are generally not caused due to explosion, but by the brittle dynamic fracture and fragments of masonry walls, window glass panes shattering, and other secondary objects propelled as missiles by the blasts. In general, buildings are not designed for blast loading. For the safety of the building users, it is imperative that the walls must withstand such short-duration high-magnitude extreme loadings without not only undergoing catastrophic collapse but also not producing deadly fragments which could cause grievous injuries to the users. To protect URM walls from high-intensity blast waves, an out-of-box wall protecting technique using foams of polymer (e.g., polyurethane) and metals namely; aluminum and titanium, is considered on the face of the wall exposed to the blast pressure. This study describes a numerical technique implemented in ABAQUS/Explicit software to predict the overall anti-blast performance of URM wall strengthened externally with the above three different crashworthy foams. For this purpose, a braced URM wall made of clay bricks, with two transverse bracing walls one at each end on the same side, tested experimentally by Badshah et al. in the year 2021 under the chemical explosive loads of 4.34 kg and 7.39 kg-TNT, respectively, at scaled distances 2.19 m/kg1/3 and 1.83 m/kg1/3 is considered as the reference model and is validated against the test observations. Explosion load is modeled with ABAQUS built-in ConWep simulation program to simulate the wall-explosion wave interactions in the free field. Material nonlinearities of the brickwork have been attributed to bricks, joint-mortar, and brick-mortar interfaces through constitutive laws considering strain-rate effects. The foams are modeled using ABAQUS’s inbuilt Crushable Foam Plasticity Hardening model considering foam hardening and rate-dependent schemes. Results show that the higher Young’s modulus and inelastic stiffness of the foams contribute to dissipating more explosion energy and improve the resistance of the walls from savage explosions.

Experimental and Numerical Study on Unreinforced Brick Masonry Walls Retrofitted with Sprayed Mortar under Uniaxial Compression

The use of shotcrete or sprayed mortar is a common construction alternative to retrofit unreinforced brick masonry (URM), and extensive research has already been carried out in this area. However, most studies have been conducted on lateral strength, for example, eccentric compression or seismic forces. On the other hand, there are few studies about uniaxial compression, and the results of most studies confirm a strong relationship between the thickness of the retrofitting layer and whether it is a double-sided retrofitting section. However, most studies are exclusively experimental, with few samples, and lack numerical analysis; therefore, deeper research is required on this issue. In this sense, this paper combined experiments and finite element (FE) simulations to further study the uniaxial compression. A series of cyclic uniaxial compression experiments on URM retrofitting with sprayed mortar were performed. The experimental results were used to calibrate the FE model. Using these calibrated FE models, more variable parameters were run so that more reference results could be obtained. Moreover, the resulting damageable model of FE will be useful for studying the behavior in the inelastic phase. Results found that the compression strength of most composite walls retrofitted with sprayed mortar increases with the thickness of the sprayed layer and can improve the construction defects of the masonry itself. An over-thin sprayed layer reduces the range of the elastic phase of the composite wall. This phenomenon tends to stabilize with increasing thickness. The ultimate strength of the composite masonry is generally positively correlated with the overall increase in the thickness of the sprayed mortar but may cause a negative contribution to the ultimate strength of the composite masonry when the sprayed layer is too thin. The contribution of double-sided spraying to the ultimate strength of the composite wall was not as large as expected, but the contribution to the improvement of the elastic modulus of the wall was significant.

Damage Prediction of Monolithic and Non-Monolithic Braced Unreinforced Brick Masonry Walls under Explosion Loadings

Numerous unreinforced masonry (URM) structures worldwide face greater vulnerability to direct threats like earthquakes, wind, impact, or explosions compared to reinforced concrete and steel structures. Given the current worldwide environment characterized by dominance and extremism, the task of safeguarding structures, especially from explosive detonations, presents a growing and crucial obstacle for engineers and researchers. The Masonry Society (TMS) and the Federal Emergency Management Agency (FEMA) have recognized that the primary cause of material damage resulting from explosions is the collapse of walls made of URM. The recent catastrophic explosion at the Beirut seaport in Lebanon, the largest of its kind, serves as a stark reminder to town planners, architects, and structural designers. This tragic incident resulted in an immense loss of building infrastructure overall and specifically affected load-bearing masonry structures, leading to severe injuries and casualties. It underscores the urgent need for comprehensive attention and strategic measures in addressing the vulnerabilities inherent in these structures. This research study explores the response of URM walls, constructed with clay bricks, to out-of-plane blast forces. The walls are braced with either monolithic or non-monolithic transverse walls, and a three-dimensional micro-modeling approach is employed. The analysis is conducted using the Abaqus software, which utilizes the finite element method. Alongside the braced walls, the study also examines a free-standing URM wall without transverse walls. The exposed face of the walls is subjected to peak reflected pressures of 0.38 and 1.01 MPa, generated by explosive charges weighing 4.34 and 7.49 kg-TNT at scaled distances of 2.19 and 1.83 m/kg1/3, respectively. The Concrete Damage Plasticity (CDP) model, which incorporates the influence of strain rate, is utilized to simulate the behavior of masonry under blast loads. Comparisons are made between the computed damage patterns of a wall reinforced with monolithic transverse walls and the experimental results found in existing literature, revealing a notable level of agreement. The influence of both monolithic and non-monolithic joints on the performance of the exposed wall is thoroughly examined and contrasted with one another, as well as with the performance of a free-standing wall. The research indicates that non-monolithic joints between the exposed wall and transverse bracing walls exhibit a greater extent of damage to the bracing walls, as this is predominantly influenced by the response of the exposed wall itself.

Strength Performance of the Connection between Brick and SPF Lumber

There are many ways to strengthen an unreinforced brick masonry wall. One of the strengthening methods applies timber, which is a lightweight and easy installation. The connection between the timber and the brick masonry wall plays an important role. In this study, the experimental and theoretical methods were investigated, and the pullout and shear strengths of the chemical anchor were employed as the connection between clay brick and SPF (spruce, pine, fir) lumber. Three bolt diameters (ø8, ø10, ø12 mm) were utilized in nine pullout tests and two types of eighteen shear tests. Four types of prediction models estimated the pullout strength of the chemical anchor. The European Yield Theory (EYT) expected the shear strength of the chemical anchor, involving six failure modes. The results of all experiments were discussed as failure mode, strength, and stiffness under monotonic load. Finally, the effective result of this study highlights A12 specimens using ø12 mm bolt and employing the epoxy resin in brick and lumber. The maximum pullout load of A12 specimens is 12.1 kN, and the yield shear load is 11.2 kN.

In-Plane Seismic Behavior of Brick Masonry Walls Reinforced with Twisted Steel Bars and Conventional Steel Bars

The in-plane seismic performance of old unreinforced brick masonry walls strengthened with stainless-steel twisted bars and conventional steel bars (usually used in concrete reinforcing) was investigated in the present study. For this purpose, a total of seventeen masonry wallettes reproducing masonry walls of traditional Lisbon buildings from the 1930s–1950s (known as “placa” buildings) were constructed. The specimens were assembled using original bricks from demolished old buildings and a sand-cement bedding mortar with the same proportions as reported in building design documents of the time. Out of the fourteen wallettes tested in diagonal compression, three were unreinforced, and eleven were strengthened in different layouts. Additionally, axial compression tests were performed on the other three unreinforced masonry wallettes. The tested specimens were reproduced with numerical models calibrated based on the experimental results. The experimental and numerical results of the reinforced specimens were compared to the unreinforced specimens to draw conclusions on the effectiveness of the strengthening solutions when applied to masonry walls of the typology under study. The most important result of the strengthening was an important increase in the ductility of the specimens that were originally brittle. In addition, in some cases a slight increase of shear strength was also observed.

Strengthening of braced unreinforced brick masonry wall with (i) C-FRP wrapping, and (ii) steel angle-strip system under blast loading

Accidental detonations, and explosions made by extremists are major threats to human life and building structures. The vulnerability of the load-bearing masonry structures is more as compared to the reinforced concrete structures against explosion-induced loadings. Such events weaken the socio-economic stability and therefore necessitates the evaluation and effective strengthening strategies of masonry structures to improve their blast performance. Unreinforced masonry (URM) walls have little flexural resistance against out-of-plane loadings and exhibit a brittle mode of failure. In this research work, the clay brick masonry wall braced with two transverse walls one at each end, tested experimentally under the explosive loads of 4.34 and 7.49 kg-TNT equivalent at scaled distances 2.19 and 1.83 m/kg1/3, has been numerically analyzed using a high-fidelity commercial FEM-based dynamic computer program, ABAQUS/Explicit-v.6.15 considering micro-modeling technique and concrete-damaged-plasticity (CDP) model with strain rate effect. Damage in the exposed masonry wall in the form of (i) vertical mortar joint cracks at the center and next to the bracing transverse walls, (ii) flexural cracks near the ground; and diagonal cracking in the lower part of the bracing walls, is observed at a scaled distance, Z = 2.19 m/kg1/3. For Z = 1.83 m/kg1/3, out-of-plane catastrophic collapse of the walls occurs. The computed damage patterns are found quite similar to the experimental ones in the open literature. A novel strategy other than commonly used carbon fiber reinforced polymer (C-FRP) wrapping technique, consisting of steel angle-strip system has been devised and used to strengthen the wall against the considered blast levels. CFRP wrapping of 2mm thickness, and steel strip mesh of thickness (a) 3mm, and (b) 5mm with angles along the edges of the walls, are considered to improve the wall response and analyses are carried out. The blast load-carrying mechanisms of the walls strengthened with the two techniques are explained.

Response of strengthened unreinforced brick masonry wall with (1) mild steel wire mesh and (2) CFRP wrapping, under close-in blast

In the past few decades, the world is experiencing a number of frequent and unanticipated blast explosions. Property loss and casualties caused by these blasts are of great concern to state authorities and are of sufficient interest to the structural engineers and researchers. A common structural member in the buildings used for both commercial and residential formats is load-bearing brick masonry walls. For the safety of a structure, the masonry walls which are more vulnerable against such loadings are required to be strengthened. Many retrofitting techniques to strengthen the masonry walls are in vogue. In the present study, a detailed micro-model of 1600 mm × 2100 mm × 240 mm (length × height × thickness) clay brick unreinforced masonry wall has been developed, analyzed, and validated with the available experiment results, using the ABAQUS/Explicit software under the 5 kg-TNT blast load at scaled distance 0.58 m/kg1/3. The Concrete Damage Plasticity (CDP) model including the strain rate effects is used to model the masonry material behavior to blast loading. To improve the response of the wall, it has been strengthened with (1) mild steel wire mesh of different thicknesses 2.50, 3.50, and 4.50 mm (i) on the rear face only, and (ii) on both the faces of the wall; and (2) carbon fiber-reinforced polymer (CFRP) wrapping (i) 0.50 and 0.60 mm thick on the rear face only, and (ii) 0.30 mm thick on both the faces of the wall. Response of the strengthened walls is discussed and compared. The equivalent thickness of the wrapping to the steel wire mesh from displacement and damage point of view has been evaluated.

Experimental and Numerical Study on Unreinforced Brick Masonry Walls Retrofitted with Sprayed Mortar Under Axial Compression

Experimental and Numerical Study on Unreinforced Brick Masonry Walls Retrofitted with Sprayed Mortar Under Axial Compression

Strengthening of Un-Reinforced Brick Masonry Walls Using Epoxy Mortar

Abstract This study is carried out to investigate the effectiveness of using externally applied epoxy mortar on joints of masonry wall panels to enhance their load carrying capacity under axial compressive and lateral loads. A total of six 113 mm thick masonry wall panels of size 1200 x 1200 mm were constructed for this study. Four out of six walls were strengthened using locally available CHEMDUR-31 epoxy mortar on joints. The remaining two walls were tested as control specimens. The control and strengthened wall panels were tested under axial compression and lateral loads. In axial compression test, out of plane central deflection and vertical strain at the center of wall panel were recorded while in lateral load test, in-plane lateral displacement of wall and horizontal strain at the center were recorded at each load increment. Failure pattern of each wall panel is also studied to notice its structural behavior. The results of this experimental study showed an increase of 45% and 60% in load carrying capacity under axial compression and lateral bending, respectively by the use of strengthening technique employed in this study.

Numerical and experimental study of unreinforced brick masonry walls subjected to blast loads

Numerical and experimental study of unreinforced brick masonry walls subjected to blast loads

Experimental and numerical investigation of strengthening of openings in masonry walls using steel bars and steel wire mesh

This article presents experimental and numerical study of strengthening brick masonry walls loaded with service loads where openings are required to be made, the studied strengthening is made using steel wire mesh or near-surface mounted steel bars. The experimental program consisted of twelve unreinforced brick masonry walls loaded vertically by the service loads; six control walls were not strengthened, three walls were strengthened by steel wire mesh on both faces and steel bars were inserted around the required opening for the last three walls. Three control unstrengthened walls were not opened while openings were made in nine loaded walls; then the load was increased for all walls until failure. The experimental results showed that the applied strengthening methods managed to compensate the decrease of wall capacity due to opening. Numerical modelling and nonlinear analysis were made using finite element analysis software ANSYS v.15; the numerical results showed good agreement with the experimental results. Further, a parametric study was performed to explore the effect of several variables concerning aspects of the wall and strengthening materials. The obtained results demonstrate that the numerical approach can be used to study and design strengthening for load-bearing masonry walls in existing buildings in case it is required to make openings in the walls.

Simplified methodologies for assessing the out-of-plane two-way bending seismic response of unreinforced brick masonry walls: lessons from recent experimental studies

This paper describes a simplified methodology for the assessment of unreinforced masonry (URM) walls under out-of-plane two-way bending seismic action. The methodology involves a force-based check derived from the principle of virtual work. This check is proposed based on experimental observations of significant cracking resistance associated with two-way spanning URM walls, indicating methodologies considering such walls to be pre-cracked or to be non-laterally supported as overly conservative. The methodology incorporates several findings and developments from recent experimental campaigns: ranging from novel characterization tests on masonry couplets to incremental dynamic tests on full-scale buildings. Such incorporations include new formulation to calculate the torsional shear strength of a bed joint and accounting for possible changes in the boundary conditions of an OOP wall during dynamic loading. Testing standards as well as recommendations in several international guidelines for masonry structures addressing the input properties required to implement the proposed methodology are enlisted and reviewed. The methodology requires the definition of the period of vibration of the assessed URM walls, to calculate which plate theory based formulation is provided. Open research questions and potential avenues for further development of the methodology are ultimately highlighted.

Experimental and Numerical Study of Behaviour of Reinforced Masonry Walls with NSM CFRP Strips Subjected to Combined Loads

Near surface mounted (NSM) carbon fibers reinforced polymer (CFRP) reinforcement is one of the techniques for reinforcing masonry structures and is considered to provide significant advantages. This paper is composed of two parts. The first part presents the experimental study of brick masonry walls reinforced with NSM CFRP strips under combined shear-compression loads. Masonry walls have been tested under vertical compression, with different bed joint orientations 90° and 45° relative to the loading direction. Different reinforcement orientations were used including vertical, horizontal, and a combination of both sides of the wall. The second part of this paper comprises a numerical analysis of unreinforced brick masonry (URM) walls using the detailed micro-modelling approach (DMM) by means of ABAQUS software. In this analysis, the non-linearity behavior of brick and mortar was simulated using the concrete damaged plasticity (CDP) constitutive laws. The results proved that the application of the NSM-CFRP strips on the masonry wall influences significantly strength, ductility, and post-peak behavior, as well as changing the failure modes. The adopted DMM model provides a good interface to predict the post peak behavior and failure mode of unreinforced brick masonry walls.

Stiffness and Strength Estimation of Damaged Unreinforced Masonry Walls Using Crack Pattern

ABSTRACT After an earthquake, the residual stiffness and strength of structural elements are typically estimated based on a qualitative visual inspection of cracks that is prone to error. In this paper a new approach is proposed to automatically estimate the updated stiffness and strength of damaged unreinforced masonry walls by characterization of crack patterns by a mathematical index. It is shown that structural and textural fractal dimensions of a crack pattern reflect the extent of cracking and the type of cracking or crushing, i.e., whether the cracks pass through joints or whether bricks have been damaged and crushed. Using results of six quasi-static cyclic tests on unreinforced brick masonry walls with different failure modes at various drift ratios, it is shown that the structural and textural fractal dimensions of the crack patterns are an accurate predictor of the stiffness and strength degradation. This procedure seems therefore a promising approach for replacing the traditional assessment methods that are based on visual inspection and engineering judgment by an analytical procedure based on image processing that can eventually be completely automated.

Effect of Pre-stress in Steel Strips to Strengthen Unreinforced Brick Masonry Walls under Axial Loads

Using steel strips to strengthen the existing unreinforced masonry walls has competitive advantages, which includes no wet work, avoidance of formwork, time saving, ease of installation, minimal increase of dimensions, no requirement for material strength of the existing walls and good reversibility. In this paper, seven specimens were fabricated and tested under axial loads for obtaining the effect of pre-stress in steel strips to strengthen unreinforced brick masonry walls. Test results showed pre-compression stress in the vertical steel strips could increase the load of cracks in the single brick in the wall, otherwise steel strips only improved the load of continuous cracks and the failure load, and the axial stiffness of the wall; when the transverse steel strips were pre-tensioned, it could further improve the failure load and the later axial stiffness of the strengthened wall.

FRCM strengthening systems efficiency on the shear behavior of pre-damaged masonry panels: an experimental study

Existing masonry constructions are highly vulnerable to seismic actions, as demonstrated by the severe earthquakes which stroke the Italian territory in recent years, causing great damages, especially in old masonry buildings. Therefore, restoring damaged buildings, with the aim to recover or improve their structural capacity, is a key aspect in the post-seismic interventions. Fiber reinforced composite materials could be effectively used to this purpose. One aspect which is worth to investigate is the application of these reinforcement typologies on damaged structural elements. Even though many experimental campaigns are available concerning the mechanical improvement given by composite materials applied on undamaged structural elements, only few can be found considering strengthening of already damaged masonry walls. The objective of the work here presented is to evaluate the shear response of damaged masonry panels strengthened using fiber reinforced cementitious matrix (FRCM). Two unreinforced brick masonry walls were subjected to diagonal compression tests, producing an extended state of damage. Afterwards, the same walls were strengthened with FRCM and diagonal compression tests were again performed. Comparisons were done between the results of the unreinforced samples and the pre-damaged strengthened ones, in terms of shear strength and post-peak behavior. The FRCM retrofitting system was also used to strengthen an undamaged masonry panel, which was tested in order to analyze similarities and differences with respect to results obtained for pre-damaged samples. The experimental campaign allowed to study the sole contribution of the reinforcement to the shear capacity of the wall panels. Results showed that the presence of FRCM reinforcements on damaged masonry panels influenced the shear behavior of the samples, which experienced a more ductile failure.

Investigación del colapso de un muro de mampostería de ladrillo no reforzada bajo fuerzas de vientos moderadas

Several methodologies used for the collapse assessment of an unreinforced brick masonry wall subject to out-of-plane bending due to moderate wind loads in Medellin, Colombia are presented. Models include a rigid cantilever model of masonry elements, deformable cantilever and frame models of intermediate concrete columns and beams with and without masonry contribution to the wind resistance, and a finite element model with all concrete frame elements, masonry units and panel openings modeled explicitly. Wind demands are estimated using spatial interpolation of actual wind velocity measurements near the site. Results are presented in terms of peak deflections at the wall top, as well as peak force and stress demand-to-capacity ratios on concrete frames and masonry elements, respectively. Wind pressure distribution, P-Delta effects, interaction and relative contribution to the out-of-plane bending resistance of concrete framing and masonry elements with either one- or two-way action are shown to be the main parameters affecting results, in addition to model selection. Despite significant differences between models, recommended parameters and assumptions lead in all cases to the correct determination of the wall's imminent collapse under the estimated wind demands.