Performance Of Unreinforced Masonry Walls Research Articles

Seismic Performance of Unreinforced Masonry Walls with Various Retrofitting Methods

ABSTRACT This study proposed practical retrofitting methods to enhance the seismic performance of unreinforced masonry walls, utilizing textile-reinforced mortar (TRM) composites, glass fiber-reinforced polymer (GFRP) strips, and fiber-reinforced cementitious composites (FRCC). Retrofitting materials were applied at wall boundaries using the cast-in-place method with and without anchorage. Four masonry wall specimens, one control and three retrofitted, were fabricated and tested under lateral cyclic loading conditions to assess retrofitting efficiency. Various parameters were assessed, including hysteresis response, ductility, stiffness degradation, and energy dissipation capacity. The results indicated that TRM and FRCC retrofitting techniques exhibited an improvement in both the strength and deformation capacity. Among the retrofitting approaches, FRCC combined with steel reinforcement anchored to bottom beams showed superior performance Meanwhile, although exhibiting strength improvement, the ductility of the specimen retrofitted with FRP strips decreased post-peak due to severe splitting cracks. Lastly, an analytical strength model was proposed to predict lateral load-carrying capacity, demonstrating a reasonable correlation with test results. For the future application of the proposed retrofit methods, appropriate anchorage details for TRM and GFRP techniques are needed to be developed which could enhance deformation capacity in the post-peak stage of the retrofitted walls.

Dynamic behavior of axially loaded masonry walls strengthened with different innovative techniques under explosion loading

In the realm of construction engineering, brick masonry stands out as a pivotal structural element, renowned for its widespread application. Given the load-bearing nature of masonry structures, the ramifications of wall failure under extreme loads induced by explosions are profound. Particularly concerning is the out-of-plane failure of walls, which occurs without warning and affords scant time for assessment of their response. Brick masonry, characterized by its brittleness and susceptibility to cracking, presents inherent challenges in this regard. Recent examples, such as the Beirut explosion in 2020 and the Nashville bombing in 2020, vividly illustrate the devastating consequences of inadequate blast resistance in masonry structures. These incidents serve as poignant reminders of the imperative to fortify masonry constructions against explosive threats. While ample research exists on the behavior of free-standing braced and unbraced masonry walls subjected to explosive loading, there remains a notable gap in understanding the response of strengthened masonry walls exposed to blast loading, especially when carrying varying axial loads. This study addresses this gap by investigating different strengthening methodologies, namely (1) Cement-mortar plaster, (2) Ferro-cement, and (3) Carbon Fiber-Reinforced Polymer (CFRP) laminate, aimed at enhancing the anti-blast performance of unreinforced masonry walls. The experimentation focuses on a specific unreinforced masonry wall measuring 5000 × 2800 × 230 mm3, constructed from clay bricks and subjected to axial compressive loads of 51, 30, and 9kN/m, corresponding to the loads on the 1st, 2nd, and 3rd storey walls of a 3-storey masonry building, respectively. Utilizing a sophisticated finite-elements code, Abaqus, equipped with an explicit module and Concrete Damage Plasticity model, the blast simulations are meticulously conducted. The walls are meticulously modeled through detailed micro-modeling techniques. Results showed that the utilization of CFRP on the explosion-facing surface of the wall resulted in a remarkable reduction in damage, with the highest decrease of 64% achieved under the lowest axial compression. Conversely, the minimum decrease of 61.71% was recorded under maximum axial compression, highlighting the efficacy of CFRP in mitigating damage caused by explosions on walls. This research sheds light on effective methods to enhance the blast resistance of masonry walls, offering valuable insights for improving structural resilience and informing building codes. Its findings are crucial for ensuring the safety and security of infrastructure against explosive threats, ultimately safeguarding lives and property.

Performance of Unreinforced Masonry Walls in Compression: A Review of Design Provisions, Experimental Research, and Future Needs

Unreinforced masonry (URM) is a construction of brick or concrete block unit that is joined together using mortar, without steel reinforcement. Because of the heterogeneous nature and difference in mechanical properties of the masonry elements, analyzing and capturing the structural behaviour of URM walls under various loading conditions is therefore complex. In recent decades, research efforts have been focused on addressing and understanding the compressive behaviour of URM walls from the experimental viewpoint. However, from the existing experimental literature, there is a significant degree of variation in the mechanical and geometric properties of URM walls, especially the comprehensive comparison of apparently equivalent test parameters, which has yet to be examined. It is therefore necessary to highlight and critically examine major results derived from the experimental literature to better understand the performance of URM walls under compressive loads. This review paper presents the assessment performance with regard to axial compressive tests on URM walls, along with comprehensive comparisons among the experimental literature findings on the basis of masonry construction methods and various influencing parameters. Emphasis in the literature has been placed chiefly on the masonry elements, design provisions, axial load, slenderness ratio, openings, and stress–strain response. Based on observations from the study, experimental development trends have been highlighted to identify and outline potential directions for future studies.

Experimental Studies on Blast Performance of Unreinforced Masonry Walls: A state-of-the-art review

A large proportion of India’s residential buildings is of unreinforced masonry (URM) and falls under the category of non-engineered structures. URM walls in the residential buildings, customarily constructed from clay bricks or concrete blocks and cut stones, are found to be braced and therefore able to carry some out-of-plane loads produced by wind and earthquake, and survive. However, they are found to be more vulnerable to high air-pressure generated by explosive-induced detonations. Sufficient amount of investigations has been made by engineers to study the effect of brick strength, mortar strength, boundary conditions, wall thickness, and Young’s modulus of masonry on the blast performance of the URM walls. In this paper, available experimental studies on clay-brick and concrete block URM walls subjected to explosive-induced blast loading are briefly reviewed and summarized in tabular form. Studies conducted to improve the blast resistance of the walls using GFRP strips, GFRP rods, and Polyurea coating, and their effect on mid-span deflection, damage, and cracks have also been reviewed. It has been observed that the effect of brick strength and mortar strength on maximum mid-span deflection and damage resistance of the walls is insignificant under higher peak reflected blast pressures (> 2 MPa). Besides, the walls strengthened with the GFRP strips or Polyurea coating performed better with regards to mid-span deflection, damage, and cracking. The influence of Young’s modulus of masonry on the blast response of the walls is found to be more effective in reducing the maximum mid-span deflection. Also, the failure mechanism of the walls is found to be highly dependent upon the peak overpressure, duration of the blast, and support conditions.

SEISMIC PERFORMANCE EVALUATION OF RC BUILDINGS CONSIDERING THE IN-PLANE AND OUT-OF-PLANE PERFORMANCE OF UNREINFORCED MASONRY WALLS

An evaluation procedure of the seismic performance of overseas RC buildings with unreinforced masonry walls is proposed and applied to an urban residential building in Nepal. The structural performance of unreinforced masonry walls in the out-of-plane as well as in-plane directions is considered in the proposal. Consequently, the seismic performance of the building of interest was reliably evaluated considering the in-plane effects of brick walls; namely, it was confirmed that the brick walls did not collapse in the out-of-plane direction under the analytical conditions adopted in the present study.

Seismic performance of crack-damaged masonry wall structures via shaking table tests

Masonry fence walls in run-down areas have cracks of various shapes, and these cracks can weaken the walls very seriously. However, research on this subject has been scarce, and the effect of different crack types on the seismic performance of unreinforced masonry walls needs to be investigated. In this study, two U-shaped wall structures were built: one without any cracks and the other with diagonal, horizontal, and vertical cracks on three sides. The effects of these cracks on the seismic performance characteristics (i.e., the drift ratio and base shear) are evaluated by comparing the dynamic responses of the two wall structures. Through shaking table tests exerting horizontal bi-direction ground motions, both the out-of-plane and in-plane responses of the walls are investigated. Diagonal cracks are found to be more likely to cause the early collapse of masonry walls than vertical and horizontal cracks. These results provide valuable knowledge that will facilitate the appropriate reinforcement for damaged masonry walls that might need urgent repair.

Experimental studies on blast performance of unreinforced masonry walls of clay bricks and concrete blocks: a state-of-the-art review

Experimental studies on blast performance of unreinforced masonry walls of clay bricks and concrete blocks: a state-of-the-art review

A Numerical Investigation on the In-Plane Behavior of Perforated Unreinforced Masonry Walls

Considering architectural constraints, the existence of openings in unreinforced masonry (URM) walls is inevitable. Moreover, the observations of damaged URM buildings after previous earthquakes and the results of experimental studies on the seismic performance of masonry shear walls confirm that the in-plane behavior of perforated walls depends on the coupling of piers and spandrels. Accordingly, some improvements have been made in recent editions of international seismic retrofitting codes. This study is concerned with the in-plane behavior of perforated URM walls through a finite element (FE) study. For this purpose, 3D micromodeling is utilized for the simulation of the masonry walls in the FE software ABAQUS. At first, the FE model is verified using the results of an experimental study on large-scale perforated walls under simultaneous gravity and lateral in-plane loads. The numerical and experimental results show a good agreement with each other which confirms the reliability of the model for the simulation of URM walls. Subsequently, a parametric study is conducted by means of the validated FE model. The pier width and spandrel depth of the walls as well as the intensity of the gravity load on the piers are considered as the influential variables in the numerical investigation. Finally, the results of the numerical study are presented in terms of load–displacement curves, ultimate mode of failure, and the proportions of the internal shear force induced in piers at different story drift levels. According to the results of the current study, the geometrical properties of the walls and the gravity load have a substantial effect on the in-plane strength of the walls. Additionally, the role of spandrels in the global seismic performance of URM walls and piers is not negligible and should be considered in the seismic vulnerability assessment of existing buildings.

Effect of Uncertainty of Tensile Strength of Mortar Joints on the Behavior of Masonry Walls under Lateral Loads

AbstractAnalyzing the behavior of a masonry structure is a complex issue due to the complicated nature of masonry. Moreover, random spatial variation of masonry properties due to workmanship quality makes the prediction of its behavior even harder. This paper studies the effect of random spatial variability of mortar joint properties on the lateral strength of masonry walls under in-plane loads. Tensile strength of mortar joints is considered a random variable whose variation represents different quality of workmanship. Using a 3D nonlinear FE model, the influence of the random spatial variability of bed joint and head joint properties on the performance of unreinforced masonry walls is investigated. Results show the considerable effect of random spatial variability of bed joint properties on the performance of masonry walls under in-plane loads, while similar variation in head joint properties has a negligible effect on the wall response. The influence of correlation in bed joint properties on the wall s...

Analyzing the effect of workmanship quality on performance of unreinforced masonry walls through numerical methods

The considerable effect of workmanship quality on the performance of masonry structures is well-known. In this study, a 3D nonlinear FE model was used to investigate the effect of workmanship quality on masonry wall strength under in-plane and out-of-plane loads. Mortar joint cohesion was utilized as a random variable to represent variation in workmanship quality. In-plane and out-of-plane displacements were applied to the wall, separately and simultaneously. Results indicate that mortar cohesion has a considerable effect on wall strength under in-plane loads. However, under combined loads, the influence of workmanship quality on wall strength decreases/increases for the in-plane/out-of-plane direction.

In-plane seismic performance of unreinforced masonry walls strengthened with unbonded prestressed wire rope units

This study proposes a practical strengthening technique for enhancing the in-plane shear strength and ductility of unreinforced masonry (URM) walls using the unbonded prestressed wire rope units. Six full-scale strengthened URM walls and an unstrengthened URM wall were tested under constant axial load and cyclic lateral loads to explore the significance and limitations of the developed seismic strengthening procedure. The main variables investigated were the aspect ratio of walls, and the spacing and configuration of the prestressed wire ropes. The ductility of the walls tested was evaluated using the work damage indicator calculated at each loading step from the hysteretic loops. In addition, shear transfer capacities of masonry and wire ropes were identified based on the statistical fitting of test data for URM walls compiled from the literature and 45° truss analogy, respectively, in order to propose simple equations for shear strength of the URM walls strengthened with the developed wire rope units. Test results showed that the proposed strengthening procedure was highly effective in enhancing the in-plane shear strength and ductility of URM walls and controlling crack propagation along head and bed mortar joints. The shear strength and work damage indicator increased with the decrease of the spacing of wire ropes, showing that the inclined wire ropes were more capable of enhancing ductility than vertical wire ropes. The crack resistance capacity and stiffness of URM walls were also improved due to the additional axial compression force provided from the prestressing force applied to the wire ropes. The shear capacities obtained from the proposed simple equations were in good agreement with the test results, indicating that the mean and standard deviation of the ratios between measured and predicted shear capacities were 1.14 and 0.13, respectively.

Performance of Unreinforced Masonry Walls Retrofitted with Externally Anchored Steel Studs under Blast Loading

Six full-scale concrete masonry walls were tested under free-field blast loading using different charge sizes up to 250 kg of ammonium nitrate/fuel oil (ANFO) and at a constant stand-off distance of 15.0 m to cover a wide range of expected damage levels. Five walls were retrofitted with cold-formed steel studs anchored to the wall backs and were compared to the remaining as-built wall. Significant enhancement to the out-of-plane blast resistance of the retrofitted walls, compared to the as-built wall, was observed. This enhancement is attributed to the development of a tied-arch action in the retrofitted walls in which the masonry forms a compression strut while the steel studs serve as the tie. A simplified single-degree-of-freedom model was used to analyze the experimental results, and the model results agreed well with the observed damage levels and the resistances of the walls. In addition, the effectiveness of the proposed retrofit technique was evaluated in terms of strength enhancement and wall deflection reduction. The test results were also compared with those predicted by available blast damage assessment models for unreinforced masonry walls. However, it was found that available models, which do not account for the tied-arch mechanism, greatly underestimate the actual blast capacity of the retrofitted walls because of the assumption of a tensile flexural failure mode. Additionally, the proposed retrofit technique shifts the mode of failure from flexure to shear.

Evaluation of the seismic performance of brick masonry walls

Estimating the performance of structural elements requires the assessment of the response of those elements in terms of their response values (i.e. strengths, stresses, drifts, cracks, etc.) against loads and external forces of various kinds. For the seismic performance of masonry structures, until recently this approach was addressed in rather general terms with designers more interested in the survival of the structure in a maximum expected earthquake, with an acceptably low probability of occurrence. This traditional approach to seismic design is being replaced by performance-based design with the required performance depending on the level of the design seismic forces. This paper provides an overview of some of the methods for the evaluation of the in-plane resistance of masonry walls, which are already incorporated in national codes. Some results of recent experimental investigations of the shear capacity of in-plane loaded masonry walls subjected to cyclic loading are also presented with the aim of studying the potential for the application of these new concepts of assessment of seismic performance. The performance of unreinforced masonry walls in relation to the different design performance objectives and performance levels is then discussed. Copyright © 2008 John Wiley & Sons, Ltd.

The performance of unreinforced masonry walls subjected to low-velocity impacts: Finite element analysis

A simplified discrete-crack finite element modelling approach has been developed to model the performance of unreinforced brickwork and blockwork masonry walls subject to out-of-plane impacts. The approach involves the use of linear elastic solid elements for masonry units in conjunction with a specially formulated contact interface model for masonry joints. Key features of the latter include: (i) a Mohr–Coulomb failure criterion; (ii) a cohesive crack model for initial fracture; (iii) inclusion of dilatancy. The contact interface model has been implemented in LS-DYNA, a three-dimensional non-linear explicit finite element program. The modelling approach was used to simulate the behaviour of a series of unreinforced walls tested previously in the laboratory. It was found that the dynamic response of full-scale masonry walls could be predicted with reasonable accuracy. However, parametric studies showed that wall response was highly dependent on small changes in loading impulse, base friction, fracture energy, joint failure stress and angle of dilatancy.

Time–history analysis of URM walls in out-of-plane flexure

This paper introduces a single degree-of-freedom analytical model which has been used by the authors to investigate the out-of-plane performance of unreinforced masonry walls in vertical one-way bending subject to seismic actions. The objective of the modelling is to reduce costs on physical experimentation by supplementing and extending the limited experimental database on dynamic wall behaviour with analytical data. The procedure necessitates sufficient physical testing of specimens with representative boundary conditions to enable the analytical model to be calibrated against experimental results. A computer program which requires minimal data preparation effort and computational time has been written to conduct time–history analysis on the model. Importantly, key parameters have been incorporated in the program to facilitate calibration of the model. Details in developing representative tri-linear elastic force-displacement relationships and non-linear damping relationships to define the model are described in the paper. The developed model has been verified by comparing the computed acceleration and displacement response time-histories with results obtained from an extensive series of shaking table experiments. Seven of such time-history comparisons are shown in the paper to demonstrate the accuracy of the analytical model.

The performance of unreinforced masonry walls subjected to low-velocity impacts: experiments

Impact tests on a total of 21 full-scale unreinforced free-standing brickwork and blockwork walls have been performed in the laboratory using novel drop hammer/rotating quadrant apparatus. The impact loading generated in the laboratory had similar basic characteristics to accidental vehicle impacts (i.e. similar peak impact force and duration). The main variables investigated were wall length, wall thickness, masonry unit type/strength, impact location and end conditions. A number of different failure modes were identified. Mortar bonded walls subjected to a mid-height, mid-length, out-of-plane impact loading were observed to resist the loading in two phases: initial elastic action until fracture occurred, followed by gross displacements, resisted by friction at the base and both out-of-plane and in-plane inertial forces. When weak masonry units were used front face vertical fracture lines either side of the impact location were observed; when stronger units were used front face diagonal fracture lines were observed. Walls impacted close to their ends were observed to be significantly less capable of resisting impact loadings.

The performance of unreinforced masonry walls subjected to low-velocity impacts: mechanism analysis

The development of a rigid-body mechanism analysis capable of estimating the likely response of an unreinforced masonry wall subjected to an out-of-plane impact loading is described. The method automatically identifies the out-of-plane sliding mechanism likely to be most critical for a particular impact location, from a library of five possible mechanisms. Initially, a fracture-line analysis is performed to estimate the out-of-plane force required to crack the wall. Subsequent gross displacements of the wall panels formed are calculated using an iterative dynamic analysis. The fracture energy associated with initial crack opening is included in the calculations and checks are also conducted to determine whether the mode of failure changes during the impact event. Additionally, the possibility that wall rocking can occur, either on its own or simultaneously with the out-of-plane sliding mechanisms is considered. Results from the mechanism analysis model are compared with the experimentally observed results described in a companion paper. It was found that reasonable agreement was obtained for most of the walls subjected to mid-wall impacts, provided ‘dynamic’ rather than quasi-static values for the masonry flexural strength were used in the analysis. Sensitivity studies indicated that wall thickness and the coefficient of base friction were particularly important parameters. The analysis can readily be modified to approximately simulate the interaction between a wall and moving vehicle and is currently being extended to deal with reinforced masonry walls.