Unreinforced Masonry Walls Research Articles

Effect of in-plane damage on the out-of-plane strength of masonry walls with openings

Past earthquakes have shown that masonry walls are vulnerable to fail near the openings. Openings such as doors and windows are an essential part of the structure. The presence of an opening reduces the strength and stiffness of the masonry structures. It also affects the load-resistant mechanism of the masonry walls. The walls are subjected to simultaneous in-plane and out-of-plane forces during seismic events. Therefore, the analysis of the masonry walls either in in-plane or out-of-plane direction may not give a proper picture of the global behavior of the masonry structures. The masonry walls deform primarily in the in-plane direction if the walls are properly tied with each other, and the structure is constructed by following codal provisions. Under this situation, it is necessary to investigate the effect of in-plane damage on the out-of-plane strength of the masonry walls. Few researchers have studied the behavior of solid unreinforced masonry walls under combined loading. However, limited work can be found for masonry walls with openings. Therefore, the present study focuses on the effect of different types of opening layouts on the combined in-plane and out-of-plane behavior of masonry walls incorporating varying pre-compression. Further, in masonry buildings, walls are interconnected, making the masonry walls of various shapes. In this study, masonry walls of rectangular and I shapes have been considered to examine the effect of cross-walls under combined loading. Interaction curves have been developed for the walls subjected to the in-plane loading followed by an out-of-plane pressure. Based on the results, the maximum opening percentage in the masonry walls has been suggested, which is desirable in the case of masonry buildings constructed in high seismic zones.

Fragment velocity response of grouted and unreinforced concrete masonry walls subjected to blast loading

Very few methods are available for predicting the secondary fragment velocity and secondary fragment production of grouted and unreinforced concrete masonry unit (FGUR CMU) walls when subjected to blast loading. A novel energy-based methodology is developed that calculates the secondary fragment velocity of an unreinforced fully grouted concrete masonry unit (CMU) wall under blast loading. The computationally efficient, engineering-level methodology was originally derived for fragment velocity calculation of unreinforced ungrouted CMU walls. Existing approaches often require large computational resources or fail to predict secondary fragment velocity accurately; this approach calculates fragment velocities with minimal computational effort. The applicability of this analytical model to unreinforced fully grouted CMU walls is discussed. The selection of a resistance function and assumptions about fragment behavior are examined. Velocity calculations throughout wall fragmentation are compared to velocities from quarter-scale and full-scale experiments and reasonable agreement is observed.

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.

Effects of passive confinement on out-of-plane robustness of unreinforced masonry infill walls

Unreinforced masonry (URM) walls are vulnerable to out-of-plane (OOP) collapse under lateral loads; however, URM structures are still popular in developing countries. Even in many countries classified as developed by the United Nations, URM walls are still commonly applied as exterior and interior infills in engineered buildings, resulting in severe OOP failure during strong earthquakes. The objectives of this study were: 1) to experimentally examine the OOP behavior and performance of URM infills with construction deficiencies commonly found in Asian countries, 2) to investigate the impact of construction quality on resistance to OOP collapse and 3) to propose a promising approach using passive confinement to improve the lateral resistance of URM infills and a method to evaluate their seismic performance. To attain these objectives, the study used two full-scale, single wythe, brick masonry specimens with specific boundary conditions at the top, a control specimen representing URM infills with construction flaws frequently found in Asian countries and a well-constructed specimen subjected to passive confinement under lateral excitation. A series of incremental dynamic shaking table tests was performed on both specimens under OOP unidirectional one-way bending. The test results revealed the positive effects of construction with passive confinement on OOP performance. The results indicated that the OOP robustness of infills can be improved without specific retrofit materials, leading to advantages such as simplicity, cost-effectiveness, and swift execution. Moreover, a theoretical method to evaluate the lateral resistance of infills was presented and verified for practical applications. This method can contribute to reducing the potential for earthquake damage in engineered buildings.

Engineering methodology to assess the seismic out-of-plane response of two-way spanning unreinforced masonry walls with multiple openings

Engineering methodology to assess the seismic out-of-plane response of two-way spanning unreinforced masonry walls with multiple openings

Experimental and analytical investigation of opening effects on the in-plane capacity of unreinforced masonry wall

A test programme consisting of four half-scale URM walls was conducted under quasi-static cyclic loading to evaluate the negative influence of openings. Test results showed that the masonry adjacent to the opening experienced significant damage, and the specimens with a door opening was found to have complete detachment of the masonry pier, resulting in a reduction in the capacity of more than 25%. Furthermore, a detailed parametric nonlinear finite element analysis was performed to assess the influence of parameters affecting the in-plane load capacity of the URM wall. Numerical results showed that depending upon the size and location of openings and the material and geometric properties of walls, the in-plane load capacity was reduced by 6–82%. Considering the results of available experimental studies and present numerical analyses, a simplified equation was proposed to estimate the reduction in the in-plane load capacity of the specimen with different types of openings. The analytical study demonstrated that the proposed equation effectively provided reliable and consistent predictions of the strength reduction factor for walls with different types of openings.

Crack pattern–based machine learning prediction of residual drift capacity in damaged masonry walls

AbstractIn this paper, we present a method based on an ensemble of convolutional neural networks (CNNs) for the prediction of residual drift capacity in unreinforced damaged masonry walls using as only input the crack pattern. We use an accurate block‐based numerical model to generate mechanically consistent crack patterns induced by external actions (earthquake‐like loads and differential settlements). For a damaged masonry wall, we extract the crack width cumulative distribution, we derive a crack width exceedance curve (CWEC), and we evaluate the drift loss (DL) with respect to the undamaged wall. Numerous pairs of CWEC and DL are thus generated and used for training (and validating) an ensemble of CNNs generated via repeated ‐folding cross validation with shuffling. As a result, a method for damage prognosis (Level IV of SHM) is provided. Such method appears general, inexpensive, and able to adequately predict the DL using as only input the CWEC, providing real‐time support for decision making in damaged masonry structures.

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.

Mesoscale numerical modeling of unreinforced masonry wall response to underground dynamic loads: A comparative study utilizing FEM and DEM

This study investigates the response of unreinforced masonry walls to dynamic loading induced by underground explosions. A mesoscale numerical modeling approach is employed to capture the nonlinear behavior of the masonry wall. The Menetrey-Willam yield criterion is utilized to represent the wall's nonlinear behavior at the mesoscale level, while the cohesive zone model (CZM) is employed to simulate the behavior of mortar, thereby overcoming the limitations of linear elasticity. The soil is characterized using the modified Mohr-Coulomb model. After calibration against material characterization tests, a numerical model is developed to obtain results that closely match experimental data. Given the disturbed nature of the crater soil, both finite element and discrete element methods are utilized for soil modeling. Comparison between these methods reveals that the discrete element method yields more realistic results in terms of displacement and strain. The study's findings enhance our understanding of the response of unreinforced masonry walls to dynamic loading and offer valuable insights for future structural designs and safety assessments.

Experimental investigation of size effect on unreinforced concrete brick masonry walls under in-plane shear loading

The size effect is one of the primary structural characteristics exhibited in reinforced concrete (RC) members in shear. Even though numerous studies have been conducted on masonry walls under shear, very few studies have been conducted that definitively answer whether a size effect exists for masonry walls. Diagonal compression tests on two groups of masonry walls with different dimensions were conducted to investigate the size effect on concrete brick masonry walls. A total of sixty masonry wall panels were tested. Five bed-joint mortar mix properties were used for each specimen. Test results showed that four failure modes were observed: diagonal tension failure, combined failure, sliding failure, and toe-crushing failure. In particular, the diagonal tension strength was significantly related to the specimen size. The larger specimen size led to a lower shear strength. Also, the shear modulus was highly dependent on the specimen size. Through experimentation, this study demonstrated that masonry walls exhibit a size effect. Moreover, the size effect is valid only in cases of diagonal tension failure. Based on the test results, this study revealed a correlation between diagonal tension strength and wall size. Lastly, the adequacy of the predictions was compared to the existing masonry codes.

Wavelet technique and FEA for modal identification in damaged URM shear walls

In existing masonry buildings, the structural capacity with respect to horizontal actions is due to the in-plane response of shear walls, usually evaluated in terms of effective stiffness and drift capacity. The objective of this work is to provide first results to the damage sensitivity in diagonal cracking of URM shear walls and a study methodology based on vibration tests to assess the structural health of existing masonry buildings. The state of pre-existing discontinuities caused by previous damage events or material degradation may play a role in the in-plane response of shear walls. For this, an experimental campaign was carried out on three typologies of UnReinforced Masonry (URM) walls, simulating different damage situations, subjected to Shear-Compression (SC) and vibration tests in order to correlate the structural behaviour with changes in modal parameters. From the vibrational response acquired during the SC test, the modal parameters related to the pre-damage and post-damage condition were identified using the Continuous Wavelet Transform identification technique. The experimental results are then used to implement a Finite Element Model (FEM) with a 2D homogenization approach to simulate the behaviour of URM walls. A parametric study through FEM analysis is carried out in order to investigate the change in modal parameters for different damage configurations and for triggering strut mechanisms.

A New Macro-Element for Predicting the Behavior of Masonry Structures under In-Plane Cyclic Loading

A new macro model for the finite element modeling of unreinforced masonry (URM) exhibiting in-plane nonlinear cyclic behavior is proposed. The ultimate objective is to predict the seismic response of multi-story URM buildings. The macro model enables the modeling of URM shear walls with a limited number of degrees of freedom (DOF) at low computation times. The macro model consists of a deformable elastic frame supported by diagonal struts with nonlinear behavior aiming to capture all dissipative phenomena occurring during seismic events. The nonlinear constitutive behavior of diagonal struts is inspired by models documented in the literature, ensuring a robust foundation for the proposed approach. This paper first provides a comprehensive review of the principal models currently available for URM analysis. It then articulates the rationale behind the development of this new numerical model, aiming to address the limitations encountered in existing methodologies and to offer a simple and fast tool for predicting the seismic behavior of URM buildings. Afterward, the new model is presented and tested with the simulations of two experimental campaigns performed on different URM walls. The comparison between experimental and numerical results shows that with a limited number of DOF and parameters, it is possible to obtain a prediction of the experimental results with satisfying accuracy.

In-plane and out-of-plane one-way vertical bending behavior interaction analysis of unreinforced masonry walls with newly developed load capacity interaction curve

The structural behavior of unreinforced masonry (URM) walls under in-plane (IP) or out-of-plane (OOP) loading in masonry buildings has been extensively investigated in the public literature. However, studies focusing on the URM walls subjected to concurrent IP and OOP loadings are limited. Neglecting IP and OOP interaction effects may lead to unsafe design practices. As such, this study conducts a comprehensive numerical investigation into the behavior of URM walls under combined IP and OOP loading, focusing on the influences of aspect ratio (i.e., height-to-length ratio), slenderness ratio (i.e., height-to-thickness ratio), and pre-compression load levels. To capture the possible failure modes of URM walls under various loading scenarios, the simplified micro modeling approach is employed. The analysis results indicate that the presence of OOP loading leads to a substantial reduction in IP capacities. Longer walls, characterized by smaller AR, exhibit more pronounced IP and OOP interaction effects. Additionally, highly slender walls show significant additional moments due to second-order effects under OOP loading, thereby negatively affecting the IP capacity. Low-level pre-compression loads are beneficial in diminishing capacity interaction effects, while high pre-compression loads exert a negative influence. To facilitate the consideration of IP and OOP capacity interaction effects in an efficient manner, a simplified analytical model is developed through curve fitting, in which the effects of aspect ratio, slenderness ratio, and pre-compression load are incorporated.

Unreinforced masonry walls under two-way out-of-plane bending: Comparison of FE model predictions with analytical models

Four existing design guidelines based on the virtual work method have been compared to predict the out-of-plane (OOP) bending capacities of unreinforced masonry (URM) walls to one-way and two-way actions. The two-way OOP bending design equation as per the Australian masonry standard (AS 3700) and the three subsequent models developed by other researchers are based on specific wall geometries, support conditions, dimensions and strengths of masonry units and mortar. Due to limited experimental data available on URM walls under two-way bending, it is difficult to carry out a detailed investigation of the performance of these two-way design models against all the design parameters. This paper applies the finite element (FE) modelling technique to generate data and extensively investigate the influence of support conditions, pre-compression and aspect ratio on the two-way OOP bending capacity of URM walls. An explicit FE model previously developed by the authors where masonry is macroscopically modelled as an anisotropic composite material, is used for this purpose. Performances of three key parameters (i.e., moment capacity under horizontal bending and diagonal bending and torsional shear strength of masonry) that differentiate the four design models are investigated against varying levels of vertical pre-compression and flexural tensile strength of masonry. The OOP bending capacity predicted by the FE model is compared with the predictions of the design models. Results show that three out of four design models generally overpredict the two-way OOP bending capacities of square and taller walls. Further refinement to the AS 3700 design equation has been proposed in a modified model. The outcomes of this research will help to improve the design of masonry walls under OOP bending.

Comparison and analysis of the seismic performance of windowless and windowed confined masonry walls reinforced with TRC

Unreinforced masonry (URM) walls, especially unreinforced masonry walls with windows, have a low level of seismic protection and are prone to collapse during earthquakes. Reinforcement can improve the seismic performance of walls. In addition, some walls can remain in service after an earthquake with repair reinforcement. To investigate the seismic performance of windowless and windowed masonry walls reinforced with textile-reinforced concrete (TRC) and the effectiveness of TRC in restoring the seismic performance of damaged walls, five walls were designed and tested. The following conclusions were drawn: The TRC facing formed a good constraint on the masonry walls and improved their brittle damage characteristics, but it could not compensate for the weakening effect of window openings. Compared with unreinforced walls, TRC-reinforced walls exhibited better postpeak performance, with higher peak loads, ductility, stiffness, energy dissipation, and other seismic performance indicators. The peak load, stiffness and energy dissipation of the windowed walls were less than those of the windowless walls, but the ductility of the windowed walls was better than that of the windowless walls. For the wall that was predamaged to the peak load and subsequently reinforced, the TRC reinforcement restored the stiffness and ductility to the level of intact walls, but it did not restore the load capacity. The shear capacity calculated by the superposition approach accurately predicts the peak loads of TRC-reinforced walls.

Seismic reinforcement of buildings constructed from unreinforced masonry using shotcrete

Introduction. This work mentions the existence of traditional and non-traditional methods of seismic reinforcement of buildings and structures, including buildings built from masonry and historical architectural monuments. Concrete shotcreting, or other cementbased mortar is considered as one of the methods of seismic reinforcement, which belongs to traditional methods and is regarded the most suitable in this case, since it allows seismic reinforcement of buildings constructed from unreinforced masonry, which includes many historical architectural monuments, increasing their load-bearing capacity and at the same time almost without increasing their weight.
 
 Aim. The research is intended to contribute to the seismic reinforcement of buildings, including architectural monuments, built from unreinforced masonry to withstand future seismic impacts from natural phenomena such as earthquake.
 
 Materials and methods. A review and detailed study of the seismic reinforcement method was carried out, namely shotcrete with concrete, which is a traditional method, its advantages and disadvantages, the essence of the method and the sequence of its implementation. A review of historical earthquakes in different countries and their devastating consequences for buildings constructed from unreinforced masonry was also carried out. The in-plane behavior of unreinforced masonry supports and walls under the influence of seismic lateral forces is considered.
 
 Results. The possible practical application and steps of concrete shotcrete over a metal mesh of unreinforced masonry walls for their seismic reinforcement are proposed and clearly demonstrated.
 
 Conclusions. Conclusions have been drawn about the feasibility of using shotcrete over a metal mesh for seismic reinforcement of buildings built from unreinforced masonry, which makes it possible to save the lives of people living in them in case of earthquakes.

Structural Performance of Large-Scale 3D-Printed Walls Subjected to Axial Compression Load

Despite the growing incorporation of additive manufacturing in the construction industry, a significant gap persists in the availability of design guidelines and comprehensive structural assessments for 3D-printed components. This research employs experimental methods to evaluate the performance of large-scale hollow unreinforced 3D-printed masonry walls under axial compressive load. Furthermore, a design methodology tailored for 3D-printed masonry walls under compressive loads is proposed in compliance with both American and Canadian masonry standards. This methodology is supported by the application of linear elastic 3D finite element analysis. Moreover, supplementary insights into material behavior are garnered through the examination of small specimens extracted from an additional 3D-printed wall. The results reveal that 3D printing reduces stiffness and compressive strength. The 3D-printed infills played an important role in redistributing stress after cracking. All full-scale 3D-printed masonry walls examined in this research exceeded the performance criteria set by the American masonry standard for load-bearing walls.

Improved Bond Stress-Slip Relationships for Carbon Fibre-Reinforced Polymer-Strengthened Masonry Triplets

Carbon fibre-reinforced polymer (CFRP) emerges as a viable solution for reinforcing unreinforced masonry (URM) walls subjected to shear loads. While masonry structures are straightforward to construct, the complexity of the construction materials, especially in terms of their mechanical properties, poses challenges for numerical studies of their structural behaviour. Walls, being fundamental components in masonry construction, play a crucial role in transferring both horizontal and vertical lateral forces. This study investigates the enhancement of masonry wall behaviour through the reinforcement of CFRP. CFRP reinforcement increases ductility and strength, reducing the risk of failure under shear conditions. Additionally, CFRP composites present a practical solution to strengthening masonry structures compared to traditional reinforcement. However, brick, mortar, and CFRP have not been thoroughly investigated. Experimental tests on the bond behaviour of different configurations of CFRP-retrofitted masonry triplets have not been performed before and are therefore presented in this paper. Triplet specimens, comprising three bricks and two mortar joints, both with and without CFRP strengthening, were subjected to bond testing. The study affirms that masonry triplets strengthened with CFRP under shear loads exhibit strength levels at least four to six times greater than those without CFRP. The experimental work was carried out with eight different CFRP configurations on triplet masonry, and each test was repeated four times. Further, the bond stress-slip relationship in the case of masonry triplets with and without CFRP was predicted with new mathematical equations based on the conducted test results. These equations were included in the commercial finite element software ANSYS and used to conduct simulations of CFRP-reinforced masonry triplets. The numerical results indicate good agreement between the finite element model and the test results. The outcome of this research improves the current knowledge on the use of CFRP to reinforce masonry walls with brick and mortar, which will contribute to the understanding of the effect of CFRP on masonry structures.

Failure mode dependent shear strength of unreinforced concrete brick masonry wall panels

This study conducted diagonal compression tests to propose the failure mode dependent shear strength for unreinforced concrete brick wall panels. The test variable was the bed-joint mortar mixing ratio. Six brick wall panels were manufactured for each variable, and finally thirty specimens were tested. The test results showed five failure modes in the unreinforced masonry wall panels: diagonal tension, combined, bed-joint sliding, toe crushing, and non-diagonal failure. Furthermore, the shear strength of unreinforced brick wall panels was highly dependent on the failure mode. Based on the test results, the shear strength is suggested according to each failure mode. Additionally, the shear modulus of concrete brick wall panels was suggested as half of the value presented in the current codes for masonry structures.

Exploring the Cyclic Behaviour of URM Walls with and without Damp-Proof Course (DPC) Membranes through Discrete Element Method

Unreinforced masonry (URM) walls are common load-bearing structural elements in most existing buildings, consisting of masonry units (bricks) and mortar joints. They indicate a highly nonlinear and complex behaviour when subjected to combined compression–shear loading influenced by different factors, such as pre-compression load and boundary conditions, among many others, which makes predicting their structural response challenging. To this end, the present study offers a discontinuum-based modelling strategy based on the discrete element method (DEM) to investigate the in-plane cyclic response of URM panels under different vertical pressures with and without a damp-proof course (DPC) membrane. The adopted modelling strategy represents URM walls as a group of discrete rigid block systems interacting along their boundaries through the contact points. A novel contact constitutive model addressing the elasto-softening stress–displacement behaviour of unit–mortar interfaces and the associated stiffness degradation in tension–compression regimes is adopted within the implemented discontinuum-based modelling framework. The proposed modelling strategy is validated by comparing a recent experimental campaign where the essential data regarding geometrical features, material properties and loading histories are obtained. The results show that while the proposed computational modelling strategy can accurately capture the hysteric response of URM walls without a DPC membrane, it may underestimate the load-carrying capacity of URM walls with a DPC membrane.