Masonry Shear Walls Research Articles

System-level seismic resilience assessment of reinforced masonry shear wall buildings with masonry boundary elements

The concept of seismic resilience plays an important role in seismic assessment of structures as it assesses the capability of a system to withstand an unwanted event, such as earthquakes, by estimating the losses and determining the system’s functionality and sustainability during and after such event. In this study, a framework was utilized to assess the seismic resilience of Reinforced Masonry Shear Wall (RMSW) buildings as well as studying the impact of incorporating Masonry Boundary Elements (MBEs) at the ends of RMSW. To achieve this goal, a ten-story RMSW building was numerically modelled in OpenSees to assess the seismic performance and resilience of the system when adding confined MBEs. The selected building is located in Montreal, Canada, and initially designed to be built having rectangular walls. Subsequently, the walls were redesigned to integrate MBEs at their outermost fibre to help increase the ductility and strength of the RMSWs. A full 3D wide-column macro-modelling approach was used to simulate the dynamic response of the archetype building. Validation of the modelling approach was done against available experimental tests as an initial step to ensure the robustness of the model in predicting the inelastic response of the building. Subsequently, the models were analyzed against multiple ground motion records using Incremental Dynamic Analysis to identify the initiation of collapse alongside developing the fragility curves of the building. The system-level seismic performance of the building was assessed after incorporating MBEs. The resilience of the building was assessed using the developed fragility functions, and a comparison was made to highlight the effect of using MBEs on the response of the studied RMSW building. The results showed a significant enhancement in the seismic resilience of the building by using confined MBEs at the shear walls’ extreme.

High-resolution monitoring of the initial development of cracks in experimental masonry shear walls and their reproduction in finite element models

Induced seismicity in the north of the Netherlands has recently exposed unprepared, unreinforced masonry structures to considerable earthquake hazard. While the ultimate-limit state capacity of the structures is vital to assess the individual’s risk, their behaviour during more frequent, lighter earthquakes leading to ‘light damage’, has shown to be strongly linked to economical losses and societal unrest. To study the effect of these repeated light earthquakes, the behaviour of masonry structures, typical of the region, needs to be investigated when subjected to multiple small cycles. In particular, insight into the potential aggravation of the light damage is sought. Hence, shear walls of replicated clay brick masonry have been tested in the laboratory and exposed to a high number of low in-plane drift cycles. The experiments show, under inspection with high-resolution Digital Image Correlation, how stair-case, diagonal cracks initially distribute in multiple cracks running in joints at the centre of the walls, but later localise into a single, visible, wider crack. The tests are used to establish an interval over which light damage can be expected for these types of walls.Furthermore, this initial distribution of strains in ‘bands’ and subsequent localisation, previously observed only with computational finite element models and which could not be verified experimentally, is compared and reproduced with improved models both at the composite continuum scale (macro-model) and the brick-to-brick micro scale. The models are calibrated based on the quasi-static, cyclic experimental results and later used for extrapolation in dynamic nonlinear settings to assess the influence of natural ground motion excitations.

Effect of Ductile Shear Wall Ratio and Cross-Section Configuration on Seismic Behavior of Reinforced Concrete Masonry Shear Wall Buildings

Reinforced masonry buildings typically have a load-bearing wall structural system. Thus, the reinforced masonry shear walls must be capable of resisting both vertical forces from gravity loads and lateral forces from seismic and wind loads. Typically, because the walls are subjected to high axial loads, ensuring the ductile response becomes challenging. A possible solution at the component level would be the utilization of walls with confined ends (i.e., walls with boundary elements) to reduce the compression zone and increase the compression strain. Another solution, which is at the system level, is the introduction of a hybrid structural system composed of two types of walls: (1) ductile walls with or without boundary elements to resist the lateral forces and part of vertical forces, and (2) gravity walls that resist only axial loads. This paper proposes a combination of both solutions (i.e., at component and system levels). Additionally, it utilizes a series of linear and nonlinear static and dynamic analyses to evaluate and quantify the effect of cross-section configuration and ductile shear wall area to total floor area (i.e., ductile shear wall ratio) on the seismic response of masonry buildings. The numerical analyses are performed by a macro model detailed to simulate the nonlinear response. The primary objective is to recommend a range of ductile shear wall ratios that optimize the design and overall performance. The study targets mid-rise and high-rise masonry buildings located in regions with moderate seismic hazard. The findings emphasize that utilizing the ductile walls with boundary elements in the proposed hybrid structural system resulted in major favorable enhancements in the structural response and optimization of the design. In addition, the results demonstrate the possibility of vertically reducing and terminating the specially detailed boundary elements, thus promoting ductile reinforced concrete masonry shear wall buildings as a competitive building system.

Experimental Analysis of Seismic Performance of Masonry Shear Wall Reinforced with PP‐Band Mesh and Plastering Mortar under In‐Plane Cyclic Loading

Masonry structures are widely used in developing countries due to their low cost and simple construction, especially in remote areas, where there are a large number of houses without seismic measures. These buildings are prone to collapse and cause a lot of casualties, even under the action of small earthquakes. For the reinforcement of this structure, a cheap, effective, and easy‐to‐construct reinforcement method is urgently needed. Therefore, this article studies the reinforcement method of polypropylene bands (PP‐bands). We have carried out low‐frequency cyclic loading tests for two PP‐band reinforced masonry walls and two compared masonry walls. We mainly studied the influence of PP‐band and different compressive strengths of plastering mortar on the masonry wall’s seismic capacity. The seismic indicators mainly studied in this article include ultimate bearing capacity, energy dissipation capacity, stiffness degradation, and hysteresis characteristics. The experimental results show that the PP‐band can greatly enhance the seismic capacity of the masonry wall. The ultimate bearing capacity, energy dissipation capacity, and displacement ductility of the PP‐band reinforced wall are increased by 38%–48%, 22%–47%, and 138%–226%.

Seismic Fragility Assessment and Resilience of Reinforced Masonry Flanged Wall Systems

AbstractSeveral experimental and analytical studies have evaluated the seismic response of reinforced masonry (RM) shear walls either as a component (i.e., planar rectangular walls) or as a system ...

Detailed micro-modeling approach and solution strategy for laterally loaded reinforced masonry shear walls

Although multiple experimental investigations have been performed to characterize the structural behavior of partially grouted reinforced masonry (PG-RM) shear walls, still many knowledge gaps exist due to the complexity of their mechanical behavior. Furthermore, the fact that PG-RM is a composite material has limited the progress of the numerical modeling of these elements. In order to contribute to the knowledge of the in-plane response of PG-RM walls, this paper presents a detailed micro-modeling approach to simulate the behavior of these walls under in-plane lateral loads. Numerical results are validated by comparison with experimental results of PG-RM walls with bed-joint reinforcement. Special attention is given to the numerical implementation and solution strategy of the models due to the difficulties of solving the strong nonlinearities involved in the walls’ response. The obtained results allow us to conclude that the proposed approach is suitable for simulating the lateral response of PG-RM shear walls, including crack patterns observed during experimental tests. In addition, the performed parametric study shows that selecting adequate numerical parameters is vital to avoid misleading results.

Influence of a window-type opening on the shear response of partially-grouted masonry shear walls

This paper focuses on assessing the effects of the presence of a window-type opening on the shear behavior of partially-grouted reinforced masonry (PG-RM) shear walls. For this purpose, this work analyzes previously reported test results of three PG-RM walls tested under in-plane cyclic lateral loading. The main variable of the tested walls is the size of a central window. Therefore, all the walls had the same external dimensions (a height-to-length aspect ratio equal to 1.02). The performance of the walls is analyzed and discussed in terms of maximum shear strength, drift, degradation of stiffness, disp1acement ductility, dissipation of energy, and equivalent viscous damping. The damage evolution in the tested walls is investigated using digital image correlation (DIC) technique. Finally, the paper compares the accuracy of the Strut-and-Tie method and five existing shear equations to estimate the maximum lateral capacity of PG-RM walls with openings. In this comparative analysis, seven numerical cases of walls with openings previously validated are also considered.Based on the results, the study has confirmed that the presence of a central window in a PG-RM shear wall reduces the shear strength and ductility of the entire wall, and increases the rate of degradation of lateral stiffness. Although a significant disparity was not seen in the shear strength of the two tested walls with openings, they exhibited differences in the damage progression, the total amount of dissipated energy and the equivalent viscous damping during the tests. In addition, the experimental evidence indicates that although damage is concentrated on the piers of the walls, it also propagates to the segments below the openings. Therefore, there is uncertainty about how much the properties of wall segments near the openings affect the global behavior of the wall. The assessment of different methods to estimate the lateral resistance of a PG-RM shear wall with openings shows that the sum of individual contributions of the piers gives accurate predictions provided the expression used to estimate the resistance of piers is accurate enough.

Fragility Functions for Displacement-based Seismic Design of Reinforced Masonry Wall Structures

ABSTRACT It is well understood that in the displacement-based seismic assessment of masonry shear wall structures, it is desirable to have an estimation for lateral deformation capacity of wall segments that are linked to their different damage levels. This study focuses on the development of experimental-based fragility functions for reinforced masonry shear walls subjected to in-plane seismic loading, which can be used in the next-generation displacement-based seismic design approaches. Hysteresis responses of 91 wall specimens and their damage progression patterns obtained from a series of experiments performed at The University of Texas at Austin and Washington State University are used to generate fragility functions for different demand levels. Various damage states are proposed within this study that are associated with commonly employed methods of repair, and these damage states represent different levels of flexure, diagonal shear, and sliding shear damage in reinforced masonry shear walls. Corresponding damage limit states are defined in terms of ratio of lateral deformations to the aspect ratio of wall segment as the demand parameter for flexural damage, while those limit states for diagonal and sliding shear damage is the normalized shear demand. This paper develops drift-based fragility functions for key damage states associated with the structural performance and reparability of reinforced masonry walls. This research also shows that the proposed demand parameters formulate a more accurate correlation between the demand parameters and the damage observed in the tests in masonry walls than does from story-drift ratio, which was previously the industry standard practice.

Machine learning algorithms for structural performance classifications and predictions: Application to reinforced masonry shear walls

Current building codes and design standards classify different structural components according to their expected structural performance. Such classification is usually based on datasets of experimental results typically supplemented by analytical and/or numerical simulations. However, it is usually prohibitive to experimentally evaluate the influence of the typically large number of (and the wide numerical range of each of the) interacting design parameters, on the response of any one class of structural components. Subsequently, the current study builds on the recent advances in the area of machine learning (ML)—a class of artificial intelligence, to introduce a robust ML-based framework for performance prediction and classification of structural components. In order to demonstrate the use of the developed framework, a dataset of 97 reinforced masonry shear walls (RMSWs) is utilized. In this respect, the current study first conducts an exploratory data analysis to recognize the influence of the walls' geometrical and mechanical characteristics on the wall responses. Subsequently, an unsupervised learning algorithm is developed to cluster the walls based on their features. Finally, the training and validation datasets are used to further develop and validate a supervised learning algorithm to classify the walls and predict their lateral drifts according to their failure modes. The study is expected to introduce and demonstrate the capability of ML-based frameworks for future relevant studies within other structural engineering applications.

Out-of-Plane Behavior of Load-Bearing Reinforced Masonry Shear Walls

The increase in the number of deliberate and accidental explosion events over the past two decades has necessitated evaluating the performance of blast-vulnerable structural components and developing subsequent risk mitigation strategies. In this context, several studies have focused on the out-of-plane behavior of either unreinforced masonry walls or non-load bearing reinforced masonry shear walls (RMSWs). However, to date, few studies have focused on the interaction between the axial load and the out-of-plane (e.g., when shear walls are subjected to blast loads) demands on such walls. As such, the current study focuses on evaluating the out-of-plane behavior of seismically-detailed RMSWs with different design parameters. In this respect, the experimental results of seven scaled RMSWs, with different in-plane ductility seismic classifications and axial stress levels, subjected to out-of-plane loading are first presented. Such results include the wall damage sequence, load-displacement response, stiffness degradation, and energy dissipation. Subsequently, the resistance function predictions based on the Unified Facilities Criteria guidelines are compared with the experimental results. Furthermore, an experimentally validated analytical resistance function is developed considering the postpeak behavior of RMSWs, including second-order effects. The current study extends the database of experimental and analytical results pertaining to load-bearing RMSWs, to facilitate the development of relevant provisions within the next generation of blast design standards.

Research on the Influence of Bed Joint Reinforcement on Strength and Deformability of Masonry Shear Walls.

The areas of Central and Eastern Europe and, thus, Poland are not exposed to the effects of seismic actions. Any possible tremors can be caused by coal or copper mining. Wind, rheological effects, the impact of other objects, or a nonuniform substrate are the predominant types of loading included in the calculations for stiffening walls. The majority of buildings in Poland, as in most other European countries, are low, medium-high brick buildings. Some traditional materials, like solid brick (>10% of construction materials market) are still used, but autoclaved aerated concrete (AAC) and cement-sand calcium-silicate (Ca-Si) elements with thin joints are prevailing (>70% of the market) on the Polish market. Adding reinforcement only to bed joints in a wall is a satisfactory solution (in addition to confining) for seismic actions occurring in Poland that improves ULS (ultimate limit state) and SLS (serviceability limit state). This paper presents results from our own tests on testing horizontal shear walls without reinforcement and with different types of reinforcement. This discussion includes 51 walls made of solid brick (CB) reinforced with steel bars and steel trusses and results from tests on 15 walls made of calcium-silicate (Ca-Si) and AAC masonry units reinforced with steel trusses and plastic meshes. Taking into account our own tests and those conducted by other authors, empirical relationships were determined on the basis of more than 90 walls. They are applicable to the design and construction phases to determine the likely effect of reinforcements on cracking stress that damage shear deformation and wall stiffness.

Bestimmung des Teilsicherheitsbeiwerts für Wandscheiben aus unbewehrtem Mauerwerk

AbstractPartial safety factors for resistance applied in the design equation of semi‐probabilistic formats can be obtained from the evaluation of a test database. These partial safety factors are influenced by two factors, the material uncertainty and the model uncertainty. This topic is covered in a former publication [1]. It includes the determination of a partial factor for the model uncertainty of unreinforced masonry shear walls. In this study the authors examine the next step, and calculate the partial factor of resistance applying the same method, as recommended i n EN 1990 – Annex D. In addition to the Coefficient of Variation (COV) for the model uncertainty, the calculation of the resistance partial factor considers deviations in geometry, as well as loading and material properties. The influence of the material uncertainty on structural performance is considered in the calculation by means of a weighted average of all COV values for various types of material properties, based on the number of relevant failure modes in the test database. In the last step, the resistance partial factors for models defined in DIN EN 1996‐1‐1/NA and DIN EN 1996‐1‐1/NA – Annex K are calculated by applying the probabilistic methods recommended in EN 1990 – Annex D and the model bias.

Out-of-Plane Performance of Reinforced Masonry Shear Walls Constructed with Boundary Elements

AbstractReinforced masonry shear walls with boundary elements have been introduced recently as a seismic force–resisting system as alternative to traditional reinforced masonry shear walls with rec...

Reliability of displacement capacity prediction models for reinforced concrete block shear walls

Reinforced concrete block (masonry) shear wall construction presents an economic solution for seismic resistant low- and mid-rise buildings throughout North America. In this respect, wall displacements are output, based on wall characteristics, when force-based seismic design approaches are used. In displacement-based seismic design approaches, however, target displacements are the key input needed for wall design. As large displacement demands develop within the building seismic force resisting systems (SFRS), inelastic strain, curvature, and rotation demands are expected within specific wall zones, idealized as equivalent plastic hinges. In this study, eight different models are utilized to predict the maximum displacement capacities of reinforced concrete block shear walls (RCBSW). The experimental results of 81 RCBSW have been used to evaluate the reliability of the eight models. According to the analysis performed in this study, none of the eight models was found to be reliable in terms of predicting the maximum displacement capacity when compared to the corresponding experimental results. In an attempt to further improve the predictability of these models, calibration coefficients are introduced and the corresponding improved results are re-assessed. Based on its better capability of capturing the experimental results, one of these calibrated models is selected to further investigate the influence of altering the wall design characteristics on their maximum displacement capacities. Overall, this study aims at improving RCBSW-SFRS displacement capacity prediction models, thus contributing to the efforts towards adopting displacement-based design provisions in future seismic codes.

Fragility functions for partially-grouted masonry shear walls with bed-joint reinforcement

Fragility functions are a key component of performance-based earthquake engineering methodologies. They relate the response of the building, quantified by means of engineering demand parameters (EDPs), with the probability of reaching or exceeding different levels of damage in structural or nonstructural components. This paper develops fragility functions for partially grouted reinforced masonry (PG-RM) shear walls with bed-joint reinforcement using data from 44 and 32 full-scale in-plane cyclic tests conducted on clay brick (CLB) walls and hollow concrete block (HCB) walls, respectively. Fragility functions for two levels of damage are derived for shear-dominated CLB and HCB walls using two different EDPs: the story drift ratio and a force-based normalized shear demand parameter. Fragility data based on story drift ratio has shown that HCB walls present a higher deformation capacity as compared to CLB walls. In addition, the dispersion observed in the fragility functions has indicated that the normalized shear demand parameter is better correlated to the level of damage than the story drift ratio parameter for both types of walls. Finally, a comparison with existing fragility functions developed in a previous study for HCB walls with bond-beams is presented.

Response of slender reinforced masonry shear walls with flanged boundary elements under in-plane lateral loading: An experimental study

Past experimental studies have demonstrated that reinforced masonry shear walls (RMSWs) can provide adequate ductility and energy dissipation capacity when acting as the seismic force-resisting system in low-rise buildings. However, slender RMSWs used for these applications, characterized by high height-to-thickness (h/t) ratios, may be vulnerable to out-of-plane instability failure modes when subjected to in-plane seismic loading. Out-of-plane instability may develop when a wall end zone undergoes cycles of high tensile strain, followed by compressive strain during in-plane seismic loading. Out-of-plane instability has the potential to cause unexpected and rapid strength degradation, which can lead to a global collapse. Provisions of the Canadian masonry design standard CSA S304 currently aim to prevent out-of-plane instability by prescribing h/t restrictions. Relaxation provisions were introduced in CSA S304-14 for walls with flanges or boundary elements and for walls subjected to low axial stress, however these provisions have not been experimentally verified. Moreover, prescriptive h/t restrictions disregard many important factors that affect failure modes for RMSWs under in-plane reversed-cyclic loading, including the type of loading protocol (symmetrical or asymmetrical) and the effect of flanges for T-shaped walls. This paper presents a detailed experimental study on the influence of these latter two factors on the out-of-plane response of slender RMSWs subjected to in-plane cyclic loading. The testing program comprised three full-scale RMSW specimens (two T-shaped and one rectangular) subjected to reversed-cyclic loading. A displacement-controlled loading protocol was applied until the lateral load capacity of the specimen was reduced to 80% of its maximum value. The test specimens were designed to be vulnerable to out-of-plane instability, however, although significant out-of-plane displacements were observed in one of the tests, failure of the test specimens was not governed by out-of-plane instability. Detailed descriptions of the specimen responses and a discussion on the key factors affecting the out-of-plane instability failure modes are provided in the paper. The test results confirm that the out-of-plane behaviour of slender RMSWs is similar to reinforced concrete shear walls (RCSWs) in that it is significantly affected by the presence of boundary elements (e.g. [18,11,31,1]) and the type of loading protocol (e.g. [23,24]). This leads to the conclusion that seismic design and detailing provisions for preventing out-of-plane instability in RMSWs and RCSWs should consider these parameters.

In-plane shear strength equation for fully grouted reinforced masonry shear walls

The flexural behavior of reinforced masonry (RM) shear walls is well defined and follows the simple flexural theory of reinforced concrete structures based on plane-section assumption. Conversely, the shear behavior of RM shear walls in the plastic hinge region is more complex due to the lack of comprehensive models that quantifies the interaction of the various mechanisms that contribute to the shear capacity. This paper aims to provide a comprehensive equation for predicting the in-plane shear strength, Vn, of RM shear walls. The proposed equation was verified against the results of 68 full-scale fully grouted RM shear walls from six sources in the literature tested under cyclic lateral excitations. The main variables considered in the experimental data were: the level of axial compressive stress, shear span to depth ratio, reinforcement ratio, anchorage end detail, and the spacing of reinforcement. Then, statistical analysis was performed to evaluate the precision of the proposed equation against ten widely-used equations, including the design equations given in the Canadian Standards Association CSA S304-14 (2014), the US Masonry Standards Joint Committee MSJC (2013), and the Standards Association of New Zealand NZS 4230:2004. The results of the statistical analysis show that the proposed equation provides a precise and sufficiently conservative prediction of the shear strength (Vn). The proposed equation conservatively accounts for the contribution of masonry and axial load (Vm+p), and horizontal reinforcement (Vs) to the shear resistance (Vn) while considering the influence of the level of ductility demand. It also considers the vertical reinforcement contribution to the in-plane shear strength.

Seismic performance and height limits of ductile reinforced masonry shear wall buildings with boundary elements

The National Building Code of Canada, NBCC-15 has recently added a new Seismic Force Resisting System (SFRS) category, ductile shear walls, for Reinforced Masonry (RM) buildings. Although it was assigned a higher ductility-related force modification factor compared to that of moderately ductile walls, NBCC-15 assigned the same building height limits for the ductile and moderately ductile RM walls. This study aims to assess (i.e. numerically) the seismic performance and collapse capacity of ductile RM buildings, having heights exceeding the code limit, built using ductile RM shear walls with boundary elements as the SFRS. The main objective is to propose height limits based on solid and objective seismic performance acceptance criteria. In this regard, six archetype buildings with varying heights are designed according to CSA S304-14 with ductile RM structural walls having confined boundary elements. The reference buildings are located in two regions representing the high and moderate seismicity levels of NBCC-15. The seismic performance is evaluated using nonlinear pseudo-static pushover and Incremental Dynamic Analyses (IDA). The quantification of seismic performance and collapse capacity is executed using the procedure outlined in FEMA P695. This research study contributes to the understanding of the seismic performance and collapse capacity of ductile RM shear wall buildings with boundary elements. It provides practical design recommendations to enhance the overall system performance. In addition, the study proposes a simple, yet efficient nonlinear numerical macro-modeling approach for RM shear walls. Finally, based on the findings of this study, it is suggested to assign a 70 m limit for the height of buildings in moderate seismicity regions and a 50 m limit for the buildings in regions with high seismic hazard.

Experimental shear testing of timber-masonry dry connections for the seismic retrofit of unreinforced masonry shear walls

Abstract The mechanical coupling of timber products to the masonry walls of unreinforced masonry (URM) buildings is generating considerable interest in terms of seismic vulnerability mitigation. An extensive experimental investigation on timber panel to masonry wall connections realised with screw anchor fasteners is presented. A total of 64 shear tests under monotonic, cyclic and semi-cyclic loading conditions were performed on site in a historic URM building. The examined parameters were: masonry type, timber panel product and material, load-to-grain direction, fastener geometry and steel grade. The outcomes of the campaign are then reported and discussed focusing on the strength and stiffness properties and on the dissipation capacity and residual strength of the connection under cyclic load. Moreover, a log-normal distribution fitting is proposed for the maximum load and slip modulus measurements of all the cyclic test configurations analysed. Finally, the principal experimental observations are listed along with recommendations for future work or use in practice.

Seismic performance parameters of fully grouted reinforced masonry squat shear walls

The displacement ductility, ductility-related seismic force modification factor, and the effective elastic stiffness are important force-based seismic design (FBD) parameters for reinforced masonry (RM) shear walls. In addition, stiffness degradation and equivalent viscous damping, are crucial displacement-based seismic design (DBD) parameters. This study analyzes previously reported test results of eight RM shear-dominated fully-grouted rectangular squat walls subjected to cyclic lateral excitations to evaluate the FBD and DBD parameters. The main variables of the tested walls are the level of axial compressive stress, vertical and horizontal reinforcement ratio, anchorage end detail, and the spacing of horizontal and vertical reinforcement. However, all tested walls had the same shear span to depth ratio equal to 1.25. The evaluated FBD parameters are compared to the Canadian, European and American standards. Moreover, based on the analysis, equations for the stiffness degradation of RM shear walls relative to their top drift limit or displacement ductility, are developed and presented for the examined walls. The ductility-related seismic force modification factor is computed on average 2.6, and 3.9, based on equal energy and equal displacement idealization, respectively. The US, and European standards ignore the axial stress effect on wall’s elastic effective stiffness and highly overestimate its value for the tested walls. This study presents, based on the tested walls, a guide design values for squat shear-dominated walls category that can be used in FBD and DBD.