Reinforced Masonry Walls Research Articles

Influence of restrainer bar chairs on the compression and flexural behaviour of reinforced masonry walls

Lateral restrainers are traditionally provided in reinforced masonry (RM) walls to prevent the vertical steel bars from buckling. In the current version of the Australian Masonry Standards (AS 3700–2018), the use of lateral restrainers in RM walls is relaxed, if the vertical rebars are surrounded by grout annulus of twice the diameter of the bars. However, it is challenging to maintain the verticality of the reinforcing bars in the block cores to satisfy the grout annulus requirement without lateral restrainers. To address this challenge, restrainer bar chairs can be used in the construction of RM walls which are easier to employ in comparison to lateral restrainer ties. However, the implications of adopting restrainer bar chairs as an alternative to restrainer ties in RM wall construction are not well verified. In this study, the influence of restrainer bar chairs and conventional lateral ties restraining methods on the axial compression and out-of-plane bending characteristics of RM walls have been investigated. In total, twelve RM walls of dimensions 1390 mm height × 590 mm length × 190 mm thickness were constructed and tested, of which, four walls each were tested under concentric and eccentric compression and four-point bending. The experimental results revealed that the performance of RM walls with restrainer bar chairs and conventional lateral ties were similar, in terms of the observed failure modes, strength, load–displacement characteristics obtained under both compression and out-of-plane loading conditions. Strain measurements on rebars indicated that a composite action was ensued in both restrainer configurations. The capacities of the RM walls under compression and out-of-plane bending were also verified with three different masonry standards provisions and were found adequate with reasonable safety. Overall, it can be concluded that the restrainer bar chairs can effectively be used in RM walls to enable quick and accurate vertical positioning of the rebars and ensure adequate grout annulus around them.

Simulating the Nonlinear Mechanical Behavior of FRCM-strengthened Irregular Stone Masonry Walls

ABSTRACT Earthquakes constitute a significant cause of degradation and damage for masonry heritages, such as churches, palaces, castles, and entirely historical centers. This work aims to investigate numerically the Fiber Reinforced Cementitious Matrix (FRCM) system applied as coating- reinforcement to existing stone masonry walls. Indeed, despite the FRCM is, nowadays, one of the most widely adopted systems for the consolidation of masonry structures, the knowledge on its mechanical behavior is still incomplete. In this work, diagonal compression tests performed on reinforced stone masonry panels are simulated and interpreted by adopting a sophisticated numerical framework, based on the Lattice Discrete Particle Model (LDPM), which simulates, at the length scales of the masonry stones and coating mortar grains, the fracture and failure behavior of the quasi-brittle heterogeneous materials by modeling the interaction among irregular particles. Different assumptions on the FRCM features (bond behavior and thickness of the coating mortar, and the presence or not of the fiber grid therein the coating mortar) were investigated to better understand their effect. The computational effort of using that method was rewarded from the possibility of capturing the main aspects of the material heterogeneity on the fracture propagation and damage evolution in the reinforced masonry walls.

Improved design provisions for reinforced concrete block masonry walls under axial compression

The provisions pertaining to design of reinforced masonry (RM) walls under axial compression in the Australian masonry standard AS 3700 (2018 version) have been revised based on the recent findings that the lateral restraining ties do not significantly affect the performance under axial compression. The other design codes such as Canadian (CSA S304.1-14), American (MJSC) and previous version of Australian (AS 3700-2011) standards consider the RM walls as unreinforced masonry (URM) under axial compression, if they are not restrained with lateral ties in both directions. However, it is widely believed that these provisions are stringent and over-conservative, as proven by the experimental studies that the compression bars in RM are effectively restrained by the surrounding well compacted grout. Hitherto, no systematic studies have been carried out to determine the applicability of these provisions to the reliability of the compression design approaches of RM walls. Therefore, in this research an attempt has been made to evaluate the accuracy and reliability of the design provisions outlined in the selected design standards (AS 3700, CSA S304.1-14 and MSJC). The experimental database generated in the authors’ previous study was used to verify the reliability of the design provisions. The reliabilities of the design expressions were verified using the first-order reliability method (FORM). The reliability analyses revealed that the provisions specified in the standards are quite conservative as they have exceeded the target reliability index of 3.6 for the analysed RM walls. The current provisions of AS 3700 (2018 version) have shown to predict the axial capacities of the walls better than other standards, while satisfying the target reliability limit. Thus, it can be stated that revisions made in AS 3700 (2018 version) are effective and economical for designing the RM walls as they have eased the requirement of lateral restrainers and account for a realistic contribution of grout and compression steel strengths in determining the axial capacity.

Experimental study on shear performance of improved high-performance polymer cement mortar–glass fiber reinforced plastic reinforced masonry wall

The improved high-performance polymer cement mortar (PCM) and glass fiber reinforced plastic (GFRP) system reinforcement was used in the research to strengthen and repair the masonry structure, so as to improve its bond stress, anchoring force, and integral performance without changing the original structure and further study the shear performance of masonry structure strengthened by the combination of the two. The optimum ratio of improved high-performance PCM was determined by analyzing the bend-press ratio of PCM test block. Improved high-performance PCM and GFRP were combined to strengthen the damaged masonry wall, and a five-piece masonry wall composed of “improved high-performance PCM+ with or without GFRP+ different original wall failure modes before reinforcement” was designed. Through diagonal loading shear test, the shear strength, vertical displacement, horizontal relative displacement, and failure models of masonry walls were obtained, and the effects of five different reinforcement methods and different materials on shear strength, stiffness, ductility, and failure modes of masonry walls were studied. The results show that compared with the unreinforced original wall, the shear strength of the masonry wall reinforced with the improved O4PCM is 43.5% higher, and its stiffness is also greatly improved, but the failure mode is still brittle failure; the shear strength of masonry walls strengthened by O4PCM and GFRP is 6.5% higher than that of masonry walls strengthened by O4PCM alone, and the stiffness is also increased. Its failure mode changes from brittle failure to ductile failure; with a failure mode of ductile failure, the shear strength of masonry walls strengthened by P4PCM and GFRP and that strengthened by P6PCM and GFRP are 4.8% and 12.7% higher than that strengthened by O4PCM and GFRP, respectively, and the stiffness is also increased compared with that strengthened by O4PCM and GFRP. After experimental comparison, it is the best scheme to strengthen masonry wall with improved P6PCM and GFRP.

In-plane and out-of-plane structural performance of fully grouted reinforced masonry walls with varying reinforcement ratio – A numerical study

Most international masonry design standards include the contribution of reinforcements to enhance the capacity of reinforced masonry walls subject to seismic loading. As masonry is brittle, it can potentially fail before the reinforcing bars yield, especially in closely spaced reinforced masonry walls. The assumption that these bars yield at the ultimate load could, therefore, result in an unrealistic over-prediction of the flexural and shear capacities of the walls. This paper presents a detailed investigation of several fully grouted reinforced masonry (FGRM) walls subject to in-plane and out-of-plane loading that is independent of each other. The analyses include the level of pre-compression and a wide range of reinforcement ratios. The assessment has been carried out through an explicit finite element (FE) model. Validation of the FE model is briefly presented and the structural performance, i.e., load capacity, lateral drift index, displacement ductility and stiffness of the FGRM walls are discussed in detail. The influence of reinforcement ratio on the yielding of reinforcing bars in the FGRM walls under in-plane and out-of-plane loading is also shown. It is found that the increase in reinforcement ratio beyond a critical limit degraded the structural performance of the FGRM walls and a suitable reinforcement ratio range is proposed.

Influence of blockaid chairs on compression and amp out-of-plane behaviour of reinforced masonry walls

ABSTRACT Changes in Australian Masonry Standards and National Code of Construction for reinforced masonry (RM) under compression impress the need of a grout annulus and vertical bar confinement using 6 mm tie bars. Maintaining the verticality and centricity of reinforcement and restraining them with the tie bars is challenging and time consuming. BlockAid have designed masonry bar chairs to align and restrain the reinforcing bars central in the block cores. This paper presents an investigation to ascertain the performance of BlockAid bar chairs in supporting the reinforcing bars in the RM walls subject to vertical compression and out-of-plane loads. The mean compressive strength in the fully grouted RM walls with BlockAid bar chairs was determined equivalent to the control specimen which sustained maximum load of 3100kN, compared to 3030kN for the BlockAid sample. Strain in the vertical steel bars, with BlockAid bar chairs, remained compressive throughout the loading with no evidence of buckling. The out-of-plane test results of BlockAid walls were similar in terms of failure modes, load-displacement behaviour and steel strain variations. These observations conclude that BlockAid bar chairs are effective in restraining the vertical bars against buckling and do not compromise the compression and bending capacity of RM walls.

Numerical and Experimental Assessment of an Improved Design Detail for Partially Grouted Reinforced Masonry Wall Structures

AbstractReinforced masonry buildings predominantly are partially grouted in areas of low or moderate seismicity in North America. The walls in such structures typically contain widely spaced separa...

Experimental investigation on the effectiveness of lateral restrainers to the vertical steel in reinforced masonry walls under axial compression

Reinforced masonry (RM) walls are mostly used in low to mid rise residential/industrial buildings in cyclonic and seismic regions. They are conventionally constructed with grout embedded vertical steel reinforcements positioned in the middle of the hollow blocks. However, these reinforcing bars are rarely detailed with lateral restrainers, which are considered essential in the design standards to avoid buckling of the vertical bars. This research investigates the effectiveness of lateral restrainers to the axial compression resistance of RM by testing of 128 walls under concentric and eccentric compression with different reinforcement configurations. The tested walls (190 mm thick × 600 mm wide) consisted of various types of detailing with and without lateral restrainers, grout strengths (25–50 MPa), and three heights (800 mm, 1400 mm and 2400 mm). Two walls were constructed and tested for each configuration, out of which one was tested to determine the ultimate strength and the other tested to acquire ultimate strength, axial deformation of the wall, axial strain in the steel bars and strain on the surfaces of the face-shell. The experimental results revealed that the grout has significantly contributed to the axial capacity, whilst the lateral restrainer reinforcement detailing had no significant effect on either the steel strain development or on the overall strength of the RM walls. Under concentric compression, the strain measurements in the vertical steel bars indicated that irrespective of the absence or presence of the lateral restrainers, the vertical bars remained under compression throughout the loading history with no evidence of buckling. Effects of slenderness and eccentricity were also evaluated for the RM walls under compression. It can be concluded from this research that the RM walls designed and constructed without lateral restrainers to resist cyclonic and seismic forces need not be treated as unreinforced masonry (URM) for compression if the vertical bars are surrounded by well compacted grout.

In-plane shear strength and damage fragility functions for partially-grouted reinforced masonry walls with bond-beam reinforcement

This paper presents a study on the in-plane shear response of partially-grouted reinforced masonry walls with bond-beam reinforcement. A database of 95 tests on partially-grouted walls made of concrete hollow blocks was compiled from experimental studies reported in the literature to characterize the capacity and damageability of walls subjected to in-plane lateral loading. The database has been used to evaluate the accuracy of existing design shear strength equations for partially-grouted walls. It is concluded that the shear strength expressions in the Masonry Standards Joint Committee (MSJC) code and Canadian standard are unconservative for partially-grouted walls. A modified equation based on the MSJC expression is proposed which better estimates the shear strength of this type of walls. Seismic fragility functions are also derived based on the experimental database to calculate the probability of experiencing moderate and severe damage in a partially-grouted wall for a given story-drift ratio deformation or normalized shear force demand. The resulting fragility functions show that the normalized shear demand is better correlated with the level of damage than the story-drift ratio.

Numerical study of composite material (FRP/TRC)-reinforced masonry walls under in-plane loading

Fibre-reinforced polymers (FRPs) and textile-reinforced concretes (TRCs) are becoming increasingly common solutions for strengthening masonry walls. This study focuses on different approaches for modelling the behaviour of hollow concrete block masonry walls strengthened with FRPs and a TRC subjected to in-plane loading. Specifically, the masonry is modelled using the heterogeneous approach, wherein the damage post-peak softening behaviours of both bricks and mortar are considered, as this approach is appropriate for material and structure scales. To model the FRP/TRC-reinforced masonry walls, the reinforcements (FRPs/TRC) are perfectly connected to the substrate. Although the homogeneous approach is proposed to model the FRPs with linear elastic behaviour and is shown to be appropriate for modelling the FRP-reinforced masonry walls, the TRC is modelled using the heterogeneous approach, allowing for the real contribution of the filaments to be expressed through an ‘efficiency factor’. The numerical results show that this factor has a significant influence on the behaviour of the TRC and therefore, on the overall behaviour of the TRC-reinforced walls. However, the ‘efficiency factor’ of the TRC sample is significantly higher than that of the TRC in the strengthened wall. This result confirms that the choice of the heterogeneous approach to model the TRC in our case is appropriate. Moreover, it verifies that it is impossible to transpose this global factor from the material scale (uniaxial tensile stress) to the structure scale when the application target is a masonry wall (multi-axiality, and therefore, complexity of the stress). Consequently, the constitutive laws of the TRC composite obtained through only direct uniaxial tensile characterization procedures are insufficient to enable a suitable restitution of the overall behaviour of the masonry reinforced with the TRC. In addition, regardless of the nature of the reinforcement, the overall behaviours of the masonry walls reinforced with the FRPs/TRC are governed by both the axial stiffness of the reinforcement and the compressive strength of the masonry substrate.

Brickwork wall models strengthened with diagonal and horizontal GFRP strips

The use of fiber reinforced polymers (FRPs) as external bonded (EB) strengthening of unreinforced brickwork masonry has became a common intervention technique for restoration of masonry walls damaged by seismic actions with the aim to improve the capacity under in-plane shear loading. The exact knowledge of the behavior of system composed by masonry and EB FRP strips through the interaction mechanism between strengthening and substrate is essential for the effectiveness of interventions based on the use of FRP strips. This paper provides an investigation on the behaviour of unreinforced and reinforced masonry walls made with solid clay bricks in scale 1/3rd, considering the presence of different types of masonry, such as historic and modern, and different configuration of the GFRP strengthening. Three walls, characterized by double T shape, were tested under combined compression and shear loading. Two of them were strengthened after damage using, respectively, diagonal and horizontal EB GFRP strips; another one was strengthened with horizontal GFRP strips without damage and subjected to the same loading path until failure. The response of all models is illustrated and discussed considering the walls’ shear strength and effects on the failure mechanism due to diagonal and horizontal EB GFRP strips.

Reinforced masonry shear wall blast response limits for ASCE 59 and CSA S850

The current blast response limits for reinforced masonry (RM) walls in North American blast standards are based on parameters that neither account for the wall ductility capacities nor the influence of different design configurations on the wall damage tolerance levels. Specifically, ASCE (2011) and CSA (2012) currently assign a support chord rotation limit for each damage state (i.e., Superficial, Moderate, Heavy, and Hazardous) regardless of the different ductility capacities that structural components may possess when different design configurations are adopted. However, recent relevant studies demonstrated that wall configurations and their different design parameters significantly influence the out-of-plane performance of RM walls. For example, RM shear walls with boundary elements are considered a promising blast-resisting system due to their enhanced out-of-plane characteristics (e.g., strength and ductility) compared to those with typical cross-sections (i.e., rectangular). Nonetheless, the aforementioned standards do not assign separate design requirements or response limits for this new system due to the limited number of relevant studies available when such standards were being developed. To address this knowledge gap, the current study evaluates the blast behavior of such walls with different configurations and subsequently proposes new related blast response limits for ASCE 59 and CSA S850. An OpenSees model was developed and then validated through the results of several previous test programs under quasi-static and blast loads. Subsequently, the new response limits were generated using the model and compared to those currently available (i.e., ASCE 59–11/CSA S850-12) using pressure-impulse diagrams. Finally, the blast response of several RM walls with different configurations was evaluated when such walls were subjected to different blast demands. The results highlight the blast-resistance enhancements that boundary elements can provide to RM shear walls at different damage states and the need to develop category-specific blast response limit within blast design standards.

Experimental behaviour of unreinforced and reinforced concrete block masonry walls under uniaxial compression

This paper presents the details of experimental investigations on the compressive strength of full scale hollow concrete block masonry walls. Comparison of load carrying capacity of unreinforced masonry walls with reinforced masonry walls have been studied as part of this study. The failure mechanism of reinforced hollow concrete block masonry (RHCBM) walls and unreinforced hollow concrete block masonry (URHCBM) walls have been studied. It is observed that the load carrying capacity of RHCBM walls are about 39.40% higher compared to URHCBM walls which is due to presence of marginal amount of reinforcement (about 0.12% of cross sectional area) and grout.

A retrofitting technique using steel grids for existing masonry panels: a numerical and analytical study

The current research focuses on a numerical and analytical study aimed at investigating the efficiency of a steel-based reinforcement system suitable for existing masonry walls. The application of such a retrofitting technique, which consists of glued thin steel grids applied on both faces of a masonry panel, is reversible, cheap and easy to be executed and appears to be suitable especially for buildings with concrete slab or inter-stories beams to which the steel elements could be anchored. The study is based on a reference experimental test carried out at the “Politehnica” University of Timisoara (Romania), within the European FP6 project PROHITECH. The reference test provided the application of a constant vertical compression and cyclic horizontal displacements to an unreinforced brick-cement mortar wall in full-scale (1500 × 1500 × 250 mm), to which was conferred a double-fixed constraint condition. Based on the experimental evidences, a reference numerical model has been implemented in ABAQUS, by adopting a plastic-damage material and a macro-element approach for the masonry modelling. Hence, in order to determine a design criterion of the studied system, a comparison with the analytical formulations available in the current Italian and European codes for the unreinforced configuration is presented in this study. Then, a wide parametric study on the investigated retrofitting technique has been carried out by varying thickness and spacing of steel grid elements, as well as the geometrical ratio of the panel (height/length). On the basis of the numerical results, a capacity formulation has been proposed, which takes into account the steel distribution in the masonry panel. The obtained outcomes revealed that the strength increase achievable by adopting the studied reinforcement system could be compared to the efficiency of a reinforced masonry wall of new construction and it is strongly influenced by the geometrical ratio of the wall, as well as the steel distribution.

Experimental Testing and Numerical Modeling of Robust Unreinforced and Reinforced Clay Masonry Infill Walls, With and Without Openings

This paper presents an overview of the experimental results obtained by combined in-plane/out-of-plane (IP/OOP) tests carried out on robust clay masonry infill walls. The combined tests were carried out on eight full-scale one-bay, one-story infilled reinforced concrete (RC) frames, plus one reference RC bare frame. In four cases, the masonry walls fully fill the RC frame: two walls are made of unreinforced masonry (URM), whereas the other two are made of reinforced masonry (RM), with both vertical and horizontal reinforcement. Each pair of specimens was tested up to different levels of IP drift before carrying out the OOP tests. Four other specimens, still made of URM and RM walls, are characterized by the presence of a central opening, and in one case, the effect of a lintel is analyzed. On the basis of the tests carried out, an analytical model was developed for the analysis of the OOP behavior. It was used to calibrate IP damage degradation models based on the experimental results to define limits for the applicability of well-known flexural and arching mechanism models for the evaluation of the OOP capacity of the infill walls and to evaluate the efficiency of vertical reinforcement. In this work, the experimental campaign is presented, and the results of both experimental tests and numerical analyses are discussed.

Influence of surface reinforcement on the strength of brick masonry wall

In this article, an attempt is made to evaluate the load carrying capacity of one brick thick vertical, surface reinforced masonry wall and compared with unreinforced wall. Locally available bricks of compressive strength of 4–8 MPa is used in study. Basic properties of bricks and three types of mortars are evaluated. Compressive strength, shear bond and flexural bond strength of English bonded prisms is also explored. Experimental results indicated bond strength of English bonded prisms built with cement sand mortar and cement soil mortar was comparable. Use of lime showed reduced bond strength and compressive strength. Use of vertical reinforcement in masonry construction is mainly devoted for resisting lateral forces. Compressive strength of 0.1% externally reinforced masonry wall was 7.4% more when compared to unreinforced masonry. Similarly, modulus of elasticity of reinforced masonry wall is 2.08 times of unreinforced masonry wall.

Finite‐element modeling of the seismic response of reinforced masonry wall structures

AbstractModern design codes and performance‐based earthquake engineering rely heavily on computational tools to assess the seismic performance and collapse potential of structural systems. This paper presents a detailed finite‐element (FE) modeling scheme for the simulation of the seismic response of reinforced masonry (RM) wall structures. Smeared‐crack shell elements are combined with cohesive discrete‐crack interface elements to capture crushing and tensile fracture of masonry. Beam elements incorporating geometric as well as material nonlinearity are used to capture the yielding, buckling, and fracture of the reinforcing bars. The beam elements are connected to the shell elements through interface elements that simulate the bond‐slip and dowel‐action effects. An element removal scheme is introduced to enhance the robustness and accuracy of the numerical computation. The material models and interface elements have been implemented in a commercial FE analysis program. The modeling scheme is validated with data from quasi‐static cyclic tests on RM walls as well as with results from shake‐table tests on RM building systems.

Finite element analysis of UHPC reinforced masonry structure

Based on the existing UHPC material parameters, masonry parameters and the application of reinforcement projects on the market, ABAQUS's unique concrete plastic damage (CDP) constitutive model can be used for concrete and other brittle materials. The constitutive parameters are obtained by curve fitting experiments by other scholars, and this paper has carried out appropriate calibrations. Numerical analysis is the pseudo-static loading form of UHPC reinforced low-strength masonry walls. Through the analysis and simulation of the hysteresis curve, skeleton curve, equivalent plastic strain Moire diagram, peak stress, strain and other parameters, the changes in shear resistance before and after UHPC reinforced masonry walls are evaluated.

Evaluation of collapse resistance of reinforced masonry wall systems by shake‐table tests

SummaryThis paper presents a shake‐table test study to investigate the displacement capacity of shear‐dominated reinforced masonry wall systems and the influence of wall flanges and planar walls perpendicular to the direction of shaking (out‐of‐plane walls) on the seismic performance of a wall system. Two full‐scale, single‐story, fully grouted, reinforced masonry wall specimens were tested to the verge of collapse. Each specimen had two T‐walls as the seismic force‐resisting elements and a stiff roof diaphragm. The second specimen had six additional planar walls perpendicular to the direction of shaking. The two specimens reached maximum roof drift ratios of 17% and 13%, without collapsing. The high displacement capacities can be largely attributed to the presence of wall flanges and, for the second specimen, also the out‐of‐plane walls, which provided an alternative load path to carry the gravity load when the webs of the T‐walls had been severely damaged. The second specimen developed a higher lateral resistance than the first owing to the additional axial compression exerted on the T‐walls by the out‐of‐plane walls when the former rocked. The shear resistance of the T‐walls evaluated with the design code formula matches the test result well when this additional axial compression is taken into account. However, it must be understood that the beneficial influence of the wall flanges depends on the magnitude of the gravity load because of the P‐Δ effect and the severity of damage induced in the wall flanges when the wall system is subjected to bidirectional ground motions.

Structural Behavior of Masonry Panels Strengthened Using Geopolymer Composites in Compression Tests

Unreinforced masonry panels are the most important supporting elements in many structures, but these building elements are very vulnerable to earthquakes, and serious damage occurs. Many researchers state that the seismic performance of the masonry samples is poor and that these elements should be strengthened. In this study, the structural behavior of the strengthened masonry prism was investigated using Geogrid Geopolymer Panels (GGP) in compression tests. Six stone masonry wallettes were built to characterize them under loading systems, and the behavior of the samples was determined with different geometric strengthening methods (cross, diagonal, and parallel). Samples UCT-M1 and DCT-M1 were unreinforced masonry walls. GGP material was applied across the entire surface of reinforced samples UCT-M2 and DCT-M2. Vertical and diagonal compression tests were applied to the samples according to ASTM C1314-10 and ASTM E519-02, respectively. A linear variable differential transducer was placed on the samples, and the load–displacement curves were determined. As a result, the reinforced masonry walls had higher mechanical strength and load-carrying capacity than the UCT-M1 and DCT-M1 samples. The geopolymer composites prevented the degradation of the UCT-M2 and DCT-M2 samples. Also, the strengthened specimens displayed more ductile behavior, which depends on the failure mode and cracks patterns under the loading systems.