Shear Capacity Of Masonry Walls Research Articles

Diagonal Compression Tests on Unfired and Fired Masonry Wallettes Retrofitted with Textile-Reinforced Alkali-Activated Mortar

This paper discusses the integration of an alkali-activated mortar (AAM), based on industrial waste, into a novel composite material fit for structural upgrading purposes and rendered with high temperature endurance and a low CO2 footprint. The AAM combined with carbon fiber textiles form a new generation of sustainable inorganic matrix composites—that of textile-reinforced alkali-activated mortars (TRAAM). A test program was designed to assess the effectiveness of carbon TRAAM overlays in increasing the shear capacity of masonry wall specimens comprising solid clay bricks bonded with lime-based mortar and furnished with TRAAM jackets on both sides. The initial and the residual capacity of the reinforced walls were evaluated, the latter by performing diagonal compression tests after exposure to 300 °C and 550 °C. It was shown that TRAAM jacketing can increase the shear capacity of unfired masonry walls by 260% and 335% when a single or a double layer of textile is used, respectively. Rapid heating to temperatures up to 550 °C, one-hour-long steady-state heating, and natural cooling bore no visible thermal cracks on the specimens and had little effect on their residual capacity. Based on these results, the prospect of using TRAAM for retrofitting applications for fire-resilient structures seems very auspicious.

Behaviour of masonry walls strengthened with fibre-reinforced cementitious materials

Assessment of the mechanical properties of masonry materials is a key issue for evaluating the strength capacity of masonry walls. Two types of tests are usually adopted for experimentally evaluating the shear capacity of masonry walls: diagonal-compression and shear-compression tests. Different approaches are available in the literature for their interpretation. This paper reports an investigation into the behaviour of both unstrengthened and in-plane strengthened masonry walls with fibre-reinforced cementitious matrix materials under the two tests by means of a bi-dimensional non-linear-finite-element model. The model was first calibrated on the basis of comparisons with experimental results of diagonal-compression tests available in the literature. It was then used for comparing the numerical results obtained for the two tests in terms of local stress distributions for both unstrengthened and strengthened walls. The differences in the stress distributions in the tests, and the role of the reinforcement both on the distribution of stresses and on the global behaviour of the masonry walls, was highlighted.

Seismic Behavior of Brick Masonry Walls Strengthened with Different Types of Fiber Nets

To investigate the strengthening effect of fiber nets on the seismic behavior of brick masonry walls, carbon fiber nets (CFN), glass fiber nets (GFN) and basalt fiber nets (BFN) were applied to strengthen masonry walls with an external sticking method. Pseudo-static tests were carried out on eight walls with different strengthening conditions: one was not strengthened; six were strengthened on one side or both sides with CFN, GFN and BFN, respectively; and one was strengthened with CFN on both sides and then riveted with steel plates. The results showed that fiber nets could exchange the failure mode of the walls from shear failure to bending failure. The bearing capacity, energy consumption and ductility of the strengthened walls were improved, and the improvement of double-sided reinforcement was more notable. Epoxy polymer mortar is more suitable for masonry structure strengthened with fiber nets than acrylic polymer mortar because it can ensure the full participation of fiber nets. In addition, a calculation formula for the design value of seismic shear capacity of masonry walls strengthened with fiber nets was deduced, which can effectively predict the shear capacity of walls strengthened with fiber nets.

Triplet Tests and Numerical Validations of Stone Masonry with Dowels Under Shear

Dowels are connected to two masonry units in the vertical direction for the continuity and integrity of walls. According to the national and international literature, studies investigating the effectiveness of dowels on masonry walls are rare. This paper presents a preliminary experimental study performed on tuff stone masonry specimens with dowels to assess the effects of dowels on the shear capacity of masonry walls. For this aim, 54 masonry specimens, nine being controls without dowels and 45 with different dowel diameters and axial load levels, were tested under triplet test procedures, according to TS EN 1052-3 regulations. Numerical validations were performed using the LUSAS finite element software package. The experimental results were compared with numerical simulations. The present study reveals that dowels significantly improve the shear capacity of masonry walls. Furthermore, recommendations regarding suitable dowel ratios are made.

Simple method to evaluate FRCM strengthening effects on in-plane shear capacity of masonry walls

Fabric Reinforced Cementitious Mortar (FRCM) strengthening demonstrated to be an efficient way to improve the in-plane shear capacity of masonry walls, in particular for its high compatibility with masonry substrate. Recently, Italian CNR guidelines provided two approaches to design in-plane shear strengthening interventions for masonry with FRCM system, one is very simple and practitioner oriented, but it has clear limitations in its applicability, while the second has a more complex formulation, but it is valid for a wider range of applications. The main aim of this work is to reconciliate the two approaches and to clarify the potential of FRCM systems in masonry strengthening with design charts and manipulations of the more refined available formulations, with the goal to provide a simple method to account for the refined version in a practitioner oriented approach. The focus is on the impact of material properties on the capability of strengthening. A final worked example provides a comprehensive overview of the potential of the proposed method.

Shear capacity of masonry walls externally strengthened using Flax-TRM composite systems: experimental tests and comparative assessment

A growing environmental awareness is gradually changing the entire economic system and consequently, the building materials sector is increasingly interested in innovative sustainable solutions. The use of plant fibres as reinforcement in inorganic composite systems, generally referred to as Textile Reinforced Mortar (TRM), represents an innovative alternative to the use of more traditional high-strength inorganic fibres, which reduces the environmental impact of the composite. However, there are several unsolved issues regarding the correct mechanical behaviour of such innovative systems. Various studies have been conducted to assess the fibre-to-mortar bond properties and to investigate the tensile behaviour of TRMs based on plant textiles, such as flax, hemp, coir, sisal, and jute. Moreover, there is still a lack of experimental evidence concerning the efficiency of the composite material once applied to structural elements. Therefore, this paper reports on an experimental study on the shear capacity of walls strengthened by two TRMs characterised by a different amount of textile reinforcement. The experimental results are discussed and compared with the results of theoretical models derived from formulations proposed by the standards in this field. This study shows that Flax-TRM reinforcement enhances the strength and ductility of a masonry assemblage, confirming the potential utility of such materials. Furthermore, it points out some limitations of this reinforcement technique and paves the way for future studies aimed at improving the efficiency of the entire system.

Diagonal compression testing of masonry panels with irregular texture strengthened with inorganic composites

Inorganic composites for enhancing the in-plane shear capacity of masonry walls with irregular texture were investigated on twenty-one panels under diagonal compression tests. Three specimens were used as control and twelve specimens were strengthened with two Fibre Reinforced Mortars (FRM-A and FRM-B), characterized by a different content of fibres embedded in the lime-based matrix. The remaining six specimens were strengthened with Fabric Reinforced Cementitious Mortars (FRCM), consisting in a GFRP grid embedded in a fibre reinforced matrix (the same used for FRM-A). The influence of single-side and double-side strengthening configurations on the capacity of strengthened panels was also investigated, to point out the reduction in strengthening effectiveness in case of single-sided applications. The results showed that all the inorganic composites adopted for the strengthening techniques provided a substantial increase of shear capacity. The grid in FRCM strengthened panels played an important role in both strength and deformation capacity at peak. The different fibres content (lower than 50% in weight) in FRM systems slightly affected the overall performance of panels. Finally, analytical predictions of experimental results were reported and discussed and a preliminary analytical model for estimating the FRM shear contribution was proposed, obtaining a good agreement with test results.

Cyclic shear behavior of masonry walls strengthened with prestressed steel bars and glass fiber grids

The present study developed a new and original strengthening method to enhance the shear capacity and ductility of unreinforced masonry (URM) walls based on the unbonded prestressed units using steel bars and glass fiber (GF) grids. The strengthening efficiency was validated through the experimental analyses including the failure mode, the lateral load-displacement relationship, shear capacity, and work damage indicator measured from four specimens subjected to a constant axial load and cyclic lateral loads. In addition, new design equations for the shear capacity of masonry walls were derived based on the regression analysis of 172 datasets. In particular, the proposed equations considered the shear enhancement by the axial stresses created due to the prestressed strengthening materials. The test results showed that shear capacity of the masonry walls strengthened with diagonal steel bars and GF grids increased by 4.2 times when compared with that of the companion URM walls. The proposed design equations for shear capacity of masonry walls also exhibited superior accuracy to FEMA 306 and EC 6 models.

Shear Capacity of Masonry Panels Reinforced with Inorganic Strengthening Systems

Unreinforced masonry buildings are particularly vulnerable to brittle failures during seismic events due to the poor in-plane shear capacity of masonry walls. The use of strengthening solutions with polymeric matrices is not often recommended for masonry buildings, due to breathability issues, and the adoption of inorganic matrices is sometimes considered preferable. In this paper, the use of inorganic composite materials for improving the in-plane shear capacity of tuff masonry walls is investigated. The experimental data from 83 diagonal compression tests carried out at the University of Naples Federico II in recent years have been collected and the main results are herein discussed to outline the main features of different strengthening techniques with inorganic composite materials such as Reinforced Plaster (RP), Composite Reinforced Mortar (CRM) and Fabric Reinforced Cementitious Matrix (FRCM).

Experimental In-Plane Shear Capacity of Clay Brick Masonry Panels Strengthened with FRCM and FRM Composites

Unreinforced masonry (URM) buildings, largely found in Euroasian regions, are particularly vulnerable to in-plane shear failures during seismic events due to the poor shear capacity of masonry walls. In the case of historical masonry buildings, the use of strengthening solutions with polymeric and polymer-modified matrices composites is not recommended since the breathability of the masonry could be reduced, leading to a fast and undesired degradation. In this paper, an innovative fiber-reinforced cementitious mortar (i.e., FRCM) system was used to improve the shear capacity of old-type solid clay brick masonry walls. An experimental program on 24 masonry panels subjected to diagonal compression tests was carried out. The innovative FRCM system consisted of a basalt grid embedded in an improved inorganic matrix, made of lime-based mortar reinforced with short glass fibers (i.e., Fiber-reinforced mortar, FRM). Two sets of specimens were tested, single-leaf masonry panels and double-leaf masonry panels, to investigate the typical configurations of load-bearing walls and partition walls. The effectiveness of the innovative FRCM system was investigated for both a conventional symmetric strengthening configuration and an asymmetric strengthening configuration with anchors, a solution often adopted in the case of internal/external interventions only. Furthermore, the response of masonry panels strengthened with only symmetric FRM with a slightly greater amount of short glass fibers embedded in the matrix was also investigated. The experimental outcomes outlined that panels reinforced with symmetric FRM achieved similar effectiveness in the shear strength increase to panels reinforced with symmetrical FRCM. Conversely, a reduced deformability was observed in FRM panels with respect to those strengthened with FRCM. The experimental results also allowed the quantification of the effectiveness of FRCMs in the case of asymmetric strengthening configurations. Finally, a comparison between experimental results and American Code provisions for FRCM-strengthened systems was reported.

In-plane shear capacity of tuff masonry walls with traditional and innovative Composite Reinforced Mortars (CRM)

Abstract The effectiveness of reinforced plasters and Composite Reinforced Mortars (CRM) for increasing the in-plane shear capacity of masonry walls was investigated on a series of 32 single-leaf tuff masonry panels subjected to diagonal compression tests. Six specimens were used as control and two specimens were strengthened with reinforced plaster (steel grid 100 × 100 mm and cementitious matrix) with a thickness of 40 mm. The remaining specimens were strengthened with two different fibre reinforced lime-based mortars, characterized by different cement content ratios, and coupled with three different grids (steel grid 100 × 100 mm, GFRP grid 30 × 30 mm and GFRP grid 40 × 40 mm). Both single-sided and double-sided strengthening configurations were adopted for all strengthening solutions, to investigate the reduction in strengthening effectiveness in case of single-sided applications. The results showed that strengthening in single-sided configuration increased the shear capacity from 42% to 85% with respect to the unreinforced masonry panels (URM) average shear capacity. Conversely, strengthening in double-sided configuration led to a shear capacity increase from 138% up to 288%. Based on experimental results, reducing the matrix cement content ratios in strengthened system led to a reduction in shear capacity and energy dissipation, independently from the grid properties. Furthermore, specimens strengthened with GFRP 40 × 40 grid, although characterized by a large spacing with respect to GFRP 30 × 30, achieved an increase in the shear capacity and energy dissipation greater than other strengthened specimens clearly evidencing that the grid spacing and the interlock between grid and micro-fibres embedded in the mortar are crucial aspects for the strengthening system effectiveness.

Performance of hollow concrete block masonry walls retrofitted with steel‐fiber and microsilica admixed plaster

The weakness of existing unreinforced masonry (URM) wall buildings in resisting lateral loads is a matter of concern, especially in locations exposed to seismic hazards. In order to address this shortcoming, considerable research effort has been dedicated in the last few years on the strengthening techniques of existing URM structures. This paper presents the test results of four hollow concrete block walls, one as control, one using high steel‐fiber reinforced mortar admixed with microsilica (SFR‐MS) mortar in joints and the other two walls plastered with 10 mm thick SFR‐MS mortar on one and both sides of the wall, respectively. The shear capacity, stiffness, cracking patterns and failure modes of the walls were investigated. In addition, a nonlinear finite element simulation of the walls in an ABAQUS environment is presented and results compared with those obtained from the experimental investigations conducted. Modified analytical equations for predicting the shear capacity of masonry walls with plaster is proposed and results compared with the experimental and finite element simulation results of the investigated walls.

On the in-plane shear response of the high bond strength concrete masonry walls

Conventional unreinforced masonry walls subject to in-plane shear loading fail due to exceedance of shear and tensile bond strengths. This paper examines whether or not the in-plane shear capacity of masonry walls would increase with the increase in the bond strengths through experimental and numerical investigations. For these investigations, shear walls were built with high bond strength polymer cement mortar; they were applied in thin layers of 2 mm thickness each. Material tests were carried out to characterise the bond and the compressive strengths of the high bond strength thin layer mortared masonry; the bond strengths were found approximately double that of the conventional 10 mm thick cement mortars. The shear walls, however, exhibited significantly lower capacity (contrasting the expectation) and displayed base course sliding mode of failure. To ascertain the validity of the experimental results, a combined surface contact—interface element micro finite element (FE) modelling technique was formulated; the results adequately reproduced the experimental datasets. The validated FE model was then applied to examine the effect of the aspect ratios and pre-compression levels to the failure modes, deformation and strength of the high bond strength shear walls and is shown that once the pre-compression exceeds 15% of the masonry compressive strength, the base sliding failure mode changes to the diagonal cracking mode with corresponding increase in in-plane shear capacity. Therefore, it is concluded that the increase the bond strength without regard to pre-compression could adversely affect the safety of the high bond strength unreinforced masonry shear walls.

Shear capacity of masonry walls externally strengthened by a cement-based composite material: An experimental campaign

Composite materials are getting more and more common for strengthening existing members and structures; fiber-reinforced polymers (FRP) are widely used, while carbon-fiber-reinforced cement matrix (CFRCM) materials have been more recently proposed especially for strengthening masonry members. In the present paper, the results of an experimental campaign carried out on tuff-masonry walls strengthened in shear by a cement-based composite are reported and commented. The reinforced masonry walls failed after loss of adhesion between the strengthening layer and the masonry substrate. Comparisons between the experimental results and some analytical formulations available in the scientific literature for determining shear resistance of strengthened masonry walls are finally proposed. Huge variability can be observed by applying those alternative formulations which are not able to reproduce the premature nature of the observed failure mode. Consequently, the present study is a thorough experimental report which can be useful for developing and validating more refined theoretical models for describing the ultimate behaviour of masonry walls externally strengthened by FRP.