Key Engineering Materials Vol. 916

Abstract: Fabric Reinforced Cementitious Matrix (FRCM) materials are increasingly common for strengthening existing masonry structures. Their popularity is due to their many advantages with respect to resin-based composites, especially when applied to stone supports. The constitutive behaviour of FRCM materials is defined by the combination of their tensile response and the bond behaviour with the masonry support, both depending on complex stress transfer mechanisms between matrix and fabric, especially in the post-cracking stage. This paper presents a numerical study which aims to predict the mechanical behaviour of FRCM systems through simple 2D models of truss elements and non-linear springs to simulate the fabric-to-matrix and composite-to-substrate interaction. The comparisons between results of numerical approach and experimental responses showing that the proposed methodology is an effective and easy tool to predict the mechanical behaviour of FRCM composites.

Abstract: This paper presents a critical review of the most established analytical models for the prediction of the compressive strength of FRP and FRCM-confined masonry columns. In particular, two types of fibres are analysed, i.e. glass and basalt. A wide dataset available in the literature is used for the application of the analytical models and for the development of parametric analyses useful for the critical comparison of FRP vs. FRCM confinement technique and glass vs. basalt fibres to be adopted as reinforcement of masonry substrate. The effects of stiffness and strength of the reinforcement, the number of reinforcing layers, the compressive strength of masonry and the cross-section shape are investigated.

Abstract: Abstract. Masonry strengthened with natural fabric-reinforced cementitious matrix (NFRCM-strengthened masonry) is investigated by updating an existing discrete element model. Masonry walls are modelled by rigid blocks and elastoplastic interfaces that are able to account for mortar joints and block cracking. The reinforcement is modelled in a simplified manner considering perfect adhesion between wall and reinforcement and by adopting further spring elements connecting block centres. The model is validated by comparing it with an existing FEM based on a multi-step homogenization, where reinforced masonry is considered as a whole. Both approaches are used for performing nonlinear pushover tests with an increasing shear action applied to unreinforced and reinforced panels. The updated discrete model turns out to be able to represent the strength increment given by the reinforcement, but it is less able to represent the corresponding ductility increment.

Abstract: This paper presents an innovative modelling approach for evaluating the structural response of new and existing masonry buildings characterized by a periodic arrangement of units and mortar joints. The aim is to provide a calculation tool that allows to model the non-linear behaviour of masonry structures under lateral and vertical loads with a reduced numerical effort, without compromising the accuracy of the results. The proposed model is a typical D-FEM (Discontinuum - Finite Element Model) consisting of deformable blocks, which incorporates several masonry units. The blocks are separated by interface elements placed along predetermined surfaces on which cracks, sliding or crushing planes can develop. The surface layout is conceived to replicate all the fundamental failure mechanisms that can occur in real masonry structures. To adequately describe the non-linear behaviour of the interface elements, a Modified Composite Interface (MCI) model is formulated by modifying the "Combined Cracking-Shearing-Crushing" model originally proposed by Lourenço to simulate the cracking mechanisms along the interface elements of simplified micro-models in FEM analysis. The proposed D-FE model has been already calibrated and validated by the Authors on different masonry panels and, through an Evolutionary Polynomial Regression (EPR), expressions in closed form have been defined to calculate the mechanical parameters of the new MCI model starting from the original CI. Particularly, for each mechanical parameter, six formulas of increasing complexity have been identified through non-linear regression, progressively including a greater number of input variables to increase the precision of results. The aim of this study is to determine the accuracy of these formulas. Numerical analyses are carried out on a population of sixty-four masonry walls already used in the previous calibration phase, modeling each panel with all available equations. This allows to evaluate the average accuracy of each formula and to understand their efficiency in terms of calculation effort and correctness of the results.

Abstract: Masonry made with soft clay brick is commonly used in gravity load bearing of construction in India. The masonry piers and walls typically fail by vertical splitting. The purpose of this study is to improve the strength of masonry columns under compression using wrapping for additional confinement. The compressive load carrying performance and capacity of masonry columns wrapped with fiber reinforced composites in organic and inorganic matrixes are compared. For the purpose of overall improvements in cost and durability, glass and basalt fiber reinforcement is used. 30-40% improvement in the compressive performance of masonry prisms was achieved for both Organic and Inorganic matrixes. However, the specimens with inorganic matrixes were found to exhibit higher ductility compared to organic matrixes. Glass fibers were found to be more effective in wrapping masonry specimens compared to Basalt fiber specimens owing to its higher fiber count per unit length. Analytical models for predicting the compressive capacity of masonry columns with wrapping are verified against the experimental results.

Abstract: A large experimental study was conducted at IIT Patna, India to evaluate the effectiveness of different types of cementitious matrix grids (CMGs) in improving the flexural performance of unreinforced masonry specimens. Four types of masonry wallettes: brick-lime mortar, brick-cement mortar, brick-mud mortar and autoclaved aerated concrete (AAC) block masonry were prepared in the laboratory. In this study, eleven different CMG comprising of glass fabric and steel wire meshes embedded in the five different grades of cementitious matrix were used to strengthen the masonry assemblages. The aim of this study is to understand the role of various parameters such as tensile strength of CMG, compressive strength of masonry and cementitious matrix in influencing the efficiency of the strengthening scheme. In total 130 specimens with failure plane-parallel and perpendicular to the bed joint were prepared and tested under quasi-static displacement control loading. Considering the ease of installation, the fabric was directly placed on the masonry wallette using mechanical anchors and then covered with a thick layer of cementitious matrix.Test results highlights that all strengthening schemes are effective and can significantly enhance the flexural moment capacity in the range of 2.5 - 63.0 times the flexural moment of the respective control specimens. These strengthening schemes effectively mitigate the brittle behaviour of masonry wallettes and improved the deformation capacity by 1.2 - 18.1 times when compared to the respective control specimens. The study also illustrated that the strength of cementitious matrix can play an important role in contributing to the strength and deformability of the masonry specimens strengthened with CMG. For low strength cementitious matrix, debonding failure was commonly observed, whereas, for high strength cementitious matrix, the failure/rupture of reinforcement was noticed. In addition, the shear failure of masonry or debonding failure of reinforcing mesh was observed for specimens in which CMG had higher percentage of reinforcement.

Abstract: Textile reinforced mortar (TRM) composites are an innovative solution for strengthening existing structures. TRM composites are produced with high-strength textile embedded in inorganic mortar matrices, demonstrating compatibility with existing masonry. As TRM is externally bonded to the surface of the structure, the bond behaviour between TRM and masonry substrate is a critical issue to investigate. In this study, experimental research aims to deeply understand the bond behaviour of TRMs for strengthening masonry structures. The experiments mainly consist of a series of single-lap shear bond tests on TRMs to masonry substrates. Two types of textiles (carbon and steel textile) combined with two mortar matrices (cement and lime-based mortar) were used to construct TRM. The effect of the textile and mortar matrix is presented. The test results are discussed in terms of the full range of load-slip responses and failure modes. The result showed that TRM with steel textile and cement-based mortar matrix offers better bond behaviour, but the risk of masonry damage should also be considered.

Abstract: Fiber-reinforced cementitious matrix (FRCM) composites are largely employed in Italy to improve the mechanical behavior of masonry members. Many different matrices and fiber textiles are available on the market, which entails for a large number of available composites, each with peculiar mechanical and physical properties. Among the possible applications, FRCM are often externally bonded to masonry walls to increase the wall shear capacity or to prevent possible wall out-of-plane failure. Up to date, only two guidelines are available for the design of FRCM strengthened masonry members, namely the American ACI 549.6R and the Italian CNR-DT 215. In the Italian guideline, the bending strength of an FRCM strengthened masonry wall is associated with the performance of the composite - which is investigated by FRCM coupon tensile tests and FRCM-masonry joint bond tests - through a cross-sectional equilibrium that assumes perfect bond among each material.In this paper, a database comprising 90 experimental tests on FRCM-strengthened masonry walls subjected to out-of-plane loading is collated from the available literature. The experimental results are used to compute the composite effective strain, which is then compared with the corresponding composite maximum strain obtained by characterization tests according to the CNR-DT 215 procedure. The comparison sheds light on the role of coefficients employed in the analytical procedure and helps understanding the influence of the FRCM on the wall bending capacity.

Abstract: The paper refers to the results of an experimental investigation on partially FRCM confined clay brick masonry. Seven small-scale masonry columns (square cross-section 250x250 mm, overall height 770 mm) were tested under monotonic centred load until collapse. The confining system (basalt-FRCM, SRG) and the number of the confining layers (i.e., 1, 2, and 3) were the varied parameters. Failure modes, load-displacements curves (both axial and transversal) and peak loads were reported and discussed in the paper. The performed research aims to contribute to the knowledge in the field of FRCM/SRG-confinement, mainly focusing on the influence of some of the mentioned parameters. The obtained results could be considered for the validation or the improvement of analytical design-oriented formulas.

Abstract: The paper presents compression tests of stocky and slender masonry pillars strengthened in bed joints with PBO fibres and an inorganic matrix. Five stocky pillars and four slender pillars were tested under static loading. Physical models were prepared using lime mortar similar to that used in historical structures. Fibres were applied in the grooves that were made after the mortar setting period in order to recreate real-world conditions. One of the models was subjected to preloading before the strengthening was applied. The failure modes, load-bearing capacity, cracking stresses, stiffness and deformations (longitudinal and transverse) were all determined through experimental testing. Strengthening effectiveness in terms of the increase in load-bearing capacity and stiffness, as well as anti-cracking was determined on the basis of the experimental results. The results obtained for the stocky and slender pillars were also compared, indicating the influence of slenderness on strengthening effectiveness. Special attention was also paid to failure modes and the interaction of the PBO fibres with the bed joint. Methods that strengthen pillars in their bed joints using PBO fibres increase their load-bearing capacity, stiffness and cracking resistance, while maintaining a satisfactory visual appearance which is especially important in heritage structures.