Key Engineering Materials Vol. 916

Abstract: Over the past two decades, different innovative systems have been developed for the rehabilitation and retrofitting of existing structures. In particular, SRG (Steel Reinforced Grout) strengthening systems have proven to be very effective in increasing the load carrying capacity and global ductility of reinforced concrete and masonry structures, and their use as an alternative seismic retrofitting solution is increasing rapidly. Although several studies have focused on the characterisation of the mechanical performance of SRG composites subjected to direct tension or bonded to concrete/masonry substrates, the local bond behaviour of steel cords to mortar, which is critical for the overall structural performance of these composites systems, needs to be examined in more depth. To this end, a series of pull-out tests was carried out to study the bond stress transfer of high strength galvanized steel cords embedded in two types of inorganic matrices, including a cementitious and a lime based mortar. In addition, the steel cord to mortar bond was examined through the implementation of a surface-based cohesive contact model in a non-linear finite element framework and the distribution of stresses within the mortar surrounding the steel cord was analysed.

Abstract: This paper presents a comprehensive experimental campaign performed on natural stone masonry wallettes jacketed with 14 different combinations of mortars, meshes, and connectors. After characterizing the mortars and the bare masonry, diagonal compression tests were performed on three specimens for each jacketing solution. The performance of a fiber-reinforced, high-performance mortar without reinforcing mesh was investigated, considering its application to one or both sides of the wall, with and without connectors. Then, two different fabric reinforced cementitious matrix solutions were tested, using unidirectional or bidirectional textiles. Finally, the effects of FRP mesh spacing, mortar composition, and connector type and density were explored on reinforced plaster applications. The test outcomes were analyzed in terms of failure mode, tensile strength, and corresponding shear deformation capacity. All combinations proved effective at increasing the tensile strength compared to the bare masonry, with ratios between 1.9 and 4.7.

Abstract: Adobe masonry (AM) dwellings are a considerable portion of existing buildings stock worldwide, particularly in developing countries. Several earthquakes occurred during last decades dramatically showed a high seismic vulnerability of such constructions, which are not generally engineered. Therefore, several research groups have been involved in the investigation about effective and viable retrofitting solutions for AM buildings. Currently, most of studies available in literature addressed the issue by means of experimental programs consisting of dynamic or static tests on reduced- or full-scale specimens, representing partial or complete AM dwellings. Nevertheless, in those works, limited or no attention was generally paid to the crucial issue of the spatial variability of material properties within AM, which can produce critical forms of mechanical response and premature failure. In this study, three series of seven AM wallets were tested under monotonic diagonal compression load: one series consisted of unreinforced specimens (used as benchmark) and the remaining series were strengthened with two textile reinforced matrix (TRM) systems, made of either hemp or glass meshes. Masonry joints and matrix were produced using the same mud mortar, which is a typical mortar of existing Italian AM buildings. Experimental outcomes of tests in terms of observed damage and response curves are presented, along with a comprehensive characterization of mortar and bricks. Then, with the aim to draw out general and robust trends about TRM effectiveness as strengthening solution in the improvement of shear strength and ductility capacity, the response variability was quantitatively investigated via statistical analysis of recorded stress–strain samples.

Abstract: In the context of the mechanical behaviour of FRCM (Fiber Reinforced Cementitious Matrix) composites as strengthening materials for masonry structures, an important issue is the evaluation of the shear transfer mechanisms between the FRCM material and the masonry. In this work a wide database of more than 500 experimental results of shear bond tests on FRCM-masonry specimens is collected. The data concern specimens made with different masonry supports and various FRCM materials. The data are subdivided into homogeneous classes. The occurrence of the different failure modes is studied and some considerations are assessed. Furthermore, the average peak shear stress and its variability is evaluated and a critical analysis is performed. Finally, a comparison among the failure tensile stress in the yarns obtained by i) the tensile tests on the dry textile meshes, by ii) the tensile tests on the FRCM specimens, and by iii) the bond tests on FRCM-masonry panel is provided.

Abstract: Fiber Reinforced Cementitious Matrix (FRCM) composite materials represent one of the most interesting retrofitting methods for improving the out-of-plane flexural capacity of masonry walls. Despite their use is becoming more and more widespread, the actual knowledge about the out-of-plane behavior of FRCM-strengthened masonry panels needs further improvements, analyzing in particular the effectiveness of the reinforcement under cyclic loads. In this framework, an innovative experimental set-up, capable of applying a vertical axial load and cyclic out-of-plane horizontal forces on full-scale masonry panels, was used for testing walls retrofitted with glass, aramid-glass, basalt and steel fabrics. The presented experimental study is focused on the analysis of the effectiveness of the different FRCM systems, analyzing in detail failure modes, maximum capacity and the potential performance degradation of the strengthened panels under cyclic actions, providing also a useful comparison with the corresponding monotonic results.

Abstract: Fiber Reinforced Cementitious Matrices (FRCM) represent a very efficient strengthening solution for the retrofitting of masonry structures. When dealing with stone masonry walls, the use of these composite materials is usually combined with grout injection, which can be crucial to ensure a monolithic behavior of the structural element. The objective of this research was the study of the shear behavior of stone masonry samples subject to grout injection and strengthened by two different FRCM systems. Nevertheless, on few samples, grout injection only was performed. Before the execution of the diagonal compression tests, sonic tests were conducted with the objective of evaluating the quality of the grout injection. The Digital Image Correlation technique was also adopted to accurately measure the thickness of the FRCM layers, which can be variable according to the irregular surface of the stone masonry. The results of the experimental campaign showed that the correct execution of the grout injection is crucial for the strengthening solution to be effective since the efficiency of the FRCM system can be reduced if a monolithic behavior of the stone masonry panels is not ensured. The application of the FRCM strengthening system could influence the failure mode, further enhancing the capacity of the samples. Comparisons between the experimental results are presented in the paper.

Abstract: An experimental investigation aimed to analyze the mechanical behaviour of Carbon Fiber Reinforced Composite (CFRP) anchor spikes inserted in a brick substrate is reported in this paper. As is well known, such devices can improve the structural performance of CFRP sheets externally bonded to masonry elements (as well as others substrate materials). In structural applications, spike anchors can be subjected to both shear and/or normal actions; the first commonly occurs in structural applications, while the latter may occur in specific applications, such as CFRP sheets bonded to curved surfaces. For this reason, the experimental program described in this paper analyzes the mechanical behavior of a typology of anchor spikes loaded (separately) by pure shear or normal actions. Although, obviously, in anchored CFRP sheet reinforcements the contribution to the bearing capacity of the sheet and of the anchors cannot be additively superimposed (the total capacity is of course not equal to the sum of the capacity of the sheet and of the anchor), the results described in this paper can still give useful indications in practical applications.

Abstract: This paper discusses the experimental qualification process of Fabric Reinforced Cementitious Matrix (FRCM) composites with Polyparaphenylene BenzobisOxazole (PBO) textiles. FRCMs consist of fiber textiles incorporated within inorganic cement or lime mortar matrices and have emerged as composite materials suitable for the retrofit of unreinforced masonry structures. The Italian Ministry of Infrastructures and Transportation and the European Organization for Technical Assessment have developed guidelines defining standard tests to certify the FRCM mechanical properties for qualification and acceptance purposes. This paper presents part of the experimental qualification results for PBO-FRCM composites with two PBO textiles (unidirectional and bidirectional) applied to two different masonry substrates (clay bricks and tuff blocks), considering tensile, bond and durability behavior. Direct tension tests were carried out on PBO textiles and FRCM specimens, with or without textile lap splices. Single-lap tests allowed determining the bond properties of both FRCMs on clay-brick and tuff-block masonry substrates. The stability of the tensile properties with respect to degradation induced by environmental actions was evaluated by performing direct tensile tests also on FRCM specimens conditioned in humid, saline, and alkaline environments, or subjected to high-temperature stress.

Abstract: Existing masonry buildings become more and more outdated depending on the actual state of conservation, but also in relation to the renovation of the performance requirements stated in current code and guidelines. Therefore, two fundamental aspects emerge as drawbacks: mechanical resistance and thermal conductivity. The structural retrofitting often consists of a covering by means of Composite Reinforced Mortar (CRM), which involves a pre-impregnated fiber mesh into an inorganic binder (e.g. lime-based mortar), while an additional insulation layer is designed for thermal scope. In this study a new composite, concerning a fly-ash based geopolymer and a glass fiber mesh (namely Composite Reinforced Geopolymer Mortar - CRGM), is proposed. The goal is to demonstrate its ability of improving both the shear strength and the thermal resistance of a masonry panel (simulating an existing structure). At this scope, an experimental investigation put in contrast the proposal with respect to a traditional CRM-system (i.e. lime-based matrix and the same glass fiber mesh). The results confirmed the validity of the CRGM. Moreover, a theoretical simulation evidenced the potential impact of the CRGM on the commonly used types of masonry all around Italy from the thermal point of view.

Abstract: Arch is a structural member which provides aesthetic beauty to architectures and, at the same time, guarantees stability to structures. For this reason, it was largely adopted for masonry building in the past centuries. Nonetheless, the erection of new curved structures is poorly considered in modern time. One of the possible causes is the difficulty of constructing since it requires the use of temporary scaffolding. Thus, it may results time-and cost-consuming. Innovation in the field of arch construction is very rare until now. The present paper aims to validate a novel construction method for curved members by means of small-scaled specimens. The proposed method consists of connecting the stone blocks on one side with Fibre Reinforced Polymer (FRP) and then lift it up. The herein experimental program involved masonry arches loaded at the mid-line in order to compare the behaviour of the traditionally-made and the innovative arches in terms of load-bearing versus deflection. This is a preliminary test within a larger ongoing experimental campaign.