Bond behavior between fiber reinforced composites and quasi-brittle material interfaces

The present dissertation presents an investigation of the bond behavior of newly developed fiber reinforced composite systems applied to quasi-brittle material interfaces. Direct shear tests were performed on steel reinforced polymer (SRP) and steel reinforced grout (SRG) composite strips applied to both concrete and masonry substrates. Different types of cementitious matrices and different densities of steel fiber sheets were employed. Tests were performed investigating several parameters, i.e. bonded width, bonded length, loading rate, and face to which the composite strip was applied. Failure modes and load responses were presented and discussed. It was observed that the fracture energy GF of SRP-concrete joints is independent of the composite density but varies as the composite is bonded to different faces of the concrete prism. The width effect was considered in the evaluation of the load-carrying capacity of SRP-concrete joints, while the loading rate influenced the peak load of both SRP and SRG specimens. The behavior of SRP-concrete joints was also investigated through a numerical analysis, using lattice discrete particle model (LDPM), obtaining an excellent match with the experimental results. Some concrete prisms were reinforced and tested using a geopolymer matrix that showed interesting results. Some masonry specimens were subjected to artificially weathering cycles to investigate the durability performances of SRG strips with respect to salt attack. Furthermore, monotonic compressive tests were performed on concrete columns confined with both SRP and SRG composites. Several parameters were investigated, i.e. the density of steel fiber sheets, the concrete corner condition, the overlapping length, the number of confinement layers, the scale effect, and the shape effect. Failure modes and load responses were presented and discussed. Finally, several applications of basalt-fiber reinforced cementitious matrix (B-FRCM) composites bonded to masonry substrates were showed, including full scale tests on existing masonry arches

An investigation on the 'width and size effect' in the evaluation of the fracture energy of concrete

The parameters that describe the fracture behavior of concrete are crucial to investigate numerically the response of reinforced concrete (RC) structures. Among them, the fracture energy plays a key role in all those applications that aim to simulate the behavior of RC structures. The fracture energy is a characteristic property of a material but its experimental evaluation could be difficult for quasi-brittle materials such as concrete due to the "width effect" and "size effect" that can lead to some uncertainties in the definition of this parameter. This study presents the results of an experimental campaign conducted on notched specimens to evaluate the fracture energy of concrete. Concrete prisms with different sizes were tested using a three-point bending (TPB) set-up to evaluate the influence of the width and the size on the results. The setup has been designed to become potentially part of the ACI 446 report on fracture. Digital image correlation (DIC) was used to qualitatively and quantitatively study the strain field near the crack tip. Preliminary numerical simulations were performed to investigate the "width effect" in a discrete element framework. Copyright (C) 2017 The Authors. Published by Elsevier B.V

A comparison between the bond behavior of SRP and SRG strengthening systems applied to a masonry substrate

Strengthening and rehabilitation of existing masonry buildings is a topic that attracts the interest of the scientific community worldwide. Fiber reinforced polymer (FRP) composites have been largely employed for structural rehabilitation of masonry structures due to their ease of installation and their high strength-to-weight ratio, since the end of the previous century. Recently, fiber reinforced cementitious matrix (FRCM) composites have become an appealing alternative to traditional FRPs, because they employ an inorganic matrix to embed the fibers, which provides a better vapor compatibility with masonry substrate and better resistance to high temperatures than FRPs. To reduce the cost of carbon and glass fibers, the use of new types of fibers, such as high strength steel cords, has been explored. Steel reinforced polymer (SRP) and steel reinforced grout (SRG) are still moving their first steps in the world of structural rehabilitation, but they have shown potentials to become a suitable alternative to other FRP and FRCM composites, respectively. In this work, SRP and SRG composites are bonded to masonry blocks and tested using a direct single-lap shear test set-up to investigate the debonding phenomenon. Two different types of mortar grout are employed for the SRG. A comparison between SRP and SRG composites is presented in terms of debonding capacity and failure modes

Verifiche di vulnerabilità sismica del complesso di Palazzo Poggi: la Ca' Grande dei Malvezzi

La tesi verte sulle verifiche statiche e sismiche eseguite sulla Ca' Grande dei Malvezzi, edificio facente parte del Complesso di Palazzo Poggi

An investigation on the \u201cwidth and size effect\u201d in the evaluation of the fracture energy of concrete

The parameters that describe the fracture behavior of concrete are crucial to investigate numerically the response of reinforced concrete (RC) structures. Among them, the fracture energy plays a key role in all those applications that aim to simulate the behavior of RC structures. The fracture energy is a characteristic property of a material but its experimental evaluation could be difficult for quasi-brittle materials such as concrete due to the "width effect" and "size effect" that can lead to some uncertainties in the definition of this parameter. This study presents the results of an experimental campaign conducted on notched specimens to evaluate the fracture energy of concrete. Concrete prisms with different sizes were tested using a three-point bending (TPB) set-up to evaluate the influence of the width and the size on the results. The setup has been designed to become potentially part of the ACI 446 report on fracture. Digital image correlation (DIC) was used to qualitatively and quantitatively study the strain field near the crack tip. Preliminary numerical simulations were performed to investigate the "width effect" in a discrete element framework. Copyright (C) 2017 The Authors. Published by Elsevier B.V

Flexural behavior of RC beams strengthened with SRG - Comportamento a flessione di travi in c.a. rinforzate con SRG

Negli ultimi decenni si sono diffusi nel pano-rama internazionale nuovi materiali per il rinforzo degli edifici del patrimonio edilizio italiano. Questi nuovi sistemi di rinforzo so-no stati sviluppati per migliorare la capacit\ue0 resistente degli elementi strutturali esistenti permettendo cos\uec di adattarsi alle sempre pi\uf9 stringenti richieste delle normative vigenti. La campagna sperimentale presentata in questo lavoro \ue8 progettata per valutare l\u2019efficacia di compositi realizzati con un tessuto in fibra di acciaio e una matrice inorganica (Steel Reinfoirced Grout), applicati per il rinforzo flessionale di travi in calcestruzzo armato (c.a.), tramite prove di laboratorio su quattro punti. Il numero di strati applicati e la densit\ue0 del tessuto di fibra utilizzato sono stati studiati per analizzare l\u2019efficienza di tali sistemi. Inoltre, sono state svolte delle prove di taglio diretto su campioni prismatici in calcestruzzo rinforzati con strisce di composito SRG per valutare l\u2019aderenza. I risul-tati ottenuti e le modalit\ue0 di rottura riscontrate sono stati analizzati e discussi.In the last decades, new materials have been employed for strengthening and rehabilitation of existing historical buildings that are part of the Italian cultural heritage. Among the newly developed strengthening systems, steel reinforced grout composites (SRG) have recently considered as an alternative to other composite to increase the capacity of existing structural ele-ments and allow to conform to more stringent code requirements. The experimental campaign presented in this work is aimed at in-vestigaing the influence of steel reinforced grout (SRG) composites, used as an external layer of reinforcement, on the flexural be-havior of reinforced concrete (RC) beams. Four-point bending tests were performed in displacement control on concrete beams. Several aspects, as the number of composite layers and fiber sheet density have been investigated in order to analyze the effective-ness of the strengthening system. In addition, direct single-lap shear tests were performed on SRG-concrete joints to investigate the bond behavior of SRG composites. Results and failure modes of the flexural and bond tests performed are analyzed and discussed in terms of flexural capacity (beam), ductility (beam), and bond capacity (single-lap

Effects of rising damp and salt crystallization cycles in FRCM-masonry interfacial debonding: Towards an accelerated laboratory test method

Fiber-reinforced composites with inorganic matrix (FRCMs) have been recently proposed as a more compatible and durable route to strengthen masonry structures with respect to FRPs (fiber-reinforced polymers), but their weathering mechanisms in aggressive environments are still scarcely known. In this paper, brick masonry specimens were reinforced with FRCM strips, made of galvanized steel fibers embedded within a hydraulic lime-based mortar, and were subjected to an artificial weathering procedure designed by the authors, involving capillary water absorption and salt crystallization cycles. Finally, direct shear tests were performed on the FRCM-masonry joints. To reproduce conditions that may be found in real buildings, shear tests were also carried out after applying the FRCM composite on salt laden masonry blocks. Interfacial debonding behavior was interpreted based on the salt distribution within the masonry joints and the porosity of materials. The permeable matrix did not hinder the migration of the saline solution used in some cycles, which in turn resulted in no significant accumulation of salts beneath the composite strip, and no micro-crack opening in the composite after accelerated weathering. Some corrosion of the galvanized steel cords in presence of high amount of chlorides was observed in the composite

An Investigation of the Debonding Mechanism between FRCM Composites and a Masonry Substrate

Fiber reinforced cementitious matrix (FRCM) composites have recently become a hot topic in Europe as an alternative to traditional fiber reinforced polymer (FRP) composites for several strengthening applications of existing masonry buildings. The terrific success of this new retrofitting system is mainly due to some advantages that it offers when compared to FRP, such as the possibility of application of the composite to wet surfaces and the vapor permeability featured by the inorganic matrix. In this work, the stress transfer between FRCM composites and a masonry substrate is investigated. FRCM strips comprised of ultra-high-strength steel fibers embedded in a cementitious grout are externally bonded to masonry blocks. Single-lap direct shear tests are performed. Parameters studied are bonded length and density of the steel fibers. Load responses are presented and failure modes are discussed. Change in the bond behavior and load carrying capacity with increasing bonded length is analyzed to determine the effective bond length

Bond analysis of FRCM strengthened masonry subjected to salt attack

Externally bonded reinforcement of masonry structures with Fiber Reinforced Cementitious Matrix (FRCM) composites has received increasingly attention in the last years. Notwithstanding the vast literature on short-term behavior and structural performance of these systems, very little is known about their durability. During their life-time, masonry buildings are affected by weathering processes due to, among the others, environmental causes such as rising damp and salt attack. Thus, the assessment of the mechanical characteristics of strengthened masonries in on-site conditions is fundamental for evaluating their real structural performance. To this aim, masonry blocks strengthened by steel FRCM composites were built and subjected to weathering cycles constituted by a wetting phase and a drying phase. The cycles aim at reproducing the on-site conditions of masonry, usually subjected to daily and seasonal climatic changes. After conditioning, the FRCM-masonry joints were subjected to direct shear tests in order to investigate the effects of the cycles on the interfacial bond between composite and masonry substrate. Further, materials characterization on constituent materials was conducted in order to interpret the results from direct shear tests

Effects of rising damp and salt crystallization cycles in FRCM-masonry interfacial debonding: Towards an accelerated laboratory test method

Fiber-reinforced composites with inorganic matrix (FRCMs) have been recently proposed as a more compatible and durable route to strengthen masonry structures with respect to FRPs (fiber-reinforced polymers), but their weathering mechanisms in aggressive environments are still scarcely known. In this paper, brick masonry specimens were reinforced with FRCM strips, made of galvanized steel fibers embedded within a hydraulic lime-based mortar, and were subjected to an artificial weathering procedure designed by the authors, involving capillary water absorption and salt crystallization cycles. Finally, direct shear tests were performed on the FRCM-masonry joints. To reproduce conditions that may be found in real buildings, shear tests were also carried out after applying the FRCM composite on salt laden masonry blocks. Interfacial debonding behavior was interpreted based on the salt distribution within the masonry joints and the porosity of materials. The permeable matrix did not hinder the migration of the saline solution used in some cycles, which in turn resulted in no significant accumulation of salts beneath the composite strip, and no micro-crack opening in the composite after accelerated weathering. Some corrosion of the galvanized steel cords in presence of high amount of chlorides was observed in the composite