Fiber-reinforced polymers (FRPs) have been considered as an alternative reinforcement for concrete structures to prevent corrosion that occurs in steel reinforcement. FRP reinforcing bars are composed of fibers and resin and show many advantages, such as non-corrosiveness, high tensile strength, fatigue-resistance, and light weight. Thus, FRP bars are used for concrete structures exposed to highly corrosive environments, such as waterfront concrete structures and concrete structures exposed to deicing agents, e.g., bridge decks. Among other types of FRP reinforcing bars (carbon, aramid, and basalt), glass fiber–reinforced polymer (GFRP) bars perform adequately in the alkaline environment present in concrete and are economical (ACI 2015). In these bars, the glass fibers contribute to the strength and stiffness, whereas the resin provides the mechanism of load transfer and protection. Several test methods and different codes have been developed for the qualification and quality control of GFRP bars. To provide a complete guide for the deployment of a new material system, in this thesis, a comparison of the test methods requested by different codes is presented. In particular, the focus is on the mechanical properties and the associated test methods: tensile strength, transverse shear, apparent (inter-laminar) horizontal shear, and bending. Following the path previously discussed, an experimental campaign (tensile, transverse, horizontal, bending) has been conducted for the mechanical characterization and the development of a thermoplastic GFRP bar that is recently gaining attention due to its potential for being heated and bent in the field, overcoming the problem of traditional thermosetting resins such as vinyl ester and epoxy. Not only the mechanical behavior of the material itself is important for design, but also the behavior inside a structural element. For this reason, two series of beams have been tested. The first series was reinforced with GFRP bars, and the second series was reinforced with steel bars. The experimental results Have been analyzed with respect to the theoretical expected values, calculated according to ACI 440.1R-15 and EC2 for the case of steel reinforcement. The behavior of GFRP and steel reinforced beams were compared and discussed.
I polimeri fibro-rinforzati (FRP) sono considerati un’alternativa per il rinforzo di elementi in calcestruzzo armato al fine di prevenire la corrosione delle armature in acciaio. Le barre per il rinforzo interno in FRP sono composte da fibre immerse in una matrice polimerica, presentano numerosi vantaggi, non si corrodono, hanno un elevata resistenza a trazione, a fatica e sono molto leggeri. Vengono utilizzate in strutture in calcestruzzo esposte ad ambienti corrosivi come strutture in contatto con acqua di mare, strutture in contatto agenti chimici antigelo o impalcati per ponti. Tra i vari tipi di barre in FRP (carbonio, aramide e basalto), quelle composte da polimeri rinforzati con fibra di vetro (GFRP) hanno delle buone performance in ambiente alcalino tipico del calcestruzzo e sono economiche (ACI 2015). La fibra di vetro contribuisce a dare resistenza e rigidezza mentre la resina permette la distribuzione degli sforzi e protezione. Un tema importante per lo sviluppo e l’applicazione di nuove tecnologie sono i metodi di qualificazione e controllo di qualità, a riguardo delle barre in GFRP sono stati sviluppati diversi metodi di test nelle differenti normative di ogni paese. In modo da fornire una guida completa per la caratterizzazione di un nuovo materiale/elemento, all’interno della tesi, dopo una generale panoramica dell’argomento, sono stati presentati e messi a confronto i differenti metodi di test ad oggi presenti nelle diverse normative. In particolare il focus riguarda le proprietà meccaniche e i metodi di test associati: trazione, taglio trasversale, taglio orizzontale apparente ( o inter-laminare) e flessione. Seguendo il percorso analizzato nel precedente capitolo e stata condotta una campagna di test (trazione, taglio trasversale, taglio orizzontale e flessione) per caratterizzare meccanicamente e sviluppare una barra di GFRP con matrice termoplastica che ha recentemente guadagnato molta attenzione (premiato come il progetto di maggior successo e innovativo nell’ambito dei materiali compositi in edilizia dalla JEC World Innovation awards) per le potenzialità di essere riscaldata e piegata in cantiere, superando le problematiche delle resine termoindurenti come il Vinilestere e le epossidiche. Per la progettazione di una struttura non e’ importante solo il comportamento meccanico del materiale (barra di GFRP) ma anche il comportamento globale dell’elemento strutturale. A tale riguardo sono stati testati due gruppi di travi , il primo con rinforzo interno in barre GFRP e il secondo rinforzato con barre in acciaio. Sono stati messi a confronto i risultati sperimentali con quelli calcolati teoricamente secondo normativa ACI 440.1R-15 e EC2 ed inoltre e’ stato comparato il diverso comportamento delle travi rinforzate con GFRP rispetto a quelle rinforzate con acciaio.
Mechanical characterization of GFRP rebars for structural elements
BRAGHIROLI, NICCOLÒ
2017/2018
Abstract
Fiber-reinforced polymers (FRPs) have been considered as an alternative reinforcement for concrete structures to prevent corrosion that occurs in steel reinforcement. FRP reinforcing bars are composed of fibers and resin and show many advantages, such as non-corrosiveness, high tensile strength, fatigue-resistance, and light weight. Thus, FRP bars are used for concrete structures exposed to highly corrosive environments, such as waterfront concrete structures and concrete structures exposed to deicing agents, e.g., bridge decks. Among other types of FRP reinforcing bars (carbon, aramid, and basalt), glass fiber–reinforced polymer (GFRP) bars perform adequately in the alkaline environment present in concrete and are economical (ACI 2015). In these bars, the glass fibers contribute to the strength and stiffness, whereas the resin provides the mechanism of load transfer and protection. Several test methods and different codes have been developed for the qualification and quality control of GFRP bars. To provide a complete guide for the deployment of a new material system, in this thesis, a comparison of the test methods requested by different codes is presented. In particular, the focus is on the mechanical properties and the associated test methods: tensile strength, transverse shear, apparent (inter-laminar) horizontal shear, and bending. Following the path previously discussed, an experimental campaign (tensile, transverse, horizontal, bending) has been conducted for the mechanical characterization and the development of a thermoplastic GFRP bar that is recently gaining attention due to its potential for being heated and bent in the field, overcoming the problem of traditional thermosetting resins such as vinyl ester and epoxy. Not only the mechanical behavior of the material itself is important for design, but also the behavior inside a structural element. For this reason, two series of beams have been tested. The first series was reinforced with GFRP bars, and the second series was reinforced with steel bars. The experimental results Have been analyzed with respect to the theoretical expected values, calculated according to ACI 440.1R-15 and EC2 for the case of steel reinforcement. The behavior of GFRP and steel reinforced beams were compared and discussed.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/147460