1,721,071 research outputs found
A review on the bond behavior of FRP composites applied on masonry substrates
No full textThe need of repairing and retrofitting masonry buildings, typical of Italian and European built heritage, determined a growing interest towards the development of effective and cost efficient innovative strengthening solutions. Among the different techniques currently available, the adoption of composite materials, such as Fiber Reinforced Polymers (FRPs), proved to be one of the most viable solutions for the strengthening of masonry structures. If not properly fixed, a common failure mode of this system is the early debonding of the reinforcement from the substrate. For this reason, several experimental tests and numerical analyses are currently available in the literature, clarifying and predicting the bond behavior of FRP glued to masonry substrates. The purpose of this paper is to provide an overview of the results obtained by the different experimental works, of the numerical analyses performed both for evaluating and validating experimental results and of the simplified analytical models currently available for the prediction of the maximum capacity of the strengthening systems. Results of extended experimental campaigns, carried out also within different Round Robin Test (RRT) series, with several laboratories involved, and recent model calibrations will be discussed together with the approach proposed by the actual guidelines
Nuova tecnologia per la riduzione del rischio sismico: le pareti in CLT post tese a basso danneggiamento
No full textL’articolo descrive i principali risultati ottenuti nell’ambito del progetto di ricerca TIRISICO
“Tecnologie innovative per la riduzione del rischio sismico delle costruzioni” finanziato dalla regione
Emilia Romagna (POR-FESR 2017-2019). In particolare l’articolo riporta la descrizione e la
caratterizzazione sperimentale di un sistema costruttivo innovativo del tipo a pareti CLT (Cross
Laminated Timber – pannelli X-LAM) post-tese assemblate con dispositivi isteretici esterni e
sostituibili a valle di un evento sismico
Structural Characterization of an Historical Building by Means of Experimental Tests on Full-Scale Elements
Full text linkIn order to properly design strengthening intervention of existing buildings, careful assessment of the structural behavior is certainly required. This is particularly important when dealing with historical constructions made of heterogeneous materials like masonry or stonework. In this context, this paper presents the results of knowledge process on a large monumental nineteenth century building located in Trieste. The traditional investigation approach considering a wide number of destructive tests for characterization of materials and evaluation of the structural details were not admissible due to the valuable cultural and historical importance of the building. Therefore, an alternative and not conventional investigation approach has been considered. After a wide historical research and a detailed structural survey, it has been possible to identify the main structural systems of the building. Then, to characterize the structural response, a limited number of nondestructive tests but on full-scale typological systems have been preferred to a larger number of destructive tests on specimens of the different materials. The selected experimental load tests have been conducted in order to assess the actual structural response of the main systems that constitute the building, thus allowing for a fine tuning of both the rehabilitation interventions and the numerical finite element models
Effect of hot and cold temperature on the mechanical behaviour of macro-synthetic fiber reinforced concretes
No full textFiber reinforced concretes (FRCs) are used in many civil engineering applications, i.e. industrial floors, tunnels, etc., given their ability of reducing concrete cracking. Besides their mechanical characteriza-tion, the effect of the environmental conditions, i.e. temperature, need to be properly understood.
The present paper presents results of experimental tests on the effects of hot and cold temperatures, from -30 °C to + 60 °C, on the mechanical performances of FRCs containing polypropylene fibers. The results show that the temperature affects the compressive, tensile and residual flexural strength of the material
Rinforzo di pareti per azioni fuori dal piano con materiali compositi FRCM
No full textDiversi terremoti avvenuti nel corso
degli ultimi decenni hanno
mostrato la vulnerabilità degli
edifici in muratura, tipici del patrimonio
culturale italiano ed europeo, nei
confronti delle azioni simiche. In particolare,
l’analisi dei danni post-sisma ha evidenziato
una manifesta sensibilità delle pareti
in muratura alle azioni orizzontali agenti
fuori dal piano, con conseguenti collassi
parziali o totali dell’edificio. Per far fronte
alla necessità di ripristinare e rinforzare
le costruzioni in muratura, nell’ottica di incrementarne
la sicurezza, nel corso degli
ultimi anni sono state proposte ed impiegate
diverse tecniche di rinforzo tradizionali
o innovative. Tra queste ultime, il rinforzo
strutturale basato sull’impiego di materiali
compositi sta diventando sempre più
diffuso, in virtù dei diversi vantaggi che
questi offrono rispetto a quelli tradizionali.
In questo contesto, l’uso di materiali
compositi FRP (Fiber Reinforced Polymers)
o FRCM (Fiber Reinforced Cementitious
Matrix) ha dimostrato di essere
una delle soluzioni più adatte, ma la
conoscenza relativa all’utilizzo della seconda
tipologia di sistemi di rinforzo, in
particolare, una volta applicati a pareti in
muratura, è ancora limitata, soprattutto
se si analizza il loro comportamento per
azioni fuori dal piano [1-3].
L’obiettivo dell’articolo è analizzare il comportamento
di pareti in muratura rinforzate
con materiali compositi FRCM sollecitate
da sforzo assiale e azioni orizzontali
fuori dal piano (in modo da simulare la
loro risposta nei confronti di azioni sismiche),
riportando le prime evidenze di una
campagna sperimentale in corso presso
l’Università di Bologna. A tale scopo, è
stato sviluppato un nuovo set-up in cui
poter testare campioni di pareti in muratura
in scala reale, rinforzate con diverse
tipologie di fibra di vetro e acciaio.
Verrà presentata una breve analisi relativa
al comportamento dei muri rinforzati
testati, verificando l’efficacia dei sistemi
impiegati e descrivendo modalità di crisi
e aspetti peculiari emersi nel corso dei
test sperimentali. La disponibilità di risultati
relativi a prove di flessione fuori piano,
insieme ai risultati di prove di trazione
e aderenza tradizionali, condotte sulla
stessa tipologia di materiali, ha consentito
di indagare l’estendibilità delle evidenze
sperimentali ottenute su campioni in
scala ridotta a campioni in scala reale.
La campagna sperimentale in corso ha
come obiettivo quello di ottenere dati utili
allo sviluppo di future formule di progetto
e prescrizioni normative da applicare per
questa categoria di materiali compositi
Experimental characterization of the mechanical behaviour of U-shaped dissipative devices
Full text linkEnergy dissipation devices are used in earthquake engineering in order to reduce the negative effects of ground-motions on structures, thus limiting damage to structural and non-structural components. Different technologies have been proposed to this aim, i.e. viscous fluid dampers, friction-based dampers, hysteretic dampers, etc. Among the different solutions available the present paper focuses on a specific type of hysteretic dampers, U-shaped dissipators. They were first proposed in the 70s and to date have found limited application in the design practice, mainly in buildings with structural walls, exploiting the relative displacement between adjacent walls to dissipate energy.
The paper presents the results of an experimental campaign aimed at characterizing the mechanical behaviour of energy dissipators with linear movement, based on U-shaped steel plates. Different configurations were designed and tested, imposing displacement cycles of increasing amplitude. The paper discusses the observed energy dissipation capacity and the stability of the hysteretic cycles
Destructive In Situ Tests on Masonry Arches Strengthened with FRCM Composite Materials
No full textIn the last few decades, fiber reinforced polymer (FRP) composites have been widely
employed in several strengthening and rehabilitation applications of existing masonry buildings.
Fiber reinforced cementitious matrix (FRCM) composites are a newly-developed strengthening
technique comprised of high strength fibers embedded in a cementitious matrix. FRCMs usually
offer several advantages such as the high resistance to fire and high temperatures or vapor
permeability with masonry substrate, therefore they appear to be a promising alternative to
traditional FRP strengthening systems. In this experimental work, the results of destructive in situ
tests performed on existing masonry arches strengthened with FRCM composites are reported.
FRCM strips consist of a balanced bi-axial mesh made of basalt fibers embedded in a cementitious
grout. Three different configurations of the strengthening system have been considered. Load
responses and failure modes are presented
Study of temperature variation effect on MSFRC long term behaviour
No full textThe long-term behaviour of Fiber Reinforced Concrete is a topic still under investigation. Apart from the conditions related to the serviceability states, environmental conditions affect the material behaviour. The present work is focused on macro-synthetic fibres used as reinforcement. In fact, polymers suffer from creep and temperature affects their mechanical characteristics. Therefore, it is important to understand and develop predictive models for these phenomena. The paper presents the results of an experimental campaign on cracked FRC cylinders in uniaxial tensions, under sustained loads at temperatures from 20°C to 40°C. Moreover, a first approach towards a numerical predictive model accounting these phenomena is described. / Il comportamento dif-ferito nel tempo di materiali compositi fibrorinforzati è un tema ancora oggetto d’indagine. Oltre alle condizioni di servizio, le con-dizioni ambientali influiscono sul comportamento del materiale. Il presente lavoro fa riferimento al comportamento di calcestruzzi rinforzati con fibre macro-sintetiche. I polimeri infatti presentano deformazioni viscose e le loro proprietà meccaniche sono influen-zate dalla temperatura. Risulta quindi importante comprendere e prevedere come questi fenomeni possano influenzare il comporta-mento di elementi strutturali e non strutturali. La memoria mostra i risultati di una campagna sperimentale su provini fessurati in cal-cestruzzo fibrorinforzato in regime di trazione, mantenuti sotto carico costante ed esposti a temperature crescenti tra 20 °C e 40° C. Inoltre, è descritto un primo approccio verso la calibrazione di un modello numerico predittivo dell’effetto di queste variabili sul comportamento del materiale
Bond behavior of FRCM composites applied on concrete and masonry
No full textI materiali compositi FRCM (“Fiber Reinforced Cementitious Matrix”) sono stati recente-mente introdotti nelle applicazioni di ingegneria civile per il rinforzo di elementi in muratura e c.a. Lo scopo dello studio sperimentale è quello di valutare il comportamento, in termini di aderenza, di materiali compositi FRCM in carbonio e vetro, nella forma di reti bidirezionali o tessuti unidirezionali, applicati su diversi supporti utilizzando una malta cementizia e un promotore di adesione. Le evidenze sperimentali ottenute sulla muratura utilizzando malta a base cementizia sono state confrontate con i risultati derivanti dagli stessi sistemi di rinforzo applicati con malta a base calce. Tutti i campioni sono stati sottoposti a prove di aderenza, in modo da valutare le possibili modalità di crisi, la capacità massima e il comportamento globale in termini di spostamenti e deformazioni (grazie alla tecnica della Digital Image Correlation). I risultati sperimentali hanno evidenziato le buone prestazioni dei sistemi di rinforzo testati se applicati in combinazione con il promotore di adesione.Fiber Reinforced Cementitious Matrix (FRCM) composite materials have been recently introduced in civil engineer-ing applications for the strenthening of masonry and reinforced concrete elements. The aim of the presented experimental study is to evaluate the bond behavior of carbon and glass FRCM composite materials, in the form of bidirectional grids or unidirectional sheets, applied on different substrates by using a cementitious mortar together with an adhesion promoter. Experimental outcomes obtained on masonry using a cementitious mortar have also been compared with the results coming from the same strengthening sys-tems applied with lime mortar. All specimens were subjected to single-lap shear tests until failure, in order to evaluate failure modes, maximum bond capacity and the whole samples behavior in terms of displacement and strain maps (thanks to Digital Image Correla-tion technique). Experimental outcomes highlighted the good performance of the strengthening systems tested when applied in com-bination with the adhesion promoter
An Investigation of the Debonding Mechanism between FRCM Composites and a Masonry Substrate
No full textFiber 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
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