Experimental investigation on high-strength fibre-reinforced concrete beams subjected to bending and shear

The results of an experimental campaign carried out on a number of high-strength concrete beams loaded in 4-point bending are presented in this paper, where the roles of the both steel hooked fibres and the transverse reinforcement are investigated, for different values of the shear span. All tests were displacement-controlled. The results – mostly in terms of load-deflection curves – confirm what is well known in the literature, that an adequate amount of steel fibres can turn a brittle shear-type failure into a ductile flexural-type failure, to the advantage of the ultimate bearing capacity in flexure and shear, that can be fully exploited without increasing the transverse reinforcement. …

Flexural behaviour of calcarenite masonry walls reinforced with FRP sheets

The use of fiber-reinforced polymers (FRP) for structural strengthening has become increasingly popular in recent years. Several applications of FRP have been proposed and applied, depending on the target of the technique, kind and/or material of the structural member. In particular, because of their great tensile strength, FRP materials are commonly used to enhance the out-of-plane behaviour of masonry walls, allowing to increase their strength, ductility and improving safety against overturning. For these reasons, FRP laminates are often applied in vulnerable ancient buildings in seismic areas to reinforce façades and walls with poor structural features. However, some issues arise when ad…

Temporary Strengthening Technique of Marble Columns with Steel Wires and Wood Spars

Granite, marble and heavy stone columns have been used in the architects from all the ages to answer to both aesthetical and structural requirements in ancient churches and historical buildings. Such materials offer great visual impact and have mechanical properties that allow their use in construction and to obtain bright and slender structures. Marble is a very high strength but brittle material. It often occur that marble or granite columns of historical building are cracked along their height due to external actions and the risk of buckling occurs. Because this kind of failure is sudden and very brittle in stone and rocks, an immediate strengthening of the columns is needed. Among e tem…

An experimental study on the compressive behaviour of calcarenite masonry columns wrapped by fiber reinforced mortar wraps

The use of Fiber Reinforced Cementitious Mortar (FRCM) systems for structural retrofitting of masonry structures has become increasingly popular in the last years, due to the capability of this technique in overcoming some of the drawbacks related to the adoption of resin-based composites. In fact, FRCM systems ensure good compatibility between the reinforcing layers and the substrate, achieving also the removability requirement, which is of fundamental importance for historical constructions. Recent research studies focused on the mechanical performance of FRCM materials, by studying its tensile behaviour and bond between the strengthening layer and masonry, pointing out as failure is alwa…

Strengthening of masonry walls subjected to out-of-plane loads using CFRPs

This paper presents an experimental investigation carried out on masonry panels subjected to axial load and bending moment in the plane of minor inertia. The masonry type consist of calcarenite ashlars and mortar joints; the reinforcement is made of Carbon Fibres Reinforced Polymer (CFRP) strips applied with the wet-lay-up system. Tests are carried out with controlled displacements. Results have been recorded at each step in terms of: horizontal force and corresponding displacements; moment and curvature at the base of the wall; strains on the CFRP strips near the base of reinforced specimens in order to observe the delamination phenomen. Comparison between the results relative to unreinfor…

Il recupero parziale di opere in muratura di interesse storico in zona sismica

Load Carrying Capacity of Glass Columns with Rectangular, T and X Transverse Cross-sections

In this study, the load carrying capacities of glass columns with rectangular, T and X cross-sections having different lengths were calculated. The proposed analytical procedure allows to calculate the load carrying capacity associated with strength of transverse cross-section including local and global flexural and/or torsional buckling phenomenon. Moreover, initial imperfections and time dependant effects, the latter associated with the viscoelastic behaviour of interlayer (PVB), were included in the model as suggested in the literature. Those effects were calculated by introducing the equivalent thickness of glass panels, which takes into account the shear modulus of PVB and the viscolea…

Flexural response of ordinary and fibrous reinforced concrete deep beams

Indagine sperimentale su travi in media scala in calcestruzzo fibrorinforzato soggette a taglio e flessione

Sostenibilità di interventi di miglioramento sismico di strutture in c.a. non danneggiate

Strength and strain capacity of fiber reinforced polymer confined concrete in elliptical columns

Indagine sperimentale sull'impiego di materiali compositi per il rinforzo di volte in muratura

A numerical study on the effect of the interface material model on the tensile behaviour of FRCM strips

Fibre Reinforced Cementitious Matrix (FRCM) composites are becoming increasingly popular for strengthening masonry structures for which the compatibility of the inorganic matrix with the chemical and physical properties of the support makes it advantageous to adopt such systems. However, despite the large use of FRCMs for strengthening applications, the characterization and modelling of the mechanical response in tension of these systems is an open issue. In fact, the constitutive tensile law of the composite shows to be affected by different variables, such as the clamping system adopted during tensile test, the gauge length used for recording strains, the monitoring of the number of yarns…

Travi in calcestruzzo fibroso in zona sismica: sperimentazione e progetto

Analysis Methodologies and Ameliorative Techniques for Mitigation of the Risk in Churches with Drum Domes

Analisi In Regime Non Lineare Dei Sistemi Strutturali Cupola-Tamburo Finalizzata Alla Mitigazione Del Rischio Sismico

Structural behavior of the old masonry bridge in the Gulf of Castellammare

Abstract Masonry arch bridges represent a very significant part of the heritage of road and railway artworks all over the word and especially in the Mediterranean area, both in terms of: numbers; reduced environmental impact; and static efficiency. In these cases, the cost of maintenance is often limited to the content and channeling of surface water and control of vegetation, which can eventually take root on the joints of the masonry at the shoulders. In masonry bridges, there are no expansion joints or hinges with support equipment or trolleys, as in metal bridges and reinforced concrete ones, or paint, or resin surface protection, all items that affect the cost of maintenance. The perma…

Effect of corner over-reinforcing strips on the compressive behaviour of TRM confined masonry columns

Several recent works studied the efficiency of inorganic matrix composites, namely Textile Reinforced Mortar (TRM) or Fabric Reinforced Cementitious Matrix, for enhancing the strength and shortening capacity of masonry columns subjected to axial load. Literature studies were addressed to study the great number of variables involved in the problem, such as the nature and the grade of mortar, the strength of the fabric, the number of reinforcing layers, the type, the arrangement and the strength of the masonry, and helped to draw the first technical guidelines for practitioners and designers. All the experimental works highlighted that the actual performance of TRM confinement in masonry memb…

Interface behaviour of bonded CFRP-Calcarenite stone joints

This paper presents the results of an experimental study investigating the interface behaviour between calcarenite stone and Carbon Fibre Reinforced Polymer (CFRP) reinforcement. The analysis of the results has allowed to deduce the local behaviour at the interface, which can be modelled by means of a bi-linear shear stress-slip law, according to several codes. The experimental investigation was carried out on specimens subjected to double shear pulling tests by varying the bond length of the CRFP strips. Tests enabled determination of the bond strength of the joint and the effective bond length. The parameters of the stress-slip law were calibrated on the experimental results in order to c…

Shear design of high strength concrete beams in MRFs

This paper presents the criteria for the shear design of high strength concrete (HSC) beams in moment resisting frames (MRFs). The formulation of an analytical model is provided for the case of beams with longitudinal reinforcement in the presence of transverse stirrups. The model is of additive type, in the meaning that the shear resistance of the beam is evaluated as the sum of several contributions. In particular, the contribution of concrete, longitudinal rebars, and transversal reinforcement are taken into account. Furthermore, for assessing the concrete contribution, a classical approach is followed, according to which two effects arise in the shear mechanism: the arc and the beam eff…

Behavior in compression of lightweight fiber reinforced concrete with hooked steel fibers and transverse steel reinforcement

Effect of FRP strengthening on the flexural behaviour of calcarenite masonry walls

The use of fiber-reinforced polymers (FRP) for structural strengthening has become increasingly popular in recent years. Several applications of FRP have been proposed and applied, depending on the target of the technique, kind and/or material of the structural member. In particular, because of their great tensile strength, FRP materials are commonly used to enhance the out-of-plane behaviour of masonry walls, allowing to increase their strength, ductility and improving safety against overturning. For these reasons, FRP laminates are often applied in vulnerable ancient buildings in seismic areas to reinforce façades and walls with poor structural features. However, some issues arise when a…

Finite element analysis of the out-of-plane behavior of FRP strengthened masonry panels

Abstract In the present study a numerical model is proposed for the response of out-of-plane loaded calcarenite masonry walls strengthened with vertical CFRP strips applied on the substrate by means of epoxy resin. A simplified structural scheme is considered consisting in a beam fixed at one end, subjected to constant axial load and out-of-plane lateral force monotonically increasing. Two different constraint conditions are taken into account: in the first one, the panel is assumed free to rotate at the top end while, in the second one, the rotation is restrained. Three-dimensional finite elements are used for the calcarenite parts and an equivalent constitutive law available in the litera…

Safety verification and non-destructive testing on the masonry della Porta bridge in the Gulf of Castellammare (TP)

I ponti ad arco in muratura rappresentano una parte assai rilevante del patrimonio di opere d’arte stradali e ferroviarie del nostro paese, sia per quanto riguarda la loro consistenza numerica, sia per la qualità del loro inserimento ambientale e l’efficienza statica [1-6]. In questi casi il costo di manutenzione è spesso contenuto e circoscritto alle canalizzazioni delle acque superficiali ed al controllo della vegetazione, che può eventualmente radicarsi sui giunti della muratura in corrispondenza delle spalle o dei cappelli di rostro delle pile. Nei ponti in muratura non ci sono giunti di dilatazione, né apparecchi di appoggio con cerniere o carrelli, come nei ponti metallici e in cement…

Flexural bearing capacity and related ductility demand for masonry sections under nonlinear constitutive law

This paper aims at examining the maximum bearing capacity of rectangular masonry cross-sections subjected to eccentric compression, by assuming a nonlinear constitutive law characterized by two parameters defining stress-strain curve of the material. The variation of these parameters permits us to represent a wide variety of materials; therefore the ductility required of these materials in order for a section to achieve the maximum bending moment compatible with an average normal stress is also determined. The proposed approach can be utilized to evaluate the safety condition of masonry bearing walls, like those characterizing buildings of historical and/or monumental interest, for which th…

Steel fibre and transverse reinforcement effects on the behaviour of high strength concrete beams

An experimental program was carried out to investigate the influence of fibre reinforcement on the mechanical behaviour of high strength reinforced concrete beams. Eighteen beams, loaded in fourpoint bending tests, were examined by applying monotonically increasing controlled displacements and recording the response in terms of load-deflection curves up to failure. The major test variables were the volume fraction of steel fibres and the transverse steel amount for two different values of shear span. The contribution of the stirrups to the shear strength was derived from the deformations of their vertical legs, measured by means of strain gauges. The structural response of the tested beams …

CRITERI E TECNICHE DI VALUTAZIONE E RIDUZIONE DELLA VULNERABILITÀ SISMICA DEL CENTRO STORICO

Una valutazione della vulnerabilità sismica, sia attraverso approcci fenomenologici che attraverso più accurati modelli meccanici non può prescindere dalla conoscenza (il più possibile accurata) di tali caratteristiche del costruito, che può essere acquisita spesso soltanto attraverso campagne di rilievo e di indagini sul costruito. In questo contesto, vengono inizialmente descritte le caratteristiche salienti del centro storico di Modica, per poi passare in rassegna i metodi di valutazione della vulnerabilità sismica a scala territoriale; infine verranno presentate alcune tecniche di mitigazione della vulnerabilità sismica, e presidi antisismici da mettere in atto per evitare che trasforma…

Simplified model for compressive response of RC column footing with square cross-section

Abstract In this paper, a simplified calculus model for the prediction of the compressive response of RC column footing with a square cross-section is presented. As it is well-known RC concrete footing are designed adopting uniform contact pressures on the substrate and assuming a strut and tie model in deep members and a cantilever beam or slab model in flexible members. Deep and flexible members are distinguished in literature only based on the tangent of the angle expressed as the ratio between the depth and the shear span of the footing. In this paper, several subgrade contact pressures distribution for column footings (rigid or soft soils) were considered in developing a mechanical mod…

Debonding Phenomena in CFRP Strengthened Calcarenite Masonry Walls and Vaults

In this paper the results of an experimental investigation on full-scale reinforced masonry elements like vaults and walls are presented. The masonry type is constituted by calcarenite ashlars and bed joint mortar and the reinforcement is constituted by Carbon Fibre Reinforced Polymer (CFRP) strips. Preliminary experimental results obtained in a previous research by the authors on the local behaviour at the interface CFRP-calcarenite are summarized. Tests with controlled displacement are carried out on out-of-plane loaded walls and cylindrical vaults loaded at a quarter of the span. Results of tests carried out before and after the application of the reinforcement made it possible to evalu…

TELAI DISSIPATIVI IN ACCIAIO PER LA MITIGAZIONE DEL RISCHIO SISMICO DI SISTEMI MURARI DI INTERESSE STORICO

Il lavoro riguarda la possibilità di impiego di dispositivi fluido viscosi per il miglioramento o l’adeguamento sismico di edifici in muratura appartenenti all’edilizia storico monumentale. In questi casi, per evidenti motivi legati alla tutela dei valori architettonici dell’opera, non è possibile adottare interventi di tipo tradizionale per il rinforzo statico della muratura (FRP, CAM). Una soluzione alternativa, di maggiore efficacia, può essere ottenuta attraverso l’inserimento di dispositivi fluido viscosi, con il risultato di aumentare la capacità dissipativa della struttura con conseguente riduzione della domanda di spostamento. A riguardo, si descrive una procedura, già proposta da a…

Strengthening of Solid Brick Masonry Columns with Joints Collared by Steel Wires

This work presents the results of an experimental investigation on the behavior of columns made of solid clay bricks strengthened by stainless steel wires placed in the joints. The characterization of each constituent property (bricks, mortar, and steel wires) and the compression tests on columns show the effectiveness of the proposed strengthening technique with the result of increased ductility of brick columns. From the analytical point of view a model is proposed which gives the response in terms of the stress-strain curve, by taking into account the presence of steel wires placed in the joints, and the consequences on the effective confinement pressure with the following resulting enha…

Nonlinear FE analysis of out-of-plane behaviour of masonry walls with and without CFRP reinforcement

Abstract The out-of-plane behaviour of unreinforced and CFRP reinforced masonry wall is studied by means of experimental investigation and numerical FE modelling. The latter is based on a linear constitutive law both for ashlars and mortar joints constituting masonry and the lines of potential delamination are taken into account by means of an interface element with bi-linear law, reproducing the opening failure mode. When reinforcement is introduced, an interface element with bi-linear law is also used, reproducing sliding failure mode. Comparison between numerical and experimental results show the reliability of the modelling. Moreover, a parametric analysis is carried out in order to inv…

Effectiveness of stirrups and steel fibres as shear reinforcement

This paper presents the results of experimental tests carried out on rectangular simply supported beams made of hooked steel fibre reinforced concrete with and without stirrups, subjected to two-point symmetrically placed vertical loads. The tests, carried out with controlled displacements, allow one to record complete load-deflection curves by means of which it is possible to deduce information on dissipative capacity and ductile behaviour up to failure. Depending on the amount of transverse reinforcement, volume fraction of fibres added in the mix and shear span, the collapse mechanism is due to predominant shear or flexure, thus showing the influence of the aforementioned structural para…

Comportamento sperimentale di regioni diffusive di elementi in c.a.

Nel presente lavoro si esamina il comportamento in compressione di pilastri in calcestruzzo ordinario con e senza armature e soggetti a carichi applicati su aree ridotte in assenza ed in presenza di fori praticati per l’effettuazione di indagini non distruttive. I risultati ottenuti hanno mostrato che la diminuzione dell’area di impronta del carico rispetto all’intera sezione trasversale dei pilastri o la presenza di un foro riduce la capacità potante dell’elemento ed infragilisce la risposta strutturale. Dal punto di vista teorico modelli disponibili in letteratura forniscono sulla base di adeguati schemi resistenti tirante-puntone valori del carico di rottura prossimi a quelli rilevati sp…

Effect of the different data survey scale on assessment of seismic exposure and vulnerability of the historic center of Caltabellotta

The results of the prediction of exposure and seismic vulnerability for the buildings of the historic center of Caltabellotta, obtained with databases of different levels of accuracy, are compared. In particular, the results obtained on the basis of the estimation of the characteristics and of the distribution of the typologies derived from the filling in of the CARTIS sheets on a sector scale are compared with those obtained through a survey from the outside to a building scale. In this latter area, indicators contained in the CARTIS are suitably supplemented with those available in the literature, partly modified to adapt them to the local reality. The vulnerability is evaluated on the ba…

Comportamento meccanico di una volta rinforzata con CFRP

Il presente lavoro riguarda il progetto e l'esecuzione di un intervento di rinforzo di una volta a padiglione lunettata di una Villa di interesse storico-monumentale del 700. Tale volta è realizzata con conci di calcarenite inzeppati con cunei di legno e senza malta di connessione, tipologia molto diffusa in tutta l'area del mediterraneo. L’intervento è stato preceduto dallo studio del comportamento meccanico della volta in laboratorio e da prove dinamiche in sito. Particolare attenzione è stata rivolta al sistema di trasmissione dei carichi verticali allo scopo di rendere meno gravoso lo stato tensionale nella parte più alta della volta. Il sistema strutturale è stato analizzato per mezzo …

La mitigazione del rischio sismico del patrimonio costruito di interesse storico-monumentale

Flexural and Shear Resistance of High Strength Concrete Beams

In the present paper, an analytical model is proposed that is able to determine the shear resistance of high strength reinforced concrete beams with longitudinal bars, in the presence of transverse stirrups. The model is based on the evaluation of the resistance contribution due to beam and arch actions. For the resistance contribution of the main bars in tension the residual bond adherence of steel bars and the crack spacing of R.C. beams are considered. The compressive strength of the compressed arch is also verified by taking into account of the biaxial state of stresses. The model was verified on the basis of experimental data available in the literature and it is able to include the fo…

Experimental Investigation on Innovative Stress Sensors for Existing Masonry Structures Monitoring

Historical masonry structures often suffer gradual deterioration that in many cases can compromise the safety levels and the operating conditions of the buildings. In this context, Structural Health Monitoring (SHM) is an effective tool for the prediction of the structural behaviour and the state of conservation of buildings. Although many monitoring systems have recently been proposed, there is a lack of practical application of low-cost systems. This paper presents an experimental study based on the use of two innovative stress sensors—capacitive stress sensor and ceramic stress sensor—for the monitoring of existing masonry elements. In order to reproduce the actual conditions of onsite m…

Bond behavior between CFRP strips and calcarenite stone

Analytical stress-strain law of FRP confined masonry in compression: Literature review and design provisions

Abstract The use of Fibre Reinforced Polymer (FRP) wraps has become common in practical applications to retrofit existing columns with poor structural features. Wrapping the member with one or more FRP sheets makes it possible to induce confinement action and enhance strength and ductility. This application has been widely studied and adopted in reinforced concrete members for about twenty years, while its suitability to masonry columns and piers has been investigated during the last decade. The results of several studies were summarized in different design expressions for calculating effective confinement pressure, ultimate compressive stress and strain, and the overall trend of the stress…

Impiego di tecniche di identificazione dinamica per la prevenzione e mitigazione del rischio da "crolli"

Effects of circular openings on the compressive behaviour of R.C. columns

Core-drilling technique is nowadays always more frequently performed in existing reinforced concrete (RC) structures in order to investigate on the mechanical properties of concrete and for structural health monitoring purposes. Even if the engineering practice discourages to drill columns, this can be often unavoidable. In this last case the presence of the circular opening influences the compressive behavior of the column in terms of load-carrying capacity and axial deformability. The goal of this investigation was the experimental evaluation of the effects induced by circular openings on the behavior of RC columns. Twenty-four reinforced and plain concrete prisms in presence of circular …

Steel-concrete bond in lightweight fiber reinforced concrete under monotonic and cyclic actions

Experimental results of the local bond stress-slip relationship of reinforcing bars embedded in lightweight fiber reinforced concrete with expanded clay aggregates are presented. The effect of the following parameters were investigated: - dimension of specimens; - anchorage length; - percentages of hooked steel fibers; - geometrical ratio of transverse reinforcement; - confinement external transverse pressure. Prismatic specimens with deformed steel bars embedded for a fixed length equal to five and eight equivalent diameters were tested under both monotonic and cyclic reversal imposed displacements at the tip of the bars, in controlled displacement tests. The influence of the above mention…

Experimental investigation on local bond-slip behaviour in lightweight fiber reinforced concrete under cyclic actions

Flexural behaviour of glass panels under dead load and uniform lateral pressure

Abstract In the present paper the experimental results relative to flexural tests on out-of-plane loaded large scale panels made of laminated structural glass are presented and discussed. Glass panels are parts of the structural facade of the Fontanarossa International Airport of Catania (Italy). Panels are mounted on a rigid testing frame and loaded with an uniformly distributed lateral pressure. Two different kinds of tests were carried-out, cyclic and monotonic, able to reproduce the serviceability and the ultimate conditions of the glass panels when subjected to the coupled effects of dead load and horizontal forces, the latter reproducing the wind action. Results obtained focused the h…

CFRP flexural strenghtening of masonry walls: experimental and analytical approach