Validation of a Shear Model for RC and Hybrid Beams with Two Different Inclinations of Transversal Reinforcement

The validation of an analytical model recently proposed for evaluation of the shear capacity in Reinforced Concrete (RC) beams containing multiple inclination of transverse stirrups is presented. The model is a suitable extension of that currently proposed in Eurocode 2 for the evaluation of the shear resistance, and it is derived by means of the the variable-inclination stress-field theory based on Nielsen’s plastic approach. Experimental and numerical data available in the literature on Hybrid Steel-Trussed Concrete Beams (HSTCBs) are used for model validation and result discussion. Finally, also the comparison with a different analytical approach for the assessment of the shear resistanc…

Indagine sperimentale su nodi di tralicci in acciaio di travi reticolari miste

Results of experimental tests on welded joints of steel truss of encased composite steel-concrete beams are presented. The welding of the inclined web bars to top bars, both of steel type B450C, and to bottom steel plate, the latter made of S355 steel type, are tested. Two analytical expressions for prediction of welding strength are derived: the one based on a resistance criterion and the other based on a limit domain of the welding section. Guidelines for choosing the effective dimensions of the fillet weld, necessary to determine the strength, are provided. A high precision digital scanner is used to validate the suggested guidelines to determine the geometrical characteristics of the fi…

Stress field model for strengthening of shear-flexure critical RC beams

A model for the design of shear-flexure critical reinforced concrete elements strengthened with fiber-reinforced polymer (FRP) sheets and plates is presented. The model is based on the stress field approach and the equilibrium method and accounts for the different failure modes of FRP, focusing on the debonding of the FRP from the concrete surface. The efficiency of the model in the strength assessment of beams reinforced with FRP by the prediction of the shear-flexure capacity is checked by corroborating the results of several experimental tests found in the literature. Moreover, the presented model's capacity to reproduce experimental behavior is compared with the formulations suggested b…

Travi reticolari miste- Problemi locali nella trasmissione degli sforzi

Experimental test results on the local behavior of the typical Italian typology of hybrid steel-to-concrete beam are presented and discussed in order to provide insight on transfer mechanism between different components of the beam. Preliminarily, in order to investigate on the bearing capacity of the welding and on the local instability problems that can arise in the trusses before concrete casting, tensile tests on specimens reproducing different types of welded joints, and push-out tests on bare specimen have been performed. Then, the transfer mechanism between steel trusses and concrete is investigated by means of push-out tests carried out also in displacement controlled mode. Results …

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…

Modelli per l'interpretazione dei risultati di prove di push-out su travi reticolari miste

Il comportamento sotto carico delle travi prefabbricate reticolari miste prima della pubblicazione delle nuove norme tecniche sulle costruzioni, veniva solitamente interpretato in analogia a quello di travi in c.a o a quello di travi miste acciao-calcestruzzo classicamente intese. L’esplicito riferimento nelle attuali norme a questa tipologia che viene trattata in un capitolo a parte, ha fatto scaturire l’esigenza di chiarezza e come conseguenza la pubblicazione di Linee Guida emanate dal C.S.LL.PP. che classificano le diverse tipologie in tre categorie: a) strutture composte acciaio-calcestruzzo; b) strutture in c.a. o in c.a.p.; c) strutture non riconducibili alle due categorie precedenti…

CFRP sheets bonded to natural stone: interfacial phenomena

The effectiveness of the reinforcing technique consisting of fiber reinforced polymer sheets bonded to the structural elements depends on a good connection at the joint. This has to be able to ensure the transfer length of the shear stress in order to avoid a premature failure due to debonding. In this paper, the bond phenomenon at the interface is examined with reference to the calcarenite stone and carbon fiber reinforced polymer (CFRP) sheets in order to evaluate the possibility of utilizing this technique on masonry structural members, consisting of calcarenite ashlars and mortar. An experimental investigation is carried out on nine specimens obtained by applying unidirectional CFRP she…

Indagine sperimentale sul comportamento di travi reticolari miste

Nel lavoro sono presentati i risultati di indagini sperimentali condotte su travi ed elementi di travi reticolari miste in acciaio-calcestruzzo, svolte presso l’Università di Palermo, nell’ambito di un programma di ricerca tendente a validare criteri e metodi per la progettazione strutturale di tali sistemi. Preliminarmente si riporta una sintesi dei risultati, già presentati in altre memorie, ottenuti da indagini su problemi locali di trasmissione degli sforzi tra gli elementi che compongono la trave sia prima che dopo il getto di calcestruzzo; successivamente si presentano i risultati di una sperimentazione su trave continua opportunamente strumentata in modo da rilevare il comportamento …

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…

Effectiveness of BFRP confinement on the compressive behaviour of clay brick masonry cylinders

Abstract This paper presents the results of an experimental and analytical study on the compressive behaviour of small clay brick masonry cylinders reinforced with a basalt fibre reinforced polymer (BFRP) composite. Fourteen cylinders, manufactured using two assembling schemes and confined using either one or two layers of BFRP grids, were tested under monotonic compression loading. Traditional strain measuring systems were integrated with digital image correlation (DIC) technique. The BFRP confined masonry cylinders showed a ductile behaviour characterised by a softening branch of the stress–strain curve. The experimental strains, strength, and full stress–strain curves were modelled using…

Behavior of fiber reinforced concrete-filled tubular columns in compression

Experimental compression tests on steel tubular columns filled with plain concrete and fiber reinforced concrete are carried out. For each type of column three different lengths are considered in order to point out the influence of slenderness on the ductility in compression. The experimental investigations presented here have emphasized the improvement in ductility capacity obtained when fiber reinforced concrete is utilised instead of plain concrete. Moreover, the results obtained stress that the lateral displacements due to global instability are drastically reduced.

Evaluation of Flat Jack Test Method Effectiveness for Masonry Structural Investigations

Flat jack testing method is one of the most commonly used techniques for the structural assessment of existing masonry structures. Single and double flat jack are commonly adopted to evaluate the acting normal stress, or the compressive behaviour of masonry material. Test procedures are codified by international standards (e.g. A.S.T.M D4729-87; C1196-04; C1197-04, R.I.L.E.M TC 177–MDT D.4; R.I.L.E.M. TC 177–MDT D.5), which provide the preliminary calibration of an experimental coefficient (km), which determination influences significantly the reliability of the test. This paper presents the result of an experimental study on the calibration of km coefficient for flat jacks. The problem is …

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…

Colonne in C.A. rinforzate con FRP con diverso livello di confinamento

Compressive behaviour of eccentrically loaded slender masonry columns confined by FRP

Abstract Fibre Reinforced Polymer (FRP) confinement represents an effective tool for retrofitting masonry piers or columns enhancing their structural performance. This technique has been widely studied in the literature mainly with reference to short columns, while no extensive information is available on the influence of second order effects on its efficacy in case of slender members. Within this framework, the presented study concerns a simplified method able to assess the effects of FRP confinement on the compressive behaviour of slender masonry columns. A proper constitutive law of FRP confined masonry in compression is adopted for performing a sectional analysis, in which also consider…

Use of FRP fabrics and stainless steel grids for strengthening brick masonry columns

This work presents the results of an experimental investigation on 42 solid clay brick columns internally strengthened by FRP fabrics or stainless steel grids placed in the horizontal joints of mortar. Monotonic compressive loading tests were carried out under concentric and eccentric load. Eccentric tests were carried out loading the specimens on a reduced area with respect to the entire crosssection producing a D-region. The reinforcing of every course and of alternate courses are studied. The effectiveness of the proposed strengthening techniques is discussed, in terms of increase in strength and energy required to the collapse of brick columns. An analytical expression is proposed that …

Computational Study of Failure of Hybrid Steel Trussed Concrete Beams

This study investigates the failure behavior of hybrid steel trussed concrete beams (HSTCBs) under three-point bending through a series of finite-element (FE) simulations. The FE model employs well-established constitutive relations of concrete and steel with a simplified contact condition between the concrete and steel truss. The numerical model is compared with existing experimental data as well as a FE model that uses a more sophisticated concrete-steel interfacial model. The comparison shows that the present model is able to capture various failure mechanisms of the beam and its peak load capacity. The model is applied to investigate the behavior of a set of HSTCBs of different sizes, w…

Prove Sperimentali di Push-Out su Travi Reticolari Miste

Nel presente lavoro sono descritte le prove di push-out realizzate sino ad oggi in tre diverse sedi Universitarie (Università del Salento, Università di Palermo, Università di Ferrara), operanti nel Gruppo di Ricerca finalizzato allo studio delle travi Prefabbricate Reticolari Miste, in collaborazione con le aziende di ASSOPREM. Dette prove hanno l’obiettivo di analizzare il comportamento all’interfaccia fra gli elementi resistenti nelle travi suddette, realizzate con traliccio prefabbricato e getto in opera di calcestruzzo. L’indagine condotta, sebbene ancora insufficiente a condurre a risultati di validità generale, evidenzia come al variare di alcuni parametri significativi si rilevi un …

FEM analysis of push-out test response of Hybrid Steel Trussed Concrete Beams (HSTCBs)

Abstract Aiming to investigate the steel truss–concrete stress transfer mechanism in Hybrid Steel Trussed–Concrete Beams (HSTCBs), a three-dimensional (3D) nonlinear Finite Element (FE) model is developed. The constitutive relationship of the steel composing the plates and the rebars is modeled by means of a quadri-linear law, while the concrete behavior is defined by means of a Concrete Damaged Plasticity (CDP) model, suitable for modeling concrete and brittle materials. Two main failure mechanisms are considered, namely the tensile cracking and the compressive crushing. In order to accurately grasp the complicate dowel and bond phenomena arising at the steel–concrete interface, a 3D solid…

Experimental and analytical out-of-plane behaviour of calcarenite masonry walls

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

Comportamento ciclico delle connessioni tra travi prefabbricate reticolari miste e pilastri in c. a.

Stress transfer and failure mechanisms in steel-concrete trussed beams: Experimental investigation on slab-thick and full-thick beams

Abstract This study presents the results of an experimental investigation on semi-precast Hybrid Steel Trussed-Concrete Beams (HSTCBs) for analyzing the failure modes and the stress transfer mechanism between concrete and embedded steel elements (plate and truss). The available literature presents previous studies carried out by the authors mainly focused on the understanding of the local transfer mechanism by means of push-out tests. Conversely, in this paper original the results of laboratory tests conducted on six specimens of full-size HSTCBs subjected to four-point bending, with variation in the shear span, are reported on. From these results, the authors are able to assess the failure…

Mechanical Characterization of a Basalt Fabric for TRM Composites: Role of the Test Variables

Textile reinforced mortar (TRM) materials are currently receiving great attention for the strengthening of reinforced concrete and masonry structural elements. Mortars with different strength classes have been coupled with different kind of synthetic fabrics, such as carbon, glass, steel, PBO. Recently natural fibres and, in particular, basalt fibres are receiving increasing interest since they proved to be a promising alternative to the most common synthetic fabrics, thanks to the reduced production costs and the consequent benefits in terms of environmental impact. This paper presents an experimental investigation comprising forty-one monotonic tensile tests on textile strips made with a …

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

Flexural behaviour of concrete corbels containing steel fibers or wrapped with FRP sheets

In the present paper an analytical and experimental investigation referring to the flexural behaviour of reinforced concrete corbels subjected to vertical forces is presented. For fixed shape and dimensions of the corbels the experimental investigation analyses the effects of the following: longitudinal and transverse steel reinforcements; fiber reinforced concrete (FRC) with hooked steel fibers; external wrapping retrofitting technique with a thin layer of carbon fiber sheet (CFRP). The analytical model based on equivalent truss structures, allows one to determine the bearing capacity of corbels, distinguishing the different ultimate states reached. The analytical results are then compared…

Load-deflection response of concrete corbels containing steel fibers or wrapped with FRP sheets

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…

Numerical modelling of the tensile behaviour of BFRCM strips

This paper aims at investigating the tensile behaviour of basalt fibres on cementitious matrix for the strengthening of masonry structures. The use of Basalt Fibre Reinforced Cementitious Matrix (BFRCM) is favourably considered by the scientific community because it represents a natural composite material with high compatibility with stone and masonry substrate. The study is developed through the generation of Finite Element (FE) models capable of reproducing the tensile behaviour of BFRCM strips with different number of layers of grid. For the scope, the micro-modelling approach is adopted assuming different levels of detail for the simulation of the interface constitutive behaviour. Fibre…

Capacità portante di mensole tozze in calcestruzzo fibroso o rinforzate con FRP

Prove di Push-Out su travi reticolari miste

Results of push-out experimental tests on typical italian typology of hybrid steel-to-concrete beam are presented and discussed in order to provide insight on transfer mechanism between concrete and steel truss. Two specimens of a shallow beam are tested and experimental relationships between interaction force, total slip and strain in truss elements are shown; moreover, behaviour of specimens at failure is discussed.

Review of push-out and shear response of hybrid steel-trussed concrete beams

The hybrid steel trussed concrete beams examined in the present study are comprised of two principal components, i.e., a steel joist with inclined rebars, realized in industry, which is welded to a smooth steel plate and then embedded within the concrete cast in situ. The paper presents first the state of the art on laboratory tests and analytical modeling of the steel-to-concrete stress transfer mechanism investigated by push-out tests. Next, the most relevant scientific contributions currently available in the technical literature regarding experimental investigation on actual shear behavior are summarized and discussed. Lastly codes and analytical models are reviewed.

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…

Stress transfer at the interface of bonded joints between FRP and calcarenite natural stone

Performance of two innovative stress sensors imbedded in mortar joints of new masonry elements

Abstract Many historical cities enjoy the presence of masonry buildings with inestimable historical, artistic and cultural value. Old masonry buildings often suffer structural deficiencies, design faults and materials aging process. In recent years, many researchers focused their attention on the opportunities that structural health monitoring (SHM) can ensure for the health state of existing masonry structures, where damage can be difficult to be promptly predicted, pontentially causing abrupt collapses, with high risks for the community. This paper presents an experimental study on the effectiveness of two types of stress sensor for SHM of new masonry elements. Ceramic piezoelectric senso…

Stochastic seismic analysis of structures with nonlinear viscous dampers

Fluid damper devices inserted in buildings or bridges are commonly used as energy sinks for seismic protection. In the response analysis of structures with filled damper devices the main problem exists in the strong nonlinear behavior of such equipment, as a consequence the differential equation of motion remains nonlinear and the response spectrum analysis still cannot be applied. In this note, by using the concept of power spectral density function coherent with the elastic response spectrum and by using the statistical linearization technique, expressions for finding the equivalent linear damping have been found. Comparisons with results obtained by Monte Carlo simulations confirm that f…

Effects of Different Test Setups on the Experimental Tensile Behaviour of Basalt Fibre Bidirectional Grids for FRCM Composites

Fibre-reinforced cementitious matrix (FRCM) composites have been effectively used during the last ten years for the strengthening of existing concrete and masonry structures. These composite materials are made of medium- and high-strength fibre meshes embedded in inorganic matrices. Synthetic fibres are the ones that are currently the most used

Experimental calibration of flat jacks for in-situ testing of masonry

Flat-jack testing method is one of the most commonly used techniques for the structural assessment of existing masonry structures. Single and double flat jacks are usually adopted to evaluate the acting normal stress, or the compressive behaviour of masonry material. Test procedures are codified by international standards (e.g., A.S.T.M D4729-87; C1196-04; C1197-04, R.I.L.E.M TC 177–MDT D.4; R.I.L.E.M. TC 177–MDT D.5), which provide the preliminary calibration of an experimental coefficient (km) and of the effective area (Aeff), which determination influences significantly the reliability of the test. This article presents the result of an experimental study on the calibration of flat jacks…

Experimental investigation on masonry elements subjected to eccentric axial loads

The flexural behaviour of masonry rectangular cross-sections is studied in order to characterize the mechanical behaviour of structural elements under axial eccentric loads by means of a proper law. First the experimental response of walls under vertical centred loads is observed and a stress–strain law depending on two parameters is given in order to fit the experimental results. Subsequently the behaviour of walls nominally equal to the walls mentioned before is investigated under eccentric vertical loads, and the response is observed in terms of moment–curvature relation. To this point a comparison is made between the moment–curvature response obtained experimentally and the moment–curva…

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…

Experimental Tests and FEM Model for SFRC Beams under Flexural and Shear Loads

The complete load-vs-displacement curves obtained by four-point-bending tests on Steel Fiber Reinforced Concrete (SFRC) beams are predicted by using a nonlinear finite element code based on the Modified Compression Field Theory (MCFT) and the Disturbed Stress Field Model (DSFM) suitably adapted for SFRC elements. The effect of fibers on the shear-flexure response is taken into account, mainly incorporating tensile stress-strain analytical relationship for SFRC. The numerical results show the effectiveness of the model for prediction of the behavior of the tested specimens reinforced with light amount of stirrups or with fibers only. © 2008 American Institute of Physics.

MECCANISMO DI COLLASSO DI PARETE MURARIA FUORI PIANO E CONSEGUENTE CROLLO DI SOLAI: CASO DI STUDIO

La memoria riporta un caso di studio relativo al crollo parziale che ha interessato un edificio in muratura a 5 elevazioni, coinvolgendo due celle murarie all’ultima elevazione, una parete con meccanismo fuori piano e conseguentemente tre campi di solaio relativi alla stessa cella muraria a tre diversi livelli. Al fine di valutare la causa che ha innescato il crollo, allo studio della situazione in situ attraverso diversi sopralluoghi, sono state affiancate prove sperimentali su campioni di trave in legno prelevati in situ. Le analisi effettuate hanno consentito di escludere che la causa scatenante potesse essere il crollo del primo solaio, individuando invece come primo meccanismo la crisi…

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

D-Regions

Flexural behavior of fibrous reinforced concrete corbels

Experimental investigation on the effect of mortar grade on the compressive behaviour of FRCM confined masonry columns

Abstract 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. Recent studies investigated on the effect of FRCM wraps on the compressive behaviour of concrete members and demonstrated as the application of mortar-based composites allows increasing the strength and, above all, the ductility of the column. The main difference with FRP confined columns is related to the different post-peak behaviour, characterized by a softening branch. Differently, few studie…

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…

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…

Strength and ductility of fiber reinforced concrete corbels subjected to vertical loads

Behaviour in compression of lightweight fiber reinforced concrete confined with transverse steel reinforcement

Abstract The compressive behavior of lightweight fiber reinforced concrete confined with transverse reinforcement consisting of steel stirrups or spirals was analyzed. Pumice stone and expanded clay aggregates were utilized to decrease the weight of the composite; hooked steel fibers were also added. The investigation was carried out by testing cylindrical and prismatic specimens of different sizes in compression using an open-loop displacement control machine, recording the full load–deformation curves. The influence of the dimensions and shape on the bearing capacity and on the ductility of the specimens confined with transverse steel reinforcements was analyzed. The results show the poss…

La cupola del Gesù: un progetto tra empirismo e modellazione

Experimental investigation on BFRCM confinement of masonry cylinders and comparison with BFRP system

Abstract Fabric reinforced cementitious mortar (FRCM) materials have started to be employed during the last years with the aim of overcoming the drawbacks related to the use of fibre reinforced polymer (FRP) composites, proving to be potentially suitable for strengthening masonry structures. Moreover, the will to develop materials able to guarantee a certain degree of sustainability without renouncing to adequate mechanical properties has drawn the attention to the use of basalt fibres, which appear to be a valid alternative to carbon or glass fibres. This work presents an experimental investigation on a basalt FRCM (BFRCM) system to confine circular masonry columns, aimed at evaluating the…

Experimental investigation on basalt grid cementitious mortar strips in tension

Fibre reinforced cementitious matrix (FRCM) composite materials are currently receiving great attention for strengthening reinforced concrete and masonry structures, especially when specific preservation criteria need to be fulfilled. FRCM composites can be a convenient alternative to fibre-reinforced polymers (FRP) for their better resistance to high temperature and compatibility with stone and masonry structures. In this work an experimental study for the tensile characterization of basalt reinforced cementitious matrix (BRCM) strips is presented. Strips with one, two or three layers of grid were tested in tension to study the effect of reinforcement ratio on the tensile stress-strain res…

Nonlinear Analysis of Beams Reinforced in Shear with Stirrups and Steel Fibers

The modified compression field theory (MCFT) and the disturbed stress field model (DSFM) are often used to predict the nonlinear behavior of reinforced concrete structures. This study presents several extensions of the MCFT and DSFM to the case of high-strength steel fiber-reinforced concrete beams subjected to transverse loads. Experimental four-point bending tests were conducted on 12 concrete beams with a different percentage of fibers and/or stirrups. To validate the updates introduced in the analytical models, numerical analysis was performed using nonlinear finite element software. Modeling of the post-peak softening branch of the tensile and compressive constitutive curves of fibrous…

Simplified analytical model for bearing capacity of FRC corbels

Comportamento flessionale di mensole tozze in calcestruzzo fibrorinforzato ad alta resistenza

Experimental behavior of concrete filled-columns in compression

General stress-strain model for concrete or masonry response under uniaxial cyclic compression

The paper proposes analytical forms able to represent with very good approximation the constitutive law experimentally deducible by means of uniaxial cyclic compressive tests on material having softening post-peak behaviour in compression and negligible tensile strength. The envelope, unloading and reloading curves characterizing the proposed model adequately approach structural responses corresponding to different levels of nonlinearity and ductility, requiring a not very high number of parameters to be calibrated experimentally. The reliability of the model is shown by comparing the results that it is able to provide with the ones analytically deduced from two reference models (one for co…

Experimental test results vs. analytical prediction of welded joint strength in hybrid steel trussed concrete beams (HSTCBs)

The aim of the paper is to provide practical guidelines for the design of welded joints of steel truss for encased composite steel–concrete beams. The results of experimental tests are presented and interpreted. The steel truss is made of a steel plate acting as the bottom chord, made of S355 structural steel, coupled with steel rebars which form the upper chord, and steel inclined web rebars (V-reverse) welded to the two chord elements, both of them made of steel B450C. Butt welded joints of web bar to bottom steel plate and fillet welding joints of inclined web bars to top chord bars were tested, as they are different from the ones which are normally used due to the coupling of different …

Assessment and strengthening of reinforced concrete bridges with half-joint deterioration

Existing Niagara-type concrete cantilever bridges, which in Italy are called Gerber bridges, suffer from degradation due to reinforcement corrosion and a consequent reduced load-bearing capacity. The assessment of these structures is therefore an important part of the procedures for analyzing the state of existing bridges and any interventions required for their retrofitting. In particular, safety against failure of the half-joint must be evaluated with respect to the behavior of the entire bridge and its state of conservation, determining what the conditions are that lead to failure, in terms of loads, state of stress, and possibly cracking state. This evaluation has to be carried out cons…

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…

Assessment of push-out test response of hybrid steel trussed-concrete beams by FE model

Aiming to investigate the truss-concrete stress transfer mechanism in Hybrid Steel Trussed-Concrete Beams (HSTCBs), a three-dimensional nonlinear FE model is developed. The constitutive laws of the steel composing the plates and the bars is modeled by means of a quadri-linear law, while the concrete behavior is defined by means of a Concrete Damaged Plasticity (CDP) model, suitable for modeling concrete and brittle materials. The CDP model uses the concept of isotropic damaged elasticity in combination with isotropic tensile and compressive plasticity and is able to properly account for the concrete confinement effect. Two main failure mechanisms are considered, namely the tensile cracking …

Effect of FRP Wraps on the Compressive Behaviour of Slender Masonry Columns

In the last decade, Fibre Reinforced Polymer (FRP) wrapping technique has become a common method to retrofit masonry piers or columns with poor structural performances. The passive confinement effect induced by the external wrap allows increasing the compressive strength and ductility of the member. Several studies highlighted as the efficacy of this technique is affected by several key parameters, including the shape of the transverse cross section, stress intensification at the strength corner of sharp sections, amount and mechanical properties of adopted composite. Despite this technique has been widely studied from both theoretical and experimental point of view, most of studies focused…

On bottom steel plate to concrete anchorage in hybrid steel trussed concrete beams

A semi-precast hybrid steel trussed-concrete beam typology is considered. Beams are made up of a steel truss encased in a concrete beam. The steel to concrete stress transferring mechanism is analyzed by experimental tests on six specimens of the beam. Four point bending tests on three slab thick beams and three full thick beams have been carried out. The instrumentation allowed to measure global and local response. The global response was monitored in terms of load vs. midspan-deflection curves and the local response was recorded by strain-gauges placed both on the bottom steel plate and at the top concrete surface of the beam in order to investigate the stress transfer mechanism between s…

Ductility of Reinforced Concrete Members Externally Wrapped with Fiber-Reinforced Polymer Sheets

The effectiveness of external wrapping with fiber-reinforced polymer for enhancing the curvature ductility of lightly reinforced concrete members is investigated. Referring to members with circular transverse cross sections, the performances in terms of both strength and ductility capacities are analyzed, and the predictive reliability of two different recent constitutive models, available in the literature and able to take into account the softening behavior of confined concrete, is checked. A parameter characterizing the effectiveness of the confining wrapping is proposed, and characteristic values are suggested. Moreover, referring to ductility increases due to confinement effects, a com…

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…

STATE OF THE ART ON BOND BETWEEN FRCM SYSTEMS AND MASONRY/CONCRETE SUBSTRATE: DATABASE ANALYSIS AND IMPROVED MODELS

The use of the Fabric Reinforced Cementitious Mortars (FRCMs) is nowadays a promising solution for the strengthening of both reinforced concrete and masonry structural elements. The application consists of a bond-dependent face-to-face plastering of an open grid or mesh by means of an inorganic-based matrix, i.e. a cement-based mortar. The main advantage of such a strengthening technique is the good compatibility with different types of substrates since the most suitable matrix can be selected focusing on the most similar breathability and stiffness. On the other side, the strengthening efficiency could be over-estimated if the potential bond failure is neglected. The FRCM-bond behaviour de…

Analytical prediction of the shear connection capacity in composite steel–concrete trussed beams

Steel–concrete trussed composite beams are a particular types of composite girders constituted by a steel truss embedded in a concrete core. The truss is typically composed by a steel plate or a precast concrete slab working as bottom chord while coupled rebars are generally used to form the upper chord. Moreover, a system of ribbed or smooth steel rebars welded to the plate and forming the diagonals of the truss, works as web reinforcement. In the present study, the attention is focused on the evaluation of the shear resistance of the connection between bottom steel plate (the bottom chord) and concrete core through the diagonal bars of the truss developing a mechanical model able to accou…

Steel fiber-reinforced concrete corbels:experimental behavior and shear strength prediction

Corbels are structural members often used in reinforced concrete structures to transfer vertical and horizontal forces to principal members. This paper presents experimental research regarding the flexural behavior of corbels in plain and fibrous concrete and in the presence of steel bars. The study considers the influence of the type of concrete grade (normal- and high-strength concretes), of the fiber percentage and of the arrangement and percentage of the steel bars on the flexural behavior of the corbels. The results in terms of load-deflection curves and crack patterns show the effectiveness in using fibrous reinforced concrete corbels as well as in the presence of stirrups ensuring ad…

Behavior in compression of concrete cylinders externally wrapped with basalt fibers

Abstract This paper gives additional information on the use of new class of composites constituted by Basalt Fiber Reinforced Polymer (BFRP) bonded with epoxy resin to concrete specimens as an alternative confinement material for compressed concrete members with respect to carbon or glass fibers. From the experimental point of view, concrete cylinders are wrapped with continuous fibers, in the form of sheets, applying both full and partial discrete wrapping with BFRP straps, and then tested in compression. For comparison, few other concrete cylinders are wrapped with Carbon Fiber Reinforced Polymer (CFRP) sheets and tested in compression. The number and type of plies (full or partial wrappi…

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…

On the use of Digital Image Correlation (DIC) for evaluating the tensile behaviour of BFRCM strips

Abstract. Fibre Reinforced Cementitious Matrix (FRCM) composites are becoming largely adopted for retrofitting masonry structures. These materials offer several advantages in comparison to Fibre Reinforced Polymer (FRP) composites, such as good resistance to fire and high temperatures, vapour permeability, possibility to be applied on wet surfaces, higher compatibility with the masonry substrate. However, the tensile behavior of FRCM materials is more complex compared to FRP composites, due to the limited tensile strength of the cement-based matrix. For this reason, FRCM materials require appropriate tensile characterization and, in this context, the use of non-conventional measurement syst…

Experimental Investigation of the Shear Response of Precast Steel-Concrete Trussed Beams

The results of an experimental campaign of three-point bending tests on precast composite beams, named hybrid steel-trussed concrete beams (HSTCBs), are provided. HSTCBs are typically constituted by a precast steel truss embedded in a block of concrete cast in place. Two series of specimens were manufactured, designed such that shear failure would occur, and tested under positive and negative bending moment. The experimental results obtained showed that fragile shear failure occurred in almost all cases, evidencing the crisis of the compressed concrete strut involved in the collapse mechanism. Yielding of the steel members provided ductility to the system, especially in those cases in which…

Masonry columns confined with fabric reinforced cementitious matrix (FRCM) systems: A round robin test

Abstract The conservation and the preservation of existing masonry buildings, most of them recognized as cultural heritage, require retrofitting techniques that should reduce the invasiveness and assure reversibility and compatibility with the substrate. In this perspective, the strengthening system should be able to improve the bearing capacity of the structural member and, at the same time, to assure mechanical and material compatibility. The use of Fabric Reinforced Cementitious Matrix (FRCM) composites is now recognized to be suitable for these purposes. Indeed, the inorganic matrix has comparable properties with respect to the existing historical mortars while the fabric has relevant t…

Stiffness and strength of composite truss beam to R.C. column connection in MRFs

Abstract The results of experimental and numerical investigations on the cyclic behavior of composite truss beam to reinforced concrete column connection of moment resisting frames are reported. The beams are constituted by a steel truss and end zone added rebar embedded within a concrete block cast in place, so that, after curing, the steel truss and the added rebar work together with the concrete matrix as reinforcement of the composite beam. Particularly, three specimens of two-span continuous beams were tested under monotonic and cyclic actions as three point bending test. With the goal to investigate about the behavior of the end zone of the beam integrated into a moment resisting fram…

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…

Uno strumento di pianificazione per la salvaguardia degli edifici storico-monumentali. Un caso di studio: la chiesa del SS. Salvatore a Naro

Il patrimonio storico, e in particolare gli edifici monumentali, sono i manufatti tra i più vulnerabili nei confronti degli eventi sismici, e spesso determinano anche gravi ripercussioni su quello che comunemente è definito ”rischio urbano”. Per la conservazione e la tutela del patrimonio culturale nei riguardi dell’azione sismica è necessario disporre di strumenti di analisi in grado di permettere la valutazione della vulnerabilità e del rischio, nonché la progettazione degli interventi di miglioramento sismico. Le Linee Guida per la valutazione e riduzione del rischio sismico del patrimonio culturale – allineamento alle nuove Norme tecniche per le costruzioni, G.U. 26.02.2011, n°47 (di se…

La verifica sismica degli edifici in muratura

Constitutive Numerical Model of FRCM Strips Under Traction

In this paper, the tensile behavior of Fiber Reinforced Cementitious Matrix (FRCM) strips is investigated through Finite Element (FE) models. The most adopted numerical modeling approaches for the simulation of the fiber-matrix interface law are described. Among them, the cohesive model is then used for the generation of FE models which are able to simulate the response under traction of FRCM strips tested in laboratory whose results are available in the technical literature. Tests on basalt, PBO and carbon coated FRCM specimens are taken into account also considering different mechanical ratios of the textile reinforcement. The comparison between FE results and experimental data allows val…

Shear strength of steel fiber reinforced concrete beams with stirrups

The present paper proposes a semi-empirical analytical expression that is capable of determining the shear strength of reinforced concrete beams with longitudinal bars, in the presence of reinforcing fibers and transverse stirrups. The expression is based on an evaluation of the strength contribution of beam and arch actions and it makes it possible to take their interaction with the fibers into account. For the strength contribution of stirrups, the effective stress reached at beam failure was considered by introducing an effectiveness function. This function shows the share of beam action strength contribution on the global strength of the beam calculated including the effect of fibers. T…

ANALISI DELLE TENSIONI SU PIATTABANDE METALLICHE DI TRAVI RETICOLARI MISTE

Nel presente lavoro si riferisce di una sperimentazione condotta su travi reticolari miste realizzate utilizzando un traliccio in acciaio preparato in stabilimento, avente come corrente inferiore un piatto metallico e come corrente superiore e aste di parete barre da c.a., successivamente annegato in un getto di calcestruzzo, ottenendo così una trave composta accaio-calcestruzzo. Per la specificità della tipologia, la trasmissione degli sforzi tra i due materiali non è assimilabile a quella delle travi composte tradizionalmente intese né a quella delle travi in c.a. La sperimentazione condotta attraverso prove di flessione su quattro punti ha avuto come scopo principale la valutazione della…

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

EXPERIMENTAL ANALYSIS OF SMALL CLAY BRICK CYLINDERS CONFINED BY BFRP GRID UNDER AXIAL COMPRESSION

Many investigations have shown that fibre reinforced polymer (FRP) composites can be effectively used to induce a passive confinement action on masonry columns and improve their axial capacity and ductility. This paper presents the results of an experimental study on the compressive behaviour of clay brick masonry cylinders externally wrapped with basalt fiber reinforced polymer (BFRP) grids. The circular section shape was chosen to assess the pure confinement effect on the masonry material. Fourteen clay brick masonry cylinders, cored from two different masonry assembly types, were confined with one or two layers of BFRP grids. The two assemblies were used to investigate the effect of vert…

Shear strength of reinforced concrete beams with fibers and stirrups

Formulation of a truss element for modelling the tensile response of FRCM strips

Modelling the tensile behaviour of Fabric Reinforced Cementitious Matrix (FRCM) is not a straightforward task due to the inner complexity of the mechanics of this kind of composite materials. In fact, after that the matrix is cracked, the compatibility between the fibre and the surrounding mortar is lost and the system behaves as two separate elements connected by a brittle interface. For this reason, several research studies proposed computational approaches for evaluating the tensile behaviour of FRCM composites, usually referring to brick-based 3D Finite Element Models (FEM) or to complex numerical procedures. This paper shows the formulation of a simplified coupled truss element for mod…

Validation of a Shear Model for RC and Hybrid Beams with Two Different Inclinations of Transversal Reinforcement

The validation of an analytical model recently proposed for evaluation of the shear capacity in Reinforced Concrete (RC) beams containing multiple inclination of transverse stirrups is presented. The model is a suitable extension of that currently proposed in Eurocode 2 for the evaluation of the shear resistance, and it is derived by means of the the variable-inclination stressfield theory based on Nielsen’s plastic approach. Experimental and numerical data available in the literature on Hybrid Steel-Trussed Concrete Beams (HSTCBs) are used for model validation and result discussion. Finally, also the comparison with a different analytical approach for the assessment of the shear resistance…

Constitutive Models for the Tensile Behaviour of TRM Materials: Literature Review and Experimental Verification

In recent years, the scientific community has focused its interest on innovative inorganic matrix composite materials, namely TRM (Textile Reinforced Mortar). This class of materials satisfies the need of retrofitting existing masonry buildings, by keeping the compatibility with the substrate. Different recent studies were addressed to improve the knowledge on their mechanical behaviour and some theoretical models were proposed for predicting the tensile response of TRM strips. However, this task is complex due to the heterogeneity of the constituent materials and the stress transfer mechanism developed between matrix and fabric through the interface in the cracked stage. This paper present…

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

Design of RC joints equipped with hybrid trussed beams and friction dampers

Abstract The challenge of this research consists in the first attempt to apply a dissipative friction connection to beam-to-column joints with semi-prefabricated Hybrid Steel-Trussed Concrete Beams (HSTCB) and RC pillars cast in-situ. Nowadays, HSTCBs are widely adopted in civil and industrial buildings and, therefore, it is required to evaluate their compliance with the capacity design criteria and their seismic energy dissipation capability. However, the design of the reinforcement of such beams usually lead to the adoption of large amount of steel within the panel zone which becomes potentially vulnerable to the effects of seismic cyclic actions and dramatically reduce the dissipation ca…

Seismic Performance of Earthquake-Resilient RC Frames Made with HSTC Beams and Friction Damper Devices

Seismic behavior of RC frames with hybrid steel-trussed concrete beams is affected by panel zone damage due to a large amount of longitudinal reinforcement. Here the seismic efficiency of innovative frames characterized by friction damper devices (FDDs) at beam-to-column connections is compared against traditional frame. Three configurations are investigated: FDDs alone; FDDs with column-to-foundation connections having preloaded threaded bars and disk springs; FDDs with self-centering friction devices. Non-linear analyses show that FDDs alone prevent plastic hinge formation at beam ends and beam–column joint damage. FDDs with self-centering friction devices effectively limit both peak and …

Dalla Ricerca Nazionale Coordinata ASSOPREM: la duttilità delle sezioni delle travi PREM

Per supportare l'attività del Gruppo di Lavoro, nella redazione delle Istruzioni per Travi Prefabbricate Reticolari Miste, è emersa la necessità di eseguire una vasta campagna di prove sperimentali nel più breve tempo possibile. Assoprem si è fatta carico di questa esigenza finanziando un Progetto Nazionale Coordinato di Ricerca redatto dallo stesso GdL. Si tratta di un Progetto, del valore approssimativo di 100.000,00 €, che si snoda su 9 Centri di Ricerca Universitari ed 1 privato coordinati da un organismo nazionale.

Stress transfer mechanism investigation in hybrid steel trussed-concrete beams by push-out tests

Abstract Results of push-out tests carried out on Hybrid Steel Trussed–Concrete Beams (HSTCBs) before and after the concrete casting are presented and interpreted. Firstly, in order to check the ability of weldings before casting, tensile tests were performed on specimens reproducing different types of welded joints. Simplified design formulae were used to predict their ultimate strength. Secondly, results obtained by push-out tests on specimen representative of the beam before and after the concrete casting are presented and discussed. Finally, simplified analytical models proposed by the current European building code were adapted to the specific typology to roughly predict the ultimate s…

Some comments on the experimental behavior of FRC beams in flexure

In the present paper the experimental results, recently obtained by the authors, regarding the monotonic and the cyclic flexural response of normal and high-strength concrete beams reinforced with steel bars and discontinuous fibers, are shown. From the experimental results, all referred to low values of shear-to-depth ratios, it emerges clearly that the shear failure is brittle especially under cyclic actions highlighting the role of the fibers in the flexural behavior of the beams. The cyclic action produces a significant decay in the stiffness and in the strength capacity of the beams, and the addition of fibers reduces these negative effects. Form theoretical point of view good agreemen…

Shear capacity in concrete beams reinforced by stirrups with two different inclinations

Abstract A model for the estimation of shear capacity in Reinforced Concrete (RC) beams with web reinforcement is provided by introducing a generalization of classical plastic Nielsen’s model, which is based on the variable-inclination stress-field approach. The proposed model is able to predict the shear capacity in RC beams reinforced by means of stirrups having two different inclinations and longitudinal web bars. A numerical comparison with the results of experimental tests and those provided by a Finite Element Model (FEM) based on the well known theory of Modified Compression Field Theory (MCFT) is carried out for validating the robustness of the proposed model. Finally, a set of para…

Numerical Modelling of the Constitutive Behaviour of FRCM Composites through the Use of Truss Elements

The modeling of the mechanical behavior of Fabric Reinforced Cementitious Matrix (FRCM) composites is a difficult task due to the complex mechanisms established at the fibre-matrix and composite-support interface level. Recently, several modeling approaches have been proposed to simulate the mechanical response of FRCM strengthening systems, however a simple and reliable procedure is still missing. In this paper, two simplified numerical models are proposed to simulate the tensile and shear bond behavior of FRCM composites. Both models take advantage of truss and non-linear spring elements to simulate the material components and the interface. The proposed approach enables us to deduce the …

Some recent results on the compressive and flexural behaviour of composite members

Experiemntal results from compression and flexural tests on steel tubulare columns having circular or rectangular transverse cross-section and infilled with plain or fiber reinforced concrete (FRC) are analysez. for composite members differenti lengths and different dimensions of transverse cross-section were considered in order to assess the influence on behavior in flexure and in compression.The fiber investigated with different percentage were syntetic, carbon and deformed steel fibers. The constituent materials were characterised through compressive and split tests on conconcrete cylinders. Load.shortning and load-delection curves were determined including the sotnening response. Simpli…

Performance of a historical cantilever reinforced concrete bridge with half-joint degradation

The lack of maintenance of roadway concrete bridges built from the Second World War until the 70 s of the 20th century has led in recent years to an ever-increasing request for safety assessments. When bridge performance in terms of Serviceability Limit State (SLS) and Ultimate Limit State (ULS) has to be evaluated, in-situ visual inspections and load tests for safety and maintenance assessment have to be coupled with structural analysis. In order to identify a sound bridge structural model and to assess the actual conservation state, more refined models than those usually considered for section and reinforcement design should be used to reproduce the results of load tests and perform globa…

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…

Experimental application of digital image correlation for the tensile characterization of basalt FRCM composites

Abstract Composites made with inorganic matrix, namely fabric reinforced cementitious mortar (FRCM) composites are becoming widespread as strengthening materials for existing masonry structures. These composites are made of a dry grid of fibres embedded in an inorganic matrix. FRCMs can be considered a valid alternative to traditional organic composites such as fibre reinforced polymers (FRPs) because of their better compatibility with the masonry support. This work presents an experimental study for the tensile characterization of a basalt fabric reinforced cementitious mortar (BFRCM) composite. Tensile tests were carried out on coupons reinforced with one, two or three layers of grid to i…

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 and analytical response of masonry elements under eccentric vertical loads

The flexural behaviour of masonry rectangular cross-sections is studied in order to characterize the mechanical behaviour of structural elements under axial eccentric loads by means of a proper law. First the experimental response of walls under vertical centred loads is observed and a stress-strain law depending on two parameters is given in order to fit the experimental results. Subsequently the behaviour of walls nominally equal to the walls mentioned before is investigated under eccentric vertical loads, and the response is observed in terms of moment-curvature relation. To this point a comparison is made between the moment-curvature response obtained experimentally and the moment-curva…

Comportamento ciclico di travi in calcestruzzo fibrorinforzato

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

Analytical Prediction of the Flexural Response of External RC Joints with Smooth Rebars

Nel presente lavoro viene presentato un modello analitico in forma chiusa in grado di riprodurre la risposta flessionale monotonica di nodi esterni trave-colonna in c.a. con armature lisce. La colonna viene sottoposta a carico verti-cale costante e la trave ad una forza laterale crescente monotonicamente applicata all’estremità. Il modello si basa sul comportamen-to flessionale di trave e colonna adottando un modello di cerniera plasticità concentrata che include lo scorrimento delle armature della trave. Si assume un dominio sforzo normale-momento bilineare semplificato da cui viene derivato il momento ultimo associato alla forza assiale di progetto. Per il nodo viene adottato un modello c…

Cyclic behavior of composite truss beam-to-RC column joints in MRFS

In the present paper, the cyclic behavior of beam-to-column joints made up of Hybrid Steel Trussed Concrete Beams (HSTCBs) connected to Reinforced Concrete (RC) piers is investigated. HSTCBs are a typology of composite beam generally constituted by a steel truss with end zone added rebars embedded within a block of concrete cast in place. HSTCBs represent a structural solution for light industrialization in the civil constructions; the main advantages in their use are the higher construction speed with the minimum site labor, the possibility of covering wide spans with low depths and a final economical convenience. For these reasons, they are also increasingly adopted within seismic framed …

Numerical analysis and experimental comparison on CFRP reinforced masonry walls subjected to transverse loads

The out-of-plane behaviour of walls, unreinforced and reinforced by using CFRP strips, is studied by means of experimental investigation and numerical modelling. The FEM model is based on a linear constitutive law both for the ashlars and the mortar joints constituting the 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 the reinforcement is introduced, an interface element with bi-linear law is also used, reproducing the sliding failure mode. Comparison between the numerical and experimental results shows the reliability of the modelling. Moreover, a parametric analysis is …

CFRP flexural strenghtening of masonry walls: experimental and analytical approach

Comportamento flessionale di mensole tozze in calcestruzzo fibrorinforzato

LA CUPOLA DELLA CHIESA DEL GESU' A PALERMO: UN INTERVENTO DI RICOSTRUZIONE IN CEMENTO ARMATO

Caratterizzazione meccanica di alcune tipologie di tamponamento

L’utilizzo di modelli che prevedono l’inserimento dei tamponamenti nelle maglie di telaio richiede la conoscenza preliminare delle caratteristiche meccaniche del tamponamento. A tal fine si possono seguire diverse strade, tutte basate su prove di laboratorio: 1) determinazione diretta della risposta a taglio del tamponamento su campioni di muratura; 2) determinazione della risposta a compressione lungo gli assi principali di campioni di muratura rappresentativi del tamponamento e utilizzo dei risultati per dedurre il comportamento a taglio; 3) determinazione della risposta a compressione dei componenti della muratura (malta ed elementi resistenti) da correlare alle caratteristiche meccanich…