The analytical bond behaviour between reinforcing bars and reinforced concrete matrix is widely described in the technical literature. On the contrary, there are no analytical models for concrete reinforced with recycled steel fibre (from waste tires). The theoretical analysis discussed in this paper has been focused on the evaluation of suitable analytical models for such material in order to define, for the first time, valid design guidelines. For this purpose, were analysed the available data from a previous experimental campaign performed by the authors, in which eccentric pull-out tests were carried out, varying the type of concrete (plain, SFRC - Steel Fiber Reinforced Concrete, RSFRC – Recycled Steel Fiber Reinforced Concrete) and the ratio of concrete cover and bar diameter (c/d). Using these data, several analytical models were calibrated for plain concrete and SFRC, obtaining analytical formulations which allow to describe the bond stress-slip behaviour and to determine the peak bond stress and the post splitting stress for recycled fibre reinforced concrete.

La crescente esigenza in ambito strutturale di garantire livelli di sicurezza più elevati tanto a breve quanto a lungo termine, sia per le nuove costruzioni sia per le costruzioni esistenti, che sempre più numerose manifestano segni di degrado e di inadeguatezza rispetto alle prestazioni attese e, d’altra parte, lo sviluppo di nuovi materiali, hanno condotto verso tecnologie che si affiancano o, in alcuni casi, sostituiscono quelle tradizionali. In questo ambito si inquadrano i materiali compositi fibrorinforzati , in particolare i biocompositi e i compositi a base di fibre di acciaio che rappresentano attualmente un settore grande interesse sebbene ancora poco esplorato. Nel presente lavoro verranno presentati i primi risultati ottenuti nell’ambito di una ricerca più ampia mirata a studiare l’aderenza tra il calcestruzzo e i sopracitati rinforzi, mediante prove sperimentali di taglio non simmetrico. In particolare, i tets condotti sono relativi ad elementi rinforzati con fibre di basalto, lino, canapa e acciaio. I risultati sperimentali ottenuti, in termini di carico ultimo, tensione massima di aderenza, lunghezza di trasferimento, modalità di rottura saranno analizzati e discussi, oltre che confrontati con quelli relativi all’utilizzo di compositi più tradizionali.

The use of fiber-reinforced composite materials, as externally bonded reinforcement, for strengthening existing concrete structures, has gained an increasing success, as shown by the wide available literature on this topic and the extensive practical applications worldwide. However, as well known, some key aspects need further investigations like as the bond performance between the reinforcement and substrate. At the same time, the need of standard test to evaluate the bond performance as well as the assessment of law of general validity increases in the designer area. In the present work single face shear tests were carried out on concrete elements reinforced with different types of FRP reinforcement and considering both FRP sheet applied with hand-lay-up technique and FRP pre-cured laminate. The experimental results are analyzed and discussed.

The need to guarantee higher safety levels of masonry structures under both short and long term conditions, have led to the use of new materials and technologies, in conjunction or in place of traditional ones. In this context fiber-reinforced composite materials have gained an increasing success, mostly for strengthening, retrofitting and repair existing structures. As well known, the bond performance between the reinforcement and the masonry substrate is a critical aspect as it influences the effectiveness of the technique. The bond depends on many parameters as mechanical proprieties of the substrate, interface and reinforcement, bond length, type of test, environmental conditions etc. The research work of the authors was devoted to this topic from many years and several of the above parameters were analysed. In the present paper the most recent experimental results are reported and discussed; they refer to the analysis of bond between masonry made by natural stones and reinforcement. At this scope a single face shear test has been carried out, varying the substrate configuration and the stiffeness of the FRP reinforcement. In particular a kind of calcerous stone, typically used in the Mediterranea area, was considered and syntetic and natural fibers were used as reinforcement. The effect of these analysed parameters was investigated in terms of bond strength, mode of failure and strains path along the bonded length. In addition a theoretical analysis was done based on the suggestions available in the Italian guide-line. The obtained results show that both the stiffness of the reinforcement and the presence of the mortar joints influence the interface behavior; in particular the tests on masonry substrates furnish higher bond strength with respect to those made using stone unit subtrates, despite the poorer mechanical properties of masonry. In addition the analytical bond strengths evaluated according to the Italian Guideline furnish a good estimation of the excperimental data in the case of specimens realized with stone units.

In the field of strengthening and/or upgrading of existing structures with non-metallic reinforcements, an extensive worldwide work has been expended into investigating the bond characteristics between Reinforced Concrete (RC) elements and composite materials. On the contrary little efforts were undertaken about masonry structures. The present paper reports part of a large research project, still in progress, devoted to the analysis of the bond performance between FRP sheets and different types of masonry, considering natural stone, brick, and the correspondent masonry element realized with hydraulic mortar joints. Six different types of fiber reinforced polymers (FRP), of which three with natural origin (basalt, flat and hemp), were also considered in order to evaluate their influence on bond performances. The global experimental results in terms of bond strength and kind of failure were analysed in order to evaluate the influence of the analysed parameter and the bond mechanism especially when FRP with natural fibres are used. In addition the effect of the presence of the mortar joints on the bond was analysed. Finally, the comparison in terms of strain along the bonded length has highlighted that the physical performance of the substrate could influence the stress transfer mechanism

The manufacturing technology of reinforced concrete with the use of steel fibers to improve its mechanical properties is well-known and commonly used in civil engineering. Generally, steel fibers as discontinuous reinforcement of the concrete matrix are used to limit the cracking growth following the load application. Thus, the obtained concrete is characterized by an improvement of the typically brittle behavior of the ordinary matrix, mainly referring to toughness and post-cracking behavior. In this paper the results of a recent experimental campaign carried out at the University of Salento will be discussed. It was designed to study the optimization of concrete mixtures reinforced with recycled steel fibers from end of life tires (ELTs) to be used for the realization of precast panels. This experimental campaign is part of a wider research project aimed to validate the idea that the constituent elements of the ELTs, especially rubber and steel, can be effectively reused in concrete mixtures. Taking into account the high annual amount of ELTs generated around the world and their negative impact on the global environmental sustainability, the recovery of their constituent materials and their reuse as raw materials in different technologies, is certainly an excellent way for a sustainable development.

their related negative impact on the environment. One of the strategies to reduce this impact is represented by the recovery of the constituent materials to be reused as raw materials in different technologies, including concrete products. The introduction of steel fibres into a concrete matrix to improve its mechanical characteristics is quite known and established in FRC technologies. Generally, steel fibres are used as discontinuous reinforcement of the concrete matrix to limit the cracking growth and to enhance the post-cracking behaviour. Thus, the obtained concrete is characterized by an improvement of its toughness and its post-cracking residual strength. The results of an experimental campaign, carried out at the University of Salento, will be discussed herein. This work is a part of a wider research project aiming to introduce recycled materials as new raw constituents in concrete mixtures such as in the production of precast panels. The results of experimental work underline the good reproduction of the laboratory scale in production plant. In addition the realized precast panels did not show shrinkage cracks or oxidation of the unplaster surface

The experimental research presented herein is focused on the study of the flexural behaviour of Fibre Reinforced Concrete (FRC) beams. Ten full scale specimens were prepared and tested under a four point bending scheme. The beams were built without transverse steel reinforcement along the region that was tested with a constant flexural moment and shear null. Experimental variables were the concrete mix, the type of short fibres used as dispersed reinforcement (steel and polymeric fibres) and volume fraction of fibres used in the concrete matrix. Two repetition specimens were tested for each concrete mix. Experimental results show strain monitoring in the longitudinal steel at increasing loads, strain monitoring in compressed concrete, flexural deflection along the beams. The results highlight the great importance of the beneficial role exercised by the short fibres dispersed in the cement matrix in reducing cracking of reinforced concrete (RC) beams. In particular results obtained herein in absence of the web reinforcement provide new original data since it was avoided to have the onset of the cracks along the stirrups. In correspondence of different five load levels the distance, the height and the maximum width of the cracks were also measured over the whole length of the beams, with particular attention to the constant moment region. The steel fibres demonstrated to be more effective than respect to polyester fibres as crack arrestors. The experimental data were also compared to the design values obtained by applying the analytical models of the new FIB Model Code 2010.

Nel lavoro di ricerca presentato si illustra lo studio del comportamento sezionale di elementi in c.a. confinati trasversalmente con materiali compositi fibrorinforzati a matrice polimerica FRP (Fiber reinforced polymers), definendo un indice di duttilità non legato alle proprietà post-elastiche dell'acciaio, bensì alla incrementata deformazione ultima del calcestruzzo per effetto dello stato tensionale tri-assiale generato dalla pressione elastica di confinamento. Con riferimento alle grandezze introdotte nella trattazione analitica è descritto un esempio applicativo progettuale di un intervento di rinforzo effettuato su una struttura in calcestruzzo armato, fortemente degradata, e soggetta, per effetto della sua funzione d'uso di impianto di frantumazione inerti, ad azioni di tipo dinamico da oltre 30 anni. I risultati, relativi alle verifiche di sicurezza, sono stati ottenuti applicando le raccomandazioni progettuali contenute nel Documento Tecnico CNR 200/2004. Saranno messi in luce, pertanto, gli effetti dei coefficienti limitativi contenuti nelle linee guida sulla capacità ultima degli elementi confinati. risultati saranno discussi, inoltre, in relazione ai benefici ottenibili in termini di duttilità locale delle sezioni presso-inflesse, oltre che al notevole ripristino di resistenza, così come ampiamente evidenziato nei numerosi lavori sperimentali disponibili in letteratura.

Over the last years, the use of raw materials derived from End of Life Tires (ELTs) has found several applications, which have al-lowed a gradual waste reduction through its reuse in different production sectors. In this context, the present paper deals with the mechanical characterization of reinforced concrete with steel fibres recycled from ELTs. Concrete is generally considered a brittle material with a low tensile strength and a slight ultimate strain. Steel fibres are often used as discontinuous reinforcement in the concrete matrix to bridge the cracks that develop when a load is applied, improving its toughness and post-cracking behaviour. The discussed experimental work is part of a wider scientific investigation concerning the introduction of recycled steel fibres in civil en-gineering production sectors. The main founds on the mechanical behaviour of the proposed concrete, comparing the results with the corresponding ordinary concrete will be discussed.

Current design codes and technical recommendations often provide rough indications on how to assess effective stiffness of Reinforced Concrete (R/C) frames subjected to seismic loads, which is a key factor when a linear analysis is performed. The Italian design code (NTC-2008), Eurocode 8 and ACI 318 do not take into account all the structural parameters affecting the effective stiffness and this may not be on the safe side when second-order P-Δ effects may occur. This paper presents a study on the factors influencing the effective stiffness of R/C beams, columns and walls under seismic forces. Five different approaches are adopted and analyzed in order to evaluate the effective stiffness of R/C members, in accordance with the scientific literature and the international design codes. Furthermore, the paper discusses the outcomes of a parametric analysis performed on an actual R/C building and analyses the main variables, namely reinforcement ratio, axial load ratio, concrete compressive strength, and type of shallow beams. The second-order effects are investigated and the resulting displacements related to the Damage Limit State (DLS) under seismic loads are discussed. Although the effective stiffness increases with steel ratio, the analytical results show that the limit of 50% of the initial stiffness turns out to be the upper bound for small values of axial-load ratio, rather than a lower bound as indicated by both Italian NTC-2008 and EC8. As a result, in some cases the current Italian and European provisions tend to underestimate second-order P-Δ effects, when the DLS is investigated under seismic loading.

External bonded reinforcements (EBR), made by fibrous meshes embedded in a cementitious/hydraulic lime mortar, are getting a great deal of attention, mostly for strengthening, retrofitting and repair existing structures. In this context, the interest versus the FRCM (Fiber Reinforced Cementitious Matrix) is growing. The mechanical performance of these mortar-based reinforcements is not well known at the date and it needs to be investigated in terms of bond and tensile strength, strain and stiffness, in relation to the type of both substrate and fibers. The present work reports the results of an experimental study, still in progress, on different pre-cured GFRP grids embedded in inorganic matrices and applied on clay brick masonry. First, the mechanical properties of both pre-cured GFRP grid and GFRCM reinforcements were obtained through tensile tests. Then, the experimental investigation on bond behavior was carried out by direct shear bond test. The test results were collected and processed to evaluate bond strength, failure mode, load-slip relationship.

The positive effect of fibers on the bond of reinforcing bars in concrete is widely recognized and supported in literature. The present research analyze the results of pull-out tests carried out on both unreinforced and recycled steel fibers reinforced concrete (RSFRC). The recycled steel fibers were derived, through a mechanical procedure, from the disposal of scrap tires. The tests were performed varying the ratio between the concrete cover and the bar diameter in order to evaluate the effect of the fibers on bond behavior when the splitting failure occurs. The experimental results, in terms of mechanism of failure, maximum bond stress and bond stress versus slip behavior are analyzed and discussed

The paper presents a Round Robin Test (RRT) devoted to the characterization of the shear bond performance of fibre-reinforced strengthening systems bonded with epoxy resin to brick masonry. The research was carried out by six laboratories involved in the RILEM TC 250-CSM (Composites for the Sustainable strengthening of Masonry) as a continuation and an extension of a previous RRT1 performed within the RILEM TC 223-MSC (Masonry Strengthening with Composites). In this second investigation (RRT2), the same FRP (basalt, carbon and glass textiles) and SRP (comprising steel textiles) composites were tested, but shear bond tests were carried out on both brick units and masonry prisms. The role of the bed joints of mortar was investigated in terms of shear bond strength, load–displacement response curve, axial strains profile along the bonded area and effective transfer length, for each of the four considered strengthening systems. Single lap and double lap testing setups were used and the comparison of experimental outcomes provided a validation of both results and test methods. Finally, test outcomes led to the determination of the mean and the characteristic values of the experimental-based calibration coefficient provided by design codes for the evaluation of the composite-to-substrate bond strength.

The use of recycled steel fibres from waste tyres as reinforcement in concrete matrix appears a promising solution thanks to the performance of the material in terms of toughness and post-cracking behaviour. The main objective of this paper is to analyse the bond behaviour between Recycled Steel Fibre Reinforced Concrete (RSFRC) and steel bars and to compare the results with those of Industrial Steel Fibres Reinforced Concrete (ISFRC). The paper focuses on the characterization of the mechanical properties of concrete reinforced with short steel fibres from waste tyres and on the results of pull-out tests executed both on RSFRC and ISFRC. The experimental results, in terms of failure mode, maximum bond stress and bond stress versus slip behaviour are analysed and discussed. Finally a theoretical analysis of the bond-slip behaviour has been performed. The experimental results show as most of the known performance of the ISFRC can be extended to RSFRC. Referring to the bond performance, an improved behaviour of RSFRC with respect to ISFRC in terms of bond-slip law has been observed.

The sustainability of construction materials is a mandatory issue that started to be strongly felt in view of a global perspective of environmental protection. Wasted materials often may find a new lifecycle if well re-engineered, even in structural applications. In this field short steel fibers obtained from used tyres at the end of their life may find promising applications within a concrete matrix. In the present research the mechanical properties of recycled steel fiber-reinforced concrete in terms of workability, compressive and tensile strength, toughness and shear behaviour are analysed and compared with those of industrial steel fiber-reinforced concrete and ordinary Portland concrete. An experimental campaign is illustrated, and an extensive comparison in terms of shear strength has been studied considering different experimental works available in scientific literature. Moreover, a theoretical analysis aimed at evaluating and comparing the shear modulus of the analysed concrete type was carried out. The results obtained through this study show a satisfactory behaviour of the concrete reinforced with recycled steel fibers compared with industrial new steel fibers reinforced concrete, both in terms of toughness and shear behaviour.

Fibre-reinforced composite materials have gained an increasing success, mostly for strengthening, retrofitting, and repairing existing structures. However some problems may arise with the use of traditional FRP (Fiber Reinforced Polymer), particularly when the compatibility with the substrate and the reversibility of the intervention are required, as in case of cultural heritage buildings, or specific exposition conditions may compromise the long term effectiveness of the reinforcement, as in presence of high temperature and humidity. Starting from these considerations new composite materials are emerging as a more effective solution in certain fields of application and under specific service conditions; in this context, mortar-based composite systems, consisting of one or more layers of uni- or bi-directional fibre nets embedded in cement/lime-based matrix layers, can be used as reinforcement of both concrete and masonry structures. However, the research work dealing with these emerging materials and their performances when used as a strengthening system for existing structures is still limited. Both experimental and theoretical investigations are needed in order to deliver reliable design methodologies. In this work, a Round Robin Test aimed to the characterization of both bond with the existing substrate and tensile performance of glass fabric (in the form of grids) coupled with inorganic mortar matrices is presented. The investigation was conducted at fifteen laboratories involved in the RILEM Technical Committee 250-CSM (Composites for the Sustainable Strengthening of Masonry). With the aim of studying the bond behaviour between Fabric Reinforced Cementitious Matrix (FRCM) composites and masonry substrate, single and double lap shear tests were carried out on brick-masonry prisms. Results provide useful informations about the mechanical properties, the bond capacity and the failure mechanisms of different commercially available glass FRCM systems. Finally, critical aspects are underlined to address the progress of the research work.

It was estimated that about 3,3 million tonnes of used tires are generated every year in Europe. Despite several years of efforts to address the waste tires management, large stockpiles continue to be a problem across the EU States. Many EU states are trying to reduce the landfill disposal of waste tyres through directives, national laws and codes, promoting the development of sustainable options for the disposal, recovery, and reuse of tires. In this regard, the most important factor is to facilitate the development of new markets for these by-products. Tires are 100% recyclable: the rubber, metals and textiles can all be recovered and used in many applications, as well as in consumer and industrial products and numerous examples are published in the literature. One of the possible areas of application is the realization of concrete elements, in particular the use of the steel contained in a tire as discontinuous reinforcing fibre in the concrete matrix. Concrete is generally considered a brittle material because of its low tensile strength. Consequently, steel fibres are widely used in the concrete technology as discontinuous reinforcement into the matrix with the objective to bridge the cracks that develop when a load is applied to the concrete element. The concrete obtained by adding these fibres is characterised by a satisfactory improvement of the brittle matrix, mostly in terms of toughness and post cracking behaviour. The main objective of this work is to develop and to characterize the concrete reinforced with steel fibres recovered from waste tires in terms of both fresh properties (such as workability and air content), hardened properties (such as compressive strength, flexural toughness and stress-strain behaviour in compression). Finally, the bond behaviour between the concrete matrix and the reinforcing steel bars is analysed. On the basis of the satisfactory obtained results it may reasonably be supposed that the application of such recovered steel fibres in concrete technology could lead to economic advantages, non-minor physical-mechanical properties respect to concrete reinforced with industrial steel fibres and could contribute to the well-known pollution problem related to waste tires.

The positive effect of fibers on the bond of reinforcing bars in concrete is widely recognized and supported in literature; on the contrary information are not available on recycled steel fiber reinforced concrete. The experimental work discussed in this paper represents a part of a wider analysis, performed by the authors, on the mechanical performance of RSFRC. In particular the main objective is to investigate on the bond behavior between steel bar and recycled steel fiber (from waste tires) reinforced concrete. To this aim eccentric pull-out test on prismatic samples were designed varying the type of fiber (recycled and industrial steel fibers) and the concrete cover-bar diameter ratio; in addition similar tests were carried out on plain concrete for comparison purpose. The experimental data in terms of peak bond stress, mode of failure and bond stress-slip curves are analyzed and discussed evidencing the good bond performance of specimens realized with recycled steel fiber reinforced polymer compared with both those realized with both plain and industrial fiber reinforced concrete.

The experimental investigation aims to analyse the efficiency of the FRP (Fiber Reinforced Polymer) strengthening technique in terms of in-plane behaviour of the reinforced masonry element. In particular ten masonry panel were realized with local stone (Lecce stone) and strengthened with two types of geometric configuration (grid and diagonal) of the BFRP (Basalt Fiber Reinforced Polymer) reinforcement. The eccentricity of the strengthening was also considered as variable parameter. The obtained experimental results in terms of strength, mechanisms of failure and ductility underlined the effectiveness of the technique for all analysed configurations in comparison with unreinforced masonry panels. In particular better performances were observed in terms of ductility in the case of FRP grid configuration while the diagonal reinforcement furnished the highest value of shear strength.

The damage observed in past earthquakes, has shown as the presence of infills significantly influences the seismic performance of RC moment resisting frames. In fact, the presence of full infilled frames, with regular distribution, could improve the seismic response and mitigate horizontal displacements. On the other hand, an irregular distributions of infill could dramatically modify the stiffness and resistance of structures resulting in a brittle collapse mechanism related with soft story or torsional effects. In this study it has been evaluated the seismic behaviour of frames designed to bear only gravity load; a simulated design procedure has been adopted, according to code provisions and design practices in force in Italy between 1950s and 1970s. A parametric study has been performed to take into account the typical mechanical properties of masonry available in Italy. Infill panels have been modelled by means of equivalent struts. A pushover analysis has been carried out to evaluate the capacity curves and collapse mechanisms of infilled frames. The performed analysis allowed to analyse the influence of infill properties on the ductility of existing RC frames. The results emphasize as the properties of masonry infills should be adequately evaluated before doing a seismic analysis as the masonry shear strength significantly influences the global seismic behaviour of RC frames.

The use of epoxy bonded fibre reinforced polymer (FRP) materials as strengthening technique for existing masonry structures is becoming in the last years more and more widespread, but some topics, as the effect of the mortar joints on the bond performance at the reinforcement/masonry substrate interface, still represents an open question. This paper is focused on studying in detail the effect of the mortar joints on the bond performance of FRP materials made of different type of fibres (carbon, glass, basalt, steel) externally bonded by means of epoxy resin to three different masonry substrates, very common in Italy: tuff stones, Lecce stones, and clay bricks. Firstly, the experimental results of bond tests carried out by three laboratories on three different masonry substrates were discussed in detail in order to highlight the effect of the mortar joints as the masonry typology changes. Successively, statistical analysis were performed on a more extended database of bond tests coming from literature and carried out on similar masonry substrates. The analysis were aimed to define design formulations for calculating the debonding load of FRP materials bonded to different masonry substrates with and without mortar joints.

The masonry infills significantly modify the seismic behavior of reinforced concrete (RC) buildings. The damages observed in past earthquakes showed as an irregular distribution of infills could involve in a soft story mechanism or in local damages due to the interaction with the surrounding frames. On the other hand, if regularly distributed, the masonry infills could significantly increase the shear capacity of RC structures. Generally, the infills are realize of masonry elements and mortar joints. As well known, the experimental studies available in the literature underlined as the mechanical properties of masonry materials varied in a wide range. For this reason, in the assessment of seismic behavior of structures, the mechanical properties of the infills should be taken into account. In this study a parametric analysis has been carried out to study the influence of mechanical properties of masonry infills on the seismic behavior of RC frames; in particular, the Young modulus and the shear strength of masonry infills have been varied in the range usually proposed in literature. The influence of infills has been evaluated by means of increasing accuracy of the analysis (linear, push-over and IDA analysis) to study the main parameters involved in the seismic response.

The positive effect of fibers on the bond of reinforcing bars in concrete is widely recognized and supported in literature; on the contrary information are not available on recycled steel fiber reinforced concrete. The experimental work discussed in this paper represents a part of a wider analysis, performed by the authors, on the mechanical performance of RSFRC. In particular the main objective is to investigate the bond behavior between steel bar and recycled steel fiber (from waste tires) reinforced concrete. To this aim eccentric pull-out test on prismatic samples were designed varying the type of fiber (recycled and industrial steel fibers) and the concrete cover-bar diameter ratio; in addition similar tests were carried out on plain concrete for comparison purpose. The experimental data in terms of peak bond stress, mode of failure and bond stress-slip curves are analyzed and discussed evidencing the good bond performance of specimens realized with recycled steel fiber reinforced concrete compared with both those realized with plain and industrial fiber reinforced concrete

The damage observed in past earthquakes, has shown as the presence of infills significantly influences the seismic performance of RC moment resisting frames. The reduction of the elastic period related with the increase of stiffness due to infills causes a different seismic behaviour and in particular a variation in the seismic demand. In this work the elastic period of infilled RC frames designed only for gravity loads and according to the Italian code available before the introduction of seismic design has been evaluated. A parametric analysis has been carried out, including the influence of the infills mechanical properties. Obtained results allowed to calibrate a relationship able to furnish the first elastic period of the frames taking into account all the parameters investigated. Finally, the comparison between the proposed relationship and that provided by the Italian Code evidences in some cases significant scatters in terms of seismic demand, suggesting the need of further investigations and validations.

The analysis of the resistance to fire of masonry vaults represents an open issue due to the lack of analytical and/or experimental investigations in the technical literature as well as to the absence of national and international standard treating the specific topic. However, the Italian building heritage is often characterized by vaulted structures that need to be analysed also from a fire resistance point of view. To this scope in the present work, a first approach to study the behaviour of masonry vaults under thermal actions is reported taking into account the effect of the main influencing parameters.

According to recent data, every year approximately 2.5 million tons of used tires (about 250 million units) are either recycled or recovered in Europe. Generally, end of life tire (ELT) enters a waste management system based on product/material recycling and/or energy recovery. The application of ELTs in civil engineering (such as foundation for roads and railways, draining material, erosion barriers, etc.) in 2013 was 11% of ELTs sent to material recovery. However, the most important material recovery is represented by recycling of rubber granulates and powder (82%). In this context, the experimental work herein discussed is part of a wider scientific investigation on the application of steel fibers recycled from ELTs as discontinuous reinforcement in concrete matrix. As a matter of fact, the main role of the steel fibers within the matrix is to control the crack opening and propagation, increasing the overall ductility of concrete elements. As soon as the cracks widen out, the toughness increases and the cracking process is modified from brittle to ductile, allowing the material to redistribute the stresses. This cracking control also improves the durability of the material. On the basis of previous research studies and also considering the available literature the main issue of the proposed research is to extend the characterization of the recycled steel fibers and to develop the study of their structural behavior when applied for a new eco-friendly concrete. Using these recycled steel fibers in concrete production could ensure a surplus value in terms of environmental and ecological benefits and consequently a significant reduction in landfilling of ELTs. Fresh and hardened properties of concrete reinforced with recycled steel fibers are discussed as well as the post-cracking behavior properties. The obtained results evidenced the good behavior of the proposed material when compared with concrete reinforced with industrial steel fibers. A concrete pavement was finally realized applying the proposed reinforced mixture with recycled steel fibers. As discussed in the following, this application was successful and it fulfilled the specific requested properties.

Recent seismic events that occurred in Italy revealed the vulnerability of masonry buildings with vaulted roof with respect to horizontal forces. Assuming that a large part of the architectural heritage is made by vaulted masonry buildings, measures aimed at improving the seismic response of such structures is a strategic objective. In the present work the behavior of masonry vaults is modeled through equivalent plane element (diaphragm), and a modeling procedure is proposed for design. Different types of vaulted structural roofs were studied, considering geometries with simple and double curvature. An extensive parametric analysis was conducted by varying significant structural parameters: vault thickness, in-plane dimensions, constraint conditions and presence or not of side walls. In the proposed model the complex geometry of the vault is replaced by an equivalent plate, with the intent of modeling the entire building as a frame being equivalent to the real structural with respect to the seismic response. The equivalent plate is defined as an element generally orthotropic with the same in-plane dimensions and same thickness of the vault from which it is derived.

Unreinforced masonry infilled R.C. frames are a widespread structural system worldwide; even if the damages observed during past earthquakes highlight the influence of masonry infills on the seismic per- formance of structures, the common practice considers the infill as nonstructural elements. The infills are made with a large variety of materials and with different construction typologies; nevertheless, a large number of studies have been carried out in the last years to investigate the interaction between the infill panels and the surrounding R.C. frames, few researches have been focused on the influence of mechanical properties of masonry infills on the structural performance. In this study the seismic performance of R.C. frames designed for gravity loads according to the code prescription in force in Italy between 1950s and 1970s has been evaluated. A parametric analysis has been to investigate the influence of the mechanical and geometrical properties of masonry infills on the whole structural response; the seismic behaviour has been analyzed in terms of capacity, ductility and collapse mechanisms. The results showed as the mechanical properties of masonry infills should be adequately evaluated before to proceed to the seismic vulnerability assessment of existing structures because they significantly affect the global behaviour of R.C. frames.

L’impiego di materiali derivanti da PFU ha trovato negli anni numerose applicazioni che consentono una progressiva riduzione della produzione di rifiuti attraverso il riutilizzo come materia prima secondaria all’interno di diversi sistemi produttivi. Peraltro, la legislazione vigente prevede la possibilità di perseguire finalità di tutela ambientale ottimizzando, anche tramite attività di ricerca e sviluppo il recupero dei pneumatici fuori uso. In questo contesto si inserisce il presente lavoro sperimentale che riguarda la caratterizzazione meccanica di calcestruzzo rinforzato con fibre da riciclo provenienti dai PFU; lo stesso è parte di un’indagine scientifica più ampia finalizzata allo sviluppo di soluzioni che introducano tale tipologia di fibre da riciclo in filiere produttive connesse all’ingegneria civile. In particolare, l’obiettivo del presente lavoro è la valutazione della resistenza a taglio dei calcestruzzi rinforzati con fibre di acciaio riciclate da PFU, confrontando i risultati con calcestruzzi realizzati con fibre commerciali.

in the work the experimental compressive stress-strain behaviour for both unreinforced and steel fibres reinforced concrete was evaluated. Two different types of steel fibres were used: industrial steel fibres and recycled steel fibres. The recycled steel fibres were derived, through a mechanical procedure, from the disposal of scrap tires. The experimental work was carried out by the structural Engineering group of the University of Salento with the support of Italcementi S.p.A.

The use of Fiber Reinforced Polymer (FRP) composites has recently experienced a steep increase in civil engineering applications, because of the high mechanical and low density properties of such materials. Over the last few decades, concrete columns externally confined with FRP sheets were largely investigated for their use in structural rehabilitation and seismic strengthening of civil constructions. Scientific literature is rich in experimental results and both analytical or empirical models, focusing on such phenomena. There exist, in fact, several numerical models and analytical procedures able to predict the behavior of FRP-confined structural elements subjected to axial or seismic loads, and researchers worldwide have experimentally studied and analytically calibrated a wide range of significant variables. Nevertheless, there are still a few results concerning the durability of FRP-confined concrete exposed to severe environmental conditions, even if this is a main topic in design. The objective of this study is to raise awareness about the durability of FRP-confined concrete. To do so, the authors collected and analyzed the results of about 760 pure axial compression tests, taken from 17 different experimental studies published in the scientific literature, in order to present a critical comparison between the results of experimental studies and the theoretical models provided by design guidelines and codes. The study was conducted according to the following steps: at first, experimental data available in literature was collected; secondly FRP-confined concrete cylinders subjected to axial load were classified according to the different experimental variables investigated (mainly according to the type of environmental agent they were exposed to); thirdly, experimental results were compared with the provisions proposed by the American Concrete Institute and contained in ACI 440-2R/2008, and with the guidelines presented on CNR DT-200/2012 and proposed by the Italian National Research Council. Finally, strength and limits of the technical codes were analyzed in terms of safety factors, and formulation of design equation in the short and long-term was critically studied.

L’irregolarità strutturale rappresenta una delle più diffuse carenze in termini di requisiti antisismici sia nelle costruzioni esistenti, sia nelle opere di nuova progettazione, ove le esigenze architettoniche non appaiono armonizzate con quelle strutturali. I danni strutturali evidenziati a seguito dei vari terremoti occorsi fino ad oggi hanno evidenziato infatti la maggiore vulnerabilità sismica delle strutture irregolari. Ciò a causa di effetti deformativi indotti proprio dalle discontinuità strutturali, che associati ad una insufficiente resistenza degli elementi interessati producono i disastri ben noti agli studiosi. Nel presente lavoro di ricerca gli autori hanno focalizzato lo studio del comportamento sismico di telai piani in c.a. con irregolarità in altezza, generata a seguito di una distribuzione non uniforme di elementi secondari non strutturali come le tamponature. Modellando le tamponature come bielle equivalenti agenti in sola compressione, è stata valutata la variazione delle caratteristiche dinamiche dei telai in funzione della disposizione delle tamponature in elevazione; in tal modo è stata studiata la variazione del periodo naturale di vibrazione riconducibile all’assenza di tamponature ad uno specifico piano. Il comportamento sismico dei modelli irregolari generati è stato analizzato in questa fase mediante l’impiego di analisi in campo lineare e variando specifici parametri in funzione della diversa tipologia di irregolarità analizzata. Le analisi parametriche effettuate permettono una critica valutazione dell’effetto di irregolarità sulla risposta sismica.

The paper presents the experience of a working group within the RILEM Technical Committee 223-MSC ‘Masonry Strengthening with Composite materials’, aimed at developing a standardized, reliable procedure for characterizing the bonding mechanism of masonry elements strengthened with composite materials under shear actions. Twelve laboratories from European universities and research centers were involved. Two different set-ups were compared, for single-lap and double-lap shear tests (the latter in two versions). Four kinds of fiber fabrics, i.e., glass, carbon, basalt and steel, were applied with epoxy resins (wet lay-up system) to clay brick units, for a total of 280 monotonic tests. The results provided information regarding the response of externally bonded-to-brick composites in terms of observed failure mechanisms, load capacity, effective transfer length, and bond shear stress–slip behavior.

The 2009 L’Aquila earthquake and the 2011 Emilia earthquake caused widespread damage to the heritage masonry buildings showing the high vulnerability of the Italian historical monuments. In this context, the seismic vulnerability assessment is a relevant issue in order to preserve the historical identity of entire regions. In the present work the seismic vulnerability of a cultural heritage building has been investigated; the building is used as museum and it is located in the south of Italy. In particular, the seismic vulnerability of the Castle of Manfredonia has been analyzed. This study was conducted within a larger campaign (ARCUS) promoted by the Italian Heritage Ministry (MIBACT) in the entire Country. The main objective of this program consisted of individuating possible seismic fragilities in important heritage buildings used for public purposes. This would be the starting point for programming future interventions of strengthening and mitigation of the seismic vulnerability. The seismic assessment has been performed both in terms of local and global behaviour. The obtained results are reported and discussed in the paper; it can be emphasized, as the level of vulnerability is comparable when performing local and global analysis for the investigated case study.

The shear behaviour of masonry walls subjected to in-plane lateral forces is strongly dependent on the quality of the mortar used in the joints and on the strength of the blocks. In heritage buildings, where masonry was fabricated by using weak materials, collapse due to sliding forces acting along the loaded diagonals of the walls, following the joints directions, are frequent during earthquakes. This typical vulnerability of URM walls in historical buildings can be mitigated by using new strengthening techniques that result simply and quick to be applied, if compared with traditional techniques or with epoxy-bonded FRP sheets (Fiber Reinforced Pol-ymers). Different innovative strengthening techniques based on the use of Fiber Reinforced Mortars (FRM) were studied and compared in the paper. Different types of fibrous grids were grouted to the wall surfaces by using cementitious or non-cementitious mortars. Totally thirty unstrengthened and FRM-strengthened half scale masonry walls were tested until failure by using a shear-diagonal test set-up. Results of the diagonal shear tests revealed the effectiveness of the strengthening systems, that contributed to increase the ultimate load and at the same have helped to establish a dissipative behaviour. This pseudo-ductility was due to diffuse cracking of the mortar that developed after the peak load. High load levels were maintained during the pro-gress of the cracks that extended well beyond the initial compressed strut. Conclusions will illustrate how the mechanical properties of the URM walls subjected to diagonal shear can be upgraded through the use of the tested strengthening systems.

The environmental damage caused by improper management of waste tires increased over the past years creating a relevant problem to be solved. In the field of civil engineering results possible to re-utilize the steel fiber and the rubber of the waste tires. In particular the concrete obtained by adding recycled steel fibers shows a good mechanical improvement of the brittle matrix, as a consequence it appears to be a promising candidate for both structural and non-structural applications. In the present experimental work, as a continuation of the research already performed in this field by the authors, the post-cracking performances of RFRC (Recycled Fiber Reinforced Concrete) were evaluated by means tests on flexural elements and slabs. The effectiveness of the recycled fibers was evaluated in comparison with the experimental data obtained for specimens realized with IFRC (Industrial Fiber Reinforced Concrete). All fresh and hardened proprieties of concrete mixes were experimentally estimated. The post-cracking behavior of the RSFRC, obtained by flexural tests, was comparable with that of ISFRC. RSFRC specimens showed good energy absorption and good residual strength after cracking. However, technological issues related to fibers production and concrete mixes preparation, must be still investigated and a wider research is still required to validate the interesting founds.

Calcium sulphoaluminate (CSA) cement became progressively more used in recent years, considering both the mechanical per-formance and the environmental aspects linked to the CO2 manufacturing emissions lower than ordinary Portland cement (OPC). In this study, the mechanical behavior of steel-reinforced concrete beams made using various binders, such as pure CSA or blends with OPC was investigated experimentally, in terms of flexural resistance, crack pattern (number, length and crack width). For this purpose, a mechanical characterization of the various concrete mixtures at early and later ages was performed. Moreover, an ad-hoc experimental set-up was designed in order to study the durability of structural beams for different concrete types, under specif-ic environmental and service conditions. The results showed a satisfactory behavior of the CSA mixtures when compared with the OPC reference mixture in terms of early age resistance, mechanical performance and crack evolution during the time.

The need to guarantee higher safety levels of masonry structures under both short and long term conditions, have led to the use of new materials and technologies, in conjunction or in place of traditional ones. In this context, fiber-reinforced composite materials have gained an increasing success, mostly for strengthening, retrofitting and repair existing structures. As well known, the analysis of the interface performance of FRP (Fiber Reinforced Polymer) composites and masonry substrate is a critical problem as it influences the effectiveness of the technique. The present paper reports part of a large research project, still in progress, focused on the analysis of the bond performance between FRP sheet and different type of masonry substrates. The obtained experimental data were analysed in terms of bond strength and the kind of failure. The influence of the deformability of the strengthening material as well as the mechanical performance of the substrates are also discussed.

The paper deals with the structural response of mechanically fastened fiber-reinforced laminated thermoplastic composite joints. An experimental investigation was carried out to analyze the behavior of single-pinned joints made with woven glass-reinforced polypropylene composite laminates. A detailed experimental analysis was performed in order to predict the bearing response, failure strength, and failure mode of composite laminates containing a pin-loaded hole. The results obtained allow one to evaluate the influence of geometric parameters and the stacking sequence of laminates on the behavior of such joints.

Technological development in recent years has allowed the use of smart materials in civil engineering, as the Shape Memory Alloys (SMA). These materials change their physical and mechanical properties to changing environmental conditions. At this moment, the SMA are smart materials that can better exploited in civil engineering; their main properties are the superelasticity and shape memory. In the present study, where the SMA are used as active system, the effectiveness of the external reinforcement with FRP and SMA bending concrete elements is evaluated at the ultimate and service conditions.

Nella progettazione antisismica, la stima della rigidezza effettiva degli elementi in calcestruzzo armato (c.a.) gioca un ruolo determinante quando si adottano metodi di analisi lineare. Il presente studio vuole evidenziare come le NTC08 e l'EC8 non tengano conto di tutti i parametri che influenzano la determinazione della rigidezza effettiva ed in taluni casi possono risultare non conservativi, specialmente nei telai in cui l’effetto P-Δ può divenire significativo. Il presente studio mira ad investigare l'influenza dei fattori essenziali per il calcolo della rigidezza effettiva di telai in c.a. soggetti ad azioni sismiche. A tal fine sono stati esaminati cinque differenti approcci tratti dalla letteratura scientifica e da norme internazionali di progettazione. Si è fatto riferimento ad un edificio reale in c.a. per il quale è stata studiata e discussa l’importanza delle seguenti varabili: quantità di armatura longitudinale, entità del carico assiale applicato, resistenza a compressione del calcestruzzo e tipologia di trave (travi a spessore di solaio e travi alte). Sono stati poi valutati gli eventuali effetti del secondo ordine in termini di spostamenti di piano risultanti da analisi eseguite allo Stato Limite di Danno per azioni sismiche. I risultati delle analisi portano a concludere che la rigidezza effettiva è particolarmente sensibile al rapporto geometrico di armatura. Inoltre, il valore limite inferiore secondo NTC08 e EC8, pari al 50% della rigidezza integrale, risulta essere piuttosto un valore superiore per i casi di basso rapporto di carico assiale. Infine, si mostrerà che in alcuni casi le due normative tendono a sottostimare gli effetti del secondo ordine nell’analisi sismica allo Stato Limite di Danno.