The structural analysis of six circular steel silos 12,75 m high with 9 m diameter, used for wheat storage in an industrial plant of southern Italy, was conducted due to an uncontrolled hoop strain, shown by the silos in correspondence with the walls of the lower regions after twenty years of service conditions. Analytical results were obtained in three steps, a simplified model based on the elastic theory of tanks was constructed using a cylindrical shell. However, the solutions resulted in insufficient accuracy due to the lack of accurate hypothesis. Subsequently, the theory of Janssen was applied in accordance to the Eurocode equations given for the design of steel silos. The presence of three CFRP (Carbon Fibre Reinforced Polymer) external rings were tensioned and modelled in order to apply an active external confining stress. A numerical finite element analysis (FEA) was also pursued and analytical results were found to be in good accordance with each other. The effectiveness of the design strategy (external confinement) was confirmed by the theoretical analysis. The application is then presented, three CFRP pultruded plates were placed as external “belts” and post-tensioned along the perimeter of the silos by using a simple dedicated device.

Many areas of Europe, especially Italy, Greece, Slovenia and other Balkan States, are generally associated with earthquakes. In the last two decades Fiber-reinforced polymers (FRP) have gained an increasing interest, mostly for upgrading, retrofitting and repair of masonry and timber structures belonging to the architectural heritage. Recent researches demonstrated that masonry constructions or single structural elements are likely to be effectively repaired or enhanced in their mechanical properties using FRPs. The objective of the research presented in this paper is to study the long-term behavior of composite grids, made of E-CR glass fibers and epoxy-vinylester resin, subjected to harsh environmental factors including fatigue loading and ageing in aqueous solution. The paper presents new original test results on the relationship between the durability and the governing material properties of GFRP (Glass Fiber Reinforced Polymers) grids in terms of tensile strength and axial strains, using specimens cut off from GFRP grids before and after ageing in aqueous solution. The tensile strength of a GFRP grid was measured after conditioning in alkaline bath made by deionized water and Ca(OH)2 solution. The reduction in terms of tensile strength and Young’s modulus of elasticity compared to unaged specimens is illustrated and discussed. This degradation indicated that extended service in alkaline environment under fatigue loads may produce reductions in the GFRP mechanical properties which should be considered in design.

Nowadays, Fiber Reinforced Polymers are extensively applied in the field of civil engineering due to their advantageous proprieties such as high strength-to-weight ratio and high corrosion resistance in aggressive environments. It is well-known that the compressive strength of concrete significantly increases if a lateral confining pressure is provided. The present paper aims to present an analytical model, able to predict the strength of FRP-confined concrete, which is based on Artificial Neural Networks. The innovation of the proposed model consists of a formulation of an analytical relationship that does not consider the traditional effectiveness parameter commonly found in the models presented in the literature. An extensive experimental database was used to define the variables of the proposed equations. The proposed model is recommended for circular columns with continuous FRP wrapping. The validity of the predictions is indicated through a parametric study and the accuracy is tested by an experimental versus theoretical comparison. An additional comparison is shown by considering the theoretical predictions obtained from the proposed model and the outcomes of equations adopted by important international design codes. The results evidence that the proposed model is adapt for the design of FRP-confined concrete and guarantees an improved accuracy with respect the available competitors.

It is well known that fibers are effective in modifying the cracking pattern development of concrete structural element, causing an higher number of cracks and, consequently, lower crack spacing values and narrower crack widths compared to the matrix alone. This effect could be exploited to improve durability of Reinforced Concrete (RC) structures, especially of those exposed to aggressive environments. The analytical prediction of crack width and spacing in Fiber Reinforced Concrete (FRC) structural elements in bending is still an open issue. A crack width relationship for RC elements with fibers similar to those developed for classical RC structural members would be desirable for designers. The recent development of important technical design codes, such as RILEM TC 162 TDF and the new MC2010, embrace this idea. However further validation of these models by experimental results are still needed. On the other hand, the study of the influence of a sustained load on crack width in presence of the fiber reinforcement is a topic almost unexplored and important at the same time. In the present work, the cracking behaviour of full-scale concrete beams reinforced with both traditional steel bars and short fibers has been analyzed under short and long term flexural loading. A theoretical prediction of crack width and crack spacing was carried out according to different international design provisions. The analytical results are discussed and compared in order to highlight the differences between the models and to check the reliability of the theoretical predictions on the basis of the experimental data.

In the future Fiber Reinforced Polymer (FRP) materials will be considered a common strengthening system for civil structures thanks to several research efforts made in the last decades. For those applications in which FRP materials show some restrictions such as, above all, the incompatibility with heritage buildings, a new generation of fibrous materials has been developed. Researchers have investigated Fiber Reinforced Mortars (FRM) as external structural and seismic reinforcement. One of the most attractive applications of these materials is related to the in-plane shear strength of masonry walls. In this scenario, an analytical model based on Artificial Neural Network (ANN) is proposed and discussed in respect of the geometrical and mechanical variables that control the mechanical problem. An ANN is presented in the paper by showing its possible productive application in the civil engineering field. The proposed model seems able to predict the shear strength of FRM strengthened masonry; the approach is considered efficient since it includes both a theoretical method and a large test calibration, illustrated herein. Thanks to a quite small input database of laboratory results, ANN seems able to provide a theoretical solution to the problem with accuracy and precision.

The flexural capacity of reinforced concrete (RC) beams can be increased by applying carbon fibre reinforced polymers (CFRP) in the form of fabric or laminates. Concrete elements strengthened with bonded FRP systems are often showing a brittle failure mode with premature delamination of the FRP ply at the concrete-FRP interface. This can be quite catastrophic and is undesirable since it does not allow exploiting the FRP mechanical properties to be fully utilized. The failure is often brittle. It has been was demonstrated that the use of anchoring systems (i.e., U-wrap or anchor spikes) are effective in order to raise the ultimate load; failure of the beam remains essentially brittle with a substantial drop of the load after the peak. This paper basically focuses on flexural strengthening with pre-cured FRP laminates applied on RC beams with different anchoring devices chemically and mechanically applied. One beam was maintained as un-strengthened control sample. Two beams were strengthened using CFRP pre-cured laminates: for one of them, glass fibre anchor spikes were applied, the other was kept without anchoring. Two other beams were strengthened using hybrid pre-cured laminates having high longitudinal bearing strength: the laminate was bonded on one beam (steel anchors were also used to prevent/delay peeling) while was mechanically fastened (MF system) to the other one. The results showed that the ultimate load of the strengthened beams was 35-80% higher than the control beam, depending of the type of strengthening system applied. The lower value corresponds to the beam strengthened using CFRP without anchor spikes, whose use increased the ultimate load of about 14%. The best performance of the strengthening was obtained for the beams strengthened with the hybrid laminates: steel anchors reduced the load drop after the peak while, in the case of hybrid system and mechanically fastened CFRP, the use of the MF system resulted in a pseudo-ductile mode of failure. The experimental results were compared with analytical results obtained from the application of recently developed guidelines, that were published by the Italian Research Council (CNR). It is shown that design equations, even if material safety coefficients are disregarded, resulted conservative in both cases of unanchored and anchored FRP plate.

In this work Ultrasonic Pulse Velocity (UPV), Schmidt Hammer Rebound (SHR) test and strength assessment on microcores (UCSm) and standard cubic samples (UCSc) were used to detect the uniaxial compressive strength of stone masonry units. The analysis of the variability of the measurements allowed to investigate the significance of each test to differentiate the masonry blocks. The latter was evaluated by a Variability Index (VI), as the ratio between the variances at block scale and among the blocks. VI was found higher for UCSc and UPV than for UCSm and SHR measurements. A regression analysis aimed to the correlation of uniaxial compressive strengths evaluated by conventional destructive test on stone cubes with the other test results. The findings showed a good linear correlation among UCSc and UPV values (R2 = 0.83), thus supporting the reliability of UPV to screen the masonry units and to estimate their uniaxial compressive strength. The correlation of UCSc with UCSm was reasonable (R2 = 0.76), while it was low with SHR results; some limits related to the use of SHR and UCSm tests are also discussed.

The current design codes and technical recommendations often provide rough indications for the assessment of the effective stiffness in R/C frames subjected to seismic loads, which is a key factor when a linear analysis is performed. The Italian design code (NTC-08), the Eurocode 8 and ACI 318 do not take into account all the structural parameters affecting the effective stiffness, something that may not be on the safe side when second-order effects P-Δ occur, or when incorrect distributions of the internal forces are obtained. In this paper the factors influencing the effective stiffness of R/C beams, columns and walls under seismic forces are analyzed. Five different approaches are adopted in order to evaluate the effective stiffness of R/C members, in accordance with the scientific literature and the international design codes. A parametric analysis is performed on an actual R/C building and its results are presented and discussed, as a contribute to the improvement of design practice. The main variables considered in the analysis are: the reinforcement ratio, the ratio of the axial load, the compressive strength of the concrete, and the type of the shallow beams (ordinary or wide beams). The second-order effects are quantified and the resulting displacements related to the Damage Limit State (DLS) under seismic loads are discussed. The analytical results show that, although the effective stiffness increases with the steel ratio, the limit of 50% of the initial stiffness turns out to be an upper bound for small values of the axial-load ratio, rather than a lower bound as indicated by both the Italian Design Code and EC-8. 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.

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

Nello studio presentato sono riportati i risultati di una indagine sperimentale di durabilità su provini in calcestruzzo confinati mediante fibre di vetro E-glass in matrice epossidica (GFRP). In totale sono stati fasciati con tecnica manuale (wet lay-up) trentadue cilindri in calcestruzzo mediante un materiali composito unidirezionale, i quali sono stati sottoposti a cicli gelo-disgelo, immersione in acqua, immersione in ambiente salino, acido e alcalino. Lo studio ha riguardato anche le proprietà della resina epossidica impiegata come matrice, per la quale sono state simulate diverse temperature di cura (applicazione del composito) al fine di misurare eventuali variazioni nelle proprietà di diffusione di fluidi all’interno della stessa e nella temperatura di transizione vetrosa. I risultati ottenuti sul sistema strutturale hanno evidenziato importanti implicazioni che hanno messo in luce il grado di sensibilità ai diversi agenti aggressivi.

I recenti eventi sismici avvenuti sul territorio nazionale hanno evidenziato la vulnerabilità delle coperture voltate in presenza di azioni orizzontali. Le normative di recente concezione evidenziano che la deformabilità ed il grado di connessione degli orizzontamenti curvi deve essere adeguatamente considerato poiché in funzione di tali prerogative si può attivare una modalità di risposta che interessa più maschi murari piuttosto che i meccanismi locali. Nel presente lavoro, allo scopo di mettere in conto il contributo degli impalcati voltati nell’analisi di strutture in muratura soggette ad azioni sismiche, si simula il comportamento delle volte con quello di un elemento piano ortotropo avente la medesima luce e stesso spessore della volta originaria ma con moduli elastici ridotti Ex, Ey, Gxy, valutati in funzione delle proprietà geometriche e meccaniche della copertura, prescindendo dal dall’eventuale contributo del riempimento. La semplificazione dell’impalcato curvo in elemento piano è svolta considerando l’influenza di numerosi parametri: luce e spessore della volta, tipologia, presenza di pareti laterali e condizione di vincolo. I dati dei moduli elastici equivalenti ottenuti per la volta a botte sono stati utilizzati per un caso di studio relativo ad un edificio sito nel comune di Lecce, denominato “Masseria Tagliatelle”, di origini cinquecentesche. L’edificio, fortemente irregolare, è stato modellato attraverso l’approccio del telaio equivalente. Al termine delle simulazioni numeriche, svolte sul modello semplificato e sul modello reale, sono stati confrontati e discussi i risultati in termini di periodi, masse partecipanti e caratteristiche della sollecitazione.

As well known the confinement is an effective intervention for increasing the compressive strength of an axially loaded column. During the decades, different materials have been adopted in order to provide confining action, such as steel, reinforced concrete and latest high-performance fibers. Fibers application resulted a powerful solution mainly because of the high ratio between mechanical properties and weight and the absence of electrochemical corrosion. On the other hand, fiber needs to be impregnated with a matrix in order to be applied around the column and to exert an effective confining pressure. Polymers manifest excellent performance in this role, but unfavorable result if breathability of the structural element is a key-issue as well as reversibility and compatibility of the new materials with the existing substrates (e.g. in historical masonry construction). In this scenario, the interest in non-polymeric matrix has been increased in the last years, as the use of a cement/lime based mortar. In the present paper, a state-of-art regarding experimental programs on concrete and masonry samples confined by Fiber Reinforced Mortar (FRM) and subjected to pure compressive test is preliminary reported. Therefore, a multiple linear regression analysis was implemented in order to identify the possible influence of the interaction between the properties of the matrix and those of the fibers on the effectiveness of the confining pressure. Two new analytical formulations were assessed and discussed in the present study (the first related to concrete and the second related to masonry columns), evidencing the importance of taking into account the characteristics of the confining mortar besides those of fibers. A deep comparison (experimental vs. predicted) of the proposed formulae with Design-Oriented-Models (DOM) from the literature was also provided in terms of accuracy, precision and correlation. Finally, simplified relationships are also furnished and addressed to a possible contribution for design guidelines on the topic.

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

Crack formation within concrete members undergoing flexural loading is a complex mechanism, which governs the serviceability and durability of concrete structures. As for reinforced concrete (RC) members, a number of works based on empirical or theoretical approaches are published in the scientific literature. All the models propose a formulation for the estimation of crack spacing and crack width taking into account several parameters. Mechanical properties of concrete matrix, reinforcement ratio, concrete cover, bar diameter and size effect are the most influencing parameters on the cracking pattern of RC members, while tension stiffening can be influential as well. In Fiber Reinforced Concrete (FRC) elements the presence of short fibers modifies the crack pattern within the members due to the development of a residual tensile stress and greater toughness. Normally the number of cracks within the length of FRC members is higher while the mean crack spacing and the crack width are lower. In fact the crack bridging effect of fibers consists in post-cracking stresses at the between the crack faces. Such mechanism is mainly governed by the interface bond between fiber and concrete matrix. Therefore, the volume fraction and the geometrical properties of fibers strongly influence the overall contribution in the cracking phenomena. A limited number of design codes have taken into account the modified behaviour of FRC members (especially in the case of steel fibers) by providing specific equatios for crack width. This work presents the results of an experimental campaign on RC beams subjected to sustained service loads and environmental exposure for 72 months. In some beams, short steel or polyester fibers were added to the concrete matrix. The results presented in the paper show that the addition of fibres in concrete reduces both flexural displacements and crack widths, by modifying also the long-term behaviour of FRC members.

It is well known that the durability of concrete is intimately related to its permeability; moreover the presence of cracks significantly increases the ability of aggressive agents to penetrate into concrete, accelerating the deterioration process. Short fibers, embedded into concrete, may improve matrix durability: in fact, fibers influence crack development by causing more distributed cracks with smaller widths. This paper presents the first results of a wider experimental research, aimed at studying the durability of FRC beams exposed to marine environment under service load. In particular, accurate measurements of crack spacing, crack width and crack height are reported as the first step in the analysis of the influence of fibers on durability of full scale structural members.

The extensive research activity carried out over the last decades on fibrereinforced concrete (FRC) has shown that such material has enhanced mechanical and durability properties compared to plain concretes. The presence of short fibres in the concrete mass allows to control cracking and have moderate time-dependent effects. Compared to plain concrete, FRC flexural members show a higher number of cracks with reduced mean width. The experimental study presented herein discusses the mechanical behavior of FRC flexural beams subjected to sustained service load and environmental exposure for 72 months. The effects of different short fibers (polyester and steel), sustained loading and aging were investigated. A comparison with the results of a previous research is shown, with reference to the same kind of beams exposed for 17 months under the same conditions. The results show the beneficial effects of the fibers in terms of reduced crack width and increased flexural stiffness. The mechanical tests also highlighted how the presence of short structural fibers could play an effective role in mitigating creep effects in the concrete elements.

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.

Corrosion of steel reinforcement is one of the principal causes of deterioration in concrete structures. Corrosion mechanisms are accelerated by the presence of cracks which represent a preferable way for ingress of water and aggressive agents. Fibers embedded into concrete matrix generally reduce the crack widths of ordinary reinforced concrete structural elements and hence may improve durability of reinforced concrete structures especially of those exposed to aggressive environments. To date quantitative results on the effect of fibers on durability of cracked RC members under service loads is still lacking in the literature. The present research aims at studying the influence of fibers on durability of ordinary reinforced beams exposed in a coastal area under sustained load. Durability tests were performed in order to assess the influence of the presence of fibers on carbonation depth and chloride content.

Confinement of reinforced concrete (RC) columns by using fibre-reinforced polymer (FRP) composites is commonly used as a modern strengthening technique. The high mechanical properties of the fibres, the light weight and low installation costs of FRP composites have contributed to making them a successful solution for column confinement. Although previous studies have demonstrated the high performance of FRP systems bonded to concrete elements, several concerns are related to the long-term behaviour of wrapped columns, which had limited implementation in terms of results and guidelines. Environmental effects, such as freeze-thaw cycles, wet-dry cycles, ultra violet (UV) radiations exposure, high temperatures and de-icing salts, may affect the material properties and the structural response of the wrapped elements. In this paper an experimental work is presented in order to study the long-term behaviour of Glass FRP-confined columns. A commercial GFRP system was used to wrap thirty-two small-scale concrete cylinders that were subjected to extreme conditions such as freeze-thaw cycles, immersion in water and saline solution, immersion in alkaline or HCl solutions. Epoxy adhesives, cured at four different temperatures, used for FRP bonding, were also studied after immersion in water, diffusion properties were measured after different times of exposure, also changes in glass transition temperature were monitored by using a differential scanning calorimeter. Changes in mechanical and physical properties of FRP-confined cylinders and adhesives are discussed herein.

Fiber Reinforced Concrete (FRC) is a material obtained by adding fibers to the concrete matrix. Fibers resist the crack opening and develop tensile residual strength. The extensive research activity carried out over the last decades on FRC has shown that such material has enhanced mechanical and durability properties as compared to plain concretes (PC) due to the cracking control. In fact, FRC flexural members show a higher number of cracks with reduced width; this occurrence involves an improved mechanical behaviour mostly under service conditions and a higher durability due to the reduced attacks of aggressive agents and to the more controlled effect of long terms phenomena. The experimental study presented herein discusses the long-term behaviour of FRC flexural beams subjected to sustained service load and environmental exposure up to 72 months. The effects of different short fibers (polyester and steel), sustained loading and aging were investigated. The results show the beneficial effects of fibers in terms of reduced crack width and increased flexural stiffness. The experimental data on cracking behaviour are finally compared with the analytical predictions obtained according to the formulation provided by 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.

In this study the results of a large test program are presented with the objective of examining the effect of various experimental parameters on the confinement effectiveness of FRP jackets on both circular and rectangular concrete columns with solid or hollow core. The experimental parameters include: different concrete strength, type of fibres, number ofwrap layers, geometry of the column, corners radius, full/hollow core and cross-sectional aspect ratio (only for prismatic elements). FRP-confined and unconfined specimens have been loaded in uniaxial compression until failure. Totally 128 specimens were prepared and tested, 89 of them were strengthened with Carbon FRP (CFRP) and Glass FRP (GFRP), the remaining 39 were tested as plain concrete reference. Compressive stress, axial and hoop strains have been measured to evaluate the stress–strain relationships, ultimate strength, stiffness, and ductility of the specimens. Results confirmed that external confinement produced by FRP can significantly enhance compressive strength, ductility and energy absorption capacity if compared to those of plain concrete. The effects of test parameters are evidenced and compared in order to show the sensitiveness of the mechanical problem for each of them. Important design information are furnished to researchers and practitioners also by comparing the results of the experimental campaign with the prediction of different analytical models, based on well-known and widely accepted mechanical assumptions. Design equation recommended by CNR (Italian National Research Council) were also applied by assuming unitary values for safety factors, in order to see the reliability of the mechanical model proposed by CNR

Fabric Reinforced Cementitious Matrix (FRCM) materials are composed of a dry fiber grid embedded in an inorganic matrix, which may contain short fibers. These materials are particularly well-suited for the reinforcement of masonry structures due to their high compatibility with the substrate, vapor permeability and durability against environmental agents. The most important information needed for the characterization of these composite systems, for use as strengthening materials of masonry structures, are the tensile behaviour and the shear bond properties. A Round-Robin Test was organized by the RILEM Technical Committee 250-CSM and the Italian association Assocompositi in order to experimentally characterize different FRCM systems composed of PBO, carbon, glass, basalt, aramid and steel textiles embedded in cementitious or lime-based mortars. The systems were tested at different universities and research centers in Europe in order to investigate the influence of samples preparation, test set-up and instrumentation. In this paper, the experimental tests performed on Carbon-FRCM systems are described and discussed. Important aspects are analyzed herein: differences in the testing procedure and instrumentation, influence of textile geometry and mechanical properties of the constituent materials, importance of specimen preparation and curing conditions. Moreover, a comparison between tensile and shear tests is reported in order to determine a reliable procedure towards the complete characterization of an FRCM material

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 results of an experimental program performed on full-scale masonry columns strengthened with different composite systems are provided in the present paper. The same kind of study has been previously performed by the authors on medium scale masonry columns, using the same materials for both the masonry core and for the FRP systems. Masonry was formed by prismatic block of calcareous stone and joints were made by using a lime/pozzolan based-mortar, with a thickness of 10 mm. The experimental program involved six full scale masonry columns with a square cross section having a side length of 40 cm, and 210 cm height. The following test schemes were studied: control unconfined columns; column with continuous wrapping by using unidirectional Glass FRP (GFRP) sheets; column with discontinuous wrapping by using GFRP unidirectional sheets; column with continuous GFRP wrapping and internal carbon FRP (CFRP) bars bonded in the transverse directions with an epoxy resin; column wrapped with continuous alkali resistant GFRP grid and steel spikes bonded together in lime based matrix. The experimental results are presented and discussed in the paper; failure modes, strength and ductility are discussed by comparing the different strengthening techniques that were tested. The results confirmed that FRP-confinement may be considered an effective technique able to increase the load-carrying capacity and at the same time the axial deformability of the compressed columns. A ductile behaviour was observed in confined columns as also expected from the previous results available for small and middle scale columns. A comparison between experimental data and theoretical predictions provided by the new analytical model found in the guidelines of the CNR-DT 200/2012 technical document is also illustrated.

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.

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.

Mechanical behaviour of fibre-reinforced concrete is influenced both by the properties of the fibres (geometry, aspect ratio, dosage) and the properties of the matrix (concrete grade, curing time, water-to-cement ratio). Many research studies have been published that focus on the influence of different kinds of fibres on the final properties of concrete. Against this the influence of the matrix grade on the mechanical properties of fibre-reinforced concrete is a topic that is almost unexplored. A mechanical characterisation of fibre-reinforced concrete in the hardened and fresh states is carried out, varying the concrete grade, the fibre dosage and the fibre type (steel and polyester). The results of the experimental research indicate the importance of the matrix grade on the bond between the steel fibre and the matrix and, consequently, on the mechanical performances of the composite material. Furthermore the concrete grade also influences the minimum volume fraction of polyester fibres affecting the matrix toughness.

The use of short fibers inside concrete matrix is an effective method for reducing the vulnerability of concrete constructions subjected to harsh environment. The action of the short fibers in reducing the crack opening is the main issue that needs a research effort in order to optimize the expected results. At the moment the analytical prediction of the crack width and spacing in Fiber Reinforced Concrete (FRC)structural elements under bending loads is still an open problem. A crack width relationship for FRC/RC elements similar to those developed for plain concrete structural members would be desirable for designers and engineers involved in the design of FRC structural elements. The recent development of important technical design codes, such as RILEM TC 162 TDF and the new Model Code (MC) 2010, embrace this idea. However further validation of these models by experimental resultsis still needed. On the other hand the study of the influence of a sustained load on crack width in presence of a short fibers reinforcement is a topic almost unexplored and important at the same time. In this research the cracking behaviour of full-scale concrete beams reinforced with both traditional steel bars and short fibers has been analyzed under short and long term bending condition. A theoretical prediction of crack width and crack spacing was carried out according to international design provisions based on different analytical models.The theoreticalresults are discussed and compared in order to highlight the differences between the available models and to check the reliability of the theoretical predictions on the basis of the experimental data.A modified relationship to take into account of the presence of stirrups has been proposed on the basis of experimental results; furthermore, some critical aspects, such as the influence of the type of fibers and the effect of loading-time, have been underlined that should be addressed in future research work.

Many of the properties of Fiber Reinforced Concrete (FRC) may be used to improve the structural response, under service conditions, of conventional concrete beams reinforced with steel bars (RC members). It is well known that fibers embedded into concrete matrix, enhance its ductility and toughness, increase its tensile strength acting as crack arrestors. In particular, fibers are effective in modifying crack propagation causing an higher number of cracks having a lower crack spacing values and narrower crack widths compared to the plain matrix. This effect could be exploited to improve durability of reinforced concrete structures, especially in those buildings exposed to aggressive environments. Few results are present in the literature on durability of full scale FRC structural element. A quantitative correlation between the effect of fibers in reducing crack widths, and deterioration of RC members exposed to aggressive agents, is still lacking in the literature. Furthermore, the effect of fibers on cracking has generally been studied considering short term loading test; thus few data are available on cracking behaviour of FRC members under sustained loading. In the present research, the influence of steel and polymeric fibers on durability of plain reinforced concrete beams has been investigated. In particular, beams with and without fibers have been exposed for 17 months to natural weathering, in a coastal zone close to industrial plants, under a sustained flexural load in a three point bending scheme. The influence of sustained loading on the cracking behaviour and consequently on durability of the beams, with and without fibers, has been analyzed. After the exposure period, the beams have been tested in laboratory up to failure and their mechanical and cracking behavior has been studied. Durability tests have been conducted on crashed beams to evaluate carbonation depths and chlorides contents after the exposure period.

The present paper is aimed at assessing analytical formulations and calibrating an accurate and reliable design formula for FRP-confined masonry columns. After a short introduction about the key issues regarding the confinement of masonry columns by means of composite wrapping, a wide experimental database is assembled in a second section of the paper. Such a database has been obtained by merging the test results presented by the authors in a companion paper with other ones available in the scientific literature. The content of the database, the nature of the specimens and the range of variation of the relevant parameters are reported in the paper. The most well-established analytical formulae for FRP-confined concrete members are summarised in the third section of the paper; their effectiveness when applied to confined masonry elements is investigated on the basis of the collected database. The very limited number of models currently available for masonry members are also reported and discussed; they generally result in inaccurate and non-conservative predictions, as they have been commonly calibrated on experimental results carried out on specific types of masonry. Finally, a general expression for a design-oriented formula is calibrated with respect to the above-mentioned experimental database. As a matter of principle, different levels of accuracy can be achieved in calibrating such an expression, depending on the number of parameters considered in its calibration: the higher the number of such parameters, the lower the expected residual error of the resulting formula. Thus, three different proposals of design formulae for FRP-confined masonry columns are reported and commented with the aim of describing their accuracy in terms of scatter, average error and distribution of the experimental-to-theoretical ratios.

The mechanical behaviour of masonry columns having a circular cross section, confined with glass and basalt FRP systems was studied in this paper. An extended experimental investigation is presented in order to show the results of axial compression tests on circular masonry columns built with natural calcareous blocks that may be commonly found in Italy and all over Europe in historical buildings. Totally twenty masonry columns were built, instrumented and tested. Different fibres were used including glass and basalt (sheets and grids), different strengthening schemes were applied for confinement of the columns, including complete jacketing and discontinuous FRP strips, different bonding agents were employed including epoxy resin and polymer/cement-based mortar. In four GFRP-confined columns the strengthening action was activated by the presence of Shape Memory Alloys (SMA) filaments immersed in the FRP system. This novel technique is also presented in the paper.

The present paper deals with the mechanical behaviour of masonry columns confined by means of fiber reinforced (FRP) composites. In particular, it presents the key results of a wide experimental work carried out in the Laboratories of the Universities of Salerno and Salento (Italy). Several kinds of masonry, made out of either natural or artificial bricks and characterized by different dimensions, have been considered in this experimental program. A total number of 54 specimens have been realized and tested in pure compression. Moreover, several composite systems (mainly based on glass fibers) have been utilized for confining those specimens in a variable number of layers with the objective of developing different levels of lateral pressure. The present paper reports the complete information about the geometric and mechanical parameters characterizing the tested specimens as well as the key aspects of the structural behaviour observed during the compression tests. In particular, the maximum load levels and the (average) corresponding axial stresses and strains are clearly derived. Finally, some behavioural observations drawn out by the observed experimental performance of such specimens are pointed out for the various groups of specimens with the aim of pointing out the key differences in terms of structural response due to the various materials utilized for both masonry and external wrapping. Such observations will be quantitatively developed in a companion paper in which further tests available in the scientific literature will be assembled to the ones reported in the present one and a design formula will be formulated and calibrated.

The vulnerability of masonry constructions under seismic forces, or more generally under the mechanical actions during the centuries, has been highlighted in the last years by several events that caused the loss of significant heritage buildings. Faced with this difficulty, the use of composite materials, fiber reinforced polymers (FRP) may be a solution for mitigating the vulnerability of masonry buildings. This solution has been tested in the laboratory by researchers in the last decade. In particular, studies regarding elements such as walls, arches and vaults, strengthened with FRP materials are available. A few numbers of studies are known for columns, which have been tested only as small or middle scale samples. The current state of the art does not report studies on FRP-confined masonry columns tested in real scale. The research presents the results of an experimental program performed on full-scale masonry columns strengthened with different composite systems. The same kind of study had been previously performed by the authors on medium scale masonry columns, using the same materials for both the masonry core and for the FRP system. Prismatic columns with a square cross section were subjected to compression tests according to the following test schemes: two control unconfined columns; column with continuous wrapping by using unidirectional glass FRP (GFRP) sheets; column with discontinuous wrapping by using GFRP unidirectional sheets; column with continuous GFRP wrapping and internal carbon FRP bars bonded in the transverse directions; column wrapped with continuous alkali resistant GFRP grid and steel spikes bonded together in lime based matrix. The experimental results are presented and discussed in the paper along with the comparison with the results obtained from the experimental tests on medium scale specimens. The comparison between experimental data and theoretical predictions provided by the analytical model found in the guidelines of the CNR technical document is also illustrated.

It is well known that fibers embedded in a cementitious matrix enhance its toughness, increase its performance in tension and act as crack arrestors. While the interaction between fibers and concrete, as well as their effect on cracking has been extensively investigated, the interaction between fibers and rebars in a R/C member is still open to investigation. In fact, a consolidated model to predict crack width in structural members embedding fibers can hardly be found in the literature; hence, further experimental efforts are needed to better understand the fiber-reinforcement interaction. Furthermore, the results found in the literature on Fiber-Reinforced Concrete mainly refer to steel fibers, while the effect of other fibers on concrete cracking and on R/C mechanics is a topic still requiring dedicated research efforts. In this research project, an experimental study on the effect that steel and polyester fibers have on the mechanical and cracking behavior of ordinary reinforced-concrete beams, is presented. The objective is to investigate the role that fiber amount, geometry and type have on the cracking behavior of the beams in terms of crack width and spacing.

In this paper, the use of ultrasonic pulse velocity (UPV) testing as a reliable technique to determine the compressive strength of a calcarenitic stone typical of Salento (South of Italy), known as Lecce Stone (LS) has been investigated. The scope of the experimental research is to establish correlations between the results obtained by non-destructive and destructive tests, in order to reduce the use of destructive methods within the diagnostic procedures for the mechanical analysis and qualification of ancient masonries. Furthermore, the presence of water as a variable affecting the test was investigated. The results of the tests show that the UPV values are well correlated with the compressive strengths and this method showed to be efficient in predicting the strength of LS.

In this paper, the use of ultrasonic pulse velocity (UPV) testing as a reliable technique to determine the compressive strength of a calcarenitic stone typical of Salento (South of Italy), known as Lecce Stone (LS) has been investigated. The scope of the experimental research is to establish correlations between the results obtained by non-destructive and destructive tests, in order to reduce the use of destructive methods within the diagnostic procedures for the mechanical analysis and qualification of ancient masonries. Furthermore, the presence of water as a variable affecting the test was investigated. The results of the tests show that the UPV values are well correlated with the compressive strengths and this method showed to be efficient in predicting the strength of LS.

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.

I danni osservati durante i passati terremoti hanno messo in evidenza l’elevata vulnerabilità del patrimonio edilizio italiano prevalentemente realizzato nel secondo dopoguerra. Attualmente sono disponibili in letteratura numerose metodologie di calcolo della vulnerabilità sismica di crescente livello di difficoltà. Le metodologie semplificate consentono di effettuare una mappatura su larga scala delle strutture maggiormente a rischio, mentre le metodologie più complesse, come l’analisi dinamica non lineare, vengono adottate per studi di dettaglio su strutture particolarmente a rischio o strutture sensibili di notevole importanza. Nel presente lavoro è stata analizzata la vulnerabilità sismica di un edificio scolastico realizzato negli anni ’70 con struttura portante in calcestruzzo armato. Il principale obiettivo dello studio è quello di valutare le differenze tra i risultati forniti da metodologie di calcolo semplificate e metodi di calcolo più accurati, cercando di mettere in luce le carenze fondamentali insite in metodi di calcolo semplificati tipicamente utilizzati nella comune pratica professionale.

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.

Among the strengthening techniques based on Fibre Reinforced Polymer (FRP) composites, the use of near-surface mounted (NSM) FRP reinforcement has recently become an attractive option for increasing flexural and shear strength of deficient reinforced concrete (RC) structural elements. In order to widen the existing test database, which is currently more limited than that related to externally bonded FRP laminates, this project investigated flexural strengthening by testing six 4.3-m long RC beams with 200x400 mm rectangular cross-section, of which two control and four strengthened beams. In the latter, carbon FRP (CFRP) round bars were embedded in grooves cut onto the bottom concrete surface and filled with a two-component, high-viscosity epoxy paste. The concrete compressive strength was very low (cylinder strength equal to 15 MPa), and all the beams were designed to fail by concrete crushing after yielding of the steel reinforcement. The incidence of debonding failures under these conditions could then be evaluated. The investigated variables were the ratio of internal steel reinforcement and the ratio of FRP superficial reinforcement. Experimental results are discussed in this paper, and their comparison with predictions of an analytical model is also presented.

The extensive research activity carried out in the last few decades on fibre-reinforced concrete is showing - beyond any doubt - that FRC has very interesting properties for structural applications. The dispersion of short fibres - made of steel, polymers, carbon, etc. - in the concrete mass brings in a 'crack bridging' effect, which prevents or delays cracking, and – at the same time – provides concrete with a ductile behaviour both in tension and in compression, given that relatively large amounts of stiff fibres are used (as for example in high-performance fibre- reinforced concretes - HPFRC). As a result, the use of such concretes significantly improves significantly the structural performance of R/C members, not only under static and fatigue loading, but also under dynamic and seismic loading. However, considering their higher costs and more complex technology, high-performance fibre-reinforced concretes are only suitable for critical areas of R/C beams and columns, as well as in the beam-column joints of R/C frames, where the actual Italian code (2008) may require an excessive amount of reinforcement, even in the design of low-ductility members. Within this context, this paper investigates the benefits of using high-performance fibre-reinforced concretes in the nodal and inelastic regions of R/C seismic-resistant plane frames are investigated in this paper, focusing on typical frames which are commonly found in residential buildings, with two-four bays and two-eight storeys. Ordinary mixes (C25/30 and C40/50) are adopted for frame members, while higher-performance fibre-reinforced mixes (FRC40/50 and FRC80/85) are used in critical areas and in the joints. The joint regions are modelled with or without rigid end-sections and in-plane stiffness of the floors is introduced as well. The frames are designed according to the actual Italian code (NTC08) and to EC8. In the nonlinear static analyses, considering either triangular or uniform load profiles, a diffused-plasticity model is adopted for frame members. In terms of global capacity and ductility, the use of HPFRC - instead of plain concrete – offers considerable benefits.

Fiber Reinforced Polymer (FRP) composites are widely used for strengthening and conservation of historic masonry, even if research problems are still open. The mechanical behavior of masonry columns having a circular cross section, confined with glass and basalt FRP systems was studied in this paper. An extended experimental investigation is presented in order to show the results of axial compression tests on circular masonry columns built with natural blocks (calcareous stone). Active confinement was also studied by using a novel technique that employs Shape Memory Alloys (SMA). Totally twenty-four masonry columns were built, instrumented and tested. Different fibers, strengthening schemes and matrix/adhesive were used for the confinement of the columns. Unstrengthened columns were tested as reference specimens. Axial strain of the columns and tensile strain of the fibers in the direction perpendicular to the primary axis of the columns were measured with the applied load. Experimental results revealed the effectiveness of the FRP-confinement for masonry columns. Active confinement was found to be effective at early loading stages since an increased stiffness of the SMA/GFRP-confined columns was measured. A prediction of the compressive strength was obtained by using the model of the Italian guidelines CNR DT 200 (National Research Council) in order to compare the experimental results with the design approach, also for new types of fiber like basalt which were not included in the technical codes. Finally, the experimental results were compared with theoretical values calculated according with to two existing analytical models in order to test their effectiveness for the analyzed configurations.

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.

Innovative materials such as Fiber Reinforced Polymer (FRP) have been widely used for the seismic upgrade and reparation for a couple of decades. This testifies the effectiveness of such techniques, especially when they apply to vulnerable masonry structures. In this study, the seismic upgrade of a large building, used as a theatre in the south of Italy, is illustrated. After a seismic analysis based on the study of the collapse mechanisms of the masonry walls, a strengthening program was individuated and successfully applied in-situ. The analysis was conducted with reference to the local mechanisms that can be activated by the seismic acceleration in the considered site. The kinematic analysis was performed as linear and non-linear. In the first case, the control parameter is represented by the minimum value of the seismic acceleration that can be supported by the excited sub-structure. When a non-linear analysis is implemented, the controlling parameter is the maximum displacement that guarantees the ultimate equilibrium configuration. It will be shown how the linear analysis may be more conservative with respect the non-linear one. Once the seismic vulnerability was quantified in terms of acceleration and displacement, an innovative strengthening system was designed. The seismic upgrade was evaluated by the comparison with respect the un-reinforced state of the construction. In order to avoid out of plain failure mechanisms, an active confinement was designed by using pre-tensioned carbon-aramid fiber wires, anchored trough steel plates to the masonry substrate. Four tensioned CFRP-AFRP (Carbon FRP – Aramid FRP) wires were placed along three sides of the building at different levels; each of them had a length of about 40 meters. The installation of the wires, the anchoring system and the tensioning procedure will be illustrated in the paper. The choice of composite materials allowed this type of innovative technique, by guaranteeing a high durability, speed of installation and safe operations in elevation. The conclusions will show how the designed strengthening technique is able to preserve the stability of the structure and improve its performance in case of seismic events, with no impact on the architectural aesthetics of the building. The intervention can also be considered removable according to the ISCARSAH’s recommendations

A deep knowledge of the physical and mechanical properties of the constituent materials of ancient masonries is of crucial importance in the choice of the proper intervention technique. In case of historical buildings sustainable diagnostic procedures responding to the conservation constraints, should have the lowest degree of intrusion and the fullest respect for their physical integrity. The sample’s extraction from existing structures for laboratory tests is one of the major problems in the field of diagnosis of ancient buildings and this has moved the scientific community to propose alternative non-destructive techniques to evaluate the mechanical and physical properties of the building stones. In the present work non-destructive and destructive tests have been investigated as tools for assessing the compressive strength of “Lecce stone”, a soft calcarenitic stone used as traditional building materials in the Southern Italy. Ultrasonic pulse velocity (UPV), Schmidt hammer test and compressive tests on microcores have been compared with mechanical destructive tests on cubes in order to found correlations between the results. The final aim is to assess the reliability of the non-destructive investigated methods in describing the mechanical performance of the stone, reducing the use of destructive analyses on masonries.

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.

Gli errori di natura progettuale ed esecutiva, che possono causare gravi insufficienze stati-che anche su strutture di recente costruzione, richiedono spesso interventi poco invasivi, risolutivi e durevoli al tempo stesso, visto l’elevato costo di dismissione e ricollocazione delle sovrastrutture. Quando le insufficienze statiche riguardano non solo requisiti di resi-stenza, bensì anche un recupero di rigidezza degli elementi inflessi, il problema richiede una particolare valutazione al fine di recuperare e salvaguardare i requisiti di stato limite di esercizio della costruzione. Nel caso in questione sarà descritto l’intervento di recupero e rinforzo strutturale attuato su un campo di impalcato di ca. 180 m2 posto al piano terra di un edificio a telaio in C.A. adibito a civili abitazioni, realizzato nel 2006, che sin dai primi anni di vita aveva manifestato dissesti statici nel solaio e fessurazioni nelle sovrastrutture, a causa di insufficienza nelle armature metalliche poste in opera. Il lavoro presentato riporta le fasi dello studio effettuato in sede progettuale, per il dimensionamento dei rinforzi, e in sede applicativa per l’attuazione degli stessi che è avvenuta dopo controllati sollevamenti dell'impalcato, al fine di conferire maggiore rigidezza al nuovo sistema strutturale. Sono riportati i risultati sperimentali relativi alle procedure di rinforzo e di controllo in fase di nuovo collaudo della struttura. L’esito raggiunto alla luce della problematica affrontata mostra come le tecniche innovative, ove opportunamente utilizzate, possano essere di notevole aiuto per il progettista in tutte quelle situazioni di rinforzo e riparazione locale così come riconosciute ai sensi di legge nel § 8.4.3 del D.M. 14/01/2008.

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.

According to most of current design standards, the need for high strength and ductility of reinforced concrete frame structures is accomplished utilizing a high amount of transverse reinforcement in beam–column joints. Reinforcement congestion can be overcome by means of Fiber Reinforced Concrete and High Performance Fiber Reinforced Concrete, which are known to improve the structural performance of single structural members or beam–column joints. Through an extended numerical simulation, this paper elaborates the overall benefits of using fiber reinforced concrete materials in critical regions to the seismic behaviour of regular reinforced concrete frame structures. An extensive number of non-linear static and dynamic analyses with distributed plasticity and fibre sections are performed to compare the behaviour of simple reinforced concrete and mixed reinforced concrete/fiber reinforced concrete frames in terms of total base shear and fragility curves and failure mechanisms. Even if execution and technological aspects are beyond the scope of the present work, the use of fiber reinforced concretes in critical regions of mixed frames seems to improve the structural performance of reinforced concrete frames at a global level.

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.

Although masonry is an extremely popular material in the building industry, it’s very weak in tension, as compared to its strength in compression. Smart pre-stressing of masonry with shape memory alloy is a promising solution to this limitation. The shape memory effect of SMA (Shape Memory Alloy) materials seems to be an innovative suitable solution for active strengthening of masonry structures. Strengthening masonry element with SMA wires and FRP (Fiber Reinforced Polymers) is possible in order to obtain permanent confining effect on the structural element even after the SMA activation. If pre-strained SMA wires are heated under constraint, actually, tensile stresses are produced in the wires, causing stress state on the surface of masonry element. Unconfined and passive confined masonry cylinders were tested for compressive strength and the results were compared to those of cylinders confined by SMA and FRP active confinement technique. This solution can improve the compressive strength and ductility of the columns due to the permanent confining effect of the SMA. Differently from others works, in the proposed concepts, the activation of SMA and the cross-linking of the matrix takes place simultaneously in order to achieve a final and durable effect. This work showed the potential of the proposed method to retrofit unreinforced masonry columns using SMA wires and FRP to protect them from earthquakes.

Over the past two decades, composite materials, in forms of Fiber Reinforced Polymers (FRP), have been widely spread worldwide in the field of civil and monumental construction. Design guidelines and provisions were developed and provided by national and international institutions. In the last years, a new generation of materials, named Fabric Reinforced Cementitious Matrix (FRCM) were introduced as strengthening devices for concrete and masonry structures. Their application in the field of historical masonry has grown as a result of the recent Italian earthquakes. In this paper, starting from a retrospective on what has been done in recent years in the field of FRP applications, insights will be discussed for future research and applications of FRP and FRCM in heritage buildings. Some differences between FRP and FRCM materials will be highlighted, in terms of fiber-matrix interface and delamination mechanisms. The different micromechanical behavior in terms of fracture energy will be highlighted, and the macro mechanical implications in terms of ductility will be pointed out, as a first attempt to quantify this complex problem. By considering the last innovative and pioneering applications of FRP/FRCM in heritage buildings, criteria for structural enhancement will be shown and discussed. This is done with a special focus on the ability, shown by these new technologies, to inhibit failure mechanisms in masonry artifacts.

According to the capacity design approach, reinforced concrete frame structures must have high ductility, which is achieved by adopting a high amount of transverse reinforcement in dissipative regions. The use of Fibre Reinforced Concrete (FRC) can solve the problem due to the development of significant residual tensile strength. To date, it is widely known that the use of FRC results in an improvement of the structural performance for elements subjected to gravitational and cyclic loads. Benefits can be achieved in terms of shear strength, ductility, cracking behaviour, energy dissipation, tolerance to damage and fatigue. However, the available studies on FRC and new HPFRC (High Performance Fibre Reinforced Concrete) focus on individual members only. This paper aims to investigate the overall effects of using FRC materials in dissipative regions of RC framed regular structures. To this scope, a numerical investigation is run to simulate the seismic behaviour of plane RC frames with or without FRC in inelastic zones and beam-column joints. The frames are analysed by means of non-linear static analysis with distributed plasticity and fibre sections. The behaviour of simple and mixed frames is compared in terms of capacity curves and, therefore, behaviour factor q. The variables taken into examination are investigated by means of statistical analysis (ANOVA and Tuckey test). Mainly the adoption of fibre reinforced concrete in dissipative zones of mixed frames proves an increase in the behaviour factor q compared to concrete frames ordinary

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.

In the research work presented herein a study of the cracking behavior of fiber reinforced concrete (FRC) beams is illustrated. The beams were tested in bending and were designed according to the guidelines of the National Research Council DT-204/2006, without stirrups in the constant moment region. This choice is due to the fact that consolidated experiences, reported in the literature, show how the presence of transverse steel reinforcement generates a localization of cracks. In the present study FRC with short steel and polyester fibers were investigated. The study was divided into three phases: 1) design of concrete-mix, 2) destructive tests on beams, and 3) analysis of results and analytical comparisons. Scientific investigations in the field of FRC provide information in order to develop an affordable design approach for FRC beams in bending, therefore this research work aims to provide an in-depth knowledge in the field. A comparison with the recent analytical models provided by the National Research Council and 2010 Model Code of CEB-FIB is shown and commented. The case study presented here shows the great importance of the beneficial role exercised by short fibers dispersed in the cement matrix in reducing cracking of reinforced concrete beams. In particular results obtained in absence of transverse reinforcement provide new original data. Stirrups are known to act as a region of discontinuity in the cement hardened paste, creating a cracking opening zone at the interface. Bending tests were performed on 10 beams (2 per concrete mix), deflection at quarter and mid-span were measured, the deformations in the compressed concrete and in the tensioned steel rebars were also measured in correspondence of the increasing applied load. In correspondence of five load levels the distance, the height and the width of the cracks was also measured over the whole length of the beams, with particular attention to the constant moment region. The steel fibers demonstrated to be more effective than respect to polyester fibers in terms of crack arrestors. The experimental data were also compared to the theoretical prediction obtained by applying the analytical models of CNR DT-204/2006 and Model Code 2010.

The ultrasonic pulse velocity (UPV) method can be conveniently used for non-destructive testing of physical–mechanical properties of the stones within historical masonry, as well as to check the state of damage and microcracking. Before to proceed with in situ measurements, it is important to assess the contribution that both intrinsic characteristics of the stones and external factors may give to the ultrasonic response. In this work the effect of different wave frequencies, sample geometry and application of a compression load on the response of a natural stone to UPV test has been investigated. An extensive experimental campaign in laboratory conditions was carried out on a soft limestone, used in the historical building heritage of the Southern Italy. A negligible UPV dispersion was found at the used frequencies of 1 MHz, 120 and 55 kHz when a compression load was not applied; the measured velocities were found to be influenced by the stone inhomogeneity rather than by the sample size. They showed a slight decrease and still negligible dispersion under load up to the visible damage. Dispersion increased with the cracking progression. This indicates that enhanced capability of UPV, in checking material quality and damage conditions, can be obtained by combining the use of different wave frequencies.

Nowadays, the employment of Fibre Reinforced Polymer (FRP) composites in civil engineering field has been successfully experienced. Different potential applications of solid concrete-filled FRP tubes are exploitable in marine piles, overhead sign structures, poles and posts, bridge columns and piers, girders, large pipes and tunnels (mainly circular cross-section). This technique is also used for the confinement of masonry columns, typically encountered in monuments and historical buildings (both rectangular and circular cross-section); hence the need of providing formulas for the design of an appropriate strengthening. Several analytical models are available in the scientific literature for assessing the increase of strength and ductility of concrete or stone solid elements externally confined with FRP or for hollow columns internally steal enclosed and externally FRP-confined but, there is still a lack of research about hollow columns only externally confined. The presence of an empty core implies a different stress state in the inner cylindrical surface with respect to the outer one. Inwards deformations are more significant and this behaviour is not taken into account by available models. The present study aims to illustrate a detailed summary of the existing analytical models and to provide a unified procedure for concrete and masonry hollow columns valid for both circular and square cross-sections. An iterative method that updates the geometrical parameters according to step-by-step uniaxial compressed column is shown in order to capture the real deforming behaviour of the compressed solid. This analytical approach has two important implications: the first is the ability of calculating the stress state of the column and of the external FRP reinforcement at each step; the second is that of theorizing a procedure, which is independent on the type of material used for the column. The outputs of the proposed method are then compared with experimental results currently available in the scientific literature. A good matching is obtained between the available experimental results and the analytical predictions in term of axial stress–strain curves.

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.