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

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

In the present paper the experimental results, recently obtained by the authors, regarding the monotonic and the cyclic flexural response of normal and high-strength concrete beams reinforced with steel bars and discontinuous fibers, are shown. From the experimental results, all referred to low values of shear-to-depth ratios, it emerges clearly that the shear failure is brittle especially under cyclic actions highlighting the role of the fibers in the flexural behavior of the beams. The cyclic action produces a significant decay in the stiffness and in the strength capacity of the beams, and the addition of fibers reduces these negative effects. Form theoretical point of view good agreement can be found utilizing the recent analytical model proposed by the authors. © 2008 American Institute of Physics.

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

Experimental results on the shear behaviour of the steel trusses in composite steel-concrete beams are presented. Preliminarily tensile tests have been performed on specimens reproducing different types of welded joints. Tests are addressed to investigate on the bearing capacity of the welds and on the local instability problems that can arise in the elements of the truss. A FEM model is also presented in order to reproduce the behaviour of the steel truss subjected to shear load. Moreover, simplified relations are used to obtain the ultimate load on the welds for the different type of node and simplified models based on truss behaviour are used to foresee the stiffness and the strength of the steel truss specimens.

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

Corbels are structural members often used in reinforced concrete structures to transfer vertical and horizontal forces to principal members. This paper presents experimental research regarding the flexural behavior of corbels in plain and fibrous concrete and in the presence of steel bars. The study considers the influence of the type of concrete grade (normal- and high-strength concretes), of the fiber percentage and of the arrangement and percentage of the steel bars on the flexural behavior of the corbels. The results in terms of load-deflection curves and crack patterns show the effectiveness in using fibrous reinforced concrete corbels as well as in the presence of stirrups ensuring adequate strength and deformation capacity in reinforced concrete corbels. A simplified analytical model is proposed to calculate the shear strength of fibrous reinforced concrete corbels as well as in the presence of stirrups. The expression proposed for the calculation of the shear strength is then compared with other expression from the literature. The experimental results generated in terms of bearing capacity and those available in the literature are compared with the results obtained through the proposed model and with existing analytical expression. They show a good level of approximation, highlighting the role of the individual contributions from bars, concrete and fibers in the resistant mechanisms.

Fluid damper devices inserted in buildings or bridges are commonly used as energy sinks for seismic protection. In the response analysis of structures with filled damper devices the main problem exists in the strong nonlinear behavior of such equipment, as a consequence the differential equation of motion remains nonlinear and the response spectrum analysis still cannot be applied. In this note, by using the concept of power spectral density function coherent with the elastic response spectrum and by using the statistical linearization technique, expressions for finding the equivalent linear damping have been found. Comparisons with results obtained by Monte Carlo simulations confirm that for the kind of nonlinearity induced by fluid dampers the statistical linearization technique gives satisfactory results in terms of second order moments, as well as in terms of absolute maximum peak response. The latter is evaluated by the semiempirical formulation of Vanmarcke.

The present paper proposes a semi-empirical analytical expression that is capable of determining the shear strength of reinforced concrete beams with longitudinal bars, in the presence of reinforcing fibers and transverse stirrups. The expression is based on an evaluation of the strength contribution of beam and arch actions and it makes it possible to take their interaction with the fibers into account. For the strength contribution of stirrups, the effective stress reached at beam failure was considered by introducing an effectiveness function. This function shows the share of beam action strength contribution on the global strength of the beam calculated including the effect of fibers. The expression is calibrated on the basis of experimental data available in literature referring to fibrous reinforced concrete beams with steel fibers and recently obtained by the authors. It can also include the following variables in the strength previsions: - geometrical ratio of longitudinal bars in tension; - shear span to depth ratio; - strength of materials and fiber characteristics; - size effects. Finally, some of the more recent analytical expressions that are capable of predicting the shear strength of fibrous concrete beams, also in the presence of stirrups, are mentioned and a comparison is made with experimental data and with the results obtained by the authors.

Experimental results of the local bond stress-slip relationship of reinforcing bars embedded in lightweight fiber reinforced concrete with expanded clay aggregates are presented. The effect of the following parameters were investigated: - dimension of specimens; - anchorage length; - percentages of hooked steel fibers; - geometrical ratio of transverse reinforcement; - confinement external transverse pressure. Prismatic specimens with deformed steel bars embedded for a fixed length equal to five and eight equivalent diameters were tested under both monotonic and cyclic reversal imposed displacements at the tip of the bars, in controlled displacement tests. The influence of the above mentioned parameters was investigated, and the effects in terms of strength and ductility of the confinement due to transverse steel, to the fibers or to the pressure applied externally are shown. © 2005 Elsevier Ltd. All rights reserved.

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

The flexural behaviour of masonry rectangular cross-sections is studied in order to characterize the mechanical behaviour of structural elements under axial eccentric loads by means of a proper law. First the experimental response of walls under vertical centred loads is observed and a stress–strain law depending on two parameters is given in order to fit the experimental results. Subsequently the behaviour of walls nominally equal to the walls mentioned before is investigated under eccentric vertical loads, and the response is observed in terms of moment–curvature relation. To this point a comparison is made between the moment–curvature response obtained experimentally and the moment–curvature response obtained by means of the stress–strain law given, in the hypothesis of a plane strained section. Once the accuracy of the model is proved, the limit domain of the cross-section is calculated in order to be used for practical applications.

The effectiveness of the reinforcing technique consisting of fiber reinforced polymer sheets bonded to the structural elements depends on a good connection at the joint. This has to be able to ensure the transfer length of the shear stress in order to avoid a premature failure due to debonding. In this paper, the bond phenomenon at the interface is examined with reference to the calcarenite stone and carbon fiber reinforced polymer (CFRP) sheets in order to evaluate the possibility of utilizing this technique on masonry structural members, consisting of calcarenite ashlars and mortar. An experimental investigation is carried out on nine specimens obtained by applying unidirectional CFRP sheets to calcarenite squared-stone by using epoxy resin layers. All specimens were submitted to tensile force until the failure of the bond joint took place. Results allow us to deduce the local bond stress versus slip relationship, which is an important step toward understanding bond behavior at the joint interface.

This paper presents the results of experimental tests carried out on rectangular simply supported beams made of hooked steel fibre reinforced concrete with and without stirrups, subjected to two-point symmetrically placed vertical loads. The tests, carried out with controlled displacements, allow one to record complete load-deflection curves by means of which it is possible to deduce information on dissipative capacity and ductile behaviour up to failure. Depending on the amount of transverse reinforcement, volume fraction of fibres added in the mix and shear span, the collapse mechanism is due to predominant shear or flexure, thus showing the influence of the aforementioned structural parameters on the load carrying capacity and the post-peak behaviour of the beam. In particular, the results show that the inclusion of fibres in adequate percentage can change the brittle mode of failure characterizing shear collapse into a ductile flexural mechanism, confirming the possibility of achieving analogous performance by using reinforcing fibres instead of increasing the amount of transverse reinforcement. The ultimate values of the shear stresses recorded experimentally are compared with the corresponding values deduced by semiempirical expressions available in the literature and the correlation is satisfactory. © 2003 Elsevier Ltd. All rights reserved.

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

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