To develop a reliable methodology for the design of steel fibre reinforced concrete (SFRC) slabs, an extensive experimental program was carried out with SFRC square panels simply supported in their contour. By adopting a moment-rotation approach, a numerical model was developed capable of taking into account the constitutive laws of the SFRC for the prediction of the force-deflection response of variety of panel tests recommended in the international standards. The predictive performance of the model was assessed by considering results available in the bibliography and those obtained on the experimental program. The proposed model was utilized in a parametric study to assess the influence of toughness classes of SFRC on the behaviour at serviceability limit conditions, on the load carrying capacity, and on the deformational response of SFRC round panels.

In recent years, the number of pedestrian bridges built from composites materials has notably increased. The combination of fiber reinforced polymers (FRP) profiles with fiber reinforced concrete (FRC) elements is being adopted in this type of structures, since the ductility, high post-cracking tensile strength, compressive stiffness and strength of FRC can be combined with the benefits derived from the use of FRP's profiles to obtain high performance structural systems. In the context of the present work a 12 m long single span pedestrian bridge with two composite Iprofiles was designed. In terms of deflection requirements imposed by serviceability limit states, the influence of the height and thickness of GFRP (Glass Fiber Reinforced Polymer) profiles, as well as the addition of a thin layer of prestressed carbon fiber sheet in the bottom flange of the GFRP profile was evaluated. Using software based on the finite element method, the structural behavior of the developed structural systems was analyzed. Furthermore, two prototypes of this structural system were built and monitored in order to assess their long-term deformational behavior when subjected to a loading configuration correspondent to the load combination for the deflection serviceability limit states. The main results obtained are presented and discussed.

a b s t r a c tThe present work describes a model for the determination of the moment-rotation relationship of a cross section of fiber reinforced concrete (FRC) elements that also include longitudinal bars for the flexural reinforcement (R/FRC). Since a stress-crack width relationship ðr-wÞ is used to model the post-cracking behavior of a FRC, the r-w directly obtained from tensile tests, or derived from inverse analysis applied to the results obtained in three-point notched beam bending tests, can be adopted in this approach. For a more realistic assessment of the crack opening, a bond stress versus slip relationship is assumed to simulate the bond between longitudinal bars and surrounding FRC. To simulate the compression behavior of the FRC, a shear friction model is adopted based on the physical interpretation of the post-peak compression softening behavior registered in experimental tests. By allowing the formation of a compressive FRC wedge delimited by shear band zones, the concept of concrete crushing failure mode in beams failing in bending is reinterpreted. By using the moment-rotation relationship, an algorithm was developed to determine the force-deflection response of statically determinate R/FRC elements. The model is described in detail and its good predictive performance is demonstrated by using available experimental data. Parametric studies were executed to evidence the influence of relevant parameters of the model on the serviceability and ultimate design conditions of R/FRC elements failing in bending.

Discrete steel fibres can increase significantly the bending and the shear resistance of concrete structural elements when Steel Fibre Reinforced Concrete (SFRC) is designed in such a way that fibre reinforcing mechanisms are optimized. To assess the fibre reinforcement effectiveness in shallow structural elements failing in bending and in shear, experimental and numerical research were performed. Uniaxial compression and bending tests were executed to derive the constitutive laws of the developed SFRC. Using a cross-section layered model and the material constitutive laws, the deformational behaviour of structural elements failing in bending was predicted from the moment-curvature relationship of the representative cross sections. To evaluate the influence of the percentage of fibres on the shear resistance of shallow structures, three point bending tests with shallow beams were performed. The applicability of the formulation proposed by RILEM TC 162-TDF for the prediction of the shear resistance of SFRC elements was evaluated. Inverse analysis was adopted to determine indirectly the values of the fracture mode I parameters of the developed SFRC. With these values, and using a softening diagram for modelling the crack shear softening behaviour, the response of the SFRC beams failing in shear was predicted.

a b s t r a c tA close-form solution is developed for the prediction of the moment-curvature relationship of cross sections of fiber reinforced concrete (FRC) elements failing in bending, and reinforced longitudinally with steel and fiber reinforced polymer (FRP) bars. The FRP bars are installed with the largest possible internal arm, e.g. with the minimum concrete cover that assures the bond conditions for a sound stress transfer from FRC to the FRP bars. The model is also able of simulating the flexural strengthening contribution provided by FRP bars installed according to the near surface mounted (NSM) technique. To have good protection conditions against corrosion, the steel bars are applied with a relatively thick FRC cover. Since steel stirrups are the reinforcement with the smaller concrete cover thickness, they are the most susceptible to corrosion. In the reinforcement concept to be developed in the present research program, steel stirrups are replaced with discrete fibers. This hybrid reinforcement aims to develop high durable prefabricated elements that fail in bending. The proposed analytical formulation can simulate FRC with strain softening or strain hardening behavior. In the present work, the formulation is described and its predictive performance is appraised.