L. Ombres

Local buckling loads of sandwich panels made with laminated faces

The paper is devoted to assessing the optimal arrangements of hybrid laminated faces of sandwich panels in order to maximize local buckling loads corresponding to the wrinkling of compressed faces. The analysis is carried out by modelling compressed faces as thin unsymmetric laminates resting on elastic two-parameter foundations. The First-order Shear Deformation Theory, in conjunction with the Rayleigh-Ritz method, has been used to evaluate buckling loads of simply supported flat laminates subjected to in-plane biaxial compression and shear forces. A numerical investigation is intended to support evidence for the influence of laminate parameters (fibre orientation, geometrical dimensions) and foundation parameters (modulus of subgrade reaction and shear modulus); obtained results are reported and discussed in the paper.

Maximum buckling loads for unsymmetric thin hybrid laminates under in-plane and shear forces

This paper assesses the optimal arrangements of thin hybrid unsymmetric laminates in order to maximize the buckling loads, varying both fibre orientation and geometrical dimensions. First-order shear deformation theory in conjunction with the Rayleigh-Ritz method has been used to determine the critical buckling load of simply supported, flat hybrid laminates under in-plane and shear forces. A numerical analysis enables us to find both the influence of shear force, varying mechanical and geometrical parameters of the laminates, and advantages furnished from the hybridization, by comparison with results relative to non-hybrid laminates.

Cracking Analysis of FRP-Reinforced Concrete Flexural Members

The paper is dedicated to the cracking analysis of FRP (Fiber-Reinforced Polymer)-reinforced concrete elements. A general nonlinear calculation procedure, based on the slip and bond stresses, is described and adopted for the prediction of the crack width and crack spacing in FRP-reinforced concrete beams. An analytical expression of the bond-slip law is estimated using the corresponding experimental results available in the literature. A numerical investigation is carried out and the influence of the mechanical and geometrical parameters of the material (bond-slip law, reinforcement ratio, concrete strength, diameter of rebars, etc.) on the crack formation is investigated. Referring to glass-FRP-reinforced concrete beams, a comparison between the theoretical predictions and experimental results is made. The results obtained are presented and discussed.

Environmental Effects on the Mechanical Properties of Glass-FRP and Aramid-FRP Rebars

In the paper, the experimental results on the effect of temperature and moisture on the mechanical properties of FRP (Fiber-Reinforced Polymer) reinforcements are presented. FRP rebars made from glass and aramid fibers were subjected to cyclic thermal actions at temperatures ranging between 20 and 70°C, typical of natural hot-climate environments. Tensile tests were also carried out on FRP rebars. The effect of moisture was investigated by cyclic wetting and drying the FRP rebars under laboratory conditions before their testing in tension. Finally, the elastic modulus and tensile strength of the FRP rebars exposed to these cyclic actions were compared with those obtained for unexposed ones, in order to evaluate the mechanical damage caused by environmental conditions.

Modeling of the Behavior of Concrete Tension Members Reinforced with FRP Rods

The paper is devoted to the analysis of cracking and deformability of concrete tension members reinforced with fiber-reinforced polymer (FRP) rods. A theoretical nonlinear model, derived from a cracking analysis founded on slip and bond stresses, is adopted for evaluating the crack width, crack spacing, and elongation of tension members. The procedure takes into account the local bond-slip law, experimentally determined by means of pullout tests, and allows us to evaluate the influence of tensile stiffening. The analysis is performed with considering all parameters influencing the behavior of tension members, such as the concrete strength, the kind of FRP rebars, the surface treatment of FRP rebars, and the concrete cover thickness. The theoretical predictions are compared with available experimental results, obtained on cylindrical concrete specimens reinforced with carbon FRP (CFRP) rods, and with predictions of the traditional models usually adopted for design purposes.

Load-deflection analysis of concrete elements reinforced with FRP rebars

The behavior of fiber reinforced plastic (FRP) concrete elements under service conditions is analyzed. Taking into account the real constitutive law of materials and local bond-slip law which adequately describes the interaction between the FRP reinforcement and concrete, a numerical procedure is proposed for obtaining moment-curvature relationships for a cracked beam element. Using the moment-curvature laws, the load-deflection analysis of FRP concrete beams is carried out. To study the influence of geometric and mechanical parameters, a numerical investigation was carried out and the results obtained were compared with those from other methods and Codes. The results of the experimental investigation are described and compared with those of the proposed procedure; the comparison shows good agreement between the theoretical and experimental results.