Luciano Feo

Modeling of composite/concrete interface of RC beams strengthened with composite laminates

In this paper a finite element model for predicting shear and normal stresses in the adhesive layer of plated reinforced concrete beams has been developed. The numerical results carried out agree with those obtained in previous studies by other authors. It is found that shear stresses and high concentrations of peeling forces are present at the ends of the plates when the composite beam is loaded in flexure. These concentrations can produce premature failure of the strengthened beam because of debonding of the plate or cracking of the concrete cover along the level of internal steel reinforcement. The numerical simulation captures the actual interfacial stresses and, in particular, the maximum values of shear and normal stresses.

A numerical evaluation of the interlaminar stress state in externally FRP plated RC beams

The present work deals with the structural plating of reinforced concrete beams with composite materials. Some numerical results obtained via finite element method (FEM) are given. The FEM analysis has been performed by using a suitable mechanical model introduced by the authors in previous steps of the research. This model allows to accurately predict the actual stress state at the interface between concrete core and reinforcing plate. Such interfacial stresses play a fundamental role in the mechanics of plated beams, because they can produce a sudden and premature failure. A simplified procedure for verifying the interfacial stress state is also presented.

On a Moderate Rotation Theory of Thin-Walled Composite Beams

A small strain and moderate rotation theory of laminated composite thin-walled beams is formulated by generalizing the classical Vlasov theory of sectorial areas. The proposed beam model accounts for axial, bending, torsion and warping deformations and allows one to predict critical loads and initial post-buckling behaviour. A finite element approximation of the theory is also carried out and several numerical applications are developed with reference to lateral buckling of composite thin-walled members. The sensitivity of critical load to second-order effects in the pre-buckling range is pointed out.

On the statical behaviour of fibre-reinforced polymer thin-walled beams

The work deals with the formulation of a one-dimensional kinematical model that is able to study the static behaviour of fibre-reinforced polymer thin-walled beams. The proposed model allows us to take into account the effects of shear deformability. Some numerical results obtained via the finite element method are provided and comparisons with the results obtained by Vlasovs classical theory are also presented.

A Refined Finite Element Formulation for the Microstructure-Dependent Analysis of Two-Dimensional (2D) Lattice Materials

A finite element approximation is proposed for the dynamic analysis of two-dimensional (2D) lattice materials. The unit cell is modeled by means of a defined number of shear deformable micro-beams. The main innovative feature concerns the presence of a microstructure-dependent scale length, which allows the consideration of the so called size-effect that can be highly relevant, due to the characteristics of the lattice at the local scale. Some numerical results show the influence of the microstructure parameter on the dynamic behavior of two-dimensional lattice materials.

OPTIMAL DESIGN AND ADDITIVE MANUFACTURING OF NOVEL REINFORCING ELEMENTS FOR COMPOSITE MATERIALS

We experimentally investigate on the use of additive manufacturing technologies for the design and fabrication of innovative reinforcing elements of novel composite materials. We perform short-beam shear tests on cement mortar specimens reinforced with additively manufactured reinforcing fibers made of photopolymers or a titanium alloy. The fracture toughness, shear capacity and first crack strength of the examined materials are estimated based on the provisions of different international standards for construction materials. We also characterize the surface morphology of the examined fibers through microscopy analyses before and after testing. The given results highlight that the microscopic or macroscopic nature of the surface roughness of the analyzed fibers greatly influences the energy absorption capacity of the final materials, while the nature of the fibers’ material (metallic/polymeric) is of central importance in terms of strength properties. The present study represents a first step in the direction of designing reinforcing elements with hierarchical structure to form fabrics, fibers and coatings of groundbreaking reinforcements for next generation composites, profiting from the rapid prototyping capabilities of additive manufacturing technologies at different scales. Fabbrocino, I. Farina, A. Amendola, L Feo, F.Fraternali

Nano-beams under torsion: a stress-driven nonlocal approach

Purpose This study aims to model scale effects in nano-beams under torsion. Design/methodology/approach The elastostatic problem of a nano-beam is formulated by a novel stress-driven nonlocal approach. Findings Unlike the standard strain-driven nonlocal methodology, the proposed stress-driven nonlocal model is mathematically and mechanically consistent. The contributed results are useful for the design of modern devices at nanoscale. Originality/value The innovative stress-driven integral nonlocal model, recently proposed in literature for inflected nano-beams, is formulated in the present submission to study size-dependent torsional behavior of nano-beams.

Concrete Open-Wall Systems Wrapped with FRP under Torsional Loads

The static behavior of reinforced concrete (RC) beams plated with layers of fiber-reinforced composite material (FRP) is widely investigated in current literature, which deals with both its numerical modeling as well as experiments. Scientific interest in this topic is explained by the increasing widespread use of composite materials in retrofitting techniques, as well as the consolidation and upgrading of existing reinforced concrete elements to new service conditions. The effectiveness of these techniques is typically influenced by the debonding of the FRP at the interface with concrete, where the transfer of stresses occurs from one element (RC member) to the other (FRP strengthening). In fact, the activation of the well-known premature failure modes can be regarded as a consequence of high peak values of the interfacial interactions. Until now, typical applications of FRP structural plating have included cases of flexural or shear-flexural strengthening. Within this context, the present study aims at extending the investigation to the case of wall-systems with open cross-section under torsional loads. It includes the results of some numerical analyses carried out by means of a finite element approximation.

A Note on Torsion of Nonlocal Composite Nanobeams

The Eringen elastic constitutive relation is used in this paper in order to assess small-scale effects in nanobeams. Structural behavior is studied for functionally graded materials in the cross-sectional plane and torsional loading conditions. The governing boundary value problem has been formulated in a mixed framework. Torsional rotations and equilibrated moments are evaluated by solving a first-order differential equation of elastic equilibrium with boundary conditions of kinematic-type. Benchmarks examples are briefly discussed, enlightening thus effectiveness of the proposed methodology.

Minimal mass design of strengthening techniques for planar and curved masonry structures

We present a discrete element model of a masonry structure strengthened through the application of reinforcing elements designed to work in tension. We describe the reinforced masonry structure as a tensegrity network of masonry rods, mainly working in compression, and tension elements corresponding to fiber-reinforced composite reinforcements, which are assumed to behave as elastic-perfectly-plastic members. We optimize a background structure connecting each node of the discrete model of the structure with all the neighbors lying inside a sphere of prescribed radius, in order to determine a minimal mass resisting structure under the given loading conditions and prescribed yielding constraints. Fiber-reinforced composite reinforcements can be naturally replaced by any other reinforcements that are strong in tension (e.g., timber or steel beams/ties). Some numerical examples illustrate the potential of the proposed strategy in designing tensile reinforcements of a three-dimensional structure composed of a masonry vault and supporting walls.