Valentino Paolo Berardi

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.

A Viscoelastic Constitutive Law For FRP Materials

The present study deals with the long-term behavior of fiber-reinforced polymer (FRP) materials in civil engineering. More specifically, the authors propose a mechanical model capable of predicting the viscoelastic behavior of FRP laminates in the field of linear viscoelasticity, starting from that of the matrix material and fiber. The model is closely connected with the low FRP stress levels in civil engineering applications. The model is based on a micromechanical approach which assumes that there is a perfect adhesion between the matrix and fiber. The long-term behavior of the phases is described through a four-parameter rheological law. A validation of the model has also been developed by matching the predicted behavior with an experimental one available in the literature.

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.

Time-Dependent Behavior of Reinforced Polymer Concrete Columns under Eccentric Axial Loading

Polymer concretes (PCs) represent a promising alternative to traditional cementitious materials in the field of new construction. In fact, PCs exhibit high compressive strength and ultimate compressive strain values, as well as good chemical resistance. Within the context of these benefits, this paper presents a study on the time-dependent behavior of polymer concrete columns reinforced with different bar types using a mechanical model recently developed by the authors. Balanced internal reinforcements are considered (i.e., two bars at both the top and bottom of the cross-section). The investigation highlights relevant stress and strain variations over time and, consequently, the emergence of a significant decrease in concrete’s stiffness and strength over time. Therefore, the results indicate that deferred effects due to viscous flow may significantly affect the reliability of reinforced polymer concrete elements over time.

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.

Initiation of Failure for Masonry Subject to In-Plane Loads through Micromechanics

A micromechanical procedure is used in order to evaluate the initiation of damage and failure of masonry with in-plane loads. Masonry material is viewed as a composite with periodic microstructure and, therefore, a unit cell with suitable boundary conditions is assumed as a representative volume element of the masonry. The finite element method is used to determine the average stress on the unit cell corresponding to a given average strain prescribed on the unit cell. Finally, critical curves representing the initiation of damage and failure in both clay brick masonry and adobe masonry are provided.

ADVANCED NUMERICAL MODELS FOR THE ANALYSIS OF UNREINFORCED AND STRENGTHENED MASONRY VAULTS

Masonry buildings realized in the last centuries are a significant part of the international architectural heritage. The optimal design of the retrofit interventions of these buildings represents a priority and requires the evaluation of their mechanical behavior under static and dynamic loads. Several mechanical models capable to study masonry structures are available in literature and are based on Heyman limit analysis approach. These models cannot be easily adopted within FEM codes. Within this context, a Genetic Algorithm is implemented within a refinement adaptive finite element model to computational mesh of shell surfaces. The proposed model researches a ‘safe’ thrust surface of a masonry vault within a design domain, by minimizing the average value of the principal tensile stresses carried by the unreinforced portion of the material (fitness function). The design domain coincides with either the vault volume, in the case of unreinforced masonry members, or an external region of the vault in correspondence with the reinforced portions, in the case of the vault strengthened with either Fiber Reinforced Polymer or Fabric Reinforced Cementitious composites. The proposed methodology allows evaluating the structural safety of masonry vault and defining an optimal design of reinforcement pattern. 5056 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 5056-5069

A Numerical Evaluation of Damage in Fast Dynamics

We investigate properties of a damage model accounting for microscopic motions responsible for damage. The model evaluates structural damage, taking into account rheological and inertia effects. We investigate the properties of the effects of the more important parameters of the predictive theory in fast dynamics. They account for the inertia of the links insuring the cohesion, for local interactions at the microscopic level and for the cohesion of the material. Numerical results are obtained with the finite element method.

An Experimental and Numerical Investigation on the Plating of Reinforced Concrete Beams with FRP Laminates

This work deals with some numerical and experimental results on the plating of Reinforced Concrete (RC) beams externally strengthened with FRP laminates. In particular, they concern the tangential interaction distributions along the reinforced boundaries of the strengthened beams. The comparisons between numerical and experimental results show the accuracy of the proposed mechanical model in evaluating the stresses distributions at the interface between concrete core and composite laminates.