Antonio Caggiano

Multiscale failure analysis of fiber reinforced concrete based on a discrete crack model

In this work the capabilities of an interface model to predict failure behavior of steel fiber reinforced cementitious composites (SFRCCs) are evaluated at both macro and mesoscale levels of observation. The interface model is based on a hyperbolic maximum strength criterion defined in terms of the normal and shear stress components acting on the joint plane. Pre-peak regime is considered linear elastic, while the post-peak behavior is formulated in terms of the fracture energy release under failure mode I and/or II. The well-known “Mixture Theory” is adopted for modeling the interactions between fibers and the surrounding cementitious composite. The effects of both the axial forces on the fibers induced by normal relative displacements, as well as the dowel action due to tangential relative displacements in the interfaces are considered in the formulation of the interaction mechanisms between fibers and cementitious composites. After describing the interface model, this work focuses on numerical analyses of SFRCC failure behavior. Firstly, the validation analysis of the interface model is performed at the constitutive level by comparing its numerical predictions against experimental results available in scientific literature. Then, the sensitivity of the interface theory for SFRCC regarding the variation of main parameters of the composite constituents is evaluated. Finally, the attention is focused on Finite Element (FE) analysis of SFRCC failure behavior at meso and macroscopic levels of observation. The results demonstrate the capabilities of the interface theory based on the Mixture Theory to reproduce the main features of failure behavior of SRFCC in terms of fiber content and involved fracture modes.

Interface model for fracture behaviour of fiber-reinforced cementitious composites (FRCCs)

ABSTRACT This paper presents a model for fiber-reinforced cementitious composites (FRCCs) based on a cohesive-frictional interface theory. A zero-thickness joint model is formulated for simulating the fracture behaviour of interfaces between the various phases of fiber-reinforced concretes. In particular, the “Mixture Theory” is used for describing the coupled action between concrete and fibers. Numerical analyses have been carried out on both plain concrete and FRCC members. Comparisons between numerical simulation and experimental evidence demonstrate the accuracy and soundness of the proposed formulation.

On the Mesoscale Fracture Initiation Criterion of Heterogeneous Steels During Quenching

A numerical model aimed at investigating the microcracking behavior in steel meso-structures during quenching process is proposed in this work. The proposal explicitly considers the material heterogeneity influencing the fracture response of the steel meso-specimen under consideration. Particularly, a finite element based model is used in a two-stage simulation: (i) the first stage deals with solving the coupled metallo-thermo-mechanical problem at macroscopic level during quenching; (ii) the second stage accounts for the mesoscopic cracking based on a discontinuous approach by means of the extended finite element method. Different strain and stress histories have been used as failure (initation) criteria and have been compared with experimental results on high speed quenching of a 100Cr6 cylindrical (SAE 52100) steel specimen. The good agreement between the numerical simulations, adopting a maximum principal stress criterion as cracking initiation rule, and the experimental results indicates the potential of the presented methodology in the failure prediction.

Degradation of concrete mechanical behavior due to temperature effects

In this work, the capabilities of a material model to describe and predict the degradation of concrete capacity and mechanical behavior due to temperature effects are presented. The predictions of the numerical model are compared with experimental results of concrete subjected to different temperatures. The results in this work show the severe consequences of the long term exposure to temperature of concrete main features such as strength and stiffness and, in this sense, it is also shown the effect of this mechanical features degradation on the safety condition of the related structures. Moreover, the numerical results demonstrate the accuracy and capacity of the mathematical model proposed by the Authors regarding concrete structure behavior subjected to combined action of temperature and mechanical loading.

Advanced Numerical Models for the Analysis of Sustainable FRC Structures

This chapter introduces some of the relevant modelling approaches that are being used to simulate the behaviour of cementitious materials reinforced with discrete fibres. The major part of these approaches were originally proposed for modelling non-fibrous reinforced cement based materials‚ therefore the main focus herein given is related to the aspects how fibre reinforcement mechanisms have been considered. These approaches were grouped in two classes‚ one where fibres are explicitly considered in the finite element mesh (FEMesh)‚ herein designated as Discrete Fibre Reinforcement Approaches (DFRAs). The other class is designated by smeared fibre reinforcement approaches (SFRAs)‚ where fibres are not part of the FEMesh and their contribution is basically considered attributing a constitutive law to the FRC that simulates the fibre reinforcement mechanisms in terms of the fracture modes of this composite material.

Cementitious Composites Reinforced with Recycled Fibres

Pneumatic tyres are nowadays among the most widespread industrial products and, hence, handling tyres that have reached their end-of-life is indeed a critical issue. This Chapter provides readers with the key facts about tyre production and consumption. Particularly, it describes the raw materials which they are made from, and summarises the main classifications currently accepted worldwide. The typical product life-cycle is shortly outlined before analysing the possibility of recycling waste tyres for producing new products. Relevant properties of concrete reinforced with recycled fibres are presented, with special focus on the post-cracking behaviour of these composite materials. Emphasis is given to the suitability of using recycled fibres obtained from waste tyres as partial or total replacement of industrial steel fibres for obtaining fibre reinforced concrete.

Constitutive Formulations for Concrete with Recycled Aggregates

In this Chapter, a thermodynamically consistent gradient model is proposed for natural aggregate concrete and then, modified to take into account the addition of different contents of recycled aggregates and its influence on concrete mechanical response. A particular and simple form of gradient-based plasticity is considered, where the state variables are the only ones of non-local character. After describing the material formulation for natural and recycled aggregate concretes, the model calibration is performed with experimental data taken from literature. A comprehensive numerical analysis is presented, where the effects of the recycled aggregate content on the performance of concrete in pre and post-peak behavior are evaluated and discussed, for different stress states. Finally, the ability of the model to capture the variation of mechanical response of concrete with different recycled aggregate contents is demonstrated for different mechanical tests.

Hybrid Industrial/Recycled SFRC: Experimental Analysis and Design

This paper is intended as a practice-oriented contribution about the use of sustainable Fiber-Reinforced Concrete (FRC) in the design of structural members according to the provisions of the current codes and guidelines. More specifically, the work focusses on Hybrid Industrial/Recycled Steel Fiber-Reinforced Concrete (HIRSFRC) realised by combining tailored Industrial Steel Fibers (ISFs) with Recycled Steel Fibers (RSFs), the latter being obtained by recycling waste pneumatic tyres. First, the results of a series of experimental tests, carried out for characterising the behaviour of the aforementioned materials, are summarised. They are specifically considered for evaluating the parameters that are generally considered for describing the post-cracking response of FRC. Then, a parametric analysis on the sectional behaviour of beams made of the aforementioned HIRSFRCs is proposed: this is intended at highlighting the influence of the material behaviour on the ultimate bending moment and curvature of structural members.

Discontinuos Approach for Meso-Scale Modeling of Porous Materials Like Concrete Under High Temperatures

In this work, the failure behavior of concrete exposed to elevated temperatures is analyzed. A thermo-mechanical and poropressure-based interface model for failure analysis of concrete subjected to high temperature is presented. The model represents an extension of a fracture energy-based interface formulation to account for the damage induced by high temperatures and for the temperature dependent pore pressure and humidity in concrete. Thereby, the non-linear response of the proposed coupled thermo-mechanical interface model for porous materials like concrete is activated under kinematic and/or temperature and/or hydraulic increments (with or without jumps). A simplified procedure is proposed to account for the temperature dependent pore pressure in concrete. This contribution focuses on both the formulation of the novel interface constitutive theory and on the strategy proposed for mesoscopic finite element analysis of concrete failure behavior under different hydro-thermo-mechanical conditions. Finally, some numerical analysis are presented which demonstrated the predictive capabilities of the proposed interface model.