P. Hamelin

Fatigue-loading effect on RC beams strengthened with externally bonded FRP

External bonding of fiber reinforced polymers (FRP) on concrete beams is particularly attractive for the strengthening of civil engineering structures in order to increase their mechanical resistance. The composite material is generally bonded on the tensile part of the beam. In order to design these bonded reinforcements, an iterative computational method based on section equilibrium and material properties (concrete, steel, adhesive and composite) has been developed: this method can be extended to describe the fatigue behavior of RC beams. This paper focuses on the damage behavior of concrete structures subjected to fatigue loading. A specific modeling coupled with an experimental investigation on large-scale beams made it possible to compare the theoretical and experimental fatigue behaviors of RC beams with and without composite reinforcements Results showed that the beam deflection and the strain in each material could be calculated with a sufficient accuracy, so that the fatigue behavior of the FRP strengthened beams was correctly estimated by the model.

Dynamic axial crushing of combined composite aluminium tube: the role of both reinforcement and surface treatments

An experimental investigation was conducted to study both the crushing behavior and the practical adhesion of multi-material structures under dynamic compression conditions. Multi-material structures were made by wrapping a carbon/epoxy composite around the outside of an aluminium alloy circular tube. Prior to bonding, different surface treatments (i.e. chemicals etching, anodizing and degreasing) were used in order to improve the practical adhesion between the composite and the aluminium tube. Two geometries of aluminium alloy tubes, allowing a stable crushing mode, were tested. The specific energy absorption values obtained suggest that the influence of surface treatments of multi-material structures was not a significant contribution. For the thinner aluminium alloy tube, with or without the fiber reinforced plastic composites, a diamond mode is observed irrespective of the surface treatments. On the contrary, from a concertina mode obtained with the thicker aluminium tube without reinforcement, a diamond mode is observed with the reinforced one irrespective of the surface treatments. As the crushing mode has changed, the reinforcement applied onto the aluminium tube has decreased the capacities of the structures tested to absorb the energy. On the other hand, the reinforcement applied onto the thinner aluminium tube increased the specific energy absorption of a tube. To get a better understanding of the shock, a high-speed camera was used. It permits to differentiate the ability of a tube to dissipate the energy (i.e. characterized by the specific energy) and the ability of a tube to deform itself (i.e. characterized by the crush distance).

Mechanical properties prediction of textile-reinforced composite materials using a multiscale energetic approach

A computer aided design tool and a numerical procedure allowing the prediction of textile reinforced composite behaviour are presented in this paper. Specifying a geometrical description, the software used allows the rebuildong of both simple or sophisticated textile structures. It also aims to become a pre-processing work for the subsequent mechanical analysis. Fabric unit cells (fibres+matrix) are regarded as a three-dimensional aggregate of subcells on which we apply a multi-scale energetic approach. First elements to validate the elastic prediction are provided by results obtained on a woven fabric material. The progressive failure procedure is validated by comparisons between simulation and experiment on 3D braided composites.

A global-local non-linear modelling of effective thermal conductivity tensor of textile-reinforced composites

This paper deals with the effective conductivity tensor modelling of textile-reinforced composites (TRC). These TRC are treated as anisotropic heterogeneous media made of regular elements on which we apply a multilevel analysis that allows considering the filament-matrix mixture, the yarn and finally the unit cell scales. Moreover, the determination of the unit-cell effective thermal properties (global properties) takes into account the non-linear thermal behaviour of the constituents (local properties). In a last part, the modellings of unidirectional, 2D and 3D composites are compared to FEM solutions and experimental results in order to validate our approach.

Stiffness and failure modelling of 2D and 3D textile-reinforced composites by means of imbricate-type elements approaches

This paper discusses the stiffness and failure behaviour modelling of textile-reinforced composites (TRCs). Different numerical and semianalytical approaches, based on a multilevel geometrical meshing which allows considering mechanical phenomena encountered at the filament, the yarn and the unit cell levels, are developed. The cases of a 2D woven and a 3D braided composites are studied and their homogenised stiffness properties are compared to solutions provided by finite element methods and the fabric geometry model. The modelled failure of both the 2D and 3D TRC are compared to experimental data.

Experimental Investigation of CF Anchorage System Used for Seismic Retrofitting of RC Columns

This paper investigates the suitability and effectiveness of CF anchorage system in strengthening the bond in between the CFRP retrofit sheet and structure junction. i.e. column beam or column slab junction. For this purpose, a detailed experimental program was conducted, which is presented here briefly. Five different anchorage systems are discussed here. Results of the experimental observations are discussed in the form of load-slip curves, ultimate capacity and failure modes. The test result, in general indicates that the use of CF anchor provides an enhancement in the overall seismic capacity of strengthened specimen.

Thermo-Mechanical Characterization of Textile Reinforced Concrete. Application to Short Concrete Column Strengthening Submitted to Fire Conditions

One of the main interest which concerns substitution of FRP (Fiber Reinforced Polymer) such as carbon epoxy composite by TRC (Textile Reinforced Concrete) for rehabilitation of existing infrastructures is its thermal stability and fire behavior. The first part is devoted to the description of experimental methodology developed by Si Larbi et al. for tensile characterization of TRC and prediction of ultimate resistance for different levels of temperature (20–600 °C). In the second part, the structural behavior of short concrete columns loaded under axial compression and confined by TRC is considered. Taking into account the design method proposed by Hamelin et al., the strength increase is estimated for different conditions of fire stability. Finally, we conclude on the interest of TRC reinforcements for steel concrete structures particularly in the case of accidental loading conditions such as fire or blast considering thermo-mechanical stability, gas toxicity and smoke opaqueness.

A Mixed Pultrusion and Braiding Process Adapted to the Production of High Performance Cement Composite Beams

The objective of the present paper is the optimization of the behavior of structural elements for civil engineering applications. A specific manufacturing process has been developed (Lamtextress patent) allowing to produce hollow beams made of mineral based pultruded composite plates. The beams are hollow with square cross section; they are realized by bonding together composite plates having the dimensions 200 × 10 × 1 cm3. In order to improve the overall performances of the beams, they are reinforced by braiding technology and hand lay-up wrapping. The shear and flexural performance of the final composite beams can be calculated taking into account different process parameters (e.g. nature of fibers, number of filaments, braiding angle).

Optimization of Quasi-isotropic Formulation of Fiber-Cement Laminates: Polar Method and Experimental Validation

The development of Textile Reinforced Concrete (TRC) requires the development of design methods. As cement based composites present anisotropic behavior at different levels, we suggest to consider the initial elastic stage of the elementary layer behavior law in tension, compression and shear, limited by a crack opening threshold. Then, we apply the polar method, allowing to optimize a multilayer stacking sequence in order to obtain an overall quasi-isotropic behavior of a composite plate.

Matrix and Fabric Impregnation Influence on Textile Reinforcement Concrete Behaviour

This study aims to analyze the textile reinforced concrete tensile (TRC) behaviour. Firstly A tensile test suitable for this type of cracking material is designed and validated. The second phase aims to highlights the influence of several parameters considered as critical (the material, the thickness of the composite, the impregnation of the fibres, the fibre volume ratio) in the textile reinforced concrete (TRC) behaviour in terms of mechanical performance (strength and stiffness) or the amount of damage correlated with the crack opening measured using image correlation analysis.