E. Ferrier

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.

Mechanical Behavior of an Innovative Hybrid Beam Made of Glulam and Ultrahigh-Performance Concrete Reinforced with FRP or Steel

The main objective of the research project reported here is to develop a new hybrid glulam beam that will increase the performance of timber structures and optimize the use of wood in such structures. The hybrid beam is made by combining glulam with ultrahigh-performance short fiber-reinforced concrete (UHPC-SFR) planks with or without internal reinforcement consisting of steel- or fiber-reinforced polymer reinforcement bars. This paper presents an experimental program of tests on eight large-scale hybrid beams under four-point bending. The results show that by combining wood and UHPC-SFR, it is possible to obtain a hybrid beam with greater bending stiffness and increased ultimate load capacity.

Concrete beams reinforced by fibre-reinforced plastics: the effect of temperature on the adhesive layer

Composite materials find applications in civil engineering for concrete and prestressed concrete structures. The bending design of these structures can be done with a non-linear calculation method. The research presented aims at determining the long-term behavior of a composite repair. The creep of a composite reinforcement/adhesive-layer interface is evaluated by a tensile/shear thermal/stimulation test and a long-term test. Analysis of the results prove that is possible to study, in a comparative way, changes in adhesive mechanical characteristic loss and the viscoelasticity response of different polymer systems. Long-term mechanical characteristics are evaluated and safety coefficients for design are there by deduced.

Composite materials contribution in strengthening concrete structures affected by alkali–aggregate reaction

Alkali–aggregate reactivity (AAR) is a chemical reaction that occurs in some concrete structures. AAR is a reaction between pore solution alkali hydroxide and some siliceous aggregates. The damage to the concrete induced by AAR is very important with expansion and cracking. The main purpose of this investigation is to evaluate the effectiveness of the use of external bonded FRP on the durability of civil engineering structures damaged by alkali reaction (mechanical behaviour determination, comparison with Larives model and confinement efficiency). In a first approach, we are working on a mortar specimen containing alkali–silica aggregates. The deterioration of mortar is determined from the expansion measures and from the measure of mechanical properties. To reduce the necessary duration of development of alkali–aggregate reaction, two accelerated mortar bar tests are evaluated: immersion in saturated NaCl solution at 50°C; immersion at 38°C (P 18 585 AFNOR standard). Two types of sample are made: no reac...

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.

Mechanical in-plane behaviour of masonry walls reinforced by composite materials: Experimental and analytical approaches

Masonry is a traditional building system in most countries of the world, including France. However, in recent decades, earthquakes have caused significant damage to masonry structures. The possibility of using textile-reinforced concrete or fibre-reinforced polymers to strengthen masonry structures has been recently assessed. This article addresses the effectiveness of externally bonded composite materials, particularly those based on newly developed cementitious matrices, to strengthen masonry structures. Experimental tests were performed in a previous study on six masonry walls, five of which were strengthened on both sides with either textile-reinforced concrete or fibre-reinforced polymers. This experimental campaign has been supplemented to determine the mechanical properties of the materials involved in design models, and it is used to check the potential of analytical models to predict lateral strength. This study identifies the interests and the restrictions governing the use of traditional empirical design approaches (employed for fibre-reinforced polymer-strengthened walls) when next-generation textile-reinforced concrete composites are used as strengthening materials. Adjustments taking into account the specificities of textile-reinforced concrete behaviour have been introduced, and their impact on the relevance of the models has been quantified.

Evaluation of one-way shear behaviour of reinforced concrete slabs: experimental and numerical analysis

Abstract The shear design of concrete slabs is still an unsolved problem. The following study presents experimental and numerical investigations on the shear behaviour of reinforced concrete slabs (without shear reinforcement) under concentrated loads. The small thick slabs of 10 cm were tested in this study. Experimental tests were conducted to quantify the shear strength and the associated failure modes. The influence of several variables was addressed such as the influence of boundary conditions, four supported side slabs instead of two supported side slabs, the influence of loading plate length. A series of eight tests on six slabs were presented. The experiments are firstly used to evaluate the pertinence of Eurocode 2 and Model Code 2010 formulations using the levels of approximation LoA I and LoA II for the shear design of reinforced concrete slabs without shear reinforcement in comparison with the French approach, and secondly validated numerical modelling using the non-linear finite element method. The proposed numerical model showed good agreement with the experimental results in terms of slab behaviour.

Mechanical behaviour of slender RC walls under seismic loading strengthened with externally bonded CFRP

Recent post-earthquake surveys have highlighted the excellent performance of reinforced concrete (RC) wall-type structures compared to frame-type structures. Any damage observed in RC walls was primarily due to design and construction work flaws. To overcome these defects, strengthening of existing RC walls is mandatory. In this article, experimental results for six RC shear walls are discussed. The walls were designed to fail in flexure. Four out of the six specimens were strengthened externally with Carbon Fiber Reinforced Polymer (CFRP) strips bonded to the wall panel, and mesh anchors were introduced at the wall foundation joint to limit CFRP debonding. Two specimens, one RC alone and one RC strengthened with CFRP, were subjected to a static load test, and four specimens, one RC alone and three RC strengthened with CFRP, were subjected to cyclic load tests. The test results discussion includes load response, cracking pattern, strength, ultimate displacement and energy dissipation. The CFRP strengthening technique adopted worked well with respect to improving specimen strength, reducing deformity and dissipating energy.

Experimental Approach to Identify the Thermomechanical Behaviour of a Textile Reinforced Concrete (TRC) Subjected to High Temperature and Mechanical Loading

Textile reinforced concrete (TRC), a new generation of cementitious material, is used for different applications in civil engineering. The aim of this paper is to propose a methodology to identify the thermo-mechanical behaviour of the TRC material. The studied TRC composite is made with a cementitious matrix and grid alkali-resistant glass textile. In this study, TRC specimens are subjected to two types of thermomechanical test designated by the loading path 1 and the loading path 2. The results of the thermo-mechanical tests are discussed. This study presents also an experimental methodology, using the digital image correlation (DIC) technique, which permits to identify the specific cracking mode, the crack width and the distance between the cracks of the preheated-cooled TRC specimens as a function of the uniaxial monotonic axial stress. The experimental study is then followed by an analytical model that aims to calibrate existing analytical models (Gibson and Bisby models) for the prediction of the evolution of properties (ultimate stress and post-cracked stiffness) of the TRC material as a function of the temperature.

Experimental Study on the Thermo-Mechanical Behavior of Hand-Made Carbon Fiber Reinforced Polymer (H-CFRP) Simultaneously Subjected to Elevated Temperature and Mechanical Loading

Among two common forms of CFRP used in strengthening/repairing construction structures (pultruded and hand-made), hand-made CFRP is popularly used with column and other structures where the strengthening surfaces are complicated. Normally, the hand-made CFRP (H-CFRP) includes woven carbon fibers, prefabricated in the factory and the polymer matrix which is added during the installation process. When a fire happens, structures and reinforced material are simultaneously exposed to high temperatures (up to 1200 °C) and mechanical loadings, which are complicated and difficult to be experimentally simulated. As far as the authors concern, the studies of CFRP and structure reinforced with CFRP in fire are rare due to expensive cost of experiments and insufficient theoretical calculations. For these reasons, this study aims to investigate the thermo-mechanical behavior of H-CFRP via two different elevated-temperature and mechanical load regimes. The first regime studies the ultimate-strength evolution as the exposed temperature increases while the second studies the variation of rupture temperature when applied load changes. The results from the first regime show that the ultimate strength and the Young modulus of H-CFRP generally reduce 50% and 25% when the applied temperature level increases from 20 °C to 400 °C. The second series show that the rupture temperature of H-CFRP steadily reduces from about 640 °C to about 467 °C as its mechanical stress ratio increases from 0.1 to 0.5 (of its ultimate strength at 20 °C). Remarkably when the mechanical stress ratio of H-CFRP increases to 0.75, the rupture temperature dramatically drops to about 50 °C. The rupture modes and correlation between two regimes will also be discussed.