François Toutlemonde

Experimental Validation of a 10-m-Span Composite UHPFRC–Carbon Fibers–Timber Bridge Concept

This paper presents the experimental study of a new structure for a 10-m-span bridge deck, which takes into account the range of possibilities offered by new and high-strength materials along with the advantages of a traditional environmental friendly material. This 10-m-span element is formed by wooden beams braced at their ends on supports, a thin 7-cm-thick upper slab made of precast ultrahigh performance fiber-reinforced concrete UHPFRC, and fiber-reinforced polymer at the lower chord of these beams. The test program has been aimed at identifying the major critical aspects involved in producing an initial estimate of safety margins as well as validations of the design process and its underlying assumptions. Under the first loading configuration derived from live traffic loads, both the transverse and local bending of the thin UHPFRC slab were activated and confirmed by means of a three-dimensional finite-element computation. The second loading configuration corresponds to pure global longitudinal bending, with the bearing capacity being monitored up to the theoretical ultimate limit state loading and then beyond, up to experimental failure. Critical mechanisms and safety factors have also been identified. Though concept feasibility has been demonstrated, some aspects still need to be further optimized in order to obtain greater ductility and safer control over failure modes and occurrences.

Innovative Design of Ultra High-Performance Fiber Reinforced Concrete Ribbed Slab: Experimental Validation and Preliminary Detailed Analyses

A new generation of cementitious composites, ultra high performance fiber reinforced concrete (UHPFRC), represents an important breakthrough for addressing civil engineering challenges. The most significant feature of UHPFRC is the nearly elasto-plastic ductile behavior in tension, which allows safe exploitation of the tensile and shear capacity in structural elements, while also potentially benefits the dynamic behavior of concrete structures. Where traditional steel elements have shown fatigue resistance problems at the connections in orthotropic slab bridge decks, an attractive application of UHPFRC has been developed within MIKTI coordinated R&D French national project. It consists in a thin 2D-ribbed slab, pre-stressed transversally, made of 2.5 m-long segments connected by post-tension, further connected to conventional longitudinal steel beams which take advantage of the slab lightness. A major critical aspect of the project consists in the safe accounting for local with respect to global bending, even under repeated local fatigue loading. Moreover, safety barriers have to be anchored at the edges of such a thin structure. The capacity of the deck to withstand the load representative of a truck shock, without being damaged before the fuse connecting system of the barrier yields, appears as highly critical also. The detailed design of this innovative structure has been carried out applying French interim recommendations for UHPFRC. However, detailed verifications of the local bending (corresponding to a wheel load directly applied and concentrated over the center of one “honeycomb” delimited by the transverse and longitudinal ribs) and of the behavior of the transverse joint under representative bending loads, require refined Finite Element analyses. Both general design and detailed analyses are being compared to scale one experiments.

Développement d'un conteneur pour l'entreposage de déchets nucléaires: résistance au choc

ABSTRACT The development of a High Integrity Container (HIC) made of Reactive Powder Concrete (RPC) for interim storage of radioactive waste is presented, namely its impact performance. RPC was chosen for durability reasons, then the remaining integrity of the container after a drop test was assessed numerically. The constitutive model developed is suited to describe the behaviour and damage of concretes under high loading rate. RPC is modelled in the frame of degrading plasticity with viscous hardening, its parameters (related to the probable casting mode) have been identified with direct tensile tests at quasi-static to high loading rates. The computations carried out with varied parameters are described. The results agree well with results of 1/3 scaled prototypes. Thus the steps of development of a scale 1:1 prototype container are considered.

Vibration Monitoring of a Small Span Composite Bridge

Small localized damages are hardly detected by global monitoring methods. The effectiveness of vibration based detection depends on the accuracy of the modal parameter estimates and is limited by the low sensitivity of the modal parameters to a local stiffness reduction. A local reduction of stiffness related to frequency changes less than 1 % was successfully detected on a 10 meter span composite UHPFRC - FRP reinforced timber beam bridge loaded in laboratory conditions up to the serviceability limit state (SLS). Such a small decrease in the stiffness was not detected by the monitoring of the static load-deflection measurements but was confirmed by non-linear local strain measurements. Statistical subspace-based damage detection successfully detected the change of the modal parameters of the investigated structure. Further analysis with a finite element model was conducted for assessing the consistency of the expected location and extent of the damaged elements.

Effets structuraux de l'alcali reaction : Apports d'une experimentation sur elements de structures a la validation de modeles

ABSTRACT Assessment of ASR-damaged structures is a major concern for bridge and dam owners in France. Thus, validated models are needed in order to predict the behavior and residual bearing capacity of such works. With this aim, a large experimental program was carried out at the LCPC with EDF as a partner. Measurements were taken from the behavior of structures and specimens placed in various moisture and mechanical environments in order to realize a complete data bank. The mechanical analysis of the measurements showed the significance of ASR-induced strains anisotropy due to stresses, and moisture effect on ASR-induced expansion amplitude, on predicted behavior. They appear to be the main parameters to be accounted for in order to obtain good predictive models.

Experimental study of the influence of the temperature and duration of heat treatments at early age on the risk of concrete expansion associated with Delayed Ettringite Formation

Delayed Ettringite formation (DEF) is an autogenous expansive reaction that can affect concrete. A long enough exposure to high enough temperature are the necessary conditions to develop DEF. The results of experimental laboratory investigations that aim to quantify the effect of thermal history on DEF characteristics (namely magnitude and kinetics of expansion) are presented. A threshold of temperature for the concrete at early age, a pessimum effect with the heating duration and a relation between thermal energy and swelling parameters (kinetics and magnitude) are highlighted.

Risk of Delayed Ettringite Formation in concrete heated at a mature stage: Experimental quantitative evidence

The conditions of development of Delayed Ettringite Formation (DEF) in concrete when submitted to excessive heating during hydration and setting have deserved recent research efforts and tend to be better understood. However, quantitative evidence of DEF risk for concrete submitted to similar heating when mature is still scarce. The experimental program described in this paper confirms the risk of DEF-induced expansion for concrete normally cured, then heated after 90 days of age, when further kept in saturated environment, both for a DEF-prone mix and for a concrete made with a low C3A, low SO3 and low-alkali content-cement.

Numerical Modeling of UHPFRC Tensile Behavior by a Micromechanics FEM Model Taking into Account Fiber Orientation

Ultra High Performance Fiber Reinforced Concrete (UHPFRC) structures are emerging in several engineering applications as their outstanding tensile strength and ductility allow engineers to develop new structural concepts and overcome construction limits. Optimization of the UHPFRC fiber ratio, which has significant economic and technical relevance, is critically related to guaranteeing ductile failure modes of such structures and components, including effects of the scatter of local material properties and post-cracking fiber contributions. A micromechanical model of UHPFRC tensile behavior taking into account fiber orientation, fiber volume ratio, and material parameters concerning the fibers and the cementitious matrix has been implemented in a FEM software. The constitutive law was developed to describe the fiber pullout and the matrix cracking mechanism within a smeared rotating crack framework. We statistically average the orientation of fibers by calibrating the model parameters on results from tomography analysis. The obtained constitutive law is applied to UHPFRC beams with and without reinforcing bars, considering two fiber volume ratios (1% and 2%). The numerical model has shown the capacity to grasp the specimens behavior with and without reinforcing bars.

A New Composite Bridge: Feasibility Validation and Vibration Monitoring

The first part of this article presents the feasibility study of a new structure for a 10-m-span bridge deck, taking into account the possibilities offered by new and high-strength materials and the advantages of a traditional environmental-friendly material. This 10-m-span element is formed by wooden beams braced at the ends, on supports atop a thin slab (7 cm thick) made of pre-cast ultra-high performance fiber-reinforced concrete, and fiber-reinforced polymer at the bottom of the wooden beams. The issue of connecting the ultra-high performance fiber-reinforced concrete to the wooden beams of high but possibly mismatching performance is addressed. An adhesive connection has been considered, following an increasing trend for composite structures where materials savings and optimal performance are searched in every component. The second part of this article presents the vibration-based damage monitoring. Small localized damages are hardly detected by global monitoring methods. The effectiveness of vibration-based detection depends on the accuracy of the modal parameter estimates and is limited by the low sensitivity of the modal parameters to a local stiffness reduction. A local reduction of stiffness related to frequency changes less than 1% was successfully detected on the bridge mockup after loading up to the serviceability limit state (SLS). Such a small decrease in the stiffness was not detected by the monitoring of the static load-deflection measurements but was confirmed by nonlinear local strain measurements. Statistical subspace-based damage detection successfully detected the change of the modal parameters of the investigated structure. Further analysis with a finite element model was conducted for assessing the consistency of the expected location and extent of the damaged elements.

Analyse, dimensionnement et optimisation d'ouvrages de protection contre les chutes de blocs

ABSTRACT The Structurally Dissipating Rock-shed (SDR) is a new kind of protective structures. It uses directly the slab motion and the deformation of slab and fuse supports to dissipate impact energy of rock blocks. In this article, a simple and efficient numerical tool for SDR analyses is firstly presented. It has then been verified by the results of experimental tests. This tool has been applied to parametric design studies of SDR structures. Finally, different kinds of rock impact conditions have been studied with the help of this tool in order to optimize the SDR concept, particularly with respect to the punching shear. All theses studies show the robustness of the SDR concept, and permit to improve its design method.