Understanding fatigue mechanisms in ancient metallic railway bridges: a microscopic study of puddled iron: in 1st International conference on structural integrity (ICSI 2015), Funchal, Madeira, Portugal, 1-4 September 2015

International audienceBeing the second oldest railway network in Europe, almost half of the metallic railway bridges in France were built before the 1900s. At the time, puddled iron was the building material of preference amongst most engineers, hot riveting was the preferred joining method.Considering the ageing of these constructions, as well as the increasing evolution of traffic in the network, the understanding of the behaviour of this type of structures to cyclic loadings is of utmost importance. However, high cycle fatigue characterization is an expensive and time consuming process. The use of a fast characterization method through the measure of self-heating of the specimens during cycling loadings is proposed and analysed.For homogeneous materials, like modern steel, the use of self-heating measurements to estimate fatigue-life related properties has shown good correlation to results obtained by the standard fatigue tests with the advantage of a lower time of characterization. In our case, non-metallic inclusions present in the puddled iron will have an important influence in the response of the material, and therefore the interpretation of the temperature's evolution needs a different approach.Due to its complexity, the integrity of the structure must be analysed from a multi-scaled point of view. For this study, we focused in the quantification of the influence that the population of non-metallic inclusions have on the mechanic and thermal behaviour of a puddled iron. For this purpose, a set of specimens previously tested by the self-heating method were prepared and observed using two different tools: a classic optical microscope and a scanning electron microscope. The relationship between geometric parameters of the inclusions found in the specimens and their temperature response to cyclic loadings was shown. The hypothesis of the presence of micro plasticity (dissipative phenomenon) near inclusions was also validated through SEM observations

Observation of failure scenarios in riveted assemblies: an innovative experimental strategy: in 1st International conference on structural integrity (ICSI 2015), Funchal, Madeira, Portugal, 1-4 September 2015

International audienceHot riveting was largely used as method of assembly in France during the appearing and expansion of the railway network (1840-1940). Present in wrought iron and steel constructions, riveted connections are commonly found in the French railway heritage. Conceived as a permanent assembly, these connections work by the shearing of the rivets and the friction between the plates, such friction is caused by the clamping force due to the cooling of the rivet after forging. The mechanical behavior of the assembly will depend on the many parameters involved in the process. However, three main failure modes have been identified: tension on the plates, shearing of the rivet and bearing in the plates (pressure of rivet on the rivet hole). To understand the influence of friction in the global behavior of the assembly, a comparison between two types of S235 steel specimens is proposed. The first was a set of several hot riveted specimens and in the second one, the rivet was replaced by a martensitic stainless steel axis with a high yield stress that kept the pieces of the connection in place (no clamping force was thus present this time). The behavior of both types of specimens was then studied in tension using 3D Digital Image Correlation to analyze local and global displacements. The comparison between the relative displacements of the connected plates of the two types of specimens allows identifying the influence of friction in the global behavior. To complete this kinematics investigation, failure scenarios are described through longitudinal cross sections analysis

Experimental investigation on hot riveted double shear connections, a friction analysis

International audienc

One-Year analysis of rain and rain erosivity in a tropical volcanic island from UHF wind profiler measurements

International audienceCommunication about One-Year analysis of rain and rain erosivity in a tropical volcanic island from UHF wind profiler measurement

Understanding the behaviour of wrought-iron riveted assemblies: manufacture and testing in France

International audienc

Influence of the MASONRY VAULTS building process on their stiffness: Numerical analysis using a homogenised DAMAGE MODEL including mortar joint shrinkage and induced crack re-closure effect

International audienceThe assessment of masonry structures is more and more useful to characterize the behaviour of masonry walls, tower and bridges. The owner of these constructions would like to understand the mechanical performance of their structures. Experiments and computational methods are two essential elements to accurately study and determine the sensitive points of the edifices. This paper presents the numerical modelling of a vault in undamaged and damaged domain with a macro-homogenisation analysis. The importance of considering the building phases in order to determine the actual stiffness of the structure is highlighted. The numerical tool is a continuous finite element model based on an original anisotropic damage model considering the masonry as a homogenised continuous media. The model is implemented in a massive finite element for three dimensional formulation. It computes the localized damage and allows indicating zones of privileged crack opening in the structure. It is able to predict the cracking zones in large masonry constructions without pre-positioning joint elements. It uses a regularization method ensuring an independence of the numerical response from the mesh. The model includes also a re-closure function for cracks. This re-closure function allows simulating the progressive stiffness restitution during the crack re-closure process. The paper focuses on this aspect in relation with the crack induced by restrained shrinkage of joint mortar during the building history. First, a state of the arts is proposed, then the damage model is presented. In order to validate the model and to propose a global methodology, the damage model is applied to analyse a thin masonry vault previously tested in a laboratory. The numerical results are discussed regarding the experimental ones

Why did most French GPs choose not to join the voluntary national pay-for-performance program?

BACKGROUND: In 2009, a voluntary pay for performance (P4P) scheme for primary care physicians was introduced in France through the 'Contract for Improving Individual Practice' (CAPI). Although the contract could be interrupted at any time and without any penalty, two-thirds of French general practitioners chose not to participate. We studied what factors motivated general practitioners not to subscribe to the P4P contract, and particularly their perception of the ethical risks that may be associated with adhering to a CAPI. METHOD: A cross-sectional survey among French general practitioners using an online questionnaire based on focus group discussion results. Descriptive and multivariate statistical analyses with logistic regression. RESULTS: A sample of 1,016 respondents, representative of French GPs. The variables that were associated with the probability of not signing a CAPI were "discomfort that patients were not informed of the signing of a P4P contract by their doctors" (OR = 8.24, 95% CI = 4.61-14.71), "the risk of conflicts of interest" (OR = 4.50, 95% CI = 2.42-8.35), "perceptions by patients that doctors may risk breaching professional ethics" (OR = 4. 35, 95% CI = 2.43-7.80) and "the risk of excluding the poorest patients" (OR = 2.66, 95% CI = 1.53-4.63). CONCLUSION: The perception of ethical risks associated with P4P may have hampered its success. Although the CAPI was extended to all GPs in 2012, our results question the relevance of the program itself by shedding light on potential adverse effects

Statistical evaluation of fatigue strength of double shear riveted connections and crack growth rates of materials from old bridges

International audienc

Relationship between the CAPI subscription and opinions regarding this contract.

<p>Relationship between the CAPI subscription and opinions regarding this contract.</p

Description of the sample in terms of socio demographic characteristics (n = 1.016).

1<p><i>A ‘Peer Group’ is constituted by 5 to 12 GPs practicing in the same area who meet regularly to exchange on their practices.</i></p