Myriam Chaplain

Simulation of synthetic climate at local scale as a mean to assess the impact of climate change on infrastructures

A global modelling approach for estimating the climate influence on corrosion activity in reinforced concrete is developed. It combines: (a) the identification of statistical properties of climates in various temperate regions, and the development of a synthetic simulator able to reproduce its dominant patterns, (b) the identification of an empirical corrosion activity model, based on the analysis of experimental data, highlighting the respective influence of temperature and humidity. Synthetic simulations combining these two models are carried out. They show the complexity of the interactions, since the influence of temperature and humidity may be adverse, and the interest to describe both random fluctuations at daily scale and at seasonal scale. They confirm that monitoring of corrosion must account for this time variability and propose a way to estimate average corrosion even with measurements which would remain limited to a short period. Synthetic simulations are also used for estimating the influence of a global warming scenario on the corrosion activity. A global increase of about 38% of corrosion activity has been estimated in response to an average temperature elevation of 3°C.

Accounting for variability and uncertainties in NDT condition assessment of corroded RC-structures

ABSTRACT The quantitative forecasting of corrosion development remains difficult, limiting the development of validated preventive maintenance strategies. Difficulties come from the spatial variability of material properties, the temporal variability of the environment and the sensitivity of non destructive measurements to changing environmental conditions. The reinforced concrete Barra Bridge, Portugal, has been thoroughly investigated, and on site data have been used for modelling the development of corrosion and its variability. A model has been derived from additional laboratory experiments, which enables to account for the influence of environment and to support the decision process regarding the corrosion state and the forecasting of its evolution.

Modelling time to failure of notched beams under random humidity variations of Atlantic environment

ABSTRACT The mechanical response and durability of timber structures is highly influenced by the atmospheric conditions. Wood mechanical properties depend on moisture content, on temperature and on their variations. To study the lifetime of timber components in their environment, climatic variations are simulated and a lifetime model is proposed. The model predicts the incubation time and the time of crack propagation until the failure. As temperature has a smaller influence on the time to failure than relative humidity, its effects are not directly taken into account in the model. Predictions of the proposed model for various air humidity simulations are compared to creep test results obtained on notched beams under various climatic conditions.

Endommagement du bois lamellé-collé soumis à un chargement de torsion cyclique

ABSTRACT The aim of this paper is to study the behaviour and the lifetime of glued-laminated small scale beams (GL) submitted to cyclic torsion. Experimental programmes have been carried out: periodic triangular alternate torques with varying amplitude are applied to GL samples with rectangular cross section. Experimental lifetime is presented by semi logarithmic SL-N curves (SL is the maximum torque stress level and N is the number of cycles to failure). From angular distortion records, we propose a method to obtain the damage evolution versus time. The prediction of load duration of GL specimens under cyclic torque is approached by a damage theory.

Experimental behaviour of wood columns under cyclic buckling: choice of damage parameters

During earthquakes, structural elements like columns can fail by loss of strength but also by geometric instability such as buckling. The aim of this work is to analyse the experimental carrying capacity of such elements. Buckling experiments on solid wood, laminated veneer lumber and glulam specimens are carried on. Monotonous buckling tests are first carried out, in order to determine loads and displacements at instability point. They are followed by cyclic tests in the post-buckling domain (after peak). The cyclic protocol is precisely defined from displacement values obtained in monotonous tests. A damage parameter is determined based on the evolution of the extreme compression or tension apparent stresses but also on the analysis of stiffness degradation and of variation of dissipated energy during cyclic tests.

Random temperature and humidity models in Atlantic environment

ABSTRACT Moisture and temperature variations have a high influence on building materials behavior, like creep and durability in timber or activity of corrosion in reinforced concrete. Improving the prediction of these behaviors requires a better modeling of these variations. Variations of temperature and humidity recorded during several years at an hourly time step have been analyzed so as to make the part between a deterministic signal (explained by astronomical reasons) and a stochastic part. The variographical analysis for temperature has revealed a correlation structure of about seven days. The humidity is considered as a random variable whose variations are constrained by temperature values and physical laws (air saturation). The combined simulation enables to build synthetic climates, which present the same patterns, in terms of statistical distribution and time dynamics than real data records. These synthetic signals will be used for studying the building materials response under long-term environmental loading. An application to timber durability will be presented in a companion paper.

Damage of Glulam Beams Under Cyclic Torsion: Experiments and Modelling

The aim of this paper is to study the behaviour and the lifetime of glued-laminated small scale beams (GL) submitted to cyclic torsion. Experimental programmes have been carried out: periodic triangular alternate torques with varying amplitude is applied to GL samples with rectangular cross section. Experimental lifetime is presented by semi logarithmic SL-N curves (SL is the maximum torque stress level and N is the number of cycles to failure). From angular distortion records, we propose a method to obtain the damage evolution versus time. The prediction of load duration of GL specimens under cyclic torque is approached by a damage theory. The usual wood damage model proposed by Barrett and Foschi has been chosen. This model does not take into account the influence neither of the frequency nor of the middle moment. Also, to perform the model, we introduce a rheological model in the damage formula and the threshold moment is supposed to depend on the middle moment.

Influence of moisture content on mode I fracture process of Pinus pinaster : evolution of micro-cracking and crack-bridging energies highlighted by bilinear softening in cohesive zone model

This paper is dedicated to the study of the effect of moisture content on fracture properties of wood through the corresponding effect on the softening function used in cohesive zone model to describe quasi-brittle failure of wood. Bi-linear softening parameters of cohesive zone model are estimated from equivalent linear elastic fracture mechanics resistance curve obtained from a significant number of fracture tests performed in mode I for a wide range of moisture contents (from 5 to

Mixed-mode fracture in a quasi-brittle material: R-curve and fracture criterion – Application to wood

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