Actions microclimatique et environnementale des ouvrages d'art routier [Microclimatic and environmental actions of road structures]

Les différentes zones d’un ouvrage d’art routier sont étudiées en fonction de leur degré d’exposition au microclimat environnant. Les conditions climatiques provenant de stations météorologiques et la cinétique des véhicules permettent de définir des zones d’exposition aux produits salants et au climat. Une division judicieuse d’un ouvrage en éléments structuraux en fonction de son exposition permet de prendre en considération l’importante variabilité spatiale et de définir des zones de sensibilité équivalente face aux détériorations. Sur la base de stations météorologiques suisses, d’un monitoring d’un ouvrage d’art routier, d’enquêtes auprès des autorités publiques, de mesures ponctuelles in situ et de recherches bibliographiques, cet article met en exergue le microclimat des structures de manière précise. Cette approche permet de définir les différentes zones d’exposition des ouvrages, à savoir les zones de brouillard salin, d’éclaboussures et de stagnation d’eau et de définir l’importance du microclimat en vue de prédire l’évolution des détériorations des structures. -- Various areas of a highway structure are studied regarding their level of exposure to the surrounding microclimate. Climate conditions from meteorological stations and vehicle kinetics are used to determine zones that are exposed to salt products and climate. Dividing a highway into structural elements based on exposure takes into account the significant spatial variation and helps define zones of equivalent sensitivity to deteriorations. Based on Swiss meteorological stations, highway structure monitoring, inquiries with public authorities, in situ spot measuring and literature surveys, this article precisely highlights the microclimate of these structures. This approach can help define the various exposure areas of the structures, namely salt mist, splash and water stagnation areas as well as determine the significance of the microclimate in order to predict the evolution of structural deteriorations.

Microclimatic and environmental actions of road structures

David Conciatori, André-Gilles Dumont

Various areas of a highway structure are studied regarding their level of exposure to the surrounding microclimate. Climate conditions from meteorological stations and vehicle kinetics are used to determine zones that are exposed to salt products and climate. Dividing a highway into structural elements based on exposure takes into account the significant spatial variation and helps define zones of equivalent sensitivity to deteriorations. Based on Swiss meteorological stations, highway structure monitoring, inquiries with public authorities, in situ spot measuring and literature surveys, this article precisely highlights the microclimate of these structures. This approach can help define the various exposure areas of the structures, namely salt mist, splash and water stagnation areas as well as determine the significance of the microclimate in order to predict the evolution of structural deteriorations.

National Research Council Canada2009

Effet du microclimat sur l'initiation de la corrosion des aciers d'armature dans les ouvrages en béton armé

David Conciatori

The deterioration of reinforced concrete structures and the associated rehabilitation work represent an economic cost of premier importance. In Switzerland, the structural maintenance expenditures amount to 40% to 65% of the initial construction cost (over a 100 year life-span). Among the maintenance and rehabilitation activities, those dedicated to combating corrosion constitute the largest portion of invested financial resources. For example, the curbs of each highway bridge need to be repaired every 20 to 30 years, resulting in extensive maintenance and user costs. The corrosion phenomenon is initiated by the presence of oxygen and water acting upon steel reinforcement with a compromised protective oxide film (a natural protective layer surrounding the steel). This protective layer is eliminated by carbonization of the concrete (the reaction between carbondioxide and concrete calcium-hydroxide paste), a sufficient chloride ion concentration around the steel reinforcement (introduced by the spreading of de-icing salts on the roads during winter), or a combination of the two phenomena. The water diffusion in the concrete cover facilitates the chloride ion movement, reducing the corrosion initiation time, and likewise, increasing deterioration rate. This research proposes a model, "TransChlor," to evaluate the duration of the corrosion initiation processes. TransChlor can therefore serve as a decision aid during the structural maintenance plan selection process and during the design of new structural elements to mitigate the steel reinforcement corrosion problem. The model can also complement and elaborate upon the existing codes. TransChlor is based on a structural analysis approach that groups the elements of a structure into distinct groups. Each group is defined by similar functional and structural qualities influencing the corrosion phenomenon (concrete cover permeability, degree of exposure to aggressive corrosive agents, local defects). The model in particular distinguishes the elements exposed to mist and liquid water. This model is based on in-situ measurements (structural monitoring) and inspections performed by trained inspectors. TransChlor employs a deterministic approach to simulate water diffusion, chloride ion diffusion, gas penetration, and thermal conduction. The penetration of liquid water into the concrete pours, called capillary suction, was experimentally studied in the laboratory at low temperatures to match in-situ conditions. These experiments formed the calibration base of this model. TransChlor also incorporates a probabilistic model to consider the variable and indeterminate aspects of the corrosion problem, such as the permeability space, the concrete cover thickness, and the reinforcing steel physical-chemical resistance to chloride ion attack. The deterministic model is refined by the probabilistic approach and together TransChlor offers a more exact evaluation of the corrosion deterioration risks and can facilitate the objective dialogue and discussion between owners and maintenance specialists. For locations exposed to liquid water and brine, the standards should impose additional protective provisions such as periodic hydrophobic impregnations, implementation of stainless steel reinforcing bars, etc. For other locations (exposed to salt spay and carbonated concrete not exposed to chloride ions), the codes should require complementary construction and maintenance provisions.

EPFL2006

Model-free data interpretation for continuous monitoring of complex structures

Daniele Posenato

Structural Health Monitoring (SMH) has the potential to provide reliable, quantitative data on the real condition of structures. Early detection of damage or deterioration can enable preventive repair and reduce maintenance costs. Although obtaining data from monitoring may be easy and fast, the phase of data interpretation is usually complex and expensive in terms of time and resources. An approach to damage detection involves comparisons between predictions from behavioral models and measurements. However, civil engineering structures are difficult to model accurately and this challenge is compounded when structures are built in uncertain environments. Such situations encourage the enhancement of traditional approximate structural assessments through in-service measurements and interpretation of monitoring data. Practitioners encounter difficulties in selecting the data interpretation technique that is most appropriate for continuous monitoring. Only a few studies exist on statistical methods for interpretation of measurements from continuous monitoring. These studies have not included the complexities that arise in practical situations such as measurement noise, missing data and outliers. Moreover, structures are today equipped with hundreds of sensors that measure aspects related to the response and the environment. Therefore algorithms that are able to analyze enormous amounts of heterogeneous data are required for data interpretation. The most innovative contribution of the research work is the definition of new methodologies based on Moving Principal Component Analysis (MPCA) and Robust Regression Analysis (RRA) to detect changes in the behavior of civil engineering structures. The methodology analyzes changes in the patterns of measurement series and is thus able to indicate when and where the damage occurs. The algorithms are designed to learn characteristics of time series generated by sensors during a period called the initialization phase when the structure is assumed to behave normally. The information from the initialization phase subsequently helps in identifying behaviors that can be classified as anomalous. In this manner the proposed methodologies identify anomalous behavior without explicit (and costly) knowledge of structural characteristics such as geometry and behavior models. The methodologies have been tested on data from numerically simulated structures. Studies involved a range of measurement noise levels and a range of damage severities. A comparative study with other statistical methods demonstrates superior performance of the proposed methodologies. The MPCA methodology is extended to accommodate situations of missing data and outliers. Situations of missing complete measurements and missing a single measurement at random are managed with a minimum of extra data pre-processing. A simple and robust cleaning procedure algorithm based on the Inter Quartile Range analysis is presented to remove outliers from measurement series. A clustering algorithm to group measurement series ensures that MPCA is applicable for structures having a significant number of sensors. MPCA is applied to all clusters generated by the clustering algorithm. Finally, MPCA and RRA methodologies have been validated on full scale structures. The results show the ability to identify abrupt permanent changes due to construction stages through time-scale reversal. The results indicate that the proposed methodology can support structural assessments of civil engineering structures.