Overview
ABSTRACT
Over time bridges can lose their value. Indeed the continuous increase in the load carried leads to irreversible damage to the structure, be they visible like cracks or invisible like fatigue. In order to avoid ultimate limit states, both the physical and mechanical state of the work must be assessed. The existing method turns out to be relatively complex as it is based upon both the knowledge and reliability of certain data. This article thus offers a review of this methodology by detailing its main stages: the preliminary diagnosis (a summary assessment of the bridge) and the recalculation (precise assessment of the state of stresses and of the safety margins).
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Read the articleAUTHORS
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Daniel POINEAU: Ingénieur divisionnaire des Travaux Publics de l'Etat – Former Technical Director of Sétra's Major Structures Division - Professor at the École Nationale des Travaux Publics de l'Etat, the École Spéciale des Travaux Publics and the École Supérieure des Ingénieurs des Travaux de la Construction - Consultant
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Jean-Armand CALGARO: Ponts et Chaussées chief engineer - Professor at the École nationale des ponts et chaussées and the Centre des hautes études de la construction - Head of the Research and Regulations Department at Sétra (Service d'études techniques des routes et autoroutes) - This edition is an update of the article by Roger LACROIX and Jean-Arnaud CALGARO, entitled Projet de renforcement ou de réparation d'un pont, published in 1999.
INTRODUCTION
When the intensity of a loading system applied to a structure is progressively increased, its effects cease to be completely reversible beyond a certain threshold, either apparently (e.g. cracking or plasticization) or not immediately (fatigue). In other words, the structure gradually loses its "value". Schematically, this "loss of value" function has two stages, corresponding to the appearance of two families of phenomena idealized by the concepts of "serviceability limit states" and "ultimate limit states". The appearance of disorders is the tangible sign that certain service limit states have been exceeded.
Evaluating an existing structure involves assessing its physical and mechanical condition. It is necessary when it is planned to modify its operating conditions (e.g., increase the number of traffic lanes), or to remedy certain disorders indicative of incipient or advanced pathology (affecting the structure and/or materials). One of the components of the assessment is the estimation of the structural reliability of the structure in question. This is a complex notion, involving both :
determined and random data;
more or less precise knowledge of these data;
the reliability of this knowledge.
On the other hand, elapsed and residual lifetimes can take on a certain importance.
Methods for estimating the structural reliability of an existing bridge are highly sophisticated and the subject of a great deal of theoretical research. What follows is a description of the basic methodology for assessing existing structures.
This dossier follows on from a series of TI articles to which the reader should refer
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Pathology and assessment of existing bridges
Evaluation steps
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