Abstract
The problems in giving significance to the experimental control of deformability at short-term loadings of large-span prestressed structures in order to draw reliable conclusions on their static behaviour have been examined. With this aim the necessity of an exact evaluation of the elastic modulus of concrete together with the importance of its experimental measurement, which is too imprecise if deduced from the strength of concrete, have been pointed out. The work also shows how, by reducing uncertainty in calculating deflection, modulus measurement directly on the structure's concrete (and not only on specimens cast during construction) improves reliability in the evaluation of the static validity of the construction and the exactness of its modelling. In this regard the ultrasonic method can prove very useful. However, we have shown that it can give wrong results—especially when the load test is carried out long after the casting—if we do not make suitable corrections to take into account the evolution with time of the correlation between static and dynamic moduli, an aspect that is usually neglected.
Resume
On examine les problèmes relatifs à la signification du contrôle expérimental de la déformabilité de structures précontraintes de vaste portée soumises à des chargements de courte durée afin de tirer des conclusions sûres sur leur comportement statique. On souligne la nécessité, dans ce but, d'une évaluation exacte du module élastique du béton, en même temps que l'importance de sa mesure expérimentale, qui est trop peu précise si on la déduit de la résistance du béton.
Ce travail montre aussi comment, en réduisant l'incertitude dans le calcul du fléchissement, la mesure directe du module sur le béton de la structure (et pas seulement sur des éprouvettes coulées pendant la construction) améliore la sûreté de l'évaluation de la bonne statique de la construction et la justesse de son modèle.
A ce propos, la méthode ultrasonique peut se révéler très utile. Toutefois, nous avons montré qu'elle peut donner de mauvais résultats—en particulier quand l'essai de charge est effectué longtemps après les moulages—si nous n'effectuons pas les corrections qui conviennent afin de tenir compte de l'évolution dans le temps de la corrélation entre le module statique et dynamique, alors que cet aspect est d'habitude négligé.
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Martinez y Cabrera, F., Pozzo, E. Experimental control of deformability at short-term loadings in testing large-span prestressed structures. Materials and Structures 25, 231–238 (1992). https://doi.org/10.1007/BF02473068
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DOI: https://doi.org/10.1007/BF02473068