Abstract
Three series of novel tensile and flexural creep tests on partially-damaged concrete specimens were carried out in order to gain some insight into creep crack growth and failure of strain-softening materials. In the tests, each specimen was initially loaded to a given point in the descending branch and thus had a lower load-carrying capacity than that at the peak-point. Then, the specimen was unloaded and reloaded to sustain a load which was from 70% to 95% of its current load-carrying capacity. Experimental creep curves display a three-stage process, consisting of primary, secondary and tertiary stages, with a decreasing, constant and increasing creep rate, respectively. The secondary stage dominates the whole failure lifetime, whereas both the secondary and tertiary stages are important in terms of creep deformation. Failure life-time seems to be more sensitive to the change of load level in flexural tests rather than in tensile tests. The decrease in load-carrying capacity due to damage tends to result in a shorter failure lifetime and a lower critical load level for creep rupture. The descending branch of the static load-deflection or load-CMOD curve may be used as an envelope criterion for creep fracture.
Résumé
Trois séries d'essais innovants de fluage à la traction et à la flexion ont été effectuées sur des éprouvettes de béton partiellement endommagées pour étudier la propagation de la fissuration et la rupture des matériaux radoucis. Chaque éprouvette a d'abord été chargée jusqu'à un point donné de la branche descendante, de manière à ce que sa capacité de charge soit inférieure à la charge maximale. Ensuite, l'éprouvette a été déchargée et rechargée pour supporter une charge entre 70% et 95% de sa capacité de charge existante. Les courbes expérimentales du fluage révèlent un processus en trois phases: primaire, secondaire et tertiaire, ayant une vitesse de fluage respectivement décroissante, constante et croissante. La phase secondaire domine pour la durée de vie jusqu'à la rupture, tandis que les phases secondaire et tertiaire sont importantes pour la déformation de fluage. La durée de vie jusqu'à la rupture semble être plus sensible au changement du niveau de charge dans les essais de flexion que dans les essais de traction. La réduction de la capacité de charge due à l'endommagement semble entraîner une plus courte durée de vie jusqu'à la rupture et un niveau inférieur de charge critique pour la rupture de fluage. La branche descendante des courbes statiques chargefléchissement ou charge-CMOD peut être utilisée comme critère enveloppe pour la rupture de fluage.
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Editorial note Prof. A. Carpinteri is a RILEM Senior Member. He was awarded the Robert l'Hermite Medal in 1982 for his outstanding research work. Prof. Carpinteri is involved in the work of RILEM Technical Committees 147-FMB on Fracture Mechanics applications to anchorage and Bond and 148-SSC on Test methods for the Strain Softening response in Concrete, and participates in the Editorial Group of 090-FMA on Fracture Mechanics of Concrete-Applications. Professors A. Carpinteri, S. Valente and F. P. Zhou work at the Politecnico di Torino, Italy, a RILEM Titular Member. Dr. G. Ferrara is a RILEM Senior Member. He also participates in the work of TC 148-SSC.
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Carpinteri, A., Valente, S., Zhou, F.P. et al. Tensile and flexural creep rupture tests on partially-damaged concrete specimens. Mat. Struct. 30, 269–276 (1997). https://doi.org/10.1007/BF02486351
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DOI: https://doi.org/10.1007/BF02486351