Il rinforzo a taglio di travi in c.a. mediante materiali compositi

Vengono presentate delle relazioni analitiche per progettare il rinforzo a taglio di travi in cemento armato mediante materiali compositi fibrorinforzati (FRP). Le equazioni elaborate consentono di prevedere il contributo del rinforzo in FRP allo stato limite ultimo, da sommarsi a quelli del calcestruzzo e dell’acciaio, in relazione alla configurazione prescelta per il rinforzo. Queste equazioni consentono di esprimere in termini analitici la resistenza efficace dei fogli/strisce di FRP in funzione delle caratteristiche geometriche e meccaniche del rinforzo e dalla geometria del problema. L’accuratezza delle equazioni è stata verificata attraverso studi di correlazione con risultati sperimentali raccolti da numerose prove esistenti in letteratura e da prove eseguite su 13 travi opportunamente progettate e sperimentate in laboratorio con diverse configurazioni del rinforzo in FRP

Structural concrete with recycled aggregate: advances in mechanical properties, durability and sustainability

A large number of tests has been carried out in the last 15 years all around the world to study the possibility to use recycled concrete aggregates (RCA) to produce structural concrete. Earlier tests indicated that RCA concrete had lower properties in comparison to ordinary concrete, such as lower elastic modulus, a more brittle post-elastic behavior, lower workability, higher shrinkage and creep. Most of these issues have been addressed to the content of cement mortar remaining in adhesion to the aggregate after the recycling processes and that cannot be totally eliminated without high economic and ecological costs. This cement mortar which has undergone the crushing process creates zones of weakness in the RCA, causes higher water absorption, higher concrete porosity and causes the decay of the aforementioned properties. More recent tests prove that Recycled Concrete shows this peculiar problems only with a percentage of substitution of standard aggregates with RCA higher than 30%. Under this percentage recycled aggregate concrete (RAC) can be considered as a standard concrete, on condition that an appropriate mix design is performed

Shear strengthening of beams with composite materials

This paper presents the results of an experimental/analytical study aiming at obtaining a clear understanding of the underlying mechanisms of the shear strengthening of reinforced concrete beams with fibre reinforced polymers (FRP). Through the definition of the generalised constitutive law of a bonded FRP sheet, of the compatibility imposed by the shear crack opening, and of the appropriate boundary conditions depending on the strengthening configuration, analytical expressions of the stress field in the FRP sheet crossing a shear crack are obtained. These expressions allow to easily define closed-form equations for the effective strength of FRP strips/sheets used for shear strengthening, as function of both the adopted strengthening configuration and some basic geometric and mechanical parameters. The FRP contribution is then added to those of concrete and steel. The equations accuracy has been verified through correlation studies with experimental results obtained from the literature and from laboratory tests on purposely under-designed real-scale beam specimens, strengthened with different FRP schemes