The mechanical performance of FRC to be used for design is measured through standard tests on small beams, of which the RILEM 3-point bending test is one of the most broadly renowned and utilized. Among researchers and practitioners major concerns are being raised about the representativeness of such standard beams for measuring the mechanical properties of FRC for structural design, since such beams could have a better overall post-cracking performance than FRC in a real structure. This is due to their geometry and casting procedure which leads to a more favorable fiber orientation along the longitudinal direction. Hence, more and better oriented fibers could be found bridging the tensile crack of the standard beam than in the respective real-scale structural element. To address this problem, a wide experimental campaign was conducted to compare beams cast according to the standard casting method with beams having different fiber orientations, like isotropic or unfavorable, as typically found in structural elements. Beams with an almost one-dimensional favorable fiber orientation were also tested as an upper bound. The mechanical results are compared with fiber orientation assessments obtained through Image Analysis. This photographic method proves useful to detect the amount and orientation of fibers on a cross-section close to the crack plane of the beams, and a good correlation between mechanical performance and orientation is found. The experimental results show how the standard beams have mechanical performance and orientation values significantly greater than those of typical real structural elements, even if still lower than the best achievable ones. On this basis, a discussion on the safety factors accounting for fiber orientation is presented.
The role of fiber orientation: from standard beams to the real structure
Medeghini F.;Tiberti G.;Plizzari G.;Mark P.
2023-01-01
Abstract
The mechanical performance of FRC to be used for design is measured through standard tests on small beams, of which the RILEM 3-point bending test is one of the most broadly renowned and utilized. Among researchers and practitioners major concerns are being raised about the representativeness of such standard beams for measuring the mechanical properties of FRC for structural design, since such beams could have a better overall post-cracking performance than FRC in a real structure. This is due to their geometry and casting procedure which leads to a more favorable fiber orientation along the longitudinal direction. Hence, more and better oriented fibers could be found bridging the tensile crack of the standard beam than in the respective real-scale structural element. To address this problem, a wide experimental campaign was conducted to compare beams cast according to the standard casting method with beams having different fiber orientations, like isotropic or unfavorable, as typically found in structural elements. Beams with an almost one-dimensional favorable fiber orientation were also tested as an upper bound. The mechanical results are compared with fiber orientation assessments obtained through Image Analysis. This photographic method proves useful to detect the amount and orientation of fibers on a cross-section close to the crack plane of the beams, and a good correlation between mechanical performance and orientation is found. The experimental results show how the standard beams have mechanical performance and orientation values significantly greater than those of typical real structural elements, even if still lower than the best achievable ones. On this basis, a discussion on the safety factors accounting for fiber orientation is presented.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
