SHEAR-LAG EFFECT IN CFRP I-BEAMS UNDER 3-POINT BENDING

Shear-lag effect in CFRP (carbon-fiber-reinforced plastic) I-beams is investigated by applying Reissner's method concerning box beams to CFR P I-beams. This modified beam theory (MBT) assumes that the flanges ar e orthotropic and includes the effect of the shearing rigidity of the web and the deformation of the flanges themselves. The anisotropy of t he flanges causes the decrease of the flexural rigidity of I-beams. Th e decrease, however, is restrained by a preventive action on the shear -lag effect in the flanges with a decrease of the anisotropy ratio due to the selection of fiber orientation. In order to verify this MBT, I -beam structures were fabricated from carbon fiber and epoxy resin usi ng three different lay-up schemes: unidirectional, quasi-isotropic, an d a +/-45-deg angle-ply. The stiffness and shear-lag effect of these I -beams were measured and compared with results from the composite beam theory and MBT. The theoretical load-deflection curves and the strain distributions agreed well with the corresponding experimental results .