Due to the mismatch of mechanical properties in composite laminates, propagation of delami-nation is considered as a severe damage mechanism in beams with various lay-up configurations. Delamination can be generated due to matrix cracking propagation or it can also be initiated due to the manufacturing process before using composite beams. Using a micromechanics model, this study is aimed to investigate the bending moment required for matrix cracking and induced de-lamination in cross-ply composite beams. To that end, a unit cell is selected from the lamina sur-face in a composite beam containing matrix cracking and delamination. Later, the governing equation of stress and displacement fields are extracted in the unit cell to calculate the strain energy release rate due to the propagation of matrix cracking and induced delamination. In or-der to validate this method, the stiffness variations in Carbon-Epoxy cross-ply laminate [90/02]s is examined and the obtained results are compared with the numerical results. It concluded that there is a favorable agreement between the results of the proposed micromechanics model and available numerical results.

This paper aims to experimentally investigate and compare the structural behavior of reinforced concrete straight beam and other beams there made with one, two, and three out of plane parts. The study focused on the effect of the number and location of the out plane parts on the beams mid span deflection, and rotation, as well as the ductility index, cracking loads, and failure modes. Four beams were manufactured with a cross-sectional width of 150 mm and a depth of 200 mm, and 2000 mm in length. All the beams were made with normal strength concrete and constant longitudinal reinforcement ratio 0.011 for negative and positive moment. All the beam specimens were clamped by a special steel fixed ends and subjected to the two-point load up to their failure. The obtained results presented that the load bearing capacity of straight beam was higher than the beams with out of plane parts. Furthermore, the beam with two out of plane parts has capacity higher than the beams with one and three out of plane part by 5.86%, and 55.07%. In addition, the results showed that the ductility increased with increasing number of out of plane parts by 5.52%, and 32.71% as copared with the beam with one out of plane part.