The object of the present work hereby described is to obtain some information about the stresses in reinforced plastic bars. Part one of tests was carried out under bending on a bar with a composite reinforced semi-circular notch. The bars were of epoxy resin reinforced with duralumin. The reinforcements of the semicircular notches are of the concentric, crescent, and arch-types. The relations between the maximum shear stress and breadth of bars are obtained. The most suitable reinforcements are discussed. Part two of tests was carried out under central bending on a composite bar with a hole. The bars were of epoxy resin stiffened with duralumin strips. The relations between the stress-concentration factors of the stiffened models and radii of holes ars obtained.