Abstract: This paper diseusses periodio stiffened strips made with two different kinds of materials and each strip with a random oraek or hole. The strueture is under extension along the longitudinal direction. Stress intensity factors at the craek tips are computed by complex variable functions and perturbation method and formulas are given in power series forms. For applied structures in engineering, numerical tables and figures are given for stress intensity factors. These results extend further the contents of "Handbook of Stress Intensity Factors".