The use of the damage tolerance concept is growing in the design of civil engineering structures. The aim of this paper is to provide some guides to help designing anchorages according to the damage tolerance concept. The paper shows the importance of the small defects, idealized like small cracks, in the structural integrity of these elements. The Stress Intensity Factors (SIFs) induced by small cracks in an anchor head of post-tensioned strand anchorage system are calculated. The study includes the evaluation of the influence of the shape of the anchor head on the SIF. The numerical predictions are compared with experimental results of ½ scaled specimens of Poly-methyl-methacrylate (PMMA).