As a result of bad quality sealing, moisture and de-icing agents penetrated into pre-stressed hollow core slabs of the top floor in a freely exposed parking garage. Caused by the chlorides the slabs showed especially heavy damage in the support regions near the joints. The theoretical shear bearing capacity according to the technical approval of these slabs was strongly questionable because of the damage. With the help of an experimental loading test in-situ the influence of the damage on the shear bearing capacity of the slabs with different damage-levels could be determined.