The necessity of systematization has been widely discussed for maintanance, diagnosis, repair and rehabilitation of existing bridges. This study was intended to give objective and quantitative basis for the rating and the evaluation of serviceability of cracked reinforced concrete slabs. The factors used to judge the serviceability of slabs were selected and rated quantitatively, and the applicability of the reciprocal averaging method and the fuzzy analysis were tested as the synthetic rating method. The results obtained are summarized as follows:
(1) The current rating method based on “crack density” was not able to evaluate the extent of crack penetration into the slab, and the crack density did not correspond to the load carrying capacity of the slab when it exceeded a certain degree.
(2) The reciprocal averaging method as one of the synthetic rating methods was found to be effectively used by taking more than 3 evaluating factors. It was possible to evaluate quantitivly the relative serviceability by selecting the upper and the lower limits.
(3) The fuzzy analysis may possibly be used to do rating accurately without trying extra measurments and to estimate the type of damage in reinforced concrete slabs.