In the process of bridge design, it is necessary to select the best from a number of feasible alternatives by comparison and selection or elimination.The set of criteria used to evaluate and select the satisfactory alternative consists of many qualitative and quantitative factors.Therefore, the selection is a problem of multi-criteria and semi-structural decision making.A new framework and methodology for evaluation of bridge alternatives, which differs from the traditional methods used in semi-structural decision making, is presented in this paper.First the set of criteria for the evaluation of alternatives is established.Next, the method of construction of the relative membership degree matrix, in which both qualitative and quantitative factors are consistent with the uniform calculating standard, is studied.A new weight-assessing method is then developed for calculation of the weightings, based on the relative membership degree matrix and finally a fuzzy optimum model is adopted to select the various alternative bridge designs that satisfy the criteria.A case study is then presented, to show the efficiency and robustness of the new framework and methodology.