This paper presents a heuristic algorithm for discrete design optimization, based on the optimality criteria method. Practical applicability is the first concern; special attention is therefore paid to the implementation of technological constraints. The method is generally applicable, but in order to clarify the idea, it is used in this paper for the optimal design of a Warren type truss composed of steel CHS members with welded joints. For each member, the optimal section is chosen from a given steel catalog. Following Eurocode 3 and the CIDECT design guidelines, restrictions are imposed on the deflections, the member forces, the layout of the joints, and the joint forces. The buildability of the design is ensured by requiring all top chord members and all bottom chord members to have the same outer diameter. The algorithm is successfully applied to a simple test case as well as the example truss design optimization problem. In terms of computational cost, the algorithm is comparable to a continuous optimization scheme based on finite differences, and much faster than an evolutionary algorithm.