A shape and section optimization method is presented for free-form steel structures considering cost of connections. Two types of rigid connections are considered. One is a conventional full-strength connection, and the other is a partial-strength connection using for example fiber reinforced mortar. The inherently different costs of the two are made continuous by introducing a cost increase function of the latter. A nest-structure optimization, consisting of a shape and section optimization as the main problem and cost minimization of each connection as the sub-problem, is proposed to minimize the total cost of members and connections. Examples of a single-layer lattice roof are shown to demonstrate the effectiveness of the proposed method.
