A corner piece is provided for interconnecting frame members. The corner piece includes a first plate member defining an inner face, an opposite outer face, a first side face, an opposite second side face, and an end face. The first plate member including a bolt-receiving bore therethrough. A second plate member defines an inner face contiguous with the inner face of the first plate member, an outer face, a first side face, an opposite second side face, and an end face. The second plate member includes a bolt-receiving bore extending between the inner face and the outer face thereof along a first axis generally parallel to the inner face of the first plate member.