The supporting frame (1) has multiple connecting bars (3,4,5) that are connected to each other and provided at their ends with corner connectors (2). The connecting bars are forming a prismatic structure that is provided with a lower base, an upper base and four sides perpendicular to these bases. Each vertex of the lower base is connected to a vertex of the upper base by two cylindrical bars (5a, 5b). The cylindrical bars are connected by a sleeve (6).
