In the paper, the short-circuit forces acting on three tubular conductors arranged in an equilateral triangle and constituting a 3-phase system enclosed by a cylindrical aluminium enclosure are examined. The relations for the time functions of the short-circuit forces are developed taking into account the transverse dimensions (diameter) of the conductors. The forces acting on such structures are compared with the forces on structures with filamentary conductors; it results that for usual structures the assumption of filamentary conductors causes a small error in the values of forces; for practical computations the simpler relations that concern forces on filamentary conductors can be used.