Abstract: The frame girder for underground drift construction comprises three or more retainer bars (3a, 3b) whose cross sections form a polygon, the retainer bars being affixed to one another by stiffener elements (4). Each stiffener element (4) comprises a number of cross struts (5) bent in their centers and inclined with respect to the retainer bars. The outer ends (9) of the struts (5) are each attached to one of the retainer bars. The stiffener element may be formed symmetrically with respect to a central plane extending obliquely to the retainer bars. The frame girder may be made from conventional round irons. It resists bending, torsion and buckling at very high loads, and no undesirable injection shadows are produced during concreting.

Abstract: The frame girder for underground drift construction comprises three or more retainer bars (3a, 3b) whose cross sections form a polygon, the retainer bars being affixed to one another by stiffener elements (4). Each stiffener element (4) comprises a number of cross struts (5) bent in their centers and inclined with respect to the retainer bars. The outer ends (9) of the struts (5) are each attached to one of the retainer bars. The stiffener element may be formed symmetrically with respect to a central plane extending obliquely to the retainer bars. The frame girder may be made from conventional round irons. It resists bending, torsion and buckling at very high loads, and no undesirable injection shadows are produced during concreting.