the i beam 12 a body member 36 formed by a pair of panels 38 spaced from each other so as to form a slot 40 therebetween outwardly projects from the outer face 26 of the first plate 24 the plate 24 is further provided with outwardly projecting spaced pintles 42 adapted to receive pintles 44 positioned on the inner edge of the body member 38 a pin 46 is adapted to extend through the pintles 42 44 such that the body member 38 is hingedly connected to the first plate 24 the outer edge of the body member 38 is appropriately shaped to receive a second plate 48 in the open slot 40 such second plate 48 is generally formed from a body portion or tongue 50 of generally triangular configuration which extends into the slot 40 and is fixed in position by a series of bolts and nuts 52 extending through aligned holes not shown extending through the panels 38 and the inner portions of the second plate body portion 50 in this regard the lower portion of the body member 36 is not provided with an open slot 40 but either provided with a lower member welded to both the panels 38 or configured so as to form a shelf 54 upon which the lower edge 56 of the tongue 50 is adapted to rest the outer edge of the tongue 50 is provided with a outer planar surface 58 disposed at right angles thereto and adapted to in turn support the ends of the rigid anchoring platform 20 in contact therewith in that regard the second plate.