Abstract: When beams are to be welded to large plates, temporary supporting structures comprising a pair of L-shaped horses, are used, each horse being provided with a slot extending mainly at 45.degree. upwardly/outwardly from the corner formed by the base flange and the waist of the L. A plate member, having a middle portion corresponding to the thickness of the beam and two flanges, angularly disposed with respect to the middle portion, connects the two horses. In use, the weight of the beam rests upon the middle portion of the plate member and locks the horses in supporting position. The horses are preferably provided with screws for clamping the flanges in the slots.