GB718301A - Improvements in or relating to sheet metal nailable structural members - Google Patents

Abstract

718,301. Sheet metal nailing beams. NATIONAL STEEL CORPORATION. March 18, 1952, No. 6956/S2. Class 20 (2) A sheet metal nailing beam, e.g. an I-section beam, Fig. 1, or a box-section beam, Fig. 7, has web portions defining tortuous nail receiving slots so arranged that a nail driven through a slot is bent through two reverse curves, the second curve having a radius larger than the first curve, and the curved web portions being so relatively proportioned in relation to the two mutually perpendicular co-ordinate axes of the cross-sectional area intersecting at the centre of gravity that both axes are principal gravity axes for the portion of the area formed by the curved web portions, and the cross-sectional area of the nailing beam exclusive of the curved web portion being symmetrical about at least one axis so that the axes are principal gravity axes of the beam. As shown in Fig. 1 an I-beam is bent from a single piece of steel sheet and has spaced web portions 31, 32 and 33<SP>1</SP>, 34 defining tortuous nail receiving slots 33 and 35 of constant width joined by a flat web portion 36. Axes X-X, Y-Y, are mutually perpendicular co-ordinate axes of the cross sectional area and intersect at 0. The web portion 36, flanges 11 and 12 are symmetrical about axes X-X, Y-Y and these axes are gravity axes for this portion of the cross sectional area. The centre line 37 of.the slot 33 is curved through two reverse curves formed by two main axes having centres 52, 5S and two small axes with centres 47, 59, the radius 58 of the second main arc being larger than the radius 54 of the front main arc. The centre line 37 first curves to one side away from the axis Y-Y, then towards it and crossing it, then through an arc on the other side and recrosses it again. An exactly similar arrangement applies to the curved web portions 33', 34 having the centre line 60. The curved web portions 31, 32, 33<SP>1</SP>, 34 have a cross-sectional area which is symmetrical about axis X-X but assymmetrical about axis Y-Y but the curvature of these portions is so arranged in relation to the axis Y-Y, that the axes are both principal gravity axes for this cross-sectional area and therefore for the cross-sectional area of the beam as a whole. The web portions 31, 32 and 33<SP>1</SP>, 34 may be joined by fastening means 90 as described in Specification 595,145. In another embodiment an I-beam, Fig. 4, comprises a pair of channels 100, 101, connected back to back with the webs 104,107 spaced apart to provide the tortuous nail receiving slots 109, 110 each formed with two reverse curves and spaced by flat portions 119, 120. The portion of the cross sectional area of the beam exclusive of the curved web portions is symmetrical about axes X-X, Y-Y, so that there are principal gravity axes for this portion. The cross-sectional area of the curved web portions (and hence the cross-sectional area of the beam as a whole) is however assymmetrical about both axes X-X, Y-Y. The two reverse curves in each of the curved web portions are, however, so arranged in relation to axes X-X, Y-Y, that these axes are principal gravity axes for the curved web portions and therefore of the beam as a whole. To effect this, the second reverse curve portion of the slot 110 must balance the first reverse curve portion of the slot 109 and vice versa, and to do this the area of each second reverse curve portion must be larger than the area of the first reverse curve portion because the distance of the centre of gravity of the second reverse curve portion from axis X-X is less than the distance of the centre of gravity of the first reverse curve portion from the axis X-X. Thus the second reverse curve portions must have a relatively greater area and be curved more gradually than the first reverse curve portions. In a further embodiment an I-beam, Fig. 6, is formed from a single piece of sheet metal and the nail receiving slots have a common second reverse curve and in this case the cross sectional area of the beam is neither symmetrical nor assymmetrical about either axes X-X, Y-Y. The cross-sectional area of the beam except for the curved web portions is symmetrical about axis Y-Y but assymmetrical about axis X-X. The flanges 215<SP>1</SP>, 216<SP>1</SP> 217<SP>1</SP>, 218 are so arranged, however, that the outer surface of the flanges are the same distance from axis X-X and the area of the flanges 217<SP>1</SP>. 218 is at a slightly greater distance from axis X-X than is the area of the flanges 215<SP>1</SP>, 216<SP>1</SP> and for this reason each flange 217<SP>1</SP>, 218 is not quite twice the width of each flange 215<SP>1</SP>, 216<SP>1</SP>. This arrangement together with the reverse curves permit axes X-X, Y-Y to be principal gravity axes of the nailing beam. Fig. 7 shows a box-section comprising two channel members 250, 251 fastened together face to face and having web portions 254, 261 and 256, 262 defining nail receiving slots each formed with two reverse curves so arranged that axes X-X, Y-Y are principal gravity axes.