The number of rivets between the column and the shear plate or angle is determined by considering the area exposed to bending, as the outer edges of the base plate and of the shear plate. The load being uniformly distributed, the pressure per square inch is the total load divided by the total area of the base plate, and the load on rivets in the shear plate, therefore, is this unit pressure multiplied by the area over which the shear plate distributes it, as above stated. The balance of the column load may be considered as distributed by direct bearing of the line members on the plate.
It is generally not necessary to use more than six rivets in one line for connection of shear plates, and some system of plates and shear angles should be used so as not to exceed this number, or if this is not possible, a cast iron ribbed base, or a smaller steel plate bearing on steel beams should be used. The exact number of rivets determined as above may be decreased somewhat if this exceeds six, as the plate, even if not supported by the angles or shear plate, is capable of taking some of the load before bending would result. Judgment determines largely how much consideration can be given to this factor.
If the column is an upper section, and rests on the top of another section, the foot is then generally of a character similar to what is shown in Fig. 214. It is, of course, essential that the holes in the foot should match the holes previously detailed in the cap of the lower section. Where a horizontal splice plate is used, this should be large enough to bear over all the line members. Where the column be low is of greater dimension, the fillers must be shipped bolted to the foot of the column.
Cap Details. These are of the general form shown in Figs. 211 and 214. They will vary somewhat according to the sections composing the column. In high buildings it is essential to have vertical splice plates to give the necessary stiffness to the joint. Usu ally this splice plate extends far enough up to take three lines of rivets. The ends of the columns are always faced to true plates at right angles with the axis of the column, and so the splice plate is not designed to transmit any of the vertical load.
In arranging the holes in the cap, it is necessary to consider the section which comes above so as to space these holes to conform to what may he feasible in the foot of the upper section. This other
section may be of smaller dimensions, and it may then be necessary to space the holes in the lower section closer, so as to make it possible to rivet up without interfering with the line members, or coming too near the edge of the connection angle.
Shaft Details. This consists in locating all shelf and bracket angles and connection holes, or other special connections, and in spacing the rivets so as to conform to these connections, and not to exceed the maximum or minimum distance.
The rivets in shelves and brackets having been spaced, and the position of these on the shaft from the top and bottom having been fixed, it only remains to divide the space into as many equal rivet spaces as possible, and put the odd spaces near the top or bottom of the shaft.
Six inches is the maximum pitch allowed, and if the metal through which the rivet goes is less than s in. thick, the maximum pitch is sixteen times this thickness. Three times the diameter of the rivet is the minimum pitch which can be used.
Illustrations of Column Details. In making column de tails, the views are not complete views, regarded as mechanical drawings. The essential feature is clearness and, as the drawing must of necessity show as many details, it is important to omit what is not necessary. For instance, a column which is made up of four angles and a web plate should show, to be complete, the dotted lines indicating the legs of the angles riveted to the web. It adds to the clearness, however, to omit these where a connection comes on the flange. Similarly, in showing a view of the flange, it will add to the clearness to omit showing the connection angles which rivet to the web and are sometimes indicated back of the flange by clotted lines.
In the case of the web view, it is generally necessary to show what is on both sides of the web, as except in special •cases, one elevation only of the web is given.
Fig. 210 gives the detail of the cast iron column shown on the setting plan in Fig. 199. The foot of the column rests on a solid cast iron plate and sets into a ring on this plate to prevent lateral movement. There are a variety of details for holding the foot of the column in place, but this is one very generally used. The rela tion of the bottom of the base plate to the finished floor line should always be given to enable the plate to be set at the proper grade.