This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
1. The base or foot of the column.
3. The cap or top of the column.
4. The connections for other members to the column.
5. The bill of material required to make up the completed column.
A column detail is of necessity more complicated than a beam detail and may at first appear so confused as to be unintelligible. If the student will bear in mind, however, these five features and take each by itself, it will soon become clear.
Details of Base. The character of the base or foot of the column depends upon what it rests. If this is the first section of the column, it will generally rest on a cast iron ribbed base, or a plain steel or cast iron plate. It is the duty of the designer and not of the draftsman to determine which one of these will be used.
Fig. 224 shows a detail of a foot of a column resting on a cast iron ribbed base. The base is always designed so as to take the load of the column by direct bearing between the line members and the top of the base, and the angles which are riveted to the column are intended simply to hold it in position in the base.
If a plain cast iron plate is used, a connection similar to the above would generally be used, because in this case the load would be light and the plate thick enough to withstand the upward pressure without spreading the foot of the column. Such plates must be calculated in the same way explained for bearing plates under beams. See Part II, page 96. The projection of the plate beyond the shaft is exposed to bending just as the plate under a beam is where it projects beyond the flange.
If a steel base plate is used, this is generally riveted to the column and the load then must be spread out beyond the lines of the shaft by vertical plates or angles, called shear plates or angles, so as to avoid an excessive bending moment. The size and shape of this plate are determined by the area required to properly distribute the load on the masonry and the direction in which the foot can be most readily spread by means of the shear plates and angles. The thickness of the plate is determined by the same formula as before used for cast iron and bearing plates; generally it is | or 1 in. thick. The projection is the distance beyond the edge of the shear plate, or the outstanding leg of the shear angle.
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 below 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. Usually 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 be 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 3/8 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 details, 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 dotted lines.