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.
A column ordinarily has to carry only vertical loads. There are conditions in which it has to resist lateral forces, but these will be taken up under the heads of "High Buildings" and "Mill Buildings."
Shapes Used. A column may be made of any of the structural shapes that are rolled, or of any combination of them which it is practicable to connect together. In practice, however, there are certain combinations which are commonly used to the exclusion of others. Beams, channels, angles, tees, and zees are all used singly at times, as columns. The more common combination of shapes are shown in Plate I of Part I.
The component parts of these columns will be evident in most cases, from an inspection of the figures. The white spaces between the black lines indicating the different shapes do not represent actual spaces; this is a conventional form to more clearly show the shapes of which the column is composed.
Fig. 5 is a two-angle and a four-angle column. Adjacent legs of the angles are riveted together as indicated. Sometimes plates are riveted between the angles to increase the area of the column or to make simple connections.
Fig. 6 is a four-angle column to which the angles are connected by lattice bars, which come in the position shown by the light line, and run diagonally from side to side of the column for its entire length.
In Fig. 7 a continuous plate is substituted for the lattice bars.
Fig. 8 is a similar column in which one or more plates are added to the outstanding legs, on each side, to increase the area of the column.
Fig. 9 represents a column composed of two channels connected by lattice bars, riveted to the flanges.
In Fig. 10 continuous plates are substituted for the lattice bars.
Fig. 11 is a column similar to Fig. 10, but shows plates riveted to the webs of the channels to stiffen them and to increase the area of the column; these plates have to be riveted before the flange plates are put on."
Fig. 12 is a column of similar shape, but instead of the channels, angles riveted to plates are used. This has the disadvantage, common to Fig. 11, of four extra lines of rivets as compared with Fig. 10. A heavier section can be made, however, than would be possible with any of the channel sections, and a better riveted connection can be made through the flange angle than through the flanges of the channels.
Fig. 13 is known as a "Grey column," and is a patented section. The unshaded lines between the angles represent tie plates which occur about 2 feet 6 inches apart from top to bottom, and serve to connect the angles to each other.
Figs. 14 and 15 are similar to Figs. 9 and 10, the channels being simply turned in instead of out; this is of advantage some times in making connections or when a plain face is desired.
Fig. 16 is called a "Larimer column," and is also a patented section. It consists of two I beams bent in the form shown and riveted together through a special shaped filler, shown unshaded. This column has the same advantage as the Grey column, that it gives a flange on all four sides to make connections with. Neither column is very generally used, however, and when used they are subject to a small royalty charge.
Fig. 17 is a modification of Fig. 8, in which channels are used instead of plates. This gives more simple connections of beams, especially where the beams frame eccentrically with regard to the axis of the column. This section also gives a larger radius of gyration, and has many of the advantages of the Z-bar column shown by Fig. 23, although having four extra lines of rivets.
Fig. 18 is a column having four Z bars connected by tie plates spaced about 3 feet apart, and which are indicated by the unshaded lines.
Fig. 19 is similar except a continuous plate is substituted for the interior tie plates.
Fig. 20 is a section intended to give the form of Fig. 17. The rivets through the beam flanges are objectionable, however, except for light loads and short lengths.
Fig. 21 is a modification of Fig. 19, in order to increase the area.
Fig. 22 is a modification of the usual form of Z-bar column shown by Fig. 23. This gives increased area and a greater spread between the outstanding flanges of the Z bars, which is of advantage sometimes in making- connections.
Fig. 23 is the very generally used Z-bar column. This section has its metal so distributed as to give a high radius of gyration, and its shape makes connections simple. Z bars cost about 1/10 of a cent per pound more than other shapes, and it is not possible, generally, to get so prompt delivery.
Fig. 21 shows the usual method of increasing the area of a Z-bar column by adding plates to the flanges.
Effect of Connections. In order to design a column intelligently, it is necessary to know in every case how the members that are to carry the load to the column are to be connected to it. Types of connection are illustrated by Plates VII and VIII, Figs. 95 to 105.
There is hardly ever a case in which the loads on a column can be exactly balanced so that the center of gravity of the loads will coincide with the axis of the column. Practically, also, the beams on one side may receive their full load while those on the other side are only partially loaded. The effects of eccentricity
Fig 106 of loading are very apparent in tests of the carrying capacity of columns; and, where practicable, a column section should be chosen which will admit of connections bringing the loads as near to the axis of column as possible. If the beams frame symmetrically about the axis of the column and are almost equally loaded, it is not generally necessary, in calculation, to consider the effect of eccentricity. In cases, however, such as frequently occur in connections of spandrel beams and wall girders to columns, this eccentricity should be considered in the calculations.