Figs. 166 and 167 show types of built-up-sections of plates and angles adapted to meet special conditions in large columns carrying heavy and diverse loadings.

Fig. 166.

The use of these sections will be further alluded to in detail.

Fig. 167.

Figs. 168 to 170 give sections of columns composed largely of Zed sections combined with plates or latticing.

Fig. 168 is composed of four Zeds and one central plate. Fig.

Fig. 168.

Fig. 169.

169 is of similar section, with additional plates on the outside. Latticing may take the place of these outside plates.

Fig. 170 shows a similar combination with the Zeds turned the reverse way, the metal being disposed to better advantage, though the appearance of the column is perhaps not so satisfactory.

Figs. 171, 172 are sections of a more or less special nature, somewhat less simple in their end connections and the details connecting them with other members than the types above considered.

Fig. 171 is composed of four tees, or four sets of double angles, disposed as shown and connected by bent plates, or trough sections.

Fig. 170.

Fig. 171.

Fig. 172 is a section of a type of column made up of the so-called "trough sections" used for flooring and decking. This combination produces a column of great strength and stiffness, though not so well adapted for secondary connections as others.

Fig. 172.

Fig. 173.

The use of the circular column in any other material than cast iron in ordinary building construction is somewhat limited. Its use in cast iron in the type of section shown in Fig. 173 is too universal and well known to need any further description.

The circular section in mild steel may in small columns take the form of welded tubes, and in larger sections of plates bent to a circular curve and butt-jointed with covers.

In this form we find its use on a large scale in sheer legs, ships' masts, derrick poles, and occasionally in bridge work of very large span. In such structures the circular plate is frequently stiffened internally, and in sections of sufficient size manual labour inside the tube is used for the purposes of riveting.

In Figs. 174 and 175 we have the section generally known as the Phoenix. The figure gives an arrangement in four sections only, but a larger number may be employed in accordance with the size required. This form is one of great stiffness, and in wrought iron has given very high results in the testing machine, possibly owing to the mutual support given by the form of section and the stiffening ribs, and its consequent freedom from local weakness in the unsupported part of the plate.

Fig. 174.

Fig. 175.

Secondary attachments offer some little difficulty with this form of section, and the type most frequently found is that shown in Fig. 175, where filling strips are inserted between the flanges of the segments. This gives the opportunity of insertion of sketch plates wherever required for attachments, the filling strips being stopped off as required. Occasionally the strips are carried right through the diameter of the column.

If we now endeavour to institute a comparison between the sections which have been above described, based either on the grounds of efficiency or economy in first cost, it must be premised that any section can hardly be considered per se without reference to its surroundings, and the use to which it has to be put.

The requirements in detail of the various secondary members which may have to be attached to the simple column will always have an influence in the choice of selection. The design in detail of the cap and base, the attachments for such fittings as counter-shafting brackets, the counterbracing as in the case of the piers to a viaduct, the attachments of traveller, roof, or floor girders will invariably demand careful consideration, and the success of the design as a whole will be influenced by the skill with which these details are worked out.

As regards economy in first cost, other things being equal, it may be assumed that the section having the least amount of riveting will be the cheapest per unit of weight. Thus comparing the built-up sections, we find that Figs. 162, 168 show two lines of rivets, Fig. 155, which is the equivalent of Fig. 162, having no rivets. Figs. 152, 156, 157, 159, 161 will have four lines of rivets, Figs. 169, 170 have six lines, Figs. 158, 160, 163, 164 have eight lines, Fig. 166 has ten lines, while Fig. 167 has eighteen lines.

The extent, however, to which the use of simple sections, with a comparatively small amount of riveting, can be carried, is governed by all the conditions of the case, and the amount of load to be carried.