Columns

Initially there was little incentive to produce columns of wrought iron.

The initial reluctance to use wrought iron for column construction was because:

• designers were working to formulae that gave a rather optimistic view of the strength of cast iron columns.
• at first there was little recognition of the need for columns to carry bending moments due to eccentric loading.

Recognition of eccentric loading meant that the improved properties of wrought iron were needed, and a variety of forms was developed.

Once the effects of eccentric loading were recognised columns had to be assembled from small rollings to provide sections with a similar resistance to bending about both axe. The Pheonix column developed in 1862 by the Phoenix Iron Company of Pheonixville, Pennsylvania  was an early example. It was a cylindrical column assembled from a number of angles rather like the staves of a barrel, but eventually there were many competing forms available.

The Grey column was simpler than the Pheonix column, but not as effective, simply comprising four pairs of angles to form the flanges and a box shaped core of special rollings. Strobel's Z bar column, which in its simplest form was an assembly of four Z sections to form stiff columns and which was used in the Second Rand McNally Building (the first to have an all steel frame) also had the advantage that it could be made up into a wide variety of shapes.

There was understandably an incentive to use sections that were simpler to assemble even if they were less structurally efficient because of the significant costs associated with riveting the components together to form the required profile.

This is a common problem that faces designers. Should one attempt to refine the structure to make the most efficient use of the material or accept some inefficiency in the interests of reducing assembly costs? Freitag, in his thorough analysis of the construction of iron and steel buildings, examined this problem and produced a table showing the quantity of riveting required for a variety of different column sections.

Wrought iron columns were at first detailed rather like cast iron columns with end caps for each length of column to bear against the one below. Eventually, however, this method was replaced by straight splices.

Columns were also formed originally in storey height lengths until it was realised that double height columns with the joints staggered vertically could improve the speed of construction, a change that also affected the design of bracing.

In later buildings for reasons mentioned, the columns were protected by terracotta or brick.

The introduction of straight splices was facilitated by the use of ending or facing machines which ensured that the ends of the columns were 'dead square' so that the ends of the columns could bear against each other.

Terracotta (as cladding) was as important for columns as it was for floors. The stone cladding of buildings was unsuitable as a fire protection because of the tendency for the stone to shatter in a fire, especially if suddenly cooled by fire hoses. Consequently, in later buildings, the columns were protected by terracotta or brick.