Material developments
It took some time for the rolling technology to be capable of producing I sections with wide flanges that we are familiar with today. The history of early column design reveals the development of techniques such as riveted assemblies to provide the sections required.
At first one of the ways of increasing the size of rolled sections was to heat small wrought iron rollings and force a number of them through the rolls together. This is how the early rail sections were produced. The flat bottom rail used in America was not dissimilar in section to contemporary cast iron joists and thus could be used as a light joist. The Harper and Co. building used 7" (178 mm) rail sections originally ordered for the Cooper Union Building (1855-6). These have been recorded as the first beams rolled for use specifically in a building. The first true American I-beam, which was 9" (229mm) deep, was produced in 1856 for the West Virginia Custom House.
In Britain, the bull-head rail that was in use was not suited for adaptation to building in the same way. Instead it was shipbuilding sections that were used; bulb flats, bulb angles and Ts that were riveted together to form the desired sections. A patent for improving the rollings for ship deck beams came in 1844, over 20 years after angles were first rolled. Kew Palm House (completed 1849) has a rolled section 9" (229 mm) deep, similar to an I-section, but with unequal flanges. It appears that this section did not become used widely. Peterson believes that the probable reason was that it was not as easy to use this unequal flanged section as a deck beam.
Manufacturers strove to produce beams that were both deeper and had wider flanges, and some standardisation of sections was introduced in Britain in 1904.
Naturally, to carry greater loads over greater spans manufacturers strove to produce beams that were both deeper and had wider flanges. In 1867 Klowman set up a rolling mill in Pittsburgh, USA, capable of producing 20" (508 mm) deep beams but it was the universal mill that was needed for the production of wide flanges. These had separate rolls to form the web and the flanges but the development of these mills had to wait until the 1890s.
However, it was not just improvements in rolling technology that were needed. Sections for early wrought iron and steel buildings were rolled to order and different manufacturers each had their own sections. What was required to facilitate design and delivery this standardisation of sections, which was introduced in Britain in 1904 from this date the mills gradually introduced machinery to produce sections at standard sizes.
Improvements in the Bessemer process led to cheaper production of material in greater quantities and with improved properties.
Another development taking place at the same time, which increased the spans that were possible in skeletal construction, was the wider availability of Bessemer steel. The earlier methods of producing steel by the blister or crucible processes could not produce sufficient quantities of steel for construction. The Bessemer process produced steel in large quantities quickly and cheaply, so that it could now be used instead of wrought iron for rolling sections suitable for construction. It did, however, rely on the availability of suitable ores because it could not be used for those with a high phosphorous content. The Bessemer process enabled the production of steels of greater (and more reliable) strength, and also allowed columns of greater heights and beams capable of longer spans. However Bessemer steel was relatively expensive so that it only gradually replaced wrought iron.
The Manhattan Building, Chicago (1890) is a good example of the way in which the relative costs of materials and production methods often affected the choice of materials and cross-sectional shapes in late 19th Century framed buildings. Steel was only used for the major beams, because of its relatively high cost, and wrought iron was used for secondary beams while the columns were of cast iron. The first all steel building was the 2nd Rand McNally Building, Chicago, built in 1889-90 (demolished 1911).
