The move from iron to steel

Cast iron had become the standard material of construction for mill and warehouse buildings by the mid-nineteenth century.

Cast iron was a convenient material for construction and had been used successfully in a number of major buildings by the mid-nineteenth century. By then it had become the standard material of construction for mill and warehouse buildings, but problem of its brittle nature led to the search for a more elastic-plastic material.

Fairbairn commented on the difficulties in obtaining sound castings and reported on examples of collapses. Some of these may well have been the result of poor design but an obvious difficulty with such a brittle material was the catastrophic nature of any failure. The superior properties of wrought iron were well known and in 1845 Thomas Cubitt, commenting on the failure of a cast iron structure, called for the development of wrought iron structures to avoid these known defects. Rolled sections were available at that time for roof construction but better sections were needed for use in floor structures and for columns. Development along this line eventually arrived at I-Section beam that has since become the standard form.

Between 1865 and 1909 iron and steel production increased rapidly. Table 1 shows how the levels of production of iron and steel changed. In Europe and the USA between 1865 and 1909 - the critical period in relation to the birth of the steel framed building – there was a rapid rise in steel production as steel framing takes off in the USA.

Year	UK Pig Iron	UK Wrought Iron	Steel (five year averages)
			World	UK	France	Germany	USA
1870-74	6.38	2.60	0.98	0.43	0.13	0.21	0.11
1875-79	6.38	2.27	2.46	0.88	0.25	0.41	0.64
1880-84	8.16	2.01	5.48	1.79	0.45	0.97	1.56
1885-89	7.66	1.91	8.84	2.81	0.53	1.57	2.78
1890-94	7.29	1.93	12.78	3.14	0.76	2.74	4.31
1895-99	8.64	1.15	21.54	4.26	1.24	4.85	7.63
1900-04	8.68	1.16	32.72	4.95	1.67	7.28	13.40
1905-09	9.70	0.94	48.16	5.99	2.60	10.67	20.94

Production of Iron and steel 1865-1906 (millions of tons) (Source: Burnham and Hoskins (1943), Tables 2 and 70)

In the mid 1800s lack of choice of wrought iron sections for beams resulted in the extensive use of plate sections for larger members .

Large plate girders with a profusion of rivets are a common sight on the older railway structures, bridges and stations, along with the ornately capitalled cast iron columns.

Wrought iron was still being used as late as 1910.

Demand for steel grew rapidly from 1870 onwards.

It was the railway industry, in particular which generated much of the early demand, where it was used in rails, wheels and boilers.  In building structures, however, the speed of take-up of the new material was less dramatic and the evolution from the masonry box with iron beams and single (or two) storey columns to the complete frame building that is familiar today was rather tentative.

There are three principal reasons cited for the delays in introducing the steel framed building in the UK.

• the hostile response of some architectural critics to these new forms of construction.
• the lack of supply, and the questionable quality of the steel being produced.
• structural design theories for these new forms had not been developed.

Hughes (1964) comments on the critical response which Peter Ellis received in 1866 in response to his new (and now widely admired) Oriel Chambers building in Liverpool . This iron framed building has strongly expressed 6 inch square, H section columns supporting inverted T beams. It was described by a critic in The Builder as "a vast abortion – which would be depressing were it not so ludicrous".

Jackson (1998) summarises critical reviews that relate to iron and steel buildings; starting with Ruskin' s (1849) "true architecture does not admit iron as a constructive material". However, he notes that there were also numerous articles which challenged or encouraged architects to embrace and work with this new material.

Structural design methods developed were relatively complex.

Structural design methods for framed buildings were being developed over the period 1860 –80. However, they were relatively complex and took a while to filter into design practice. It was a while before the theories were simplified in such a way that they could be applied routinely in practice.  However, it is clear that the quality and reliability of the steel being produced up to about 1880 was in doubt, so it is probably this factor which played a key part in delaying the introduction of the steel frame.