Monday, February 15, 2016 - 08:39

The competition between Structural Steelwork and Reinforced Concrete in the realm of building construction can be likened to the rivalry between the Springboks and the All Blacks, in the sense that each continually attempts to better the other. The rivalries both on the construction site and on the rugby field have been going for nigh on 100 years and both have their die-hard fans. Fortunately the competition has largely been a healthy one bringing out the best in both.

Structural steelwork had a head start as it took over the design methods, connection and fabrication techniques, previously used for wrought iron, i.e. when steel was made readily available in the 1870s it was used as a one for one substitute for wrought iron. Steelwork is a dry method of construction as it is fabricated in the workshop (off-site) and transported to site, where it is erected. On the other hand reinforced concrete is a wet method of construction, as concrete is poured insitu into temporary shutters, in which steel reinforcement bars have been fixed.

At the beginning of the 20th Century reinforced concrete represented a new technology (patented in France) and was empirically based and lacked an adequate theory for the design of building frames. Plain concrete (cement, sand, stone aggregate and water) was known to the Egyptians and the Romans used it for the dome of the Pantheon in Rome (c. 123 AD), which had a span of 43.4m and still stands to this day.

Frank Lloyd Wright, the noted American architect of Welsh blood, wrote on concrete in 1928, stating that:

Certain truths regarding the material are clear enough. First it is a mass material; second, an impressionable one as to surface; third, it is a material which may be made continuous or monolithic within very wide limits; fourth, it is a material which can be chemicalised, coloured or rendered impervious to water; fifth, it is a willing material when fresh, fragile when still young, stubborn when old, lacking always in tensile strength.

The fifth point was the crux of the matter and the solution was to provide steel reinforcing bars to resist the tensile forces, i.e. in beams and slabs.

During the period between the two world wars (1919-1939), reinforced concrete gained in popularity in the construction of framed buildings, due in part to a greater understanding of its properties and also due to improved methods of structural analysis, i.e. Moment Distribution, by Hardy Cross.

During the Second World War (1939-1945), steel was essential to the war effort. When acute shortages developed it became necessary to find ways of conserving steel. There was an effort to develop other forms of frame construction using more readily procurable materials, which furthered the cause of concrete. When the war was over, Europe and Japan were in ruins and years of reconstruction lay ahead. Reinforced concrete was, with the encouragement of government departments, developed still further and drawing offices were retrained to the requirements of concrete construction.

Steel was down but not out and as the world returned to normality, in the late 1950’s, it made a come back, especially in the construction of medium to high rise office blocks, where speed of erection and hence earlier occupation was often the key advantage over concrete. In the field of single storey, wide span, pitched roofed workshops and warehouses steel has proven to have no equal.

Unfortunately, when the question is asked, why steel? Or why concrete? It frequently degenerates into arguments which attempt to discredit one in favour of the other. However all things considered neither steel nor concrete are really much without the other and there will always be a need for concrete floors and foundations, whatever the structural frame is made from. Instead of having the steel v concrete debate, one should pursue dialogue between steel and concrete, as the aim of the architect and the engineer is to provide the client with the best solution for his project, taking account of initial cost, safety, serviceability and durability.

No other building materials have advanced the built environment as much as steel and concrete and the skylines of the major cities of the world could never have been built without their strength.

 

Joburg Skyline with new Council Chamber under construction (The Heritage Portal)

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