Metal Structures

13.1

Early use of cast Iron In a London railway station.

13.1

Early use of cast Iron In a London railway station.

Basic info is found in Chapter 6.

Metal structures are relatively new in the history of building. Despite this, they have, together with concrete, become the most common structural systems in large buildings over the past 100 years. In industrialized economies, metal structures have also dominated the market for transportable and temporary buildings. Metals may twist or melt during fires but they do not burn, and are strong and durable in relation to the amount of material used; and they are 'industrial' products.

Early structures in cast iron soon gave way to steel (Figure 13.1). Aluminium is used in light structures, but steel is without doubt the most common structural metal, and is used in foundations, walls, roof and floor structures.

The steel used in reinforcement of concrete is usually unalloyed and often recycled from scrap. This means that it corrodes easily. Steel used in columns and beams is very often galvanized. High quality steel is alloyed with small amounts of aluminium and titanium. The resulting material is particularly strong, and means that the amount of material used can be reduced by up to 50%.

Steel components are usually prefabricated in different cross-sections and as square hollow sections, round hollow sections or cables, put together to make different sorts of braced or unbraced framework structures. It is common practice to weld the components together on site. Steel components can also be fixed together mechanically, with or without the use of bolts. This considerably increases ease of recycling.

The production of metal products causes high levels of environmental pollution and emissions as well as being energy intensive. Once installed there are no significant emissions. As with many other materials, one must remember that possible additives may change this picture. For example, surface treatment such as in particular the fireproof coatings required in many steel structures may contain highly toxic substances.

Metal structures can affect the indoor climate by picking up vagrant electrical currents from electrical installations and distributing them around the building. This can result in changes or increases in the electromagnetic fields in the building, which can affect health by inducing sickness and fatigue. When dumping metals, a certain level of seepage of metal ions to the soil and ground water must be assumed.

Both aluminium and steel components can be recycled. It has also proved profitable to re-use steel components in their original state (Addis, 2006). Steel is also widely used in foundation systems such as circular piles, sheet pile walls or tubular elements. Screw piles are significantly easier to withdraw subsequently and recycle (Figure 13.2).

In Denmark, the market value of well-preserved steel components from demolition has reached ten times the scrap value. Old railway lines have been used in the structure of office buildings in Sweden. When re-using metal structural elements, the risk of material fatigue has to be assessed.

13.2

Foundation with screw piling. When the building is demolished the screw piles can easily be unscrewed and re-used. Traditionally screw piling was much used for lighthouses on sandy shores. Source: RW Able, ScrewFast Foundations Ltd.

13.2

Foundation with screw piling. When the building is demolished the screw piles can easily be unscrewed and re-used. Traditionally screw piling was much used for lighthouses on sandy shores. Source: RW Able, ScrewFast Foundations Ltd.

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