Civil Engineering Reference
In-Depth Information
based on renewable resources such as timber, or on materials with rich resource
reserves such as clay, lime or stone. The production is preferably local or regional.
The amount of primary energy consumption including transport is approximately
30-40 per cent of the complete house. Pollution due to greenhouse gases carbon
dioxide and acidifying sulphur dioxide will vary from 35-70 per cent. The level of
environmental poisons will probably be much lower, and as waste products the
majority of structural materials are not a problem. As these materials are relative-
ly simple combinations of elements with large dimensions they are well suited for
recycling, but the quantity of binders and the size of the units are decisive factors.
Despite their relatively good environmental profile, the choice of structural
materials is a decisive factor in a building's environmental profile because of
their large volume and weight.
Metal structures
Metal structures are relatively new in building history. Despite this, they have,
together with concrete, become the most common structural systems in large
modern buildings over the past 100 years. Even if metal melts and bends during
a fire, it does not burn, and it is strong and durable in relation to the amount of
material used, and it is 'industrial'.
Aluminium is used in light structures, but steel is without doubt the most impor-
tant structural metal, and is used in foundations, wall, roof and floor structures.
The steel used in structural situations is most often unalloyed, pure steel recy-
cled from scrap. 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 per cent.
Steel components are usually prefabricated as beams with different cross sec-
tions and as square hollow sections, round hollow sections or cables, put togeth-
er to make different sorts of braced or unbraced framework structures. It is nor-
mal practice to weld the components together on site. Steel components can also
be fixed together mechanically, with or without the use of bolts. This consider-
ably increases the opportunities for recycling.
Metal components cause absolutely no emissions or dust problems within a build-
ing. They can, however, 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 increasing stress and depression. When dumping metals a cer-
tain level of seepage of metal ions to the soil and ground water must be assumed.
Both aluminium and steel components can be recycled by re-smelting. It has
also proved profitable to re-use steel components in their original state. In
Denmark, the market value of well-preserved steel components from demolition
