Steel Buildings in Europe

Part 2: Concept Design 2 - 67 6.3 Corrosion protection The corros ion of steel is an electroch emical process that requ ires the simultaneous presence of water and oxygen. In the absence of either, corrosion does not occur. Hence, f or unprotected st eel in dry environments (e.g. internal steelwork), corrosion will be m inimal. The principal factors that determine the rate of corrosion of steel in air are the proportion of total time during which the surface is wet, due to rainfall, cond ensation etc, and the ty pe and am ount of atmospheric pollution (e.g. sulphates, chlorides, etc.). External steelwork will need corrosi on protection. The local environm ent is important, and can be b roadly classified accord ing to EN ISO 12944-2, which describes categories from C1 (heated in teriors) through to C5 (aggressive marine or industrial environm ent). Many corrosion protection system s are available, including metallic coatings (such as galvanising) and paint system s, and should be chosen based on the environment classification. Occasionally, local regulations demand that even interior steelwork or encased members must have corrosion protecti on, but in general, hidden steelwork inside dry, heated buildings requires no protection at all. 6.4 Temperature effects In theory, steel frames expand and contract with changes in temperature. Often, the temperature change of the steelwork itself is m uch lower than any change in the external temperature, because it is protected. It is recommended that expansion joints are avoided if possible, since these are expensive a nd can be d ifficult to d etail cor rectly to m aintain a weathe r-tight external envelope. In preference to pr oviding expansion joints, the fram e may be analysed including the design e ffects of a tem perature change. The temperature actions m ay be determ ined from EN 1991-1-5, and com binations of actions verified in ac cordance with EN 1990. In most cases, the m embers will be found to be adequate. Common practice for multi-storey buildings in Northern Europe, in the absence of calculations, is tha t expansion joints do not need to be provided unless the length of th e building exceeds 100 m for simple (braced) frames, and 50m in continuous construction. In war mer climates, common pra ctice is to lim it the length to around 80 m. These recomm endations apply to the steel fram e – expansion joints should be provided in stiff external cladding such as brickwork. When expansion jo ints in multi-storey buildings are provided, they are commonly arranged to coincide with significant change s of shape on plan, or at sign ificant changes in floor level, or to separa te parts of the structure on different foundations. 6.5 Fire safety Building designers should consider the im plications of fire resistance when choosing the structural configuration and should address issues such as:  Means of escape.