Steel Buildings in Europe

Part 2: Concept Design 2 - 11 in the external temperature, because it is protected. It is generally accepted that the movement available when using bolts in clearance holes is sufficient to absorb any movement due to temperature. It is recommended that expansion joints are avoided if possible, since these are expensive and can be difficult to detail correctly to maintain a weather-tight external envelope. In preference to providing expansion joints, the frame may be analysed including the design effects of a temperature change. The temperature actions may be determined from EN 1991-1-5, and combinations of actions verified in accordance with EN 1990. In most cases, the members will be found to be adequate. Common practice for industrial buildings in Northern Europe, in the absence of calculations, is that expansion joints do not need to be provided unless the length of the building exceeds 150m. In warmer climates, common practice is to limit the length to around 80m. Although it is good practice to position the vertical bracing mid-way along the length of the structure, to allow free expansion at both ends of the structure, this is not always possible or desirable. Many orthodox industrial structures have bracing at each end, or at intervals along the length of the structure, with no expansion joints, and perform perfectly well. 1.4.3 Thermal performance and air-tightness The thermal performance of single storey buildings and enclosures is increasingly important because of their large surface area. Thermal performance also includes prevention of excessive heat loss due to air infiltration, known as ‘air-tightness’. There is a strong inter-relationship between the types of cladding and thermal performance. Modern steel cladding systems, such as composite panels, can achieve U-values of less than 0,2 W/(m 2 K). Air-tightness is assessed based on full-scale tests after completion of the structure in which the internal volume is pressurised - generally to 50 Pa (this may vary in different countries). The volume of air that is lost is measured and must be less than a given figure – typically 10m 3 /m 2 /hour. 1.4.4 Fire resistance Fire resistance requirements are dependent on a wide range of issues, such as the combustible contents of the building, effective means of escape and occupation density (e.g. for public spaces). Generally, in single storey buildings, the means of escape is good and most enclosures are designed for fire resistance periods of 30 minutes or less. An exception may be office space attached to these buildings. National regulations are often more concerned to limit fire spread to adjacent structures, rather than the performance of the particular structure, especially if the structure is an industrial building. The determining factor is often the distance to the adjacent boundary. If such regulations apply, the usual solution is to ensure the integrity of the elevation that is adjacent to the boundary. This is commonly ensured by providing cladding with fire resistance, and ensuring that the primary supporting structure remains stable – by protecting the