Steel Buildings in Europe

Part 4: Detailed Design 4 – 23 4.5 Precambering Deflections under permanent loads may be a significant part of the overall deflection of floor beams. This is particularly true for composite floor systems that are constructed without propping (as is recommended for fast, simple construction). In such cases, designers should specify pre-cambering to ensure that the primary and secondary floor systems are flat and level once the structure has been completed. Annex A1 of EN 1990 [5] makes specific provision for recognising the benefits of precambering. 4.6 Dynamic response Annex A.1.4.4 of EN 1990 states the following requirements for the dynamic response of all structures. Vibrations (1) To achieve satisfactory vibration behaviour of buildings and their structural members under serviceability conditions, the following aspects, amongst others, should be considered: a) the comfort of the user; b) the functioning of the structure or its structural members (e.g. cracks in partitions, damage to cladding, sensitivity of building contents to vibrations). Other aspects should be considered for each project and agreed with the client. (2) For the serviceability limit state of a structure or a structural member not to be exceeded when subjected to vibrations, the natural frequency of vibrations of the structure or structural member should be kept above appropriate values which depend upon the function of the building and the source of the vibration, and agreed with the client and/or the relevant authority. (3) If the natural frequency of vibrations of the structure is lower than the appropriate value, a more refined analysis of the dynamic response of the structure, including the consideration of damping, should be performed. Note: for further guidance, see EN 1990-1-1, EN 1990-1-4 and ISO 10137 (4) Possible sources of vibration that should be considered include walking, synchronised movements of people, machinery, ground borne vibrations from traffic, and wind actions. These, and other source, should be specified for each project and agreed with the client. In practice, for low and medium rise buildings for commercial or residential use, the key issue is the dynamic response of the floor system to human excitation, primarily either from walking or from a single heavy ‘foot-fall’.