58 N. Christie et al. project boundary and include footfall, MEP plant, elevators as well as other equipment, machinery and in some cases test rigs. For a new building project, structural vibration from internal sources can be influenced and controlled to some degree by design or through facility management. External vibration sources are those sources which lie outside the project boundary and include surface and underground railway, highway, construction and demolition. Typically the vibration is transmitted from the sources through the ground to the new building foundation in the form of waves. These sources are not within the control of the project but the vibration transmitted from them to the new project must be somehow controlled and managed. Structural vibration has several characteristics which need to be considered in design: frequency, amplitude, wavelength, direction, temporal and spatial. The sources and transmission paths can be complex and the evaluation of vibration and its characteristics requires survey methods as well as modelling and analysis. 7.3 Criteria Criteria for vibration are essentially limits on vibration magnitude above which it is considered that the equipment or process performance might be impaired. Criteria can take the form of generic criteria published in [1, 2] and discussed in [3]. Generic criteria cover general classes of process and vibration sensitive equipment including electron microscopes and are relevant at the planning and even design stages where it may still be too early for specific manufacturer’s equipment to be identified with any confidence. The VC criteria are presented in [3] and shown in Fig. 7.1. The VC criteria have a number of aspects to consider. The VC vibration magnitudes are 100.0 m/s, which is also the average threshold of human vibration perception so the criteria are relevant to small vibrations which are generally subperceptible. The VC criteria are defined over a specific frequency range, namely 1–80 Hz. The format of the vibration is the RMS velocity in the 1/3rd octave band, although as discussed below there are a number of methods in which this can be evaluated. The criteria apply to vibration along the vertical or two horizontal axes. The criteria in [1] are applicable to “vibration measured on the building structure” and similarly in [2], however it is actually the vibration transmitted to the equipment that will be determinative of overall vibration performance. According to the above guidance, the criteria VC-D and VC-E might apply to electron and similar microscope equipment. Manufacturer’s criteria are intended to define limits Fig. 7.1 VC criteria for vibration sensitive equipment
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