Evaluation and measurement for vibration in buildings - Part 2: Guide to damage levels from groundborne vibration Executive summary Guidelines for the evaluation and measurement of damage levels in buildings from groundborne vibration. Abstract This British Standard, a part of the BS series, gives guidance on the assessment of the possibility of vibration-induced damage in buildings due to a variety of sources, and identifies the factors which influence the vibration response of buildings. This standard is intended to provide a standard procedure for measuring, recording and analysing building vibration together with an accurate record of any damage occurring. Vibrations of both transient and continuous character are considered.
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Natural frequencies are determined by the geometry of the building and the components, the degree of fixity of these components in the structure and the stiffness and mass of each component. Older, low-rise masonry structures tend to have higher natural frequencies in comparison with modern lightweight, flexible and taller buildings.
Higher levels of strain will result when excitation frequencies are close to natural frequencies. A classification of buildings is given in annex A of BS , with an indication of the relative resistance to vibration.
Individual building components such as walls, floors, beams or ceilings have natural frequencies which are usually higher than the frequencies of the building as a whole, and are therefore more susceptible to excitation at resonance by continuously operating machinery, than the building as a whole. In assessing the effect of vibration on building components it should be noted that the dynamic stresses corresponding to a p. A method of estimating peak stress from p. Guidance on specific measurements to be carried out for the purpose of assessing the possibility of vibration-induced damage are given in 6.
Cracking occurs however, due to excessive structural strain, due to either distortion as the building follows movement of the ground or ground motion which causes inertial loading of the building . In some situations, therefore, it may be appropriate to measure strain directly. BSI The preferred method of measuring p. Where it has been demonstrated that time histories are consistent, then, as indicated in 6. The maximum of the three orthogonal components should be used for the assessment, since the majority of data on which guide values have been based are expressed in peak component particle velocity.
True resultant particle velocity is obtained by vectorily summing the three orthogonal components coincident with time. The peak true resultant particle velocity is the maximum value of the true vector sum obtained during a given time interval and should also be derived for reference. NOTE 1 The use of the maximum vector sum, which takes the maximum of each component regardless of the time when it occurs, is discouraged, because it may include a large unknown safety factor. NOTE 2 Where measurements are being made for the purposes of a detailed engineering analysis the peak true resultant particle velocity should be used, and the measuring directions should be recorded.
Measurements should be taken at the base of the building on the side of the building facing the source of vibration, to define the vibration input to the building.
Where this is not feasible, the measurement should be obtained on the ground, outside of the building see also 7. One of the horizontal vibration components should be in the radial direction between the source and the building in the case of ground measurements or oriented parallel with a major axis of the building when investigating structural response.
Vibration measurements at locations other than the base of the building should be taken for the purposes of a more detailed engineering analysis see 9. Detailed guidance is given on coupling the transducer to the building structure in 7. The overall system, and in particular the transducer, should have an adequate sensitivity and frequency range to cover the expected range of vibration frequency and velocity magnitudes. The time duration of the recorded time history will depend upon the character of the excitation, but should be such that the maximum response is recorded and the spectral characteristics are established with appropriate accuracy see 3.
Requirements for the measuring instrumentation are given in clause 6 of BS Periodic checks on the function and calibration of the instrumentation should also be carried out . Calibration of the vibration transducer, should conform to BS Case-history data, taken alone, has so far not provided an adequate basis for identifying thresholds for vibration-induced damage [1,9].
Data from systematic studies [10 to 17], using a carefully controlled vibration source in the vicinity of buildings has therefore been used as the basis for defining damage thresholds. The majority of the data at the higher levels of vibration is usually associated with the effect on residential buildings excited by blasting and constructional activities.
Where initial desk studies indicate that nearby buildings could be at risk, then trial measurements should be carried out to establish the vibration attenuation between the source and these buildings . The survey record should be consistent with the type of investigation required see 9. It is essential that data should be fully and correctly reported.
BS 7385-2 1993
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