Di Liu

High-frequency steel and concrete floors are often used to support sensitive equipment to minimize vibration response to walking. Equipment vibration tolerance limits are sometimes expressed as waveform peak acceleration, and are more often expressed as narrowband spectral acceleration, or one-third octave spectral velocity. Current methods predict the waveform peak response after a footstep. However, postprocessing beyond what is practical for typical design office usage is often required to predict responses directly comparable to spectral tolerance limits. Also, current methods are not calibrated to provide a specific level of conservatism. This paper presents new methods for predicting the waveform peak acceleration, narrowband spectral acceleration maximum magnitude, and one-third octave spectral velocity maximum magnitude. A total of 89 walking vibration tests were performed on five high-frequency floor bays. The measurements are used to assess the precision of the proposed methods and to calibrate the prediction methods to provide a specific probability that the actual response will exceed the predicted response. The measurements are compared to predictions by the proposed method and five established methods.

When occupants complain of lively floor motion due to human activity, it is often necessary to estimate the dynamic properties of the floor and ascertain the form and level of vibration response toward the goal of designing an effective retrofit solution. The most detailed and accurate experimental method is to determine the natural vibration modes using full experimental modal analysis, which requires substantial equipment including at least one floor shaker, and then determine the acceleration due to walking. However, due to cost and time constraints and possible unacceptable occupant disruption, it may not be possible to perform a full experimental modal analysis. An alternative testing procedure is to use a handheld spectrum analyzer to record floor accelerations due to heel drop and timed walking excitations. These measurements are then used to estimate the natural frequencies and vibration response level, respectively. This paper describes the procedure and compares results with experimental modal analysis techniques. The method is illustrated by a case study of an in-service floor and is shown to be economical, convenient, and effective.

It is sometimes necessary to provide retrofit solutions to objectionable floor vibrations due to human activity. Because such problems are usually detected after the design and construction phases are complete, and the owners have occupied the building, the evaluation of retrofit options must be fast and economical. This paper describes a framework for evaluating retrofit options and presents a case study.

High frequency floors are often used to support sensitive medical, manufacturing, and laboratory equipment to minimize accelerations due to walking and because most types of equipment are less sensitive to high frequency vibration. Therefore, it is important that structural engineers have accurate methods for predicting the magnitude of high frequency floor vibrations and several candidate prediction methods are found in the literature. This research investigates the accuracy of seven most widely accepted high frequency floor vibration prediction methods. In-situ modal and walking tests were performed on four high frequency floors of different types: steel framed floors supporting an operating room, an intensive care unit, and a research laboratory, and a concrete floor that would be suitable for supporting most types of sensitive equipment. Measurements are compared to predictions generated using the widely accepted methods to assess the accuracy of each method. The SCI P354 simplified method most accurately predicted the narrowband acceleration spectrum peak magnitudes and the SCI P331 method most accurately predicted the one-third octave peak magnitudes.