Floor serviceability under dynamic loading

Some structures such as floors and tall buildings that meet the code design criteria exhibit unacceptable vibrations relative to the human user. In particular, occupants of long-span floors constructed with open-web joists and light-weight concrete are likely to experience perceptible or annoying vibrations due to normal human activity that is characterized by impact, such as walking, dancing, running, and jumping. Thus, it is important that a serviceability criterion based on human response be used at the design stage to avoid costly problems after the floor is constructed and put into service. Note that human response to vibration is a function of the human body characteristics, the intensity and type of the loading, and the characteristics of the structure such as its frequency, stiffness, mass, and damping. In this paper, a serviceability criterion based on the humanload-structure system is presented. This criterion is the value of the absorbed power (rate of energy dissipation) through the human body as represented by a biomechanical model. The absorbed power levels for the thresholds of perception and annoyance were determined and compared with available human comfort curves. The close agreement demonstrates that absorbed power is a good measure of human response to vibration. To demonstrate the usefulness of absorbed power, floor serviceability was assessed due to walking, heel impact, and dancing. Also, the serviceability of forty-one floors was evaluated using absorbed power and compared to the reported subjective assessments. Absorbed power values correctly predicted the serviceability of thirty-nine of the floors. Furthermore, design curves were produced to assist the engineer in designing serviceable floors.