Vibration of Low-Frequency Floors - Dynamic Forces and Response Prediction

Doktorsavhandling, 1994

This thesis deals with methods for predictive calculations of the vibration response of low-frequency floors, i.e. floors with the lowest natural frequency below 7 to 8 Hz, subjected to pedestrian traffic and other dynamic forces. In buildings used as offices and shopping centres pedestrian traffic is the most usual internal cause of perceptible vibrations. The vertical dynamic forces produced by human activity, such as walking, running and jumping, have been established through laboratory measurements. Special attention was focused on how the step frequency and the number of persons participating in the activity influence these forces. Idealised design models of these forces, based on the laboratory measurement results, have been developed. The dynamic behaviour of low-frequency floors, and of floors constructed from prestressed concrete elements in particular, has been studied extensively. Field studies, based on the experimental modal analysis method, of the dynamic behaviour of floors in six existing buildings are presented, as well as computer analyses, based on the finite element method, of three of these structures. The experimental and computational results are compared and a method for modelling the floors to produce predictive calculations of their dynamic properties is presented. Modern buildings are often planned for mixed use. Pure office areas may thus be combined with exercise rooms, goods handling areas and even transportation terminals, within the same structure. This leads to increasing dynamic forces and a need for knowledge of these dynamic actions in order properly to design the buildings for adequate serviceability. The dynamic forces generated by certain vehicles for indoor goods handling have been studied. The thesis also contains a review of research on human sensitivity to low-frequency floor vibration and concepts for vibrational serviceability criteria. A tentative method for serviceability assessments of proposed floor designs is presented.