MS12.3 - Human-Induced Vibrations in Floors, Staircases and Stadia

Wind can create bidirectional horizontal vibrations in tall buildings, characterized by high displacement and low frequency bandwidth typically between 0.1-1 Hz. Effects of higher frequency vibrations on humans, particularly in the vertical direction, are well researched in the literature since 40s. However, effects of low frequency horizontal vibrations similar to those created by winds in tall buildings are not well understood. This research provides experimental evidences of the effects of such vibrations on human Balance and risk of falls. The experiments are carried out in the state-of-the-art Bath VSimulators facility, enabling realistic simulation of the wind-induced vibrations in tall buildings, and a fully controlled environmental conditions including temperature, and visual and audio cues. The results show significant effects of wind-induced vibrations on balance, even for low vibration magnitudes below 10mg, with up to one standard deviation deterioration in balance parameters compared to the control condition.

Android mobile devices are provided with sensors that allow to monitor several aspects in terms of motion and position of the device; these sensors are hardware-based physical components built into the device, operated by software and mobile apps, providing us with data about motion, temperature, position, and environment in general. Correlation analises on vibration data recorded on structures are at the base of many methods that allow to extract important modal information from the recorded data. This type of data acquisition demands a high level of time accuracy in order the correlation analyses to be successful. It follows that, whenever data is recorded by different mobile devices, some sort of syncronyzation between them is required to allow for the necessary precision in time of the recordings. This paper presents the results obtained with a recent solution in which vibration data is picked up with multiple Android mobile phones equipped with accelerometers, and is then transmitted to a server over a wireless connection to be analyzed in time on the base of a synchronization procedure. The subject of this study are the recodings of the floor vibrations of a recently constructed building.These are compared with the recordings coming from professional grade accelerometric sensors. The capabilities of the proposed recoding technique are discussed on the base of the precision in recovering the mode shapes of a flexible floor from the acceleration records, and also at the ligth of the ralative ease with which Android mobile phones are becoming more available, capable, and less expensive.

Current design methods for vibration serviceability assessment of pedestrian structures are generally based on footfall loading models representing walking over rigid level surfaces rather than oscillating surfaces that might affect the walking pattern. It is largely unknown how footstep forces would be modified due to human-structure dynamic interaction (HSI) if the walking surfaces are vibrating in vertical direction. A two-year project was carried out to identify vertical vibration conditions under which the human-structure interaction occurs. Part of the testing program was conducted on an outdoor footbridge. During the tests, participants walked over either the footbridge or a rigid ground surface at slow, normal and fast pacing frequencies. Ground reaction forces were measured by using insole sensors. The influence of vibration amplitudes and frequency ratios between walking and structural vibration were examined. Comparison of dynamic load factors (DLFs) of footfall loadings on the vibrating footbridge with those on the rigid overground was used to reveal force changes due to HSI. In addition, other parameters such as pacing frequency were also examined. The ultimate goal is to estimate the likelihood of the HSI occurring in any new structure and enable calculation of the vibration response in those cases when the HSI exists.