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Response of spine to vehicular vibration
Date Issued
01-12-2005
Author(s)
Manjusha, J.
Indian Institute of Technology, Madras
Indian Institute of Technology, Madras
Abstract
Drivers of vehicles, such as automobiles, trucks, buses, motor-bikes, etc., experience whole body vibration (WBV). Vibrations in vehicles are transmitted to human beings through the seat, steering system and pedals. Seats possess low natural frequencies and magnify the vibration effect at some frequencies below 10 Hz. If such vibrations are transmitted for a long period, they may even result in spine injury. This is perhaps the most common problem associated with the long-term exposure to whole-body vibration, where the back is especially sensitive to the 4-12 Hz frequency range. In this paper, response of the vibratory model of the human upper torso subjected to random vibrations at the seat of a heavy vehicle has been analysed. The two dimensional biomechanical model of the spinal column (Kitazaki and Griffin, 1997) has 87 degrees of freedom (DOF); each vertebra has fore-and-aft, vertical and rotational degrees of freedom. Initially modal analysis is conducted to obtain the natural frequencies and vibration mode shapes of the spinal column within the frequency range of seat vibrations. Subsequently random response analysis using the mode-superposition method is used to calculate the response. The responses are calculated for each vertebra for three postures (erect, normal and slouched) as well as for young, matured and old persons. The vibration measured at the driver's seat of a heavy vehicle at 30 kmph on a good road has been given as input to the vibratory model of the torso and the response computed. The locations of maximum vertical motions along the spine for normal, erect and slouched postures have been identified. The response has also been computed for young, matured and old subjects. If subjected to high strains for a long period, the ligaments and muscles around these vertebrae may get damaged and this may result in spine injury and pain.
Volume
3