Birlik G., Sezgin O.

The evaluation of vibration containing shocks (i.e., humps on the roads) can be done by making use of the methods suggested in ISO2631-1:1997 and ISO2631-5:2004.In this study the two standards are compared first using sine impulses as seat accelerations then using field data. While generating the sine impulses crest factor, CF (=2.002) was kept constant, the amplitudes (amplitude range:1-8m/s2) were varied. The range of the spinal acceleration dose, Dk, values indicated in ISO2631-5 were found to be in the range of ~ 0.7-11.The shape of the lumbar z response curve corresponding to seat accelerations, az(seat), having amplitude, A, 6 m/s 2 changed significantly, compared to the shape of the response curve corresponding to az(seat) having A=1 m/s 2.When the duration of the pulse is doubled a slight decrease in the Dk value was observed. The Dk values corresponding to single, double and triple pulses (measurement period =16s) were respectively 0.7, 0.79 and 0.84. Even though the spacing of the double pulses did not change the Dk values, its adverse effect on the psychology of the drivers can not be ignored. The field acceleration time data used in the assessment of the standards was obtained from the measurements performed in a car driven on a track having 6 humps. The cross over velocity was 30km/hr for the humps. When only one hump is considered the VDV values found according to ISO2631-1 were 0.78 on the seat and 0.83 at the lumbar level. The spinal dose value, Dk of ISO2631-5, for one (three) hump was 3.07 (3.43 in case of three humps). The spinal Dk value based on the measured lumbar accelerations however was found to be 3.56 (5.07 in case of 3 humps). It seems that ISO2631-5 overestimates the damping capacity of a person exposed to vibration.