Documents Menzel, Gertrud 2 results

"The extent of intraspinal forces under whole-body vibration (WBV) depends on several factors like multiple excitations of different body parts, stature and posture. The effects of these forces are determined by individual tolerances. Hence, there is no direct and simple relationship between WBV and health risk of the lumbar spine. The current evaluation methods with respect to health cover only part of the WBV input to the human body and do not consider all associated factors. A set of 50 finite element (FE) models was developed, based on human anatomy and adapted to different typical postures of European drivers and their anthropometric parameters. Three-dimensional matrices of transfer functions simulate these models and permit a practicable routine computation by a Matlab program with graphical user interface to predict intraspinal compressive and shear forces caused by WBV-input in x-, y- and z-directions at the seat, backrest, feet and hands, measured on mobile machinery. The effects of posture and stature on predicted WBV-related internal loads are demonstrated, for example, of numerous WBV-measurements under field conditions. The predicted static and vibration-related peak-to-peak dynamic compressive forces are processed with a method of risk assessment based on cumulative fatigue failure and implemented as a Matlab-program. The resulting risk factors of the new assessment method are compared with existing evaluation procedures of ISO 2631-1 and ISO 2631-5. They reveal significant differences."

"Modelling the response of the human body to occupational whole-body vibration provides the possibility of predicting the forces acting on the disc and/or endplates of lumbar vertebrae. Due to the complex structure of the human body, complex dynamic models based on human anatomy are required to adequately reflect the dynamic properties of the body. Based on experimental results the influence of posture and stature on the biodynamic behaviour of human subjects is described. To reflect the biodynamic response of different occupational groups of workers exposed to whole-body vibration, an existing model was adapted to five typical different postures and 10 representative statures registered of European drivers of heavy machines. The resulting 50 models were tested with white noise signals in three directions as input to the four interfaces buttock, back, feet, and hands. The results of the static and dynamic shares of the predicted spinal forces at six spinal levels show strong influences of the factors stature and posture. Calculated risk factors to estimate a probability of injuries reflect the influence of these factors. Based on these findings one frequency weighting curve for the assessment of vibration exposure is not sufficient to meet the variability of risks caused by different statures and postures."