Gallagher Sean, Marras William S
Auburn University, Department of Industrial and Systems Engineering, Auburn University, AL, USA.
Clin Biomech (Bristol). 2012 Dec;27(10):973-8. doi: 10.1016/j.clinbiomech.2012.08.009. Epub 2012 Sep 8.
The lumbar spine may experience significant shear forces during occupational tasks due to the force of gravity acting on the upper body when bending the trunk forward, or when performing tasks involving pushing or pulling. Shear force limits of 1000 N and 500 N have been recommended by previous authors for maximum permissible limit and action limit, respectively.
The present paper reviews literature in terms of shear tolerance (ultimate shear stress and fatigue life in shear stress) of the lumbar spine and develops recommended limits based on results of studies examining shear loading of human motion segments. Weibull analysis was used to assess fatigue failure data to estimate distributions of failure at different percentages of ultimate shear stress.
Based on Weibull analysis of fatigue failure data from the best available data, a 1000 N shear limit would appear acceptable for occasional exposure to shear loading (≤ 100 loadings/day); however, a 700 N limit would appear appropriate for repetitive shear loading (100-1000 loadings/day) for most workers.
Results of the current analysis support the 1000 N limit for shear stress, but for a rather limited number of cycles (<100 per day). Due to the logarithmic nature of the fatigue failure curve, a 700 N shear limit would appear to be acceptable for frequent shear loadings (100-1000 per day). This value is slightly higher than the action limit of 500 N previously recommended.
在职业任务中，当躯干向前弯曲时，由于重力作用于上半身，或者在执行涉及推或拉的任务时，腰椎可能会承受显著的剪切力。先前的作者分别建议将1000N和500N的剪切力限制作为最大允许极限和行动极限。
本文回顾了关于腰椎剪切耐受性（极限剪切应力和剪切应力下的疲劳寿命）的文献，并根据研究人体运动节段剪切负荷的结果制定了推荐极限。使用威布尔分析来评估疲劳失效数据，以估计在不同百分比的极限剪切应力下的失效分布。
根据对现有最佳数据的疲劳失效数据进行的威布尔分析，对于偶尔暴露于剪切负荷（≤100次/天），1000N的剪切极限似乎是可以接受的；然而，对于大多数工人，700N的极限似乎适用于重复性剪切负荷（100 - 1000次/天）。
当前分析的结果支持1000N的剪切应力极限，但适用于相当有限的循环次数（<100次/天）。由于疲劳失效曲线的对数性质，对于频繁剪切负荷（100 - 1000次/天），700N的剪切极限似乎是可以接受的。这个值略高于先前推荐的500N的行动极限。
