According to the principle of equivalent stiffness, we analyze the stability of the whole pipe, and thereby get a theory formula of the critical load of the whole pipe.
根据刚度等效的原则，将井管整体进行稳定性分析，并得到井管整体稳定性临界荷载的理论计算公式。
2
A working chart was constructed for calculating the loop stiffness of plastics pipes, which reflected the inherent characteristics of plastics pipe.
根据塑料管材环刚度计算公式绘编成计算图，该图显示出塑料管材的固有特性。
3
Meanwhile, during the process of filling concrete, the stiffness of steel pipe will change according to the quantity of concrete, and any carelessness may result in accident.