1.Strength under static stress: Under the action of static stress, the amusement equipment part material has two forms of damage: fracture or plastic deformation.For plastic materials, the calculation can be performed under the condition of no plastic deformation occurs.At this time, the yield limit σs of the material should be taken.As the ultimate stress, the allowable stress [σ] will be  ,So during the formula ,S should be the safety factor.

2.Selection of allowable safety factor: Reasonable selection of allowable safety factor is an important task in strength calculation.If the allowable safety factor is too large, then the machine will be bulky, and it does not meet the economic principle; On the contrary , the machine will not be safety .The amusement equipment  principle of reasonably selecting the allowable safety factor is: on the premise of ensuring safety and reliability, select the smaller allowable safety factor as much as possible.