The traditional allowable stress method considers the impact on structural safety imposed by loads and uncertainty of material strength by using single safety factor, so it is difficult to deal with safety issues of crane structures under different conditions with different loads. To make the structure more rational thus to play the material properties, the paper desisns the bridse structure by adopting limit state method based on probability theory, and calculates a variety of limit-state-method-based loads through a reasonable combination of loads that may be appear according to the situation in which most adverse effect on the structure is imposed. The paper verifies the structure for qualification in the light of strength, rigidity and stability. And it is proven that the limit state method is more accurate, reasonable, and material-saving than the allowable stress method via calculation and comparison with examples.%传统的许用应力法采用单一的安全系数考虑载荷、材料强度的不确定性对结构安全度的影响,难以处理在不同载荷作用下不同工况起重机结构的安全度问题.为使结构更加合理和发挥材料性能,采用基于概率论的极限状态法设计桥架结构,根据对结构最不利的作用情况,将可能出现的载荷进行合理的组合,计算基于极限状态法的各种载荷.按照强度、刚性和稳定性验证结构是否合格.通过实例计算对比,极限状态法比许用应力法更精确、合理、节材.
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