基于相似理论的大型桥式起重机结构安全评价试验验证方法

A new method for testing the load-shedding equivalent of giant cranes via the similarity theory

针对大型桥式起重机静载试验大吨位载荷加载困难影响起重机结构安全评价的问题,基于起重机结构设计理论,提出了大型桥式起重机降载当量试验方法,并对降载计算及计算误差进行了探讨。由相似理论建立位移、变形与载荷的关系,以确定相似控制量,通过测试起重机起升载荷较小时的变形和位移,推断起重机起升载荷为极限值时的变形和位移情况。通过逐级加载的方式测试与大型桥式起重机结构特性近似相似的50 t中型双梁桥式起重机跨中截面危险点的应力,将测试应力值与理论计算值进行比较。结果表明,适当降载比例的降载试验能实现一定精度的结构响应预测,可用于起重机结构安全评价。

This paper is aimed at introducing a new method for testing the load-shedding equivalent of giant cranes via the similarity theory. As a matter of fact, it is very difficult to assess the safety grade of large building equipment and installations like a bridge-type crane for it involves too many influential factors. To solve such a kind of complicated problem, we have come up with the load shedding calculation method based on the crane structure design theory and the calculation errors and the load shedding proportion. Due to the complexity of deformation and displacement in the inherent relation with the great load for the bridge-type crane to take the charge of, we do believe that the design theory and the method for finite element analysis should be an ideal simplified method in the case. The reason for our choice of methods is that through testing small deformation and displacement of small crane lifting load, it would be possible for us to gain the stress displacement and their relationship with the heavy lifting loads through the similarity theory, which can help us to determine the amount of similar control. At the same time, the above said theory can also help us to make clear the relation between the deformation and the weight of loading charge due to the crane＇s lifting load limit. It is on the basis of the similarity theory, we have analyzed the stress of the hazard point in the beam cross the section of a 50 tons double girder bridge, which is considered to have similar structural and boundary characteristic features with large bridge cranes. Comparing the testing results with the theoretical calculation, we have worked out the details of the relation between the load shedding calculation and the calculation error probabilities. It is also based on the study of the similarity theory that we have concluded that the derating method for large overhead cranes credibility can provide the safety evaluation means of large bridge-type cranes. From the load shedding engineering examples, the conclusion can be drawn that, with the decrease of derating ratio, the load shedding error also tends to increase, which can offer us a theoretical reference to the load shedding tests as a tool for assessing the large bridge-type crane safety.