Research On The Sudden Unloading Impact Coefficient Of The Luffing Jib Tower Crane

With the rapid development of modern construction industry, the performance of tower cranes put forward higher requirements and as a result, the study of the dynamic load impact coefficient of tower crane has attracted a lot of attention.Sudden unloading as a common working condition of tower crane is and its influence on the tower crane structure is relatively serious, so the studies towards tower crane sudden unloading impact is of important significance to optimize the performance of the tower crane and improve the design of tower crane.This paper select the sudden unloading impact coefficient of the luffing jib tower crane as the object of study, through the establishment of the reasonable dynamic model under sudden unloading working conditions, operate the research on the dynamic characteristics of tower crane structure under different unloading conditions.There are many different forms of tower crane structure.However, the impact does not take into account of the type of tower crane, the size of the level and different conditions towards the sudden unloading impact coefficient in the tower crane design specification. Instead,it simply use a simplify formula, only considering the impact of ratio of the unloading load and the lifting load, and this is not reasonable.Firstly, according to structural characteristics of the tower crane, engineering practical experience and each component contribution to the deformation and vibration, based on the modal synthesis method, this thesis selected the appropriate generalized coordinates and established the dynamic analysis of tower crane model. Through the general dynamic equation,considering the constraint relationship between the various components,it established the equations of motion of the tower crane body,the balance jib, the hanging jib and other components, and obtained the vibration differential equation of the tower crane system.Secondly, this paper established the ANSYS model of FZQ40 and FZQ500 type of tower crane, respectively,operated static analysis and modal analysis and transient analysis under sudden unloading conditions. The results obtained are compared with the results of this method, and the accuracy of the model is verified.Thirdly,this paper conducted the study of the method that the tower crane structure transform from the lattice into solid type.With other parameters unchanged,changes of sudden unloading impact coefficient of the tower crane with different amplitudes and unloading loads and other parameters were studied, and compared with calculating results by the formula in the tower crane design specification.Finally, sudden unloading experiment of FZQ40 type tower crane were carried out.After finishing the preparation for the experiment, measurement of stress of tower crane on four parts in a total of 12 kinds of different working conditions were conducted.The results are compared with the theoretical results under the same conditions, and the rationality of the method is proved.Then this paper conducted a further research about the dynamic characteristics of the tower crane under the sudden unloading conditions.The research of this paper lays a theoretical foundation for the further revision and perfection of the tower crane design specifications.