Study On The Optimal Lifting Characteristic Curves For Tower Crane Of Double-suspension And Horizontal Jib With Variable Cross-section

With characteristics of high working efficiency, large rotation radius and great lifting height, tower crane, widely used in the field of industry and civil construction etc., has become the important construction equipment in the building trade. In view of properties of high gravity center, heavy operating load and bad stability, this machine is asserted for the equipment where safe accidents frequently take place. Therefore, the design of its safety protector is especially significant. Among safe protection facilities of tower crane, the torque limiter is one of the most important security protectors. Installed and debugged according to the lifting torque curve of tower crane, the torque limiter can finally finish its debugging after the position of the moment center being confirmed firstly and then the proper lifting torque curve being drawn. At present, the determination of the moment center relies mainly on experience judgments and lacks theories to support.In order to solve the problem that the real lifting characteristics of tower crane are different from the offered lifting torque curve, this thesis, regarding tower crane with double-suspension jib as the research model, focuses study on the determination of the optimal moment center.1. Mechanics analysis on caps of tower crane with different types and the torque limiter at different installation positions is established. Meanwhile, the distortion formulas of the main chord of caps being loaded are set up.2. In analyzing loads of two suspension rods of jib, the method with good precision for composite structure with one degree indeterminacy is applied. During calculating displacement variables of mechanics equations, and , the axial displacement of jib caused by the axial force of the suspension rod of jib is considered, and effects on the optimal moment center, under with and without this axial force, are compared.3. During analyzing cap of tower carne, considering the great fluctuation range of the force of the suspension rod of balance-jib resulting from the change of load, its effects on the distortion of the main chord of caps is discussed. Meanwhile, effects on the optimal moment center, under with and without the aforementioned force, are compared. It is proven that this force cannot be ignored in calculating process.4. Taking the system composite error of the torque limiter as the objective function, the optimization algorithms are proposed based on tabu search with global search capability, and implemented by Matlab program. Experimental results show that taking the root hinge point of jib as the moment center of the torque limiter of tower crane with a double-suspension jib is unsuitable for some kinds of caps of tower crane According to this, the determination method for the optimal moment center of crane tower with different caps and its corresponding precision range are proposed. Then, lifting torque curves of the moment center at different position are obtained. Finally, the description of rules is drawn that the optimal moment center changes with the main parameters of jib.