Research on the Nature of Tower Crane Metal Structures Loading

Abstract

The analysis of the accident rate of crane structures indicates that the most common cause of accidents with tower cranes is the wind load. The wind load is considered under working and non-working condition. In the working state, the maximum wind load is considered, at which the operation of the crane with the rated load is ensured. In the non-working state, the calculation is carried out using the coefficient accounting for the change in dynamic pressure depending on the height of the location from the ground surface of the given structural element in the non-working and working states of the crane. However, the regulatory documents as a rule do not consider the random nature of the wind load, although the research materials on changes in wind speed (gusts), proposed in the scientific and technical literature, indicate the interval character of their action. The objective of the research was to study the nature of loading of the tower crane structures, which makes it possible to assess the change in the oscillatory process in the element of the crane metal structure exposed to the action of the wind load. The design scheme proposed in the article considers the change in intensity of the wind load along the height of the crane and the random nature of its change, which together lead to the occurrence of longitudinal, torsional, and bending vibrations. Oscillations of the crane metal structure were considered by the authors as oscillations of an oscillator with given parameters of the oscillation amplitude, system masses (boom and tower), and the weight of the load being lifted. The mechanical state of the system (rigidity and elasticity) was considered as well. Theoretical studies of the system under consideration were carried out in two versions:1) as of an elastic-viscous medium; 2) as of a continuous system. The results obtained made it possible to reveal the physical nature of the oscillatory process and to carry out quantitative assessment of the change in the loading of the metal structures of the tower crane. The theoretical studies allowed to obtain expression, which makes it possible to evaluate the change in the oscillatory process in the element of the crane metal structure exposed to the action of the wind load, which has a random nature of loading.