Large boom tower crane structure, stability of the detailed introduction

DATE:2021-04-20


The characteristics of large boom tower crane: pin connection and high strength bolt connection are adopted between the main structural parts of large boom tower crane, and high strength bolt connection is adopted between the standard joints of tower crane. The high strength bolt bears alternating load and is a very important force transmission connector of the tower body. Favco series tower cranes have been in mainland China for more than 10 years, and some models have been used in 2 to 4 projects. According to the requirements of domestic standard "High Strength Fasteners for Construction Machinery and Equipment" (JG/T5057) on the repeated use of high strength bolts, high strength bolts and nuts shall be disassembled and used again after use, generally no more than two times. And the bolts and nuts removed must be free from any damage, deformation, tooth slip, tooth loss, corrosion, thread roughness changes. Otherwise, it should be prohibited to be used for the connection of the stressed structure. Therefore, special care must be taken for the repeated use of such high strength bolts.

According to the calculation principle of tower crane boom stability, when the stable moment generated by the dead weight of the tower crane boom and the hook is greater than the post-overturning moment generated by the wind, the boom is stable under the working state (no load), and the boom is unstable on the contrary. Taking the installation arm length of 55m in the working state (no load) of M440D as an example, the rated wind pressure in the working state is 250N/m2, and the critical elevation Angle is set as A. Through analysis and calculation, the elevation Angle of the boom in the critical state is A =78°. This is a dangerous state when the boom tower crane is working at rated wind pressure. If there is over-elevation Angle or over-wind speed, it is easy to cause major accidents: the mechanical limit structure of the lifting boom is destroyed under the action of wind force, the top structure of the tower is deformed by impact, and the lifting boom breaks down.



According to the stability calculation principle of the whole machine, the whole machine is stable when the algebraic sum of the overturning moment generated by the wind and the stabilizing moment generated by the whole machine's self-weight is less than the allowable bending moment of the foundation surface under the non-working state of the large boom tower crane (initial installation), otherwise the whole machine is unstable. Taking M440D installation arm length of 55m in non-working state and tower height of 40m as an example, the rated wind pressure is 1100N/m2, and the allowable bending moment of M440D tower crane fixed installation foundation surface is 1120T · m. Let's call the critical elevation a. Through analysis and calculation, the elevation Angle of the boom in critical state is A =39°. This is a dangerous state when the boom tower crane is not working. If there is over-elevation Angle or over-wind speed, it is also easy to cause major accidents and the whole machine will overturn forward. According to the above calculation results and relevant national standards, it can be deduced that the safety distance of tower crane M440D at the same elevation must be greater than 26.4 meters, and it should be adjusted according to the historical wind speed of local typhoon.



Today, the main parameters of domestic large boom tower crane have reached 720t. M. We have reason to believe that as long as the performance indexes of foreign products can reach, the Chinese tower crane products will also be able to achieve. In the construction crane big family, large boom tower crane will continue to lead the way.