Investigation On Failure Mechanism And Countermeasures Of Luffing Head Structure Of Luffing-jib Tower Crane

As China’s urbanization process continues to advance,the city available building space is limited,dense high-rise building demand is highlighted,the luffing jib tower crane is increasingly widely used.The luffing head structure is an important part of the luffing mechanism of the luffing jib tower crane.During luffing operation,it bears the luffing load that changes with the elevation angle.The failure of this structure will cause the luffing jib lose its restraint and crash,causing economic loss and even casualties.This paper takes the luffing head structure that fell off in a jib-breaking accident of a luffing jib tower crane as the research object,and studies the failure mechanism and countermeasures,which has practical significance to ensure the safe operation of the luffing jib tower crane.Firstly,the direct cause of falling off failure was determined based on the failure background.The results showed that the side plates of the pin frame was severely deformed.The distance between the plates on both sides has increased.The axial movement of the pin in the left pin-connected joint reached 12 mm.The fall of the luffing structure was caused by the failure of the pin-connected joint.Secondly,the failure mechanism was assumed and verified.From the point of view of strength failure of single member,the material performance test of the side plate of the pin frame and the strength check of the pin were carried out.The results showed that the material performance and strength of the key components meet the requirements.Furthermore,from the point of the view of failure of the restraint relationship between the members,the structural load analysis was carried out,which showed that the pin was subjected to axial load when the side plate was deformed.The critical condition for the axial movement of the pin is that the deformation of the side plate is 0.8mm.Thirdly,the failure process was reproduced by simulation and the structural characteristics of the process were obtained.Using ANSYS Workbench software,the equivalent load method and equivalent displacement method were adopted to make the structure in different states,and the node displacement and stress were selected to characterize the failure characteristics.The results showed that sliding friction occurs in the left axis hole during the deformation process,which verifies the theoretical analysis conclusion,and the structural integrity affects the structural stiffness and reaches the state of failure.In addition,since the luffing head structure experienced the impact of typhoon "Shanzhu" before the failure,it is necessary to consider the impact of typhoon on the structural failure.The harmonic superposition method was used to simulate the pulsating wind velocity time course in MATLAB software,and the simulated spectrum was in good agreement with the Kaimal spectrum.The wind-induced structural response was carried out using ANSYS Workbench software,and the changes of node displacements under different states were compared and analyzed,and the results showed that the pulsating wind would increase the axial runout of the pulley shaft by nearly 1 mm.Finally,countermeasures are given according to the failure mechanism.The safety hazards in design,installation,use and environment are summarized,and targeted countermeasures are proposed.Due to the failure risk and inspection difficulty of the shaft end bolted connection,a design idea of monitoring and shaft on component clearance control system for the shaft end bolted connection is proposed.