Research On Structural Health Monitoring And Fatigue Life Of Tower Cranes Considering Dynamic Effect

With the rapid economic development,tower cranes are widely used in engineering because of their advantages of large lifting capacity,wide operating space and work efficiency.In recent years,the structural damage of tower cranes have occurred frequently.Research on structural health monitoring and fatigue life of tower cranes is necessary.Due to the complex structure of tower cranes,the research had problems,such as mass data and inefficiency.In this paper,aimed at the structure of tower cranes,deeply and systematically researchs are carried out for structural damage and life evaluation of tower cranes considering dynamic effect.Based on the analysis of the characteristics of the tower crane under different conditions,the load required by the tower crane structure health monitoring is defined.Through analyzing the stress of tower cranes' jib and counter-balance boom,the calculation model of the load is obtained,and the position of the required monitoring component is determined.At the same time,by analyzing the index of the structural damage,appraisal procedure for monitoring the structure of tower cranes is confirmed.Considering dynamic effect,based on the characteristics of tower crane with horizontal boom,the lattice is taken as solid-web structure.A simplified dynamic equation for reducing the degree of freedom is established by using the modal synthesis method in lifting plane and slewing plane.The external load is equivalent to the element node,and the modal superposition method is applied to solve the dynamic equation.The element node load is obtained by obtaining the response of the element node,and the stress response of each component is further calculated and the correctness of the dynamic model is verified.The life evaluation model of tower crane is established by nominal stress method.The stress cycles of component are calculated by the rain flow counting method.The fatigue life of component is obtained by the S-N curves.The damage of component is calculated using the linear fatigue cumulative damage theory.Analyzing the influencing factor of fatigue damage,to establish the cycle coefficient of lifting,amplitude,rotation and unloading.Based on the operating parameters of the tower crane is further proposed.The life assessment model based on the operating parameters of the QT15 type tower crane is established,and the effect of the lifting quality and working range on the fatigue damage of the main string of the tower is analyzed.The multiple loading cases experiments using QT15 tower crane are carried out.According to the external load monitoring strategy to arrange strain gauges to achieve the calculation of external load,verify the correctness and practical feasibility of external load monitoring strategy.Strain gauges are arranged at the root of the main chord of the tower body,and the stress responses under different conditions are extracted and compared with the simplified model calculation results to verify the correctness of the simplified dynamic model.The results of the fatigue damage of the main chord which is calculated based on the nominal stress method and the operating parameter life assessment model are compared to verify the accuracy and actual application value of life assessment methods based on tower crane operating parameters.This paper systematically studies the health monitoring and fatigue life assessment methods of tower cranes,establishes a universally applicable method for monitoring workloads outside work,simplifies the dynamic model and life assessment methods based on tower crane operating parameters to achieve assessment of structure health indicators of tower crane such as overload conditions,overall machine operation stability,structural strength and fatigue life.Provides theoretical monitoring methods for tower crane structure.