Structure System Dynamic Characteristics Research Of A Luffing-jib Tower Crane

With rapidly development of urbanization in our country,intensive construction buildings have sprung up,the luffing-jib tower crane plays a more and more important role in building construction.With constantly development of tower crane in the direction of bigger lifting height and weight,there's an important practical significance of studying the dynamic characteristics of the tower crane structure at the time of satisfying the requirement of static strength,stiffness and stability of the structure.This paper takes the JCD260 luffing-jib tower crane as a research object,the finite element model of the tower crane is set up,static properties and structural response under the impact of pulsating wind loads are analyzed,the dynamic characteristics of the structure system are studied and the dynamic optimization design is carried out.Static stiffness,strength and stability of luffing-jib tower crane are figured out in software ANSYS,the result show that the static stiffness,strength of each component and the stability of compression bar all satisfy the design requirements.On the basis of the method of dynamic response analysis,wind vibration characteristics of a luffing-jib tower crane are studied.Davenport power spectrum of pulsating wind and AR model method are employed to simulate wind velocity of the tower crane pulsating wind field and realized in software MATLAB.The simulation results indicate that the simulated spectrum of pulsating wind is found in good agreement with the target spectrum of pulsating wind,the simulated pulsating wind velocity is reasonable and effective.Modal analysis of the luffing-jib tower crane structure is carried out on the software ANSYS,the first eight orders natural frequency and mode of vibration are obtained.Transient dynamic analysis is adopted to study the dynamic response of the luffing-jib tower crane under the action of pulsating wind loads,comparing to the static analysis results,it indicates that the tower crane structure will have larger vibration along the wind direction and computation results will be unsafe if the pulsating wind is considered.At the initial time,the pulsating wind loads amounts to impact loads and act on the tower crane structure,the structure will be arised a great displacement and stress response,the main segments of tower body roots and the joint of the 4th jib and the 5th jib appear instantaneous abnormally high stress,the structure could be failed.Therefore,it's necessary to take the pulsation effect of wind loads into consideration in the process of wind-resistant design of a tower crane and carry out a dynamic optimization.Harmonic analysis of the luffing-jib tower crane is conducted on the software ANSYS,which finds that the 2nd order modal frequency has a big impact on structure dynamic performance;the working condition of articles suddenly lifting from the ground is determined as the dynamic calculation condition,dynamic response of the tower crane structure is analyzed and the result indicates that the maximum dynamic displacement amplitude is large and all components of the tower crane have a seriously vibration.And then,to make the tower crane structure system has a good static and dynamic performance and a lighter weight,determining the 2nd order modal frequency and the weight of the structure system as the targets of dynamic optimization design,the dynamic stress and displacement of the structure are determined as the status variables.Sensitivity analysis of the tower crane structure system is carried out on software ISIGHT based on the design of experiment method,main design variables of the dynamic optimization are determined.In order to promote the speed of dynamic optimization,response surface approximate model with manageable model errors is established and able to replace the finite element model of the tower crane.Finally,the multi-objective optimization algorithm NSGA-II is utilized in the process of dynamic optimal design of the tower crane structure system,the optimized results indicate that the tower crane has a lighter weight,the static and dynamic performance of the structure have a good improvement.