Field test and analysis of influence factors on the dynamic characteristics of self‑supporting flat arm tower crane under multiple working conditions

In order to obtain more accurate and refined dynamic characteristics of the flat boom tower crane， the field test of the dynamic response of the typical freestanding flat boom tower crane was carried out considering the influence of lifting positions， lifting heights （rope lengths） and lifting weights. The test results show that the vibration along the boom axial direction and vertical direction has good synchronization. However， the response correlation between the horizontal direction of the vertical boom and the axial and vertical direction of the tower crane boom is relatively low. The natural frequencies identified by the half-power bandwidth method and the SSI-COV method are basically the same， with the difference of lifting positions， rope lengths and lifting weights， the natural frequencies of flat boom tower crane will fluctuate around the natural frequency under no load. There are some differences in the identification results of the damping ratio between the two methods， in most working conditions， the damping ratio identified by the SSI-COV method is smaller than that identified by the half power bandwidth method. Based on orthogonal test analysis， the influence of the above factors on the natural frequency and damping ratio of the tower crane is not significant， and there is no main effect. In addition， the finite element model of the flat arm tower crane is optimized， and the frequency of the updated model is in good agreement with the test results. The boom vibration mode function under no‑load condition was fitted， the amplitude distribution along the boom length exhibits an approximately linear， however， when the lifting weight appears at the end or root of the boom， the boom vibration mode may show an obvious nonliner characteristics.