Wind loads for tower crane based on section model tests by force balance method
Tower crane is widely used in railway engineering and civil engineering.It is one kind of towering structure systems.Wind load is one of the control loads for tower crane structure design.According to the Design codes for Tower Cranes(GB/T 13752-2017)and Load for the design of Building Structures(GB 50009-2012),drag coefficients of typical wind direction are given for wind resistance design of structures,but estimation methods of wind load on oblique wind direction are lacking.Due to the influence of wind direction and the position of boom and balance arm,there are some obvious wind direction effects and the interference and shielding effects of each part itself on the wind load of tower crane.The wind load estimation for structural design needs to combine the wind load coefficient of each section according to the different position of tower,boom and balance arm.This paper carried out wind tunnel tests for head of the tower crane jib,working arm and balance arm with section model tests with force balance appliance.The effects of turbulence intensity and Reynolds number on the wind loads characteristics of tower crane are studied.Conclusions are drawn as follows.The Reynolds number and turbulent intensity has little effect on the drag coefficients.But the interference between the adjacent segments of the balance arm and the boom will reduce the drag coefficient of the test segment.Under oblique wind conditions,due to adjacent segment interference between the lifting arm and the balancing arm,the calculated values of domestic and foreign standard will be greater than the segment wind tunnel test values under interference conditions.The measured drag coefficients or standardization drag coefficients of the balance arm,crane boom and tower from current wind tunnel tests are close to the values from national standard for normal wind direction.The drag coefficients for each section of tower crane on typical wind direction are given out for design.Based on the wind tunnel test results,the calculation formula of oblique wind load of tower crane is proposed,which can be recommended to the related engineering application,or provide some suggestions for the modification of related specifications.
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