Aerodynamic Interference Effects And Transiting Test Method For Galloping Of Iced Hangers Of Suspension Bridges

Various types of wind induced vibrations of suspension bridge hangers may arise because of shape changes due to icing,which are dangerous to the structure.The icing phenomenon of hangers become more and more serious because of the frequent occurrence of extremely bad weather in recent years.Wind tunnel tests are conducted to analyze the aerodynamic interference effects of iced hangers of suspension bridges(including pin joint hangers and straddling hangers)in this dissertation.Meanwhile,this study presents a transiting test method to investigate the galloping of iced cable structure.Main contents and achievements of this dissertation are as follows:(1)To solve the problem of the inconsistency between the accuracy and efficiency of aerodynamic testing of iced cable structures,the research was carried out to investigate the interference of wind attack angle increments on the Den Hartog galloping stability of iced hangers by adopting the method of wind tunnel test.The analysis shows that considerable calculation error will be caused directly using the conventional method during the processing and analysis of Den Hartog galloping for the of iced cable structure.The curve fitting of the aerodynamic coefficients of iced hangers in which their characteristics are better presented,e.g.smooth-going characteristic,antisymmetric characteristics and symmetry characteristics,can satisfy the accuracy requirement of the derivation of lift coefficients and then examine the Den Hartog galloping coefficients of iced hangers accurately.In cases where the wind attack angle increments are more than 3°,distortions will occur when determining the range of wind attack angles of Den Hartog galloping.(2)To solve the problem of the lack of research on the aerodynamic interference effects on the iced hangers of suspension bridges(including pin joint hangers and straddling hangers).Wind tunnel tests were conducted based on the aerodynamic theory under various working conditions.The analysis shows that different icing thicknesses greatly influence the aerodynamic characteristics of leeward hangers.Theaerodynamic characteristics of iced leeward hangers are stable when the spacing L of pin joint hangers is in a range 4.8D(hanger diameter)to 6.2D,and the hanger spacings of straddling hangers are the transverse-bridge spacing of 8D and the along-bridge spacing of 4D.The shielding effect of iced windward hanger on iced leeward hanger is large for pin joint hangers within a wind attack angle of 9° and a hanger spacing of L < 6.2D,also for straddling hangers at a wind attack angle of-24°.(3)To solve the problem of the rationality of formula t in the Chinese code(JTG/T 3360-01-2018)(hereafter will be abbreviated as ‘2018 Wind resistance code')when calculating the static wind load on the hangers,the aerodynamic coefficients of leeward hangers under different icing thickness and different icing hanger spacings were studied based on the experimental data obtained from wind tunnel tests.The analysis results show that the lift coefficients must be considered when calculating the static wind load on the iced hangers.However,only drag coefficient is considered in‘2018 Wind resistance code'.While the drag coefficient in the "code" formula should be defined as the aerodynamic coefficient and classified,which can better reflect the stress characteristics of hangers.The aerodynamic coefficients in the formula for calculating static wind load of iced hangers should not be less than 1.3.(4)In order to enrich the research methods of structural wind resistance,a novel test method,named transiting test,using wind generated by a moving vehicle,which can produce relative wind field,for the galloping of iced haners were proposed.Experimental results reveal that the theoretical formula of transiting test method for aerodynamic coefficient of iced cable structure is accurate.Results of transiting test show the aerodynamic coefficient are fairly consistent with those obtained through the wind tunnel test in the related literature,and the galloping caused by transiting test is reproduced.The wake galloping-reduced wind speed0/crU Df of iced pin joint hangers with D-shaped ice and a 4D icing thickness is 165,10.3% lower than that without icing,and the leeward iced hanger is vulnerable to endurance failure.