Investigations On Ice Accretion Characteristics And Aerodynamic Performance Of Long-Span Pipeline Suspension Bridges

A pipeline suspension bridge is a suspension structure used to support pipelines(carry oil,natural gas or water)across canyon,river or other obstacle.Pipeline suspension bridges are usually narrow,flexible,lightweight,and blunt,and are really vulnerable to strong wind actions.In areas prone to rime and glaze ice,pipeline suspension bridges may confront the issue of ice accretion.As a result,the aerodynamic shape of bridge will be significantly changed by the ice,which leads decrease of wind-resistance performance of bridge.In the present study,the development of pipeline suspension bridge was firstly reviewed,the domestic and foreign research on the wind-resistance of pipeline suspension bridges in the past 20 years were systematically reviewed,and the issues that have not yet been fully resolved were pointed out.On this basis,three problems,i.e.,ice characteristic of pipeline suspension bridge,aerodynamic performance of ice-accreted circular cylinder,and wind-resistance performance of pipeline suspension bridge,were studied in depth.The main contents and conclusions were as follow:(1)Icing tests of some main components(pipelines,wind hangers and section steels)and rigid sectional model of girders of pipeline bridges were investigated in a refrigerated precipitation icing laboratory(i.e.,precipitation rate was 45 mm/h,air temperature was-7℃,and average humidity was 80%).The effect of pipeline diameter,section steel size,icing duration,and inclined angle on ice accretion characteristic on pipeline,wing hanger,and section steel were investigated.And the results found that the ice size and shape on the pipeline were closely related to the pipeline diameter and icing duration.The ice shape and size on wind hangers and section steels changed with their inclined angles.The engineering ice models on large-diameter ice-accreted circular cylinder and pipeline suspension bridge were extracted based on experimental results,which can be used to further study the effect of ice accretion on aerodynamic performance of large-diameter circular cylinder and pipeline bridges.(2)The characteristic of flow field around the finite ice-accreted circular cylinder was investigated based on force balance tests and pressure measurement wind tunnel tests.And the influence rule of ice accretion on the aerodynamic force coefficients of circular cylinder under high Reynolds number(Re)was studied.The influences of Re,ice shape,wind angle of attack,turbulence intensity,and surface roughness were comprehensively investigated.Experimental results found that the mean aerodynamic force coefficients(MAFCs)of the ice-accreted cylinders exhibited significant Reynolds number effects.The effects of surface roughness and turbulence intensity on the Reynolds number effect of drag force of the ice-accreted and ice-free cylinders were similar.The lift force and pitching moment of uniform ice-accreted cylinder were significant,and the lift force could be reduced by increasing surface roughness and turbulence.The flow-fields around the finite ice-free and ice-accreted cylinders had significant three-dimensional effects,which could be weakened by introducing the surface roughness and turbulence.It was too simplified that the glaze ice accretion on a circular structure is considered as a uniform layer around surface in the international standard ISO 12494.The influence of ice shape,surface roughness,and turbulence intensity on MAFCs should be considered in the wind-resistant design of circular cylinder.(3)Based on static force tests and free vibration tests,the effects of design parameters of section,ice accretion and Re on aerostatic characteristic of the girder of pipeline suspension bridge,meanwhile the effects of close grate plate,torsion-bending ratio and ice accretion on aerodynamic stability of the pipeline suspension bridges,were analyzed and summarized.Three typical sections of the girder of pipeline suspension bridge were selected,and the effect of perforation rate of grate plate,pipeline spacing,pipeline diameter,pipeline number,surface roughness,Re,ice class and ice shape on aerodynamic force coefficients and/or flutter derivatives were comprehensively studied.The results found that optimizing the penetration rate of grate plate and the pipeline spacing can reduce the aerostatic load on the girder;the aerodynamic force coefficients increased with increasing pipeline number;pipeline diameter and surface roughness had significant effect on aerodynamic force coefficients;the aerodynamic force coefficients of pipeline suspension bridge had a certain Reynolds number effect,closing grate plate will reduce the aerodynamic stability of the girder.Due to the larger windward area and the more asymmetric section after the pipeline bridge with ice accretion,the aerodynamic force of ice-accreted section maybe increased.The effect of ice accretion should be considered in the wind-resistant design of the same type of girder of pipeline suspension bridge.(4)The effects of pipeline diameter,ice shape on pipeline,turbulence intensity,pipeline number,initial wind angle of attack,wind cable initial tensile force,inclined angle of wind hanger,and hanger breakage on the aerostatic and buffeting response of pipeline suspension bridge were comprehensively studied based on wind tunnel tests of a full bridge aeroelastic model with 1:25 scale ratio.The varieties of displacements of girder and wind cable tensile forces were emphatically analyzed.The theoretical formulas to calculate the displacements of three-degree-of-freedom motion by using Micro-Epsilon Sensors and Video Gauge were respectively derived.The differences between the original and modified displacements were investigated.The results showed that the horizontal aerostatic displacements are prominent since the blunt section.The buffeting displacements were significant,therefore great attention should be paid to the wind-induced fatigue caused by buffeting.The aerostatic and buffeting response were significantly effect by wind angle of attack,pipeline diameter,turbulence intensity,pipeline number,and ice accretion.Optimizing the initial tension force of wind cable and the inclined angle of the wind hanger can develop the stiffness of the bridge,therefore the aerostatic and buffeting response were reduced.The aerodynamic performance of pipeline suspension bridge was little effect by the breakage of some hanger.In addition,the study found that wind cable tensile force was closely related to the lateral displacement of the girder,and it is behaved somewhat non-Gaussian characteristics.(5)The three-dimensional nonlinear aerostatic and buffeting analysis of a pipeline suspension bridge was carried out based on a finite element model.And some results of finite element analysis were compared with the test results of the typical cases,the validity of the model was verified.The effect of conjugate cables,design parameters of section,surface roughness of the pipeline,ice shape,ice class,and the Re,etc.,on the aerostatic response of the bridge were analyzed.And the effect of ice accretion,aerostatic force,self-excited force on buffeting response of pipeline suspension bridge was analyzed.The parameter analysis was done and attained useful conclusions.The research results can provide beneficial references for wind-resistant design of bridges of the similar type.