A Study On The Influence Of Bending On Hangers Consisting Of Steel Strands Of Half-through Arch Bridges And Through Arch Bridges

Hangers play an important role in connecting arch ribs and bridge decks in half-through arch bridges(HTABs)and through arch bridges(TABs)and are very important tensile members.The damage and failure of hangers will have significant influence on the safety of the bridge.To date,most researches focus on the corrosion and fatigue of hangers to illustrate the reasons for the damage and failure of hangers.At present,most of the researches on the failure of hangers focus on the corrosion and fatigue of hangers,and there are few researches on bending,which may be another factor that affects the safety of hangers.Therefore,this paper carried out systematic and in-depth analyses and researches on the influence of bending on hangers,and obtained some results with scientific significance and reference value.The results of researches are as follows:The types of hangers,boundary conditions and types of arch bridges are discussed in detail.The common types of hangers are analyzed and compared.It is found that hangers consisting of steel strands can bear large bending moment due to its large stiffness compared with other types of hangers.Thus,the research object in the study is limited to the hangers consisting of seven-wire strands.Also,the boundary conditions of hangers and the types of arch bridges are analyzed.It is proposed that the specitific boundary conditions of hangers and the specitific types of arch bridges will lead to significant bending deformation of hangers.Finally,it is concluded that that end-fixed hangers consisting of parallel sevenwire strands of HTABs and TABs with a floating deck structure can produce significant bending deformation.Then,the forms of bending deformation of hangers are studied systematically.after determining the scope of the research object.The bending caused by longitudinal deformation of bridge deck under the effect of temperature and the bending caused by rotation of bridge deck under the effect of temperature gradient are analyzed in detail.The calculation formulas of the bending angle of hangers and the maximum bending stress in hangers under two types of bending deformation are put forward.Moreover,finite element analysis are conducted to compare these two types of bending of hangers and it is found that bending stress of hangers is mainly generated by lateral bending caused by the difference in longitudinal displacement at both ends of the hangers under the effect of temperature.The main form of bending of hangers is axial offsetting bending caused by longitudinal deformation of bridge deck under the effect of temperature.The bending caused by rotation of bridge deck under the effect of temperature gradient can be neglected.The shorter the length of the hanger,the more seriously affected by bending.The influence of axial offsetting bending on hangers consisting of seven-wire strands is studied in two aspects.The first is to study the stress state of the hanger under axial offsetting bending and reveal the stress characteristics of the internal steel strands in hangers under axial offsetting bending.The stress of the steel strands inside the hanger is not uniform under axial offsetting bending.The single steel strand bearing the maximum bending stress is the most unfavorable xteel strand in the hanger(short for the most unfavorable steel strand).The most unfavorable steel strand will determine the overall strength of the hanger.Therefore,the research on hangers under axial offsetting bending can be transformed into the research on the most unfavorable steel strand.Then,the second aspect of research wass carried out,that is,the influence of axial offsetting bending on a single steel strand.Through the finite element analysis and experiment,the influence of axial offsetting bending on the static mechanical properties of steel strand is studied.It is found that the ultimate tensile strength of steel strand will be weakened under axial offsetting bending and the reduction of ultimate tensile strength can reach 23.3%.Based on the ultimate tensile strength of the steel strand under axial offsetting bending,the mathematical probability model of the bearing capacity of hangers is established,and the root cause of the sudden fracture failure of hangers caused by the bending phenomenon is found through the bearing capacity model: when hangers produce axial offsetting bending,the most unfavorable steel strand is prone to break and the remaining steel strands may break at the same time.If all the steel strands in hangers break at the same time,it will lead to the instantaneous failure of hangers.The above process explains the reason why fracture of hangers often occurs in the instant in actual engineering accidents.Finally,the relationship between the fatigue properties of the steel strands and axial offsetting bending angle is obtained based on basic S-N curve and Goodman equation.The fatigue properties of the steel strands are influenced significantly by axial offsetting bending.When the bending angle reaches about 50 mrad,the fatigue resistance of the seven-wire strands drop by almost 40%.When the bending angle is close to 60 mrad,the basic fatigue performance of the steel strand will be lost.In a word,bending has a significant adverse influence on hangers consisting of seven-wire strands.