Experimental Study On The Fatigue Performance Of Corroded Steel Strands

Throughout the decades of the history of bridge in China,cable-stayed bridge developed late,but it has played decisive roles in present bridge industry because of its unique advantages,such as economical effectiveness,practicality,and beautiful appearance.There is a very serious problem in the durability of the stay cables,as the life of cable-stayed bridge.To be specific,the actual service life of the stay cables in many engineering applications fails to meet the design working life;the stay cables of some bridges have to be replaced after a short time because of corrosion even broken wires,causing a great waste of manpower and material resources.At present,scholars at home and abroad have conducted a great number of experiments and researches about the fatigue property of steel strands.However,there are fewer researches of the fatigue performance of corroded steel strands,as well as the relationship between the degree of corrosion and fatigue performance.Therefore,it is necessary to study the above issues.Centering on the research topic,the main research contents are as follows:(1)According to the basic hypothesis of nominal stress method,the study of the fatigue life was transformed to the study of local maximum stress.The corrosion pit model with different influencing parameters was established based on control variable method through Midas Fea.Besides,the local maximum stress was calculated.The relationship between secondary corrosion pit diameter d,depth h,the center distance between secondary corrosion pit and main corrosion pit D,as well as secondary corrosion pit and the influence degree of local maximum stress corrosion of main corrosion pit y(the diameter and depth of the main corrosion pit were 1mm)was searched through regression analysis method.And a functional relation is obtained.(2)10 representative main corrosion pits and its surrounding secondary corrosion pits(group)were selected from each specimen.Their morphology and distribution were carefully observed and measured through measuring microscope.It was found that the depth and depth-diameter ratio of main corrosion pits on the surface of steel strands were positively correlated with the load stress at corrosion stage.(3)After a series of operations including steel strand specimen disassembly,cutting,labeling serial number,pickling,weighing and observation,a set of special fixture for the experiment was designed and made according to the actual situation.Finally,the fixture was sued to connect specimen and fatigue testing machine.The fatigue experiments of 6 corroded steel strands and 1 new steel strand were completed.According to the experiment results,the fatigue life of the specimens decreased with the increase of corrosion rate.Such situation was consistent with main corrosion pit morphology on specimen surface through observation.It was further proved that corrosion pit was the main factor determining the fatigue life of steel strand specimen.In addition,the clamp force performance calculation results and the actual experiment results proved that the anchorage used in the experiment and fixture designed in the paper had higher practicability.(4)Based on the observation results of corroded steel strand specimen surface state,by using fatigue analysis function of Midas Fea,the modeling analysis was conducted on the observed various corrosion pit morphology through the same way of loading with the experiment,and their fatigue life was estimated.In accordance with the finite element analysis results,the estimated fatigue life was close to the practical fatigue life,and was slightly lower;when the stress amplitude,specimen size,mean stress and other factors were the same,the fatigue life of corroded steel strand specimens showed attenuation in exponential form with the increase of corrosion rate.