Damage Evolution Mechanism And Remained Service Lives Evaluation Of Stayed Cables

Stayed cables are vulnerable to rupture, which leads to high maintaining cost during the life time of cable stayed bridges. To ascertain the cable replacing, it is necessary to assess the remained strength and life of deteriorated cables.While all kinds of cable degradations are assessed, the wire degradation was found out to be the fatal cause which leads to the decreasing of cable life. Wire degradation mainly results from corrosion. The process of strength assessment of deteriorated cables includes three steps: simulating the corrosion distribution of wires, calculating the strength of corrosion wires, evaluating the strength and remained life of cables.In order to evaluate wire corrosion practically, 8 corrosion levers are developed according to the appearance of damaged wires. The corrosion distribution state of replaced cables was inspected and the results were provided. The corrosion degree of the wire is affected by the distance between the sheath breakage and wire. Both at the radial direction and at the tangential direction, the corrosion degree degrades exponentially while the distance increases. According to these rules, the corrosion distribution could be simulated with following steps. Firstly, evaluate the corrosion degree of wires at the sheath breakage; simulate the wires at the first layer of cross section; simulate the wires at the radius of cross section.The process of damage evolution of wires includes 6 steps: scatheless wire stage, zinc coat corrosion stage, general corrosion stage, pitting corrosion stage, corrosion fatigue stage and stress corrosion stage. The wire would rupture at pitting corrosion stage, corrosion fatigue stage and stress corrosion stage. At different stages, the deterioration mechanism is different, but the degradation of mechanical properties of wires come from the same reason: the cross section decreasing or stress concentration due to surface roughness. The course of wire deteriorating could be simulated by the damage evolution model of wires, which has two parameters: a, which is equivalent crack depth and d, which is equivalent diameter. Before the corrosion fatigue stage, a and d are influented by the corrosion degree alone, while after the stage, the two parameters are influented by the corrosion and load, which means that a should be calculated according to the CFCP theory.Stayed cable may be considered as a parallel series system in which the cable consists of parallel wires and the wires are formed of wire elements in series. After the corrosion distribution being simulated, the mechanical properties of wire elements could be calculated according to the damage evolution model of wires, so do the strength of cane according to the deteriorated cable model. The strength of cable is affect not only by the strength of wires, but also by the ultmost elongation of wires. The strength of cable experience a period which increase at first and, then decrease, while the elongation of cable increases. During the period, wires full breakage gradually when the elongations of wires are less than the elongation of cable.For the porpose of evaluation the service lives of cables, the ultmost strengths of cables in different stage are calculated when the corrosion rate is counted. The Cables will fall rustily when the strengths achieve the failure criterion.