Research On Residual Bearing Capacity Of Hangers And Mechanical Properties Of Corroded Wires

The hangers play an importance role on load-bearing, whose performance directly affects the safety of the through and half-through arch bridges. However, bridge accidents due to hanger failure have been frequently reported in recent years, which had aroused the worldwide attention. As the performance of the hangers has not been fully understood, the regular replacement is still the most common approach to promote the carrying capacity of the hangers, but also a great burden to the state and local finance. With more and more arch bridges have been on service for more than a decade, the peak period of hanger replacement is coming. Therefore, it is very urgent and significant to study the distribution of wire axial force with wire breaks and assess the residual bearing capacity of hangers, and discuss the mechanical properties of corroded high strength steel wires.Hangers, replaced from an half through arch bridge in Zhejiang province, are employed in the study. Firstly, the friction characteristics, such as the average friction rigidity and the friction resistance between the steel wires in the hanger, were tested by designed friction test, which then were used to build up the series-parallel model with designated friction elements, based on the theory of the fiber bundle. Secondly, the distribution of wire axial force with wire breaks and the residual bearing capacity of hangers were analyzed by applying the proposed series-parallel model into the finite element program, implemented by FORTAN. Furthermore, the wire-break mechanism and the influence of the friction characteristics were discussed based on the residual bearing capacity and the relative displacements between layers on the hanger section respectively as computed. Besides, the degradation of the residual bearing capacity, the ductility and other mechanical performance of hangers in different corrosion level was investigated. On the aspects of corroded wire steels, the visual examination and the mass loss determination were employed to determine the corrosion level and characters of wires, and the pre-load corrosion studies, as well as the tensile test were conducted to assess the mechanical properties of wires with different corrosion extents and stress histories. Finally, though standard electronic modules photos of the broken sections of the corroded wires with different stress history, the corrosion cracking mechanism and the degradation of ductility of the corroded wires were assessed. All the studies are used for assessing the residual bearing capacity of hangers and provide evidence for inspection, maintenance and replacement of arch hangers as well.Some conclusions of this paper are drawn as follows:1) By laboratory test, the average friction rigidity of unit length is about 0.192 kN/mm2, which differs from 0.16 to 0.20kN/mm2 and the average friction resistance is 0.022 kN/mm.2) Considering the inter-wire friction of the hangers, the other wires shared the lost tensile force of the broken wires quite evenly on the broken section. While the tensile force of broken wires grew linearly with distance from the break point, and reached about 95% the tensile force when leaving the broken point about 1.5meters.3) The remaining cable strength increased slightly but the ductility decreased compared to those without considering the inter-wire friction when taking the wire break rate of 5% as the limit state.4) With the increase of the corrosion level, the residual bearing capacity and the ductility of hangers decreased, also the recovery length shorted and the bearing capacity of broken wires reduced.5) Wires with different corrosion degrees all happened ductile fracture, but the less corroded wires had larger capability of plastic deformation, while the severely corroded ones appeared more brittle. The fracture cracks grew around the critical corrosion pits, which led a serrated appearance and the expansion of the internal radiation area on the broken surface. It can be concluded that the corrosion pits influence the mechanical properties of the high-strength wires.6) There was no significant difference in the tensile properties between the wires with or without 10 months pre-load history.