Research On Damage Of Corroded Hangers In Through And Half-hrough Arch Brdiges

The hangers, with their great importance on load-bearing, have a direct relation with the safety of the through and half-through arch bridges. However, bridge accidents due to hanger failure have been frequently reported in recent years, the health monitoring and bearing capacity evaluation of in-service hangers have been focus in both academic and civil engineering field. As the hangers in many arch bridges have been on service for more than a decade, the peak period of hanger replacement is coming. Therefore, it is very important to propose a reliable method on assessing the residual bearing capacity of hangers.Firstly, hangers which have been replaced from four arch bridges in Zhejiang province are employed in this thesis. By means of visual examination and mass loss determination, the corrosion extent and corrosion character of hanger wires are investigated, and the mechanical properties and brittle mechanism of corroded wires are also studied through tension test and artificial notch simulation. Secondly, the solid models of corroded wires are developed using the finite element (FE) software ABAQUS, in order to analyze the stress concentration in the tension progress. Compared with pitting wires, the general corroded wires are studied on the aspects of stress distribution and tensile properties, besides, the impact of the pitting parameters on stress distribution, such as shape and amount, are also investigated. Thirdly, on the basis of experimental and FEM results, a calculation method for the ultimate strain of corroded wires is proposed, and a grading method is then established according to the luster and smoothness of the wires. Finally, with the theory of fiber buddle, a series-parallel model of the hanger is developed, and implemented by FORTRAN, making it possible to investigate the effects of hanger length, wire number and friction on the bearing capacity of hangers. Furthermore, a probability model for residual bearing capacity is proposed based on the nonparametric statistical theory and the Monte-Carlo method, which can be used for assessing the residual bearing capacity of hangers with different corrosion extent and provide evidence for inspection, maintenance and replacement of arch hangers as well.Some conclusions of this paper are drawn as follows:1) The elastic modulus and ultimate strength of the wires are not sensitive to pitting, however, the ductility of the corroded wires decreases sharply. The fracture of the notched wire is brittle. 2) Stress concentration is the cause of the brittleness, which always appears on the surface of pitting wires during the progress of tension, thus leading to the decline of ductility. The stress concentration is significantly influenced by the depth, width and the length-to-width ratio of the pits. This phenomenon can be eased by increasing the amount or the spacing of pits.3) The ductility of wire is the main index of the mechanical properties. After obtaining the pits parameters, the ductile index can be calculated on the basis of a fitting curve, which is proposed in the thesis.4) The wires in the hanger are almost on the same grade if the outer sheath is intact. The number of wires and the friction between wires are internal factors to the bearing capacity of hangers, while corrosion is an external factor to the ultimate capacity and ductility of hangers. Compared with the ultimate capacity, corrosion has a significant influence on the ductility of hangers.