A validated methodology to estimate the reliability and safety of suspension bridge cables

Abstract

The safety of suspension bridges depends on its main cables which are constructed of thousands of high strength steel wires radially clamped together at certain locations along the cable. After many years of service, these cables are showing signs of serious distress with many wires corroded and even broken inside. A new methodology to determine the reliability and safety of this structure is suggested in this research work. A three dimensional random field simulation is used to determine the remaining tensile strength in the cable. The key idea is to determine how individual wire break affects the load transfer to the surrounding wires. This local damage eventually causes a global reduction in the load carrying capacity of the cable, up to a complete failure. A Monte Carlo technique is used to generate realizations of the wires' strength within a finite element model. A novel technique for modeling the contact-friction mechanism between thousands of wires is proposed. The idea is to place elasto-plastic springs at the contact points between wires. These springs have varying yielding limits depending on their proximity to the clamping loads, which is highest close to the clamp and decays when moving away from the clamp. This decaying behavior is assigned according to Boussinesq's solution to a point load in half space. While traditional contact algorithms have difficulties converging on this problem, this technique converges in few iterations. Moreover, parallelization of the problem enables a full stochastic analysis to determine the effect of corrosion uncertainty on the cable's failure load. This method represents a dramatic improvement compared to the current inspection methods that are unreliable and expensive. Biography: Arturo Montoya obtained all his three degrees in Civil Engineering from Columbia University: B.S. '07, M.S '08, Ph.D. '12. He also has a degree in Physics from St.Lawrence University’05. His Ph.D. research were on the topics of safety and reliability of suspension bridge main cables, friction and fracture of corroded high strength wires, aging infrastructure, and computational approaches for large scale FEM models. He was the recipient of the Mindlin Award and Henry Michel Award in Civil Engineering at Columbia University. He was a finalist of the Student Competition for Best Paper in Computational Mechanics organized by the Engineering Mechanics Institute in 2011 Date: Nov. 20, 2012 Place: BSE 2.102 Multi-purpose Room Time: 10:00 – 11:00 a.m. UTSA Seminar: College of Engineering Dept of Mechanical Engineering