Probabilistic Fretting Fatigue Analysis of Bridge Stay Cables at Saddle Supports

Abstract

Saddle systems have been used on recent projects to support the cables in cable-stayed and extradosed bridge structures. A major design consideration for these anchorage systems is the in-service fretting fatigue behaviour of the cables within the pylon saddle. In order to better understand the fatigue behaviour of these anchorage systems, a research project was undertaken, wherein fatigue tests were performed on saddle test specimens, analytical models for calculating displacements and contact forces were developed, and a multiaxial stress-based fretting fatigue model was developed for calculating fatigue life. In the current paper, it is shown how the developed models can be used to perform probabilistic analysis of fretting fatigue life for the purpose of assessing the fatigue reliability of saddle systems, using two approaches -fretting maps, in conjunction with Monte Carlo simulation (MCS) or the multiplicative dimensional reduction method (MDRM).

Assessment of critical parameters affecting fretting fatigue life of bridge stay cables at saddle supports

“…Recent tests at TU Berlin and the University of Waterloo show that the COF of cables in contact with the saddle can range from 0.6 to 0.8 (Chehrazi 2022;Mohareb 2020). Therefore, it was decided to perform the wear modelling process and fretting fatigue life evaluation using a COF of 0.7, which falls between the reported COFs in these works.…”

“…Mohareb (2020) presented a 2D FE model of a band bent over a saddle with discrete contact points. Chehrazi et al (2020) developed fretting maps and a probabilistic framework for evaluating the fretting fatigue life of the cables in saddle systems.…”

Fretting fatigue tests and microstructure analysis of bridge stay cable wires

“…The difference between the measured loads at the top and the bottom can be later used to determine several parameters including coefficient of friction, frictional force, and slip displacement. Drawings of all test setup components can be found in Chehrazi 29 …”

“…A 3D finite element (FE) model of the contact points between a cable and saddle is discussed, and a multiaxial stress analysis approach is employed in Mohareb et al, 5 along with the Smith–Watson–Topper parameter, to determine the fretting fatigue life of the cables. Chehrazi et al 6 extended this analytical approach to a probabilistic framework. Several studies 7–9 developed closed‐form equations to determine the critical parameters that affect the fretting fatigue life of the cables at saddle supports.…”

A comparative study of several life prediction models based on the critical plane approach for fretting fatigue crack initiation

“…Sun 27 proposed a fretting fatigue life prediction model for aero‐engine dovetail assemblies considering the strain‐temperature nonlinear coupling effect, and the fatigue experiment verification results and predicted life results are in good agreement. Chehrazi 28 proposed a small‐scale fretting fatigue setup to evaluate the fretting fatigue behavior of bridge stay cable wires on saddle supports and investigated the effects of plain fatigue properties, microstructure, and defects on the fretting fatigue life of wires.…”