Long-term condition assessment of suspenders under traffic loads based on structural monitoring system: Application to the Tsing Ma Bridge

Structural health monitoring (SHM) system provides an efficient way to the diagnosis and prognosis of critical and large-scale civil infrastructures like long-span bridges. This paper presents a long-term condition assessment approach of suspenders in a cable-suspension bridge under in-service traffic loads based on structural monitoring technique. The traffic loads identified from a monitoring system, including both highway and railway traffic loads, and the finite element model of the bridge are employed to determine the axial force response of the suspender. The stochastic axial force response in the suspender is described by a filtered Poisson process, through which the maximum value distribution of axial forces in its design reference period can be derived using the Poisson Process theory. In this paper, the long-term deterioration process of steel wires in the suspender considers simultaneously the uniform and pitting corrosion and the corrosion fatigue induced by both cyclic loading and environmental attack. Such a stochastic and coupled corrosion fatigue process of steel wires is simulated using the Monte Carlo method, and the time-variant conditions of the suspender are subsequently assessed in a probabilistic way, such as crack depth, number of broken wires, ultimate strength, etc. In particular, two load conditions—the train loads alone and the combination of train load and road traffic load—are examined within this procedure in order to investigate their respective effects on the deterioration. By employing first-order reliability method, the reliability indexes of the suspender under the traffic loads are further estimated in terms of the safety under the extreme traffic load distribution in the design reference period and the serviceability specified in the design specification. The discussions of the life-cycle reliability indexes of the suspender provide guidance to the future decision making related to maintenance and replacement of suspenders, and it may also shed light on the long-term condition assessment of other structural members. Copyright © 2010 John Wiley & Sons, Ltd.