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

Abstract

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.The Tsing Ma Bridge is a cable-suspension bridge located in Hong Kong with an overall length of 2160 m and a main span of 1377 m (as shown in Figure 2). The height of the two towers is 206 m from the base level to the tower saddle. The two main cables of 36 m apart are accommodated by the four saddles located at the top of the tower legs in the main span, and

Probabilistic deterioration model of high-strength steel wires and its application to bridge cables

“…More detailed explanation of the parameters in the corrosion fatigue crack propagation model can be found in Li et al (2012).…”

“…The stay cables of long-span bridges, made of highstrength steel wires, are critical and vulnerable bridge components under in-service conditions (Li, Zhu, Xu, Chen, & Li, 2012). As one of the main types of loadcarrying components in a long-span cable-stayed bridge, stay cables are subjected to corrosive erosion, material aging and traffic-induced fatigue, which inevitably result in damage accumulation and resistance deterioration that may impair bridge serviceability under normal operation conditions and trigger catastrophic failure in extreme hazardous events.…”

Serviceability assessment for long-span suspension bridge based on deflection measurements

“…Extreme value analyses and applications of reliability theory have been conducted by several researchers with on‐site load test data or in‐service monitored data to evaluate the performance of bridges, primarily focusing on structural strength performance or ultimate limit state . For instance, Bhattacharya et al used site‐specific strain measurements for bridge rating at two different limit states, yield and plastic collapse.…”

Seismic response of a suspension bridge: Insights from long-term full-scale seismic monitoring system

“…The objectives of structural monitoring of these bridges are various depending on the specific concerns of the structure, operational condition, and the potential hazard of the bridge location. Long‐term monitoring data, which typically consist of structural static and dynamic response, temperature, strain, and wind, have been used extensively and proven useful to evaluate global structural performance and to evaluate performance of specific structural components such as suspender of suspension bridge, expansion joints, fatigue performance of welded structure, and temperature effects on structure …”