Probabilistic Assessment Approach of the Aerostatic Instability of Long-Span Symmetry Cable-Stayed Bridges

The existing safety analysis methods for the assessment of the aerostatic stability of long-span symmetry cable-stayed bridges have difficulties in meeting the requirements of engineering applications. Based on the finite element method and the inverse reliability theory, an approach for the probabilistic safety analysis of the aerostatic instability of long-span symmetry cable-stayed bridges is proposed here. The probabilistic safety factor of aerostatic instability of long-span symmetry cable-stayed bridges was estimated using the proposed method, with Sutong Bridge as an example. The probabilistic safety factors for the aerostatic instability of Sutong Bridge were calculated using the finite element inverse reliability method, based on the FORM approach. The influences of the mean value and the coefficient of variation of random variables, as well as the iterative step length of finite difference, on the probabilistic safety factors of aerostatic instability of Sutong Bridge were analyzed. The results indicated that it is necessary to consider the uncertainties of random variables in probabilistic safety factor assessments of aerostatic instability in cable-stayed bridges using the proposed method, which could be recommended for the assessment of safety factors involved in the aerostatic instability of long-span symmetry cable-stayed bridges. The randomness of the parameters had an important influence on the probabilistic safety factor of the aerostatic stability of Sutong Bridge. Neglecting the randomness of these parameters may result in instability of the structure.

Characteristics of the Wind Environment above Bridge Deck near the Pylon Zone and Wind Barrier Arrangement Criteria

Due to the complex arrangement of structural components in the vicinity of bridge pylon zones, the wind environment above bridge decks is very complicated. A sudden change in wind speed exerts an adverse effect on vehicle control stability. In order to investigate the characteristics of the flow field in the vicinity of the bridge pylon, the wind environment near an inverted Y-shaped pylon is studied by experimental and numerical methods. From the flow visualization and the wind speed measurement in the wind tunnel and the numerical simulation created using Fluent software, specific patterns of the direction and magnitude of wind speed at a range of vehicle height above the bridge deck near the pylon zone were observed along the longitudinal direction. This distribution pattern of the wind environment can effectively guide the wind barrier arrangement near the bridge pylon zone. Combined with the two safety evaluation indicators proposed in this paper, the optimal arrangement scheme of wind barriers in the bridge pylon zone of Sutong Bridge is determined. This paper deepens the understanding of the wind environment near the pylon zone and proposes an evaluation method for the wind environment near the pylon zone, which can serve as the basis for wind barrier arrangement in similar research projects.

Dynamic Property Evaluation of a Long-Span Cable-Stayed Bridge (Sutong Bridge) by a Bayesian Method

Modal identification aims at identifying the dynamic properties including natural frequency, damping ratio, and mode shape, which is an important step in further structural damage detection, finite element model updating, and condition assessment. This paper presents the work on the investigation of the dynamic characteristics of a long-span cable-stayed bridge-Sutong Bridge by a Bayesian modal identification method. Sutong Bridge is the second longest cable-stayed bridge in the world, situated on the Yangtze River in Jiangsu Province, China, with a total length of 2 088[Formula: see text]m. A short-term nondestructive on-site vibration test was conducted to collect the structural response and determine the actual dynamic characteristics of the bridge before it was opened to traffic. Due to the limited number of sensors, multiple setups were designed to complete the whole measurement. Based on the data collected in the field tests, modal parameters were identified by a fast Bayesian FFT method. The first three modes in both vertical and transverse directions were identified and studied. In order to obtain modal parameter variation with temperature and vibration levels, long-term tests have also been performed in different seasons. The variation of natural frequency and damping ratios with temperature and vibration level were investigated. The future distribution of the modal parameters was also predicted using these data.

Mechanism of Fatigue Crack Growth of Bridge Steel Structures

This study was carried out on the background of Sutong Bridge project based on fracture mechanics, aiming at analyzing the growth mechanism of fatigue cracks of a bridge under the load of vehicles. Stress intensity factor (SIF) can be calculated by various methods. Three steel plates with different kinds of cracks were taken as the samples in this study. With the combination of finite element analysis software ABAQUS and the J integral method, SIF values of the samples were calculated. After that, the extended finite element method in the simulation of fatigue crack growth was introduced, and the simulation of crack growth paths under different external loads was analyzed. At last, we took a partial model from the Sutong Bridge and supposed its two dangerous parts already had fine cracks; then simulative vehicle load was added onto the U-rib to predict crack growth paths using the extended finite element method.