Analysis Methods For Suspender Damage And System Reliability Of Existing Concrete Filled Steel Tubular Arch Bridge

Concrete filled steel tubular (CFST) arch bridges as a type of arch bridges with Chinese characteristics have many advantages in covering middle and large spans and have a broad promising prospect in China. However, due to the short history of their development, there is no published national design standard for this bridge type, or mature maintenance techniques to refer to. This fact leads to their complicated damage phenomenon and frequent engineering accidents. In order to systematically improve the service condition and safe operation of CFST arch bridges, and maximize the bridge lifespan, it is needed to study on the main and typical damage, real mechanics characteristic of key components and reliability analysis method of main members and the system about CFST arch bridge systematically. This study will help to ensure the safety of the 300 existing bridges of the same type in China and benefit the long-term development of these bridges. Under this background, following contents of CFST arch bridges are studied in this thesis(1) Research on the commonly encountered damages and their causes in the CFST arch bridge. A comparison study was conducted to analyze the difference between CFST and the traditional arch bridges. It was found that the differences in structure system, material properties and mechanical behaviors between the CFST and the traditional arch bridge are the main reasons leading to the different damage properties and examine method in the CFST arch bridges. After a comprehensive study of the damage on some existing CFST arch bridges and the related references, the damage of CFST arch bridges is summarized and classified to three types, which are damage of the main structural components, damage of the deck system and damage of the subsidiary structures. Finally concrete defects in arch rib and commonly encountered damages in cable members are identified as typical damages in the CFST arch bridges and they are the studied objective in this thesis.(2) Research on the characteristic of the randomness of suspender traffic-load effect and its modeling method. By analyzing the monitoring data, it's found that the probability density function (PDF) of traffic load effect is complicated. Due to the limit that traditional method couldn't set up the probability model of traffic load effect and its extreme value when its PDF is complicated; a new method is raised based on the nonparametric statistical theory and the extreme value theory of stochastic process. The new methods are proved practical and efficient in applications for solving the modeling problem.(3) Research on the characteristic of the fatigue load effect in the suspender and its cumulative damage calculation method. The characters of fatigue load effects and cumulative damage are analyzed based on the rain flow algorithm and linear damage cumulative theory. It is found that heavy trucks are the main causes of fatigue damages of the suspenders and their fatigue stress amplitude and mean value appear to have a linear relationship with each other. Based on this, the calculation method of the damage level of suspenders in the non-monitoring period and the prediction method for their fatigue cumulative damage are raised by introducing the probabilistic model of traffic load effect.(4) Research on the damage evolution process of steel wires, the resistance deterioration process of the suspenders and the reliability calculation method for existing suspenders. The damage evolution process is divided into three stages, which are protection measure inactivation stage, uniform corrosion stage and crack propagation stage. Based on the damage mechanism of steel wire, continuum damage mechanics and fracture mechanics, the calculation method for residual strength of steel wire is raised. The resistance deterioration process analysis for suspender is analyzed. Based on the strength model of fiber bundle and brittle steel wire model, the residual load carrying capacity calculation method for suspender at different deterioration stages is proposed. By accrediting the resistance uncertainty of existing structural members to the uncertainty of components damage or fatigue, an improved independent increment process mode for resistance deterioration is presented and applied to existing suspender(5) Research on system reliability analysis method for concrete filled steel tubular arch bridge. By analyzing the advantages and disadvantages of existing failure mode searching approaches, as well as their feasibility in bridge projects, an improved branch and bound method suitable for bridges is proposed, which solves the problem on finding the main failure modes of bridge structures. With comparison of the validation range of the bound estimation method, the PNET method and the FORM method, it is pointed out that the bound estimation method applies to estimating system reliability bound while the PNET and the FORM methods are respectively appropriate for the situations with and without obvious group characteristics. Finally, all the system reliability analysis methods are applied to an existing CFST arch bridge., in which the influence of typical arch rib damage to the system reliability of bridge is analyzed. The result of the analysis showers that influence of concrete imperfection to the system reliability of the bridge is not neglected.