State Rating And Safety Assessment For Cable-stayed Bridges In Service

More attention has been paid to the safety and service ability of long spanbridges in recent years, and the investigation of methods for safety assessment ofbridges becomes one of the most active research frontiers in civil engineering.Nowadays, many bridges have been installed structural health monitoringsystems, and methods for real time safety assessment are in demanding with themature of SHM technology.Cable-stayed bridge structures are always subjected to many variant ofenvironmental effects, so the reliability of structures will decline during theirservice periods. Therefore, it is of great significant to conduct safety assessmentfor cable-stayed bridge structures in a scientific and reasonable way, using theresults of manual inspections and structural health monitoring systems. In thisthesis, the condition assessment and safety evaluation of cable-stayed bridge areinvestigated with the aim at application to the Ningbo Yongjiang Bridge.Detailed researches are summarized as follows.Firstly, through the analysis of the structural characteristics and mechanicalproperties of cable-stayed bridges, the technical condition assessment method incurrent code is improved, and a multi-level and hierarchical model is set up. Theselection of weight for each element in the hierarchy is discussed, and detailedquantitative assessment indicators are established.Secondly, a hierarchical safety evaluation method using the real timemonitoring data is proposed. The criterion for classifying structure responses areestablished according to the design limit states of bridges. These criterion s aredetermined by finite element analysis of Ningbo Yongjiang Bridge, and safetyevaluation of this bridge is performed. The effect of variation of measuredresponses and number of monitoring responses is discussed..Finally, in accordance to principle of the bridge limit state design, a safetyassessment method for bridge components is proposed for real time monitoringsystem. With the consideration of the variability of environmental loads, themonitored structural responses are separated into different parts which are caused by different environmental loads, by use of the regression analysis. The bridgecomponentis evaluated by combing the responses caused by different loads underthe limit states. The feasibility of the assessment method is preliminarily verifiedusing bridge monitoring data.