Research On The Risk Assessment And Countermeasures Of Urban Bridges In Operation Period

With the development of three-dimensional urban transport, urban bridges play an increasingly important role. People also pay more attention to the risks that is faced by it. More and more accidents have happened to urban bridges and lead to the loss of risk increasing. In addition, there is less research on risk assessment of urban bridges in operation period in our country. So improving management mechanism of urban bridges in operation period and developing effective coping strategies of risk are the problem that are urgent need to address. Basing on the domestic and foreign research results, the theoretical framework of bridge risk assessment is summarized combined with practical experience in risk assessment of highway bridges, and the risk assessment method urban bridges in operation period is proposed in this thesis. Main works has been summarized as follows:1. The definition, common method and based model of bridge risk assessment are elaborated. According to the feature of urban bridges in operation period, the main contents of this thesis are cleared.2. Based on robustness index, redundancy factor, reserve strength factor and residual strength factor, Time-variant robustness assessment method of the complex bridge is proposed. This method can be used to assess the structural time-variant robustness affected by structural degradation and accidental loads.3. The risk of accident database of urban bridges in operation period is established. The risk of accidents is surveyed and classified according to its causes. The database can provide the basis for risk identification. A risk source identification method combined with Accident tree analysis and Analytic hierarchy process is proposed. Each source of risk can be identifyed by this method, and the importance of each major risk factor can be determined by it.4. Based on the theory of time-variant reliability, the risk estimation model of urban bridges in operation period is proposed. The estimation model of risk loss is also established, which contains structural damage, traffic delays, human casualties, environmen identifytal and social losses.5. The detailed bridge risk evaluation and accepted criteria are established; the risk equivalent estimation is introduced to estimate the quantitative risk loss. Risk coping strategies that are suitable for urban bridges in operation period are introduced briefly, and different coping strategies have been suggested for different risk factors. 6. Finally, the risk assessment of a single-tower cable-stayed bridge in operation period located in the main city of Tianjin is taken as an example for verifying the effectiveness and practicality.