Detection And Evaluation Of Structural Properties Of Long-Span Cable-Stayed Bridge Damaged By Fire

Due to their large span,beautiful shape and strong applicability,the application and construction of long-span cable-stayed bridges have become more and more extensive.However,the impact of fire accidents on long-span cable-stayed bridges cannot be ignored.Thus,the structural properties of long-span cable-stayed bridges after the fire accident and the detection/evaluation of the reinforcement quality of the damaged bridges have the clear theoretical significance and practical engineering needs.Taking Chishi Bridge damaged by fire as an engineering example,the details of the fire accident happened during the bridge construction process are introduced in this thesis.The structural performance of Chishi Bridge after the fire accident is assessed by the quality inspection and load tests.The reinforcement quality of longspan cable-stayed bridge after the fire accident is also discussed.The main research contents of this thesis include:(1)According to the stress status and characteristics of the bridge in the fire accident before its closure,an emergency treatment plan is proposed for the bridges after the fire accident.Meanwhile,the damage to the tower bridge when the tensions of the temporary cables recover to 68% and 100% is evaluated.Moreover,the damage to important stress bearing components such as the cables and girders are also estimated.Also,a corresponding treatment plan is provided based on the bridge damage.(2)A quality inspection and assessment method is developed for the maintenance and reinforcement of the damaged bridge.All maintenance components are randomly checked according to this method.The inspection contents include the appreance quality,mechanical properties and size index of the reinforcement engineering.The inspection results are sorted and analyzed to estimate the quality of reinforcement engineering.(3)To evaluate the structural performance of the bridge after the maintenance and reinforcement,a static load test method is used to analyze the static performance parameters of the bridge under vehicle load.The parameters include the deflection displacement,stress/strain,structural crack and tension of the cable.In the test the symmetrical loading is employed after dividing the whole bridge into two symmetrical structures,which include a half damaged part and another half non-damaged part.By comparing and analyzing the test results of two symmetrical structures,the structural performance of damaged bridges after reinforcement is evaluated.In addition,the dynamic load test of the reinforced bridge is also performed via the environmental random excitation method and the vehicle load excitation method.Through exciting the bridge structure by external dynamic load,the dynamic performance response parameters such as the dynamic impact coefficient and the natural frequency of the bridge are tested.Meanhile,the overall stiffness and dynamic performance of the bridge are also evaluated.The results of the load tests are analyzed to assess whether the reinforced bridge structure satisfies the original design requirements.