Study On Evaluation Method Of Fitness Level For Concrete Girder Bridge Based On Structural Reliability

The robustness of the bridge structure has become a hot research topic in engineering field with the bridge safety accidents occur frequently.In order to ensure the safe operation of bridges,it is important to analyze the mechanical characteristics of residual structure of bridge subjected to accidental damage.At present,the safety of highway bridges in China is assessed based on component-level criteria,the failure of a bridge structural is deemed to be the failure of the critical section of a critical member.However,this assessment of the existence of the following two shortcomings.On the one hand,bridges designed comply with component-level codes and regulations may not have adequate redundancy or alternative load paths due to unreasonable structural configurations,which would,in turn,result in disproportional failure or even progressive collapse.On the other hand,the safety margins of bridges designed/ assessed according to the component-based design/safety check criteria are not uniform given that system effect is ignored,which may lead to unnecessary strengthening decision and unreasonable fund allocate strategy.Based on the above consideration,the main research respects and results are as follows:(1)Study on the method of assessing the robustness level of structural system was carried out.Based on the actual situation of the active bridge,the principle and research application of the robustness evaluation method of the bridge structure system are analyzed,and the stochastic finite element method is the most commonly used method of bridge system safety assessment.Summed up the European and American countries in the bridge on the robustness of the research results,pointed out that the Chinese norms in the lack of health and the need to improve the place.(2)The paper studied quantitative evaluation methodology of the robustness of highway bridge superstructures,introduced the procedure of the assessment of robustness of highway bridges through an example of a prestressed concrete T-beam bridge composed of 5 beams with a simply supported span of 20 m.Midas Civil and Xtract were employed to conduct nonlinear pushover analyses had on the superstructure of the T-beam bridge.Then the load-deflection curves of the bridge under both intact and damage situation were obtained.Then the robustness level of the bridge is evaluated on the basis above.(3)The relationship between bridge robustness index and system reliability is established,and the reliabilities of bridge structure with different failure modes is analyzed.This paper presents a reliability evaluation method based on system index.This method provides a new bridge security evaluation method based on reliability and structural system level,along with a unified and non-subjective criterion for the evaluation of bridge bearing capacity.The result of this study would facilitate the establishement of a system-level safety check methodology of highway bridge structures in China,which can provide the basis for the maintenance decision of the bridge and reasonable distribution of the maintenance funds.