Performance And Maintenance Strategies Of Medium&Short Span Concrete Bridges

At present, the total number of highway bridges in China has amounted to more than700,000, of which small and medium span concrete bridges account for more than90%. Concrete bridges deteriorate with time due to complex service condition, environmental condition and possible overloading, and it seriously affects the safety of bridges. In this thesis, small and medium span concrete bridges are taken as the research object to study the performance of bridges. The performance situation of small and medium span concrete bridges in Quzhou is analyzed, a novel evaluation model of bridge performance condition is proposed based on fuzzy cloud theory, the static and dynamic performance of four11-year-old existing prestressed concrete hollow slabs are researched, and bridge maintenance strategies are discussed based on performance. The main conclusions are as follows:1) A thorough investigation on the performance status of small and medium-span concrete bridges in Quzhou is conducted. Detailed analysis is carried out based on the bridge span, superstructure type, load level, technical condition and the type of major diseases. At last, the causes of diseases are analyzed.2) According to the characteristics of the inevitable fuzziness and uncertainty in the evaluation of concrete bridges, a novel evaluation model of bridge condition is proposed based on fiazzy cloud theory. The case study and the result comparison with other assessment methods show that fuzzy cloud model method was feasible, reliable and effective. The proposed method also offers a new approach of condition evaluation for concrete bridges.3) Based on experimental study on the flexural and shear ultimate capacity of four11-year-old existing prestressed concrete hollow slabs, deformation and strain properties, failure mechanism and ultimate capacity are researched during the whole failure process.The results show a significant characteristic of ductile failure after a11-year-old sevice. Experimental study and nonlinear FEM analysis results show that the capacity calculation formula of the current bridge specification is rational and it provides a reference to modify the specification. Under the experimental load conditions, flexural ultimate capacity was less than shear ultimate capacity, and flexural failure may happen prior to shear failure.4) In this paper, through the analysis of numerical and experimental studies without noise and with noise, vibration characteristics of prestressed concrete beam during failure process were studied. Runge-Kutta method was used to solve the partial differential equations of vibration to obtain dynamic response under hammer excitation. Vibration characteristics of the test beam under different damage state were researched by HHT time-frequency analysis. During the failure process, the acceleration signals were obtained and HHT was used to get instantaneous frequency-acceleration amplitude curve at each damage stage. The results showed that the change of damage characteristic frequency will reflect the extent of damage in the failure process.5) Condition indicator and reliability indicator are selected as indicators of performance for highway bridges to study their deterioration models and their maintenance strategies.A maintenance strategy optimization model is established with a minimum life-cycle maintenance costs as the objective function. The different optimal maintenance strategies under multi-level performance levels in life-cycle are developed, considering the requirements of multi-level performance levels.