Prediction And Assessment Of Behavior Degeneration Of P.C. Continuous Rigid Frame Bridge

Marine structures and highway bridges usually suffered environmental loads, such as chloride ion corrosion. It caused structural behavior degeneration,bearing capacity decreasing, even structural failure, and lead to tremendous economic loss and severe social impact. According to the item of "Study on crack control technology and durability for cast-in-place box girder by large span Movable Scaffolding System (MSS)", on the background of Huang-pu Bridge project, aiming at P.C. continuous rigid frame bridge with thin-walled box section, the series studies were carried out - including experimental analysis of material durability, condition assessment, life prediction, ultimate bearing capacity analysis and prediction on service stage based on material degradation. And the primary achievements are listed as follows:(1) Chloride ion was identified as main erosion environment of Huang-pu Bridge. Corrosion mechanisms of chloride ion and damage modals of concrete structures suffered chloride erosion were discussed. The NEL method was adopted, and the chloride ion diffusion coefficient of piers & box girders of approach bridge was measured. According to the assessment standard of concrete permeability, the permeability grade evaluation of piers & box girders were performed.(2) Based on Fick's second law, a new chloride diffusion model in concrete was formulated, in which the factors of time-dependence of chloride diffusion coefficient, chloride binding capacity of concrete, and self-defects of concrete were taken into account. And the parameters value in the model was given for practical application. The model was verified by long-term field data that are available in published literatures. The practical data agreed with the calculated results very well.(3) Based on the diffusion model, three different life prediction methods were presented, with the state that chloride ion concentration on rebar surface reached the threshold value was regarded as a sign of end of life. The first method assumed parameters in diffusion model as constant, the representative value was employed to calculate; And based on classical probability theory, the parameters randomness was considered, then expected value of service life and corresponding failure probability of concrete structure were further deduced in second method; By introducing the concept of reliability, the chloride ion penetration depth in limit state was taken as environment load, and the cover thickness was taken as resistance, monte carlo method was adopted to calculate reliability of structure. Through the introduction of target reliability, life prediction could be easily performed. By using above methods, aiming at piers & box girders of approach bridge of Huang-pu Bridge, service life prediction were carried out and the results could be matched each other.(4) Based on grey correlation and fuzzy recognition, a durability assessment model of concrete members was established, in which nonlinear normalization processing method was adopted. By introducing combinatorial weight, the importance of expert experience and inspection data were taken into account. The model was testified by practical engineering example at last. By using this model, several concrete members could be evaluated at one time, and it has widely applicability, not only confined to concrete durability assessment.(5) With a case study of P.C. continuous rigid frame bridge of Huang-pu Bridge , on the basis of material performance degradation, the ultimate bearing capacity analysis of P.C. bridge structures was carried out from several aspects: space element mode, spatial prestressing effect, treatment of stage model stress, and material nonlinear effect. The results showed that material degradation has great impact on ultimate load capacity of structure: the load factor on limit state dropped rapidly and brittle characteristics was aggravated at the same time.