Research On Reliability Of Pre And Post Reinforcement For Concrete Bridge During Service Period

Bridge reliability always is one of the concerned problems in this field. Evolvement of design code for bridge, emending of load grade and extension of probabilistic limit state design concepts are accelerating the application process of reliability method. It's an urgent issue to study that evaluates the existing bridge's safety because of the increasing traffic flow and vehicle load. At present, research on reliability mainly remains at theory stage, application achievement is not abundant, which is the target of this dissertation.In this dissertation, reliability for the existing pre-stressed bridge and the reinforced concrete bridge were studied respectively based on the western assignment of Ministry of Communications-"Research and assessment method of time-reliability for the existing concrete bridge in west region"(2007 318 822 31) and "Research for design load and safety indentified load of bridge"(2008 318 494 04), the fruitful results are as follows:Based on the research results of durability and correlation regulations, the resisting force probabilistic model in the service pre-stressed concrete bridge was established for it's resisting of cut and bent, which considered bridge structure checking calculation coefficient, bearing capacity worsening coefficient, concrete section reduction coefficient, steel bar rust damages rate, rusts away steel bar intensity step-down ratio, rusts away steel bar and concrete joint operation coefficient, pipeline deviation correction coefficient, concrete intensity correction coefficient, testing influence random variable, computation pattern uncertainty influence random variable. Probabilistic model of vehicle load and crowd load effect were established based evaluation base period. And the classification principle of bearing capacity reliability was presented, furthermore, the evaluation method for bearing capacity reliability of PC bridge remembers was put forwarded.For the full pc and A-class components under serviceability limit state, the stress-resisting probabilistic model, the dead load effect probabilistic model, the vehicle load and the crowd load effect probabilistic model was established. Assessment process and the limit reliability index was put forward due to the stress failure rule. And the evaluation method for pc bridge stress reliability was presented.Random samples were collected by means of a special instrument named Stretching Force Tester for prestressing strand. Distribution and statistical parameters of effective prestress was studied based on sample collection for actual bridge. Byχ2 identifying, the KEP obeys normal distribution, KEP-N(0.97,0.09). Under the condition ofα=0.75, the representative value is 0.91, which can provide conference for reliability assessment.The reliability assessment system (V1.1) was designed by Visual Basic 6.0 according to the reliability theory of concrete bridge, which simplized the procession of evaluation for the existing bridge.Based on the statistical analysis of random traffic flow date from a domestic highway, a program was designed to simulate the random traffic flow model by means of MATLAB. And the reliability assessment method was put forward on the bases of R/(γOγRS).According to the code of Specifications for Strengthening Design of Highway Bridge (JTG/T J22-2008), the reliability of steel strengthening and fiber strengthening bending members were computed. Random samples were simulated by means of Monte-Carlo method. The statistical parameters of fiber strengthening bending members wereμKR,M=1.713,σKR,M=0.545,δKR,M=0.318, and the statistical parameters of steel strengthening wereμ'KR,M=1.696,σ'KR,M=0.543,δ'KR,M=0.320. The reliabilities of steel strengthening and fiber strengthening bending members were approximately same, and the reliability indexs were slightly lower than the code, which resulted from the increasing of variability of strengthening bending members. The reliabilities of medium-small span bridges were influented deeply by the vehicle operation states, and the bridges'designing safety degree increased with the growth of vehicle load grade under the condition ofρ=0.1 and 2.5. Ifρ=1, the reliability reached maximum when the increasing range of vehicle load effect was 0.5, so the optiomal boundary was concluded. For the discreteness of strengthened member reliability, correction coefficient was put forward to adjust the safety degree of bridge, theγβwas obtained through a solving program in this dissertation, the results showed thatγβincreased with p, and vice verse.The menthod of evaluation and analysis were applicated to an PC bridge and an strengthened RC bridge by the research fruits upwards. And it was verified in this dissertation.