Structure Reliability Analysis Of Widening And Reconstruction Of Concrete Bridge

Currently there is little of research about reliability of widened bridge which must be studied deeply. This paper combined with the national natural science fund(Fundamental Theories for the Widening and Reconstruction of Existing Concrete Bridges)(51278182)and based on the actual engineering project and theory of reliability to study the widening design of four span prestressed concrete T girder bridge.The main contents of this paper are as follows:(1) This paper used the Shrinkage and creep difference model of(Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts)to caculate the additional internal forces in the structure which Shrinkage and creep difference of concrete and foundation settlement difference produced.Results showed that shrinkage and creep difference in bridge beam and the bridge girder beam in outside produced axial tension.However,shrinkage and creep difference of centre sill and inner side beams produced axis pressure.When it is more closed to spell seam, the mainbeam axial force value became bigger.Axial force that shrinkage and creep difference produced was small and transversal moment was bigger. Additional internal force which foundation settlement difference produced i n the main girder was small.Axial force difference which main girder junction surface produced was big.The variation of axial force difference which near the diaphragm plate produced was fierce.Axial force difference which different piers produced was big. Inside edge beam side of the bridge pier is 3.37 ~ 4.38 times of beam side outside.Horizontal maximum bending moment Inside the pier was 310 k N·m;(2) This paper obtained reduction factor of the vehicle load with different design working life according to determining the reference period of widening and reconstruction and design load based on equal exceeding principle and set up the structure resistance time-varying model by considering the concrete time-varying strength and reinforcement corrosion rate;(3) This study calculated the bending capacity of the main girders and the compressive capacity of the bridge piers according to the additional inner force produced in the structure.The results showed that under the influence of shrinkage and creep difference and foundation settlement difference,the bending capacity of 6#girder increased 13.6% and the bending capacity of 7# girder decreased 7.19%.And the compressive capacity of 1#-2 pier decreased 18.79% and 1#-3 pier decreased 36.27%;(4) Based on JC method and computation method of serial system reliability index analyze the time-variant reliability of the widened bridge,results showed that:when the old bridge operated 100 years,considering the influence of shrinkage creep difference and foundation settlement difference, the reliability index of the superstructure increased 15.66% and the reliability index of the substructure decreased 29.80% and the reliability index of the composite structure decreased 2.20%. If the old bridge was not widened,it can be operated for 30 years and the reliability index of the structure started to be less than 4.2. If the old bridge was widened it can be operated for 85 years and the reliability index of the structure started to be less than 4.2.