Study On Reliability For Existing Widened T-beam Bridges Based On Support Vector Algorithm

In order to improve study on the reliability of widening bridges,this paper studied the structural force and reliability on the single side widening project of a continuous T beam bridge by different factors.(1)In this paper,it analyzed that the change of structural stress on the widening bridges by different factors.Firstly,through the analysis of the upwarp problem caused of the prefabricated beam by the shrinkage and creep in different assembly methods,the prefabricated beams can be assembled in advance in order to shorten the construction period.Then the alignment changes caused by shrinkage and creep in different period and operation time of old and widening bridges are analyzed to suggest that the best storage period is advisable for 6 months and not less than 3months.Finally,the bending moment changes of the girders under different rigidity of diaphragm wall are analyzed.It is suggested that the type of lateral connection stiffness shall be judged according to the load test of the existing bridge,and it is used for checking the structural stress.(2)If the space grillage method is used for the calcution of flexural effect function,the load effect function need to be fitted by certain methods.In this paper,the support vector method was used to analyze the fitting effect of two load effect functions which include the effect by the quadratic effect of prestressing force.The results show that the prediction values of implicit function obtained by SVM method is small but meet the requirement of engineering accuracy.This method can be used for the fitting of approximate function function of T beam bridges with little samples.(3)Based on the implicit function fitted by SVM,this paper studied the influence of three factors,such as the widening before and after,the deterioration of old beam diaphragms,and the time dependent effect of concrete,on the reliability of the structure and system reliability of the T beam bridges.It is suggested that the adverse effect of quadratic effect of prestressing force shall be considered in the studyof reliability of prestressed concrete beam bridge.The widening project can effectively improve the reliability of the old beams,especially the old beams at the stitching section.The diaphragm stiffness degradation between the old beams has no significant influence on the reliability of the new and old beams in widening bridge.After 70 years of concrete age,the reliability index of the beam is reduced obviously,and it is lower than the structural reliability index without considering the time varying effect.When the operation time of the new beam is more than 45 years,the reliability index of the structure system is lower than that of the no-time variant effect.