Reliability Analysis Of PC Rigid Frame Bridge During Construction Based On SVM

PC rigid frame bridge generally uses cantilever construction,and the structure not only get the external load,but also bear the role of material time-dependent performance during construction.In the same time,The structure changes from the short cantilever state to the long cantilever state,and internal forces and alignment are needed to focus on studying with the continuous construction.However,in actual engineering,the factors that affect the bridge linear and internal forces tend to be uncertainty.As a consequence,structural calculation and analysis are more in line with engineering requirements when the uncertainty factors are introduced into the reliability analysis of the PC rigid frame bridge during the construction period as well as considering the material time-dependent performance.Support Vector Machine(SVM)is based on the principle of structure risk minimization and has an excellent ability of small-sample learning.It overcomes high-dimensional data processing difficulties.Therefore,it has a unique advantage in the field of reliability calculation with implicit performance function.This dissertation relies on the main span 180 metres of Duifang River bridge and the main works are as follows:(1)Experimental study on mechanical properties of early age concrete.Standard prismatic concrete specimens were made in construction site,and synchronous maintenance in the deck,respectively to maintain 3d,5d,7d,14 d,28d,60 d of the concrete specimen mechanical test,obtained the relationship between the early age concrete axial compressive strength,elastic modulus and the curing time,then analysing the function formula between them.(2)Based on the basic theory of SVM,the reliability calculation process of PC rigid frame bridge based on SVM is proposed.The reliability calculation program based on support vector machine is compiled by using MATLAB.Using self-made Latin hypercube sampling program to generate sample points,the method of parameter optimization based on SVM is described by numerical examples.It is proved that the support vector machine method can be used to calculate the reliability of PC rigid frame bridge during construction period(3)The function of stress and elevation control of cantilever construction are established.The stress and deflection of the PC cantilever bridge during the construction of the largest cantilever stage are calculated by different finite element modeling methods and analysed considering the material time-dependent performance.The finite element results are compared with the measured data.The results show that the finite element model is accurate.(4)The main factors which affect the reliability analysis of the construction stage are as follows: the bulk density of concrete,the elastic modulus of concrete,the tension control stress and the elastic modulus of steel strand.The elevation control reliability indices of the short cantilever stage,the middle cantilever stage and the maximum cantilever stage are calculated under different permissible free deflection tolerance while considering the variation coefficient of factors.Then,the allowable deflection value of free end is obtained when the structure is in the respective cantilever stage.Finally,based on the orthogonal design,stochastic parameter sensitivity analysis during construction period is carried out to provide reference for the construction control of PC rigid frame bridge.