Research On Mechanical Properties Of Variable Section Continuous Girder Bridge Strengthened By A Stay Cable System

Over-sag and oblique cracking are common problems in long-span PC continuous box girder bridges.The core idea to solve these problems is to raise the height of cross-section and improve the shear capacity.At present,the traditional method has achieved certain effect,but only temporarily restrain disease.A stayed cable system(SCS)method is one of the most effective methods to solve these problems.It is seldom used in highway bridge reinforcement engineering,and the relevant research is obviously insufficient.Therefore,it is of great significance to carry out the relevant research on long-span PC continuous box girder bridge strengthened by a SCS to promote its application in the field,and improve transportation capacity in China.The structural state of main girder before reinforcement,mechanical performance of main girder in tensioning phase and force transfer system in anchorage zone are the premise and key problems for the successful implementation of SCS method.Therefore,this paper focuses on deformation mechanism of main girder strengthened by a SCS,design and calculation of connection joint,mechanical performance of local concrete in anchorage zone and overall structure of main girder in tensioning phase by the theoretical analysis and experiment method.The main research methods and contents are as follows:(1)Aiming at the time-dependent and uncertain for long-term deformation of web-cracked bridges,an uncertain analysis method of time-dependent deformation of PC box girder bridges based on web oblique cracked model is proposed.Firstly,the deterministic and stochastic factors affecting the long-term deformation of bridge are analyzed.Latin hypercube sampling method is used to reduce the number of samples,and a stochastic finite element analysis model is established.At the same time,based on the variable angle truss theory and the web oblique cracks measured,the shear stiffness degradation factor is evaluated,and embedded into the stochastic finite element model to quantitatively investigate the contribution of main girder deformation.Then,the response surface functions of main girder deformation are established by stepwise regression analysis,and the sensitivity of random variables to long-term deformation is analyzed by partial rank correlation coefficient.Finally,the objective function is established to select the optimal combination parameters,and the mechanical properties of a case strengthened by a SCS are analyzed and compared with the measured results in the tensioning-phase.(2)It is difficult to predict the deformation of main girder strengthened by a SCS in the tensioning-phase,and the traditional unequal interval grey model has the problems of low accuracy,poor adaptability in its application,and difficulty in reflecting the periodicity and random fluctuation of deformation data.Aiming at these situations,an improved unequal interval weight grey correction is put forward.In addition,Aiming at the problem that the grey model does not take into account spatial and temporal effects of deformation development and change at multiple measuring points,and uses more measured data for modeling,ant colony algorithm correction model is proposed.The calculated values of two models are compared with numerical simulation and test results.The accuracy and adaptability of the proposed model are studied,For deformation prediction of main girder by a SCS in the tensioning-phase,a new idea and method is provided.(3)According to the stress characteristics of anchorage section of long-span PC continuous box girder bridge strengthened by a SCS,a new type of friction-type high-strength bolted(FHSB)connection joint is developed.Then,the mechanical properties ofjoint under combined shear and compression are studied by experimental method.The failure mode,initial friction load,ultimate strength and change of bolt axial force are discussed in detail.Finally,the parameters of FHSB connection joint are analyzed by the numerical simulation method.The mechanical properties of the joint under different shear and compression ratios,friction coefficients and clamping forces are studied.The calculation model of bearing capacity of FHSB connection joint under combined shear and compression is proposed.(4)Aiming at the problem that it is difficult to evaluate the residual bearing capacity of FHSB connection joint after the nut corrosion under combined shear and compression,the relationship between the volume loss ratio of nuts,the mass loss ratio of nuts,the equivalent radius loss ratio of nuts and the residual clamping forces of bolts is analyzed by corrosion damage of nuts casued by manual cutting method,and then the experimental method and numerical simulation method are used to study mechanical properties of the joints after cutting nuts are studied.An approximate calculation model of residual radius,initial friction load and ultimate strength of FHSB connection joint after nut corrosion is proposed.(5)In order to verify the feasibility and reinforcement effect of long-span PC continuous box girder bridge strengthened by a stay cable system,based on the renovation project of Dongming Yellow River Highway Bridge,the scale model test of the anchorage area section of main girder subjected to symmetrical and eccentric loads is carried out to study mechanical properties of steel members and anchorage performance,and the system reliability for large-span PC continuous box girder bridge is preliminarily verified.Then,combined with the tensioning-phase,static and dynamic load test of real bridge,the stress and deformation of key section,stress of steel members,cable tower stress and deformation,cable force and typical crack state of main girder are studied,compared and analyzed with the finite element calculation results.Finally,key construction techniques of drilling and planting steel bars of main girder bottom plate,and installation of new steel members,and cable tension control are introduced.