Experimental Study And Numerical Analysis On Bearing Reaction And Bearing Capacity Of Curved Prestressed Concrete Box Girder Bridge

In the dissertation,it is reviewed the theoretical research and application of curved prestressed concrete(PC) box girder bridge.As the drawbacks of pertinent disease characteristics and current research,studies on bearing forces and ultimate bearing capacity of curved PC box girder bridge are carried out.The dissertation mainly completes the research in the following aspects:(1) Test model is employed for the first time to do parametric study of the bearings layout and bearing forces of curved PC box girder bridge.It is the first time to carry out test research of the prestressing forces' influence on bearing forces.Based on the test result,the method to improve distribution of bearing forces by adjusting the location of torsion resistant bearing and middle bearing is concluded.Moreover,the adverse effect of prestressing forces to make curved PC box girder bridge turn outward is summarized.And the basic rule of bearing forces' variation caused by prestressing forces is obtained.(2) Test study of ultimate bearing capacity of curved PC continuous box girder bridge is performed by using large scale model.According to test result,the nonlinearity characteristics and deformation rule of the model under symmetric vertical loads are found.As for the curved PC box girder bridge,critical sections,distribution and development of concrete cracks and failure mode of the whole structure are concluded,providing detailed test data as well as design and application basis of this structure.(3) The computation method and values of parameters for effective prestressing forces are determined by taking account of the spatial mechanical characteristics of curved PC box girder,and the way to simulate prestressing forces' effect is proposed.Using assembled finite element method which mainly consisting of solid element,numerical model is come up with. This model is suitable for precise analysis of bearing forces of curved PC box girder bridge. The model can simulate actual alignment of tendons and structural details,suppressing the defect of bar element model which has large error in computing bearing forces.Compared with test result,the numeric method proposed in this dissertation is proved to be explicit, accurate and reliable.Additionally,the distribution rule of bearing forces is concluded through analysis of project example.(4) According to the mechanical characteristics and pertinent disease of curved PC box girder bridge,it is proposed to use the lead rubber bearing for seismic isolation.Nonlinear dynamic time history analysis is performed for seismic isolation bearing system of curved PC box girder bridge.The way to input seismic record and characteristics of seismic response of this type of bridge are summed up.The effectiveness of seismic isolation and its adaptability was studied.The result shows combination using of lead rubber bearing and seismic restrainers can not only eliminate the usual defects of curved PC box girder bridge,but can also avoid the negative effect that caused by seismic restrainers,so it is deserved to make popularized.(5) Simulation of local members,mesh control,tendon and concrete model,and materialistic nonlinear model of concrete are studied based on the assembled nonlinear finite element method(mainly composed of solid element).Then,numeric model for precise analysis of ultimate bearing capacity of curved PC box girder bridge is come up with. Through adopting multi-type elements and subdividing mesh finely,the convergence difficulty in nonlinear calculation for concrete structure is conquered.This numerical method gets rid of the assumption on stress and strain for simplifying analysis,and can take account of spatial mechanical effect such as torsion,distortion and shear lag of box girder,so the whole process from concrete cracks' appearance,development and interactive effect to the macro crushing and collapse can be clearly described.The deformation,strain and failure mode got from this numerical method agree well with that from test.The comparison shows that this method is of high computation precision and the results are full,accurate and dependable.(6) On the basis of verified analytical method,an ideal precise numerical model of curved PC continuous box girder bridge is established.With the help of this model,the influence of the parameters such as layout of the middle bearing,curvature and prestress on ultimate bearing capacity are studied.According to the calculation results,the pertinent factors' influences on load capacity,deformation,rule of strain and failure mode are summarized.