The Study Of Super-long Span Concrete Cable-stayed Bridge Based High Performance Materials

Based on the superior performances of RPC and CFRP materials, it is putforward for the scheme of super-long span concrete cable-stayed bridge with CFRPcables and RPC girder under the financial support of Program “Structural behaviors ofsuper-long span cable-stayed based on high performance materials”. The feasibilityof the new structure was discussed based on the results from static performances,dynamic performances, stability, wind resistance behavior and seismic resistancebehavior. This dissertation involves the following work:(1) Taking a main span of1090m cable-stayed bridge with steel girder and steelcables as an example, a new cable-stayed bridge in the same span with RPC girder andCFRP cables was designed, in which the cable’s cross section was determined by theprinciple of equivalent cable capacity, the girder’s cross section was determined invirtual of its stiffness, shear capacity, punching capacity, local stability and localbending capacity, and the tower’s cross section was determined in virtual of itsstability and intensity.(2) Based on the methods of finite element analysis, the comparative analysis ofthese two cable-stayed bridge schemes about static performances such as thedeflection of main girder, deviation of tower, force, and stress, etc. were carried outunder different load including dead load, vehicle load, temperature load and aerostaticload. The results show that the proposed scheme has good static performance.Compared with steel girder, The stress of RPC girder is reduced significantly, and thestress distribution is more uniform, because of the low linear expansion coefficient ofRPC which is just1/10of the steel material, the deformation of the new schemecaused by temperature effect is about1/25of the old scheme.(3) Considering the influence of geometric nonlinearity and material nonlinearity,the static stability and the aerostatic stability of the two cable-stayed bridge schemeswere analyzed using large finite element program ANSYS. The results of staticstability analysis show that the elastic stability safety coefficient and nonlinearstability safety coefficient of these two schemes can meet the specificationrequirements, and the static stability safety coefficient of the new scheme is greaterthan that of the old scheme. Because of the higher specific stiffness and specificstrength of CFRP cables, the corresponding geometric nonlinearity could be ignored, and the buckling failure of the new scheme would be delayed with the longitudinalstiffness improvement of RPC tower. The results of aerostatic stability analysis showthat the critical wind speed of the old scheme and new scheme are179m/s and169m/sat the0degree wind attack angle, respectively, and the instability pattern of twocable-stayed bridge schemes are all bending-torsional coupling instability. Comparedwith steel girder, the vertical stiffness and the torsion stiffness of RPC girder arereduced by38%and57%, respectively, but the higher specific stiffness and specificstrength of CFRP cables and the increased dead weight of the girder would improvethe stiffness of the structure, so the critical wind speed of the new scheme is onlyreduced by about8%.(4) The dynamic characteristics of the two cable-stayed bridge schemes wereanalyzed using large finite element program MIDAS. The results show that, althoughthe vertical stiffness of the girder are reduced by38%after RPC girder replace steelgirder, the higher specific stiffness and specific strength of CFRP cables wouldimprove the stiffness of the structure, so the frequency of vertical bending vibrationmode for the new scheme is reduced by less20%. While the longitudinal stiffness andtransverse stiffness improvement of the main tower after RPC tower replace RC towerincrease the fundamental frequency of the new scheme, and delay the occurrence ofmain tower lateral bending vibration mode.(5) The elastic earthquake responses of these two schemes were analyzed basedon response spectrum method and time history analysis method, respectively, andseismic performance of proposed scheme was evaluated. The results show seismicperformance of the new scheme is almost same with the old scheme, and the stressand displacement of the new scheme can be satisfied with the requirement ofserviceability under the combination of dead load and earthquake force. Comparedwith the old scheme, the improvements of the longitudinal stiffness and the transversestiffness decrease the displacement of the tower top, increase the moment of the towerbottom, and give full play the high performance of RPC material. Althouth thevertical stiffness of RPC girder is less than that of steel girder, the higher specificstiffness and specific strength of CFRP cables improve the vertical stiffness of thestructure, so the vertical displacements of steel gieder and RPC girder are almost thesame under the earthquake, and that of steel girder is a little less than RPC girder.(6) Restoring force model of Reactive Power Concrete piers was put forward.Taking Reactive Power Concrete box piers as research object, the seismic analysismodels were built by choosing the material constitutive relation including Concrete02 and Steel02and element types including Beam-with-Hinges-Element in OPENSEES,and the comparison between the experimental results of three Reactive PowerConcrete piers samples under the invariable axial force and reversed horizontal loadand the computed results proved the accuracy of the model. At the same time, thefactors affecting the seismic behavior of RPC piers were analyzed on this basis of theseismic model. Then, basing on the results of numerical analysis and cyclic loadingtests of three Reactive Power Concrete box piers samples under the invariable axialforce and reversed horizontal load, those factors affecting the restoring force modelsof the samples were considered in order to establish restoring force model of ReactivePower Concrete box piers under biaxial horizontal load. In addition, the numericalsimulation analysis was performed with the program taking into account thesecond-order effects of the axial force and biaxial laods, and the results are in goodagreement with the experimental results.(7) Based on the biaxial bending component nonlinear analysis program,parameters which effect RPC pier plastic hinge length were analyzed, and theregression formula of RPC pier plastic hinge length was put forward. The results showthat, the plastic hinge length monotonically increases with the increase of pier heightand section size of the short side, decreases with the increase axial compression ratio,and increases at first and then decreases with the increase of horizontal loading angleand longitudinal reinforcement diameter. The strong axis plastic hinge length is lessthan the weak axis, the maximum plastic hinge length can be obtained when the loaddirection inclined about60degrees, and the plastic hinge length almost closes to zeroat high axial compression ratio. Compared the numerical results with the calculationresults of RPC pier plastic hinge length regression formula, the calculation results ofthe corresponding regression formula are in good agreement with the numericalresults and limit too much plastic hinge length.(8) Based on the proposed RPC restoring force model and RPC pier plastic hingelength regression formula, elastic-plastic seismic response analysis model of the newscheme was built by the finite element program Midas, and the ductility seismicresponse was analyzed. The results show that the restoring force model of RPC can bewell simulated by revising Takeda restoring force model in Midas. Although thebottom of the main tower has been in the plastic stage under the E2earthquake, theplastic deformation of the plastic hinge isn’t used adequately, so the section size ofRPC tower can be reduced appropriately from the point of seismic design. Finally, toimprove the seismic resistance of the proposed system, based on the elastic-plastic seismic response analysis model, the damping coefficient and the speed index of theviscous damper was optimized. The results show that, in terms of system is proposed,the damping coefficient C of2000and the velocity index α of0.4can help the damperachieving the best damping effect, meanwhile the maximal longitudinal displacementof the tower top and bending moment of the tower bottom are reduced by35%and40%, respectively.