The Study Of Hybrid Girder Cable-stayed Bridge Based On High Performance Materials

Based on the predominant property of Reactive Powder Concrete(RPC),taking a cable-stayed bridge of 260m-long main span with a hybrid girder by steel and C55 normal concrete and a tower by C55 normal concrete as an example,a new cable-stayed bridge system of the same span layout,with RPC120 substituting for steel in the girder and RPC100 for normal concrete in the tower,was designed considering the stiffness,stress and local stability of the girder,tower and cables.The comparative study on the static,dynamic properties,stability,economic and seismic performance of these two bridge structures were carried out by the finite element method.The applicability of RPC in cable-stayed bridge with hybrid girders was investigated.This dissertation involves the following work:(1)The design and demonstration of structure scheme.Based on a steel+C55 normal concrete hybrid girder cable-stayed bridge of 260m-long main span,an RPC+C55 normal concrete hybrid girder cable-stayed bridge of the same span layout was designed,involving the determination of material properties,the design of section size of the RPC girder and RPC tower,the strand layout and distribution of pressure weight,and the adjustment of cable force.(2)The checking calculations of local mechanical characteristic of the RPC box girder,including its local stabilities,punching and crack resistance.The results show that the local stabilities of the top,web and bottom plates are all enough to ensure the buckling failure not prior to material failure;the punching resistance of RPC deck slab meets the requirement and has a large surplus;the crack resisting calculation of the top slab of RPC meets the requirement of partially prestressed A component.(3)The static analysis of structures.The comparative study on the structural internal force,deformation and stress of these two bridge structures under the dead load,vehicle load,temperature load and load combination were carried out by the finite element method.The results show that the new proposed scheme has good static performance.Compared with original project,the stress of the RPC girder of the new project is reduced and its distribution is more uniform,the stress of the RPC tower is increased significantly so as to effectually use the high performance of RPC;the linear expansion coefficient of RPC between the steel and normal concrete result in more favorable structural behavior of the new project under the temperature load.(4)The analysis of stability performance of structures.The overall stability of the construction phase and operation phase under the worst-case of load was analyzed.The results show that the elastic safety factor of overall stability of these two projects meets the requirement and has a large surplus,which means the new proposed system has a good stability property.(5)Comparision of economic performance of structures.The economic performance of these two schemes was compared considering the material cost.The results show that the total cost of materials of the new scheme structure is about 1.28 times of that of the original scheme;Considering the RPC girder can be maintenance-free during the operation period,the life-cycle cost of the new scheme will be more competitive.(6)The analysis of seismic response and performance of structures.The seismic response of the structures was analysed based on response spectrum method and time history analysis method respectively,and the seismic performance of these two projects was evaluated based on the method of capacity demand ratio.The results show that the RPC tower and RPC girder has smaller earthquake response than the original project due to the lower stiffness;the tower and piers of these two projects both meet the seismic performance requirement under the combination of the dead load and seismic load,meanwhile the capacity demand ratio of cables is enough to ensure no first break when earthquake occurs.